BEGINNING JAVA™ GAME PROGRAMMING WzECOND EDITION
1-~l
ARBOUR
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For Kaitlyn Faye
ACKNOWLEDGMENTS
I thank God for the many opportunities that have come my way this year, such as the chance to write this book, and for the apparent talent needed to make something tangible of these opportunities. I am grateful to my family for their ongoing encouragement: Jennifer, Jeremiah, Kayleigh, Kaitlyn, Kourtney, Mom and Dad, Grandma Cremeen, Dave and Barbara, my extended family at Vision Baptist Church, and Pastor Michael Perham and his family-Jennifer, Ashley, Bryce, and Sage-who have been such a blessing this past year. Thank you to the students, faculty, and staff at UAT for contributing to such a wonderfully creative environment for learning. I would like to thank the Alpha Squad team, who had some influence on this book (and even helped to solve a few coding problems with Galactic War): Roy Evans, Stewart Johnston, Peter Pascoal, Travis Eddlemon, Daniel Muller, Daniel Stirk, Patrick Cissarz, David Coddington, Marc Kirschner, Jeffrey Woodard, Jonathan Allmen, Levi Bath, Douglas Cannon, Joshua Gertz, Justin Hair, Adam Knight, Eric Lacerna, Daryl Lynch, and Kevin McCusker; and the faculty sponsors: Rebecca Whitehead, Michael Eilers, and Arnaud Ehgner. I also owe my thanks to students Mark Walker and Andrew Hawken for introducing me to the angular velocity code used in Galactic War. I am also very thankful for the artwork featured in this book, provided by Ari Feldman (www.flyingyogi.com) and Reiner Prokein (www.reinerstiJeset.de). Without their wonderful graphics, Galactic War would have featured programmer art (cringen. I offer my sincere thanks to the editors at Course Technology PTR and the freelance editors who put this book together: Emi Smith, Cathleen Small, Dustin Clingman, and Kate Shoup.
ABOUT THE AUTHOR
Jonathan S. Harbour is an Associate Professor of Game Development at the University of Advancing Technology in Tempe, Arizona. His current game project, Starflight: The Lost Colony (www.starflightgame.com). will be released in late 2007. He lives in Arizona with his wife, Jennifer, and four children: Jeremiah, Kayleigh, Kaitlyn, and Kourtney. He can be reached at www.jharbouLcom.
CONTENTS
PART I Chapter 1
Introduction ..
xiii
JAVA FOR BEGINNERS
.
Getting Started with Java
. . . . . . . . . . . . . . . .. 3
Java and the Web . . Studying the Market . . Design Rules. . . . . . . . •. . . . . . . •. . . . . . . •. . . . . . . •. The Casual Games Market.
3 4
5 6 No Manual Required . . .. . ..•.. . .. .••.. . . 7 Casual Garners. . .. ... .. . ... ••. .. ... .. .. . ... .. . 8 Casual Games. 8 Installing and Configuring Java. .. ...••.. 9 Installing Java . . . . . . . . . . • • .. 10 Configuring Java 11 Java Version Numbers ........ . 14 Your Fi rst Java Program . . . . . . . . • .. 1S Java Application. . . . . 15 Java Applet . . . . . . .. .. .••. . 17 What You Have Learned. ......•.. 20 Rev iew Questions . 21 On Your Own. 22 22 Exercise 1 . . Exercise 2 .... . .. . ... . . .. . .... .• •. . . . .. . . . .. .. . . . 22
vi
Contents
Chapter 2
Java Programming Essentials . . . . . . . . . . . . . . . . . . . ..
23
Java Applets . . .
24
.
.
Web Server Technology Explained Hosting Java Applets . .
24
. ... . ... .. . .• .. ... . • . .. . . .
The Java Language .. Java Data Types. . . .
. . . .. . . . • . .. . .. . ... . . . . . . .. ..
The Essence of Class. The rnain Function . .
27
37
39
Object-Oriented Programming What You Have Learned . . . .
. . . ...... • • . .
Review Questions.
On Your Own. Exercise 1. Exercise 2. .
Chapter 3
24
25 25
Compiling Java Code . .
40 46 47 48 48 48
. 49
Creating Your First Java Game About the Game Project.
49
Creating the Game . ..
52
Creating the Project ..
53
The BaseVectorshape Class.
53 55
The Ship Class The Bullet Class
.
56
The Asteroid Class ................... • .
57
The Main Source Code File Applet initO Event. . ..... . . • . Applet updateO Event . . .
.
. ..... . •.
Drawing the Player's Ship . ... . . .• • . ... . .... .. . . • . . . .. Draw ing the Bullets. Draw ing the Asteroids. Screen Refresh. . . . . . .
. . . .. . •. • .... . • • . . ...
Thread Events and the Game Loop Game Loop Update ... . . ..• .
.
Updating the Ship. . . . . . . . . . . • • . . . . . . . . .. Updating the Bullets . .
. ... . • •. . .
Updating the Asteroids Testing for Collisions. Keyboard Events Calculating Realistic Motion .
. . • . .. . ..
58 59 60 61 61 62 63 63 64 65 65 66 68 69 71
vii
viii
Contents
What You Have Learned. Review Questions On You r Own.
73 73 74 74 74
. . . .. . • .. .. . . . .
Exercise 1
.
Exercise 2.
PART II
Java Game Programming .. . . . . . . . . . . . . . . . . . . . . .. 75
Chapter 4
Vector-Based Graphics . . . . . . . . . . . . . . . . . . . . . . . . .. Programming Vector Graphics
.
Working w ith Shapes ..
80 83 86
.
What You Have Learned. . . . • . ..... . .•... . ... .
87 87
Exercise 1. . Exercise 2
Chapter 5
87
.
88
.
89
Programming Bitmapped Graphics ... . ..... . .... .• .. . .. . . Load ing and Drawing Images. . .
89 90 92 94 9S 97 99 104 104 104
Bitmap-Based Graphics
Applying Transforms to Images. Transparency. . . . .
. ....• . . .... .•. • . . .
Opaque Images ......••...... .. .. Transparent Images ............... •• . Working Some Masking Magic .... . .. . .• ... What You Have Learned. Review Questions . On Your Own.
Chapter 6
77 78
Working w ith Polygons Rotating and Scaling Shapes Review Questions. On Your Own.
77
Exe rcise 1.
lOS
Exercise 2.
lOS
Simple Sprites
.
Programm ing Simple Sprites. . . . . . . . . The Point2D Class. Basic Game Entities The ImageEntity Class Creating a Reusable Sprite Class
.
.
.
107 107 109 110 111 114
Contents
Collision Testing. . . . . . . . . . . • .
114
Sprite Class Source Code . . . . . . • . . . . . . . . . . . . . • • . . . . . . . Testing the Sprite Class. What You Have Learned.
118 121
. . . . . . . •. . . . . . •• . . . . . •• . . . . . ..
122
Review Questions. . .
121
On Your Own . .
Exercise 1. . . . . . . . . . . Exercise 2.
Chapter 7
122 122
Sprite Animation
.
123
Sprite Animation ...
123 124
Animation Techniqu es Drawing Individual Frames
124 126
Keeping Track of Animation Frames. Testing Sprite Animation Encapsulating Sprite An imation in a Class ..... .. .•. . . . . .. Testing the AnimatedSprite Class. What You Have Learned . . Review Questions. . . On Your Own.
.
.
Exercise 1..
Exercise 2.. ..
Chapter 8
Keyboard and Mouse Input Listening to the User
.
127 132 13S 137 138 138 138 139
141
.
141 142
Listening for Keyboard Events
142
Keyboard Input... Testing Keyboard Input . . . Mouse Input ...
143
Reading Mouse Motion
146 147
145
Detecting Mouse Buttons. Testing Mouse Input What You Have Learned . .. ... . . ... .. . . ..•. ... ... . . . . .
148
Review Questions . .
153 153
On Your Own . . Exercise 1
153
154
Sound Effects and Music Playing Digital Sample Files
152
.
Exercise 2...
Chapter 9
114
. . . . . . • • . . . . . . • • . . . . . ..
1SS .
155
ix
x
Contents
Getting Started with Java Sound ... . . .•.... . .• .
157
Playing Sounds ..
164 166
Playing MIDI Sequence Files .. Loading a MIDI File
.
166
Playing Music. ....... . .. ....•..... •. ......•.. .
167
Reusable Classes. The SoundClip Class.
169 170
The MidiSequence Class ......•• . . .. .•.. . ... .•....... What You Have Learned ... Review Questions. On Your Own. Exercise 1
.
Exercise 2
Chapter 10
.
172 175 175 176 176 176
Timing and the Game loop. . . . . . . . . . . . . . . . . . . . .
177
The Potency of a Game Loop . .
178
A Simple Loop . . .
..........
178
Overriding Some Default Applet Behaviors. . . . . . . . • . . . . ..
181
Feeling Loopy . . . . . . . . . . . . . . . Recovering Long·Lost Applet Methods. . .
182 183
Stepping Up to Threads
184
Starting and Stopping the Thread. . The ThreadedLoop Program. .
184
Examining Multithreading
189
What You Have Learned.
185
........•...
... ...•.. .. .. ... .. .. .• • .. ..
Review Questions . . . .
189
.......•.
190
.......•. On Your Own. Exercise 1. . . . . . . . . . . . . . . . . • . . . . . . . . . . . . . . . . . . . . .. Exercise 2. . . . . . . . • • . . . . . . . . . .
PART III
THE GALAalC WAR PROJEa
Chapter 11
Galactic War: From Vectors to Bitmaps
.......•....
190 190
191 .
Improving the Game
.
Generalizing the Vector Classes
193 193 194
The Main Source Code File: GalacticWar.java
197
What You Have Learned .
204
Review Questions .......... .. . •• ... . ... On Your Own. . .
190
.
.
204 204
Contents
Chapter 12
Galactic War: Sprites and Collision Boxes Creating the Project. . . . . . . . . . . . . .
. . ... .. . . •.
207
The Galactic War Bitmaps. The New and Improved Source Code
Chapter 13
208 210
What You Have Learned.
224
Review Questions .
225
On Your Own . . . .
225
Galactic War: Squashed by Space Rocks
.
227
What You Have Learned . ......... . •. . . . . . •. . . .. ... . ..
233
Review Questions.
233
On Your Own.
234
Galactic War: Entity Management
.
Adjusting to Event-Driven Programming
235 236
Exp loring the Class Library . .
236
Building the New Game Class .............. ...... •. ..
237
Enhancing Galactic War. .... .. •.•.. .. Exploring the New Galactic War Source Code ...
249
What You Have Learned
273
Review Questions. . . . . .
. .
Galactic War: Finishing the Game Let's Talk about Powerups . Ship and Bonus-Point Powerups . . Weapon Upgrades. Enhancing Galactic War.
249
.
274 274
.
275
. . •.. ... . ••... .. .• . . . . ..•. . .
On Your Own..
Chapter 15
227
. ....•....
Being Civilized about Collisions.
Chapter 14
207
. . . . ..•. .... .. . .
275 276 276
. . . . .. .. . . .•. .. . . .• .... ..•...
281
New Sprite Types ...
281
New Game States.
281
New Sprite Images. . . . . . . . . . . . . Health/Shield Meters, Score, Firepower, and
.
282
Game State Variables.
283
New Input Keys . . ..
283
Sound and Music Objects . . .. . . . . . . . . . .. •• .... ....... Loading Media Files. . . ... ... . ... . • . ..
284 284
Game State Issue-Resetting the Game.
287
Detecting the Game-Over State .... . . . . .. • . . . .. .•. . .
288
Screen Refresh Updates. .
289
. ....• .. . . ..
xi
xii
Contents
Preparing to End .. Updating New Sprites. Grabbing Powerups. . .. . . . .. .... ... ..• . . ... ...... New Input Keys. Spawning Powerups . . . Making the Shield Work. . Making Use of Weapon Upgrade Powerups ..
.
Ta llying the Score What You Have Learned . . .. . .... . .• . . .. ... . .. . . . .• . .. Review Questions On Your Own
Chapter 16
. .
Galactic War: Web Deployment
.
Packaging an Applet in a Java Archive (JAR) Using the jar.exe Program Packag ing Galactic War in a Java Archive . . Creating an HTML Host File for Your Applet ... . . . • . . A Simple HTML File. .
. ... ..... . . ..•.
Testing the Deployed Applet Game . What You Have Learned. . ........ ... . . .• • . . .. ... Review Questions. Epilogue
. ...... . •. .
Appendix A: Chapter Quiz Answers Index
291 292 294 296 299 301 302 30S 306 306 307
309 309 310 312 315 315 317 319 3 19 320
321 337
INTRODUCTION
This book willicach you how to write JaVil games that will run as applcts in a wcb bT'mt..a. l"hc goal is to &vriop gal"l'lCS ror the casual gal'DC market. Gal'DC pro· gramming is a challmging subject that is not jusl difficult 10 IfU.SItt-it is difficuh just to get started. This book takes aW3Y somc or thc m)')tc-ry or gamc prog11lmming by expbining each step along the w~y, rrom one chapler to the next I assume Ihat you havea litlle la\"a programming experience, but c\"en ir you hal'C I"IeI'tt usal )aVil herorc. you should Ix- ablc 10 k<"q) up.
This book rnds IiU a hobby book. with no pressu~ and limittd pis, btcausc tht pri=ry purpose or this book is to hdp you have: fun learning how 10 progrnm wrobased games. Typing in long source code listings out of a book is not fun, so I don't
ask you 10 do Ihat in every single chapter in Ihis book-Inslead, you willieam to wrile shor1 programs to demonstratc tht major topics, and Ol'n" tinx' you will get the- hang of il ~ is no mrtl'lOr'Uation ~uirtd bm-. btcause I'm a firm bd~ that n:pdition-praclia---is the best W3y to learn, 001 throry and rnanorlzation. Note
-
lIva
~
• programming language ilwented by Sun Microsystt'lllS. The primal)' goal of Java's
1Jf'' '
~ wotS tu tu mlI'lpilc a prllgrMn DIU and ' - it run on nwny ~ ~ syslemS. The JaQ ~ CINIeS a "l:Jorteoode- file tonIaIning W1ual m.xIlirw instJuctIarts that tie lIl£ U- ~ ~ l tan cxecw (WI . " ~ S}W'II llpOll whidl it is
..
You will learn how 10 wr ile a simple la\"3 program in the first chapter. From there, rou will Icam thc dClails or how 10 writc games that will run in a web
xiv
Introduction
browsc-r. WI" W\'l"r sourCl" code at a ~e that will nolll"3vl" you brilind. Aha- rou havl" kamed enough, you will write your first ..·d>-based g;lme. and you willihen learn nl"W subjl"<:ts in each chapter to iru::rease your game programming skills. By the end of this book, you will have learned to creale ~ complete web-based game called Galactic War, and you will be able to deploy it to your website in a Ian Archive (JAR) fill". And I'm not talking about some half-baked simulation posing as a gamco I'm talking about a rmJ g;lmI'" that ill rdai] qlA.lity. suit:;lble for publishing in thl" castU1 gaml'" nurkl"t. Then att toous;rnds of casu
~
While we're on the subjl"<:t of casual garnes, you can eVell program your own Xbox 360 games, distributed on Xbox Livl" Arcade, using Microsoft's free: XNA Game Studio bpre:ss softwue. Although this subject is beyond thl" scOpl" of this book, I bring it up bromIC Microsoft's Cllanguagt' is unabuh~y similar 10 Java. Thomson published a book on this subject by Josq>h Hill. tilled XNA Gam.. 51l1flio Express: Dn~lopiug Games for lViudo>o" (IUd the Xb
What Will You Learn in This Book? This book will leach you thl" difference between Java applkations ind applets (which run in a web browsc-r). You will thcnleam about Java's graphics classes
Introduction and ~n writing graphia: code. You will lam how to get input from the user and how to play sound efT~ts and music-all within the conteJ(t of an online game. From there, the sky's the limit! Figure 1.1 shows the 8'lme you will !eMil to create in this book. Starting with the basics (and I'm talking about eXlremebasics here!), you will write a simple 2D game using V«lor graphics (using lines and filled poIygolU). You ..ill then learn new t~hniques ill each new chapter, such as how to load a bitmap file and render it in the 20 applN window using the Graphics and Graphies20 classes. You will eventually putlhc handful of game-related classes together in an e'o'ent-dril'en game library. As you can see from Figure 1.1, the final
..
F"~1.1
YoIt willNm hgw 10 0Nte fils 'Ji"ll! torn wMdlI
xv
Kvi
Introduction lPme uses some allradive arlwork and is ehlXk-full of small details! You will learn aboul simple bitnl.;lpsand then sprites hefoR' getting into animation. Along the w:ly, you will learn how to use Java's advall(ed 20 library to rotate and scale: sprites. and I'll show you some interesting code tlu.t ITIOVd bulkts, powerups, asteroids, and other game objects on 1M screen $IIlOOthly and rnIisticl1ly. The end result is a profts.\ional sprile-based game mgine that pacb a serious punc:h! By learning how to creale this rC'lail-qualily ra51111/ game, you will h.a\'e learned enough to create your own games, suilable for sale in the casual game market. No te ~ is a IWnfted type 01 reslricticJrrs, an appIel is
An
"""'d1
program not" III il«ess the is installed like any other appIO:aliOll ~a
run in a -t> ~ Oue 10 secunl\' lie system on a user's PC Iibo a J.wa applic.allOn,
~ 10
",ftw~.
Becaust this book is dedicale
men
What about the Programming language? This book is about g;.mc programming, and il assumcs thai you alre~dy know ~t least somc J~va. r rc<:ommend thm you acquire a Java primer to read ~forc delving ill10 this book, or to keep handy for those parls that may confuse you. For starters, you can pick up John Flynt's Java Progmmmiltgfor tlleAbsolutc &gilmer. 5«otld &ii/jOlt (Thomson Cou rse Technology PTR, 2006). If I lose you halfway through Ihis book, I apologiuo in advance, because we jusl don'l have enough pages to ltach Ja~d and build a complete game. I do not utiliu any advanced features of lava SE 6, ('Ven though this is the btest version of Java.
Introduction Tip
n.. _ «dII .. Ih5 boat _ COI'I'Ipifd n:l1MIN using 1wiI Sf: 6, buI: Illy Iat« -.mm 01 Jav.lI Sf: wi! be ibIe 10 ooqJile n:I roolhe «dIIlM 10 JrA's -*nt SlIpIlOI1Ior old «dII (iIso ~ b.odwMds ~ , vitaIy irnportInt ...... in sottw..... dtwIopo.... n!hat Mi(ros,oh _ to have abandoned with its products and languages-but that is' topic for another day), While cowring some of Ihe basics over Ihe next th ree chapters, you'll create a complete casual game in lava that runs in a web browser. which will be a milestooe as well as a measure of your own skill kvd at thai poinL This book is not a primer on the Java bnguage; ratber. it make$ llS(' oflhis verycapable. high· level bnguage to create games. You will lind the code in this book much easier to understand if you have at least read a primer on th.. subject. We discuss gam.. programming, not basic Java progrornrning. If this is your first experience with the lava language, then you may struggle with the sourcecooe in this book. If you fed Ihat you are up to the chalJenge, th..n you might be able 10 read th.. Jan cod.. and make sorn.. sense 01,11 of il. But I don't $ptnd very much lime trying to leach anything about th.. Ian language beyond the first thr<"(' chapt,"" b«.allS(' game programming is a difficult sub;«!, and ~ have a 101 of ground 10 cover. All of th.. projn:ts in this book will com pile with the Jan Sf 6 development kil. Although bter versions (such as lava Sf 7) will compile the code, older versions of lava may complain about classes or methods thai are nol re<:ognize:d. I recommend usi ng the v..rsion included on the book's CD· ROM. (Look in th.. \jan fold..r.) You may also broWS<" 10 http://java..sun.comtosecwhelh..ran...... v,""ion of laV1ll is aV1llilabk. (As of tile writing of this book, Java SE 7 isdue out in 2008.) You will be able to rornpik the programs in this book using the javac.ex<" program, and you will run the programs using appletviewcT.exe.
What IDE Should You Use7 The first v..rsion of this book focused on a professional IDE (Integrated {)e•.c/. orman Environment) to help organize: JaV1ll game projects.. However, much has changed in Ihe IWO years silK<" the first edition came OUi. Borland JBuilder Foundation was a free trial version of lBuilder. and we were able to supPOr1the 200S and 2006 versions al the time. BUI Borland is no longer making ~ versions available, and the only option now is tQ llS(' the 3O-day trial ofJBuilder 2007 Enterpris.- Edition, which is not ideal and is quite large.
xvii
)(\Iiii Introduction
I RaV'l: decided 10 Iry sonx1hing dilTt'renllhis lilTl(' around. If a revision is mnnt updJ.tt' a book. Ihen it may seem odd 10 S1ql away from using a professional IDE. But thai is exactly what many professional Java programmers art' doingutili7.ing a simple text edilor and the Java SE 6 Development Kit directly. There are In,my reasons why this is preferable, and the best explanation may Ix: a desire to al'(lid Ihe adoption of any single IDE, since there are no Slandard project files in the industry. and each one is dr.uNtically dilTerent.
10
Tip If yau ... famiiIr WIth . . ~1l
cimlKn cr~l.patfOfTl1 wpport and tOE ~, Yoo will
Avoiding any single comp.my·s IDE also aHo..., us 10 focus more on the Ja~"1l codt'. and this helps with cross-platform dt'vdopmmt. Tht' code in this book ..iU compilt' and run on Ihe foUo..ing syslems: • Windows XP (x86, x64) • Windows Server 2003 (x86, x64) • Windows 2000 (xS6) • Windows Vista (x86, x(4) • Linux (x86. x(4)
• Solaris (Sparc 32, 64) • Solaris (x86, x(4)
n-r
Cttm-pUrbm ............" is . . abiiIy WI ~ and IIrI lhr SMIlf a:dt on cifIemtI ~ ~ ~ oxIt M>d fllIel1f.lIllIt 8es f t ~ 00 ...., plalbms. You do lOX need WI IfCOOlIile .,.:u J.wa oxIt for - , sy;Ifm. Ilt
Due to this extensive list of supportc:d operating systems, it is obvious why we would not want to limit oUfS('lves to a singlt' IDE, but would prefer 10 support aU of tht'st' syslems. M a conSt'q~t', 00n(' of tilt' source code on tilt' CD-RO:\1 includd any projn;t fila; il merdy includa SOUIU codt' files and galTl(' ~s ( image and sound files).
Introduction Tip ¥oo will ~ using Java SE 6 On other wonh, Java Standard Edition 6). which is the IighlWei41t version of Java best suited for ereat ng web-based games. Our text edilor of dloke is TextPad 5.0. ~ Lln (Offij'lile yoor Java SQu'te code fil~ with a maml key.
My favorite text editor. which I've been using for m3ny yeMs, is called Textl'ad and is available on the CD-ROM in the lsoftware diredory, as well as at www.lextpad.com. This very small and easy-to-uS<' source code editor recQgll;u$ the Java Development Kit and is abk to compile your JJVa code with a simpk macro (Ctrl+I). By using Tcxtl'ad JS your IDE, you'll be working directly with the file system on your hard drive rather thJn on a virtual projl.'Ct mmmger (su(h :t.I the one in lBuilder). In TextPad, you'll see the 'tetual files on your drive, and there is no concept of "adding" files to a "project." because you arc working with your source files directly.
Conventions Used in This Book The following styles Jre used in this book to highlight portions of text that are important. You will find these highlighted boxes here and there throughout the
book. Note This is what a note looks like.
Not~
provide you with additional Information related 1<.l the lex!.
Tip ~
is what a tip looks like, Tips give you po
Caution This Is what a ,"ulion looks li ke. Cautions provide you with guidance and whal1<.l do (or oot 1<.l do) In a given situation. Note This is what a defin~ion looks like, Definitions el<,Olain the meaning behind a tedmKaI cOI'Kellt 01
"""
xix
PART
I
JAVA FOR BEGINNERS
The first part of the book will get you started progr..mming in Jav;!. You wiHleam how to install and configure the Java Development Kit from Java SE 6 and test your Java installati(JlI on your PC by writing your first gallle-all Apple! version of ASfrroids that runs in a web browser. • Chapter I: Getting Started with Java • Chapter 2: Java Programming Essentials • Chapter 3: C reating You r Firsl Jav;! Game
CHAPTER
1
GETTING STARTED W ITH .JAVA
la\'3 C1n 1)<' a complex progrnmming language and a challenge to learn in its entirety, bllt it iseasy to get up and running with lava very quickly using freelyavaitable dc\'dopment tools and basic code, I~va is one of th e most rewarding progmnming languages I have uSll'd, ~nd I'm sure you will ~gr« as rou gain apcrimtt with the language that it's worth your im·l$tment oftirne. This chapter will help you to get Sl~rted with J~n ~nd will be espn;iaIly helpful if you ha\'t: had 00 prior apcricna with this language. It e:xplains wlu.t you n«d, w~ to get it, and how to configure your S)'Slem to pl"t:J'"lre it for building Ja....·based g;iElK'S. H~ are .some of the topics that will be COVft'ed in this chapter. • Understanding Java ~nd the Web • Undcrst~nding the casual gJrTlC$ market • Installing and configuring Java • Writing your first Jav3 program
Java and the Web let's take a look at game design for a moment and see how Java fits in, because this is the cort" subject of the book. What truly has changed in the world of gaming since the "good old days"? By that lenn, I am referring to the infancy of the game industry that entertains the world today, back in the 1980s when arcade
,
4
Chapter 1 • Getting Started with Java
game machines were at the top of their game. Many readers were probably bam in the 1980s and have no recollC
Ninteodo has given some 01 il'i /he Past (lor the Game Boy Advance), have outsold most console and PC 9'!rnes,
Studying the Market The game industry is pushed forward by garners, not by marketing and business executives, which makes this industry somewhat unique in the world of entertainment. Isn't it obvious that professional sp
Java and the Web Can you think of a game that Blizzard has published that does not fit into theso:: two g....nres? Blizzard has consistently hit the mark dead cent....r with thdr gam . . s in terms of target audience, quality, polish, and subsequ....nt mass appeaL World of W
Design Rules [could go into other compal1ies with equally impressiv.... success stories, as well as those that have been dismal failures. But my goal is to demonstrate to you that the game industry is indeed a buyer's (gamer's) market. It's not dictated and ruled by the board of directors of one company or another or by marketing prople, who have been stymied by the reluctance of gamers to go along with traditional promotional theories. In other words, gamers are a tough audience! It's an empowering position to be in, knowing that your personal preferences and tastes are shared by millions of others who demand excellence and innovative gamepJay, and that these demands are met, more or less. Companies that produce excellent games are rewarded by garners, while those that faU short quickly close up shop and move on. Would you like another real-world example? A few years ago, a IKOW publisher . . merged in the game industry by the name of Eidos. This company's bank account was padded by millions of PlayStation owners who had all fallen in love with Lara Croft. Eidos seems to have misinterpreted the market, believing that gamers loved the image and motif of this Bond-esque heroine. Eidos <:reated a new hotshot team in Texas made up of some industry veterans in an endeavor calle-
S
6
Chapter 1 • Getting Stane
vmes
I n my experience, the fun factor of vidto has risen exponentially in the Lut two dec:ldes. along with the compleJ:ity of modem garlle$. Le'l's face it; you nn only play Pnc-Aftm for an hour or 50 umil it becomes tedious. 1lJe Slim applies to ITlOSt oftM dassjc arcade gal11('$. At o~ time, you wuld 6tl"\'ery vidto game in existence in a single room, and those quarter-fueled machines were housed in stand-up cabinets. Sincl!' that tilm, thl!'rt" have been about a half miUion gamts created, though we might narrow down that figure to a few thousand good games, out of which we find a fcw hundred "Hall of Famc" grl!'3tS.
The Casual Games Market In the last two yea rs a new genre has arisen in the game industry calltd msulll
games. This genre has been relegattd to secondhand status for many years. .....hil.. the numbers of ganxT$ has risen from the hardcor<' "gttk" fans to include more and mort" prop"'. The averagl!' gamer pb)'"$ games for a few hours a wed;, while 1M hardwr<' gamn spends 20 or mort hour'S plajing pmcs I"\.tty "ttk (lik(' a part-time job). Casual garners, on the other hand, will only spmd a few minutes pbying a gamt r1(lW and thtn-ptmaps I"\.try day, but r1(lt al....';))'$. Tht casual gamer doa not becolfl(' addicted to any gamt the way a hardoor<' gamer does. with gaffi('S such as ''''orld of warCmft, StIlr Wnl'S Gnlnxies. Tire Matrix OtJlirrr, E""rQ"est, and so on. So, whal is a c"sual g;l1ne anyw;]y? A c;lsual game is any gaillc that can be playcd in a shon timcframc and requires no instructions on how to play. In this context, almost every classk arcad.. gamc ever made falls into this category. It is only recently that publisher and game industry pundits have btgun to rtaliu that
The
C3~ ...al Game~
Market
garners renlly don't want the long, drawn·oul experience of instnlling a gnmc, downloading ~ patch, ~nd spending eight hours karnillg how to play it. Sometimes it is rdreshing to just fire up n game nnd play for 10 or 20 minutes without having to ,rrcw with il all evening! This was a gripe of mine for a long time. [t is why 1spend far morc time playing console games than PC gnmes, and I'm sure many readers share that scnliment.
No Manual Required Yl'S, there are some PC games that are so compelling ()f innovative that they arc worth the effort to gel them illstall~'" and running. The best ex.1mple of late is WorM of lVarCraft. 1 have spoken to many gamers who dnim that if Blizurd's games were not so darned much fun, they would boycott llli7.:t.Jrd altogether! (How's that for a contradiction?) The impression I gel is that these gmners have a lore/hale relationship with Bliz7.Jrd and many other !}1me publishers as well. (Lest you suspe<:t that 1suffer from memory lapse over Blizza rd, let me dear up one important point-l love their games, bill dislike their terrihle installersl).
CaS<' in point, [ could not inst all World of W",Cr
7
8
Chilpter 1 • Getting St,rted with Jav,
dealing with computer problems .md coping with them without incidmt, But do you t\'er wonder, if you-a smart, experienced, knowkdgeable computer expert-;ln- having problems with a game, how on earth ...ill an .. \~ge user figure out thl'Sl' problems! Wdl, the short answer is, they dOIl't, which accounts for most game returns.
Casual Garners Casual garners include professionals such as doctors and lawyers. business eucutives, wftware developers. and, well, n>eryollr rls<-. Casual games aunCl pcopk from all cultures, classes. genders. religions. ethnicities, and polilical orienlatioll$. Given lhat lll(l5I pottlltiDl game playet'$ art' THlI willing or able to cope ...ith the issues involved in PC games. is it any wonder that this burgtQning markt'! has hem ilJe'\1table for Sl"\~1 years now? While casual games are cur· rently played mainly in a web browser using technology such as 1.1\';1 and Rash, the console systems ate featuring online gameplay as well, and this trend will continue to gain popularity.
Casual Games The casual game market was limited a f~ years ago. Only recently has this subject started 10 show up on the radar of publisher$, schools, and retail store;, even though gamen ha,"<' hem playing casual games for two dtotdes. (I predicted casual games would take off a f~ years ago, but my dog ate that article.) Casual games are a win-"in situation because they are just as easy to create as they are to play, so the developer iii able to create a casual game in a short timefrome, and the gamer has an enjoyable experience with a 101 of choices. Casual games have a very simple distribution model (most arc put up on a website for online pby), a respectable compensation model (developers receive a percentage of net sales or a single lump sum), an often meager development cycle measured in weeks or a f~ months. and almost no testing required. As a casual gamedevelopcr, you can come up with an innoY.ltive gamt idea, develop the gamt, and gt'! il onto store shelves (that is, a website) all within the timeframe of just the concept-art stagt'of a full-blown rebil gamt. Jay Moore is an l"V3.ngelist for Garage GaIl1l'5 who promotes the Torque game engine around the country at conferen,es and trade shows. He spoke at the 2005 Technology Forum at the University of Advancing Technology, where he addressed the possibility of ea rning a living as a casll,l l g.1me developer. Garage Games' Torque engine has been port ed to Xbox, and they have published two
Installing and Configuring Java games on Xbox Live Arcade that you can download and play if you are a Live user. Marblf' Blilst is one such game, and Garage has m,my more games planned for release on Live and through relail channels. In fact, when you purchase the entire Torque game engine for SIOO, you have the option of publishing through Garage Games, which does the contractual work and provides you with a contract (subject to quality considerations, of course}. Microsoft has really embraced casual games by making it possible for independent developers to publish games directly on Xbox Live Arcade without going through retail channels. Xbox 360 is the first con:;ole video game system in history to provide downloadable games right out of the box without first purchasing retail software. If you arc interested in casual games, you can enjoy playing on Xbox Live Arcade without buying a retail gmne at all, because many games arc available for free trial and purchase on Xbox Live Arcade (with a membership account, that is). I attended the Austin Game Conference in 2005, and the focus of the show was casual games. Microsoft's booth w;lS titled "Microsoft C1sual Games," and they were giving away USB nash drives with the MSN Messenger SDK and showcasing some of their Xbox Live Arcade games, as just one example. One of the most impressive games available on Live Arcade is RoboBlilz. This S'ulle was built using the Unreal Engine 3 (which Epic GanK'S developed for U"rrlll TOllrtJllmcut Ro/JpRljtz also makes usc of the impressive Ageia PhysX physics engine to produce realistic gameplay. Another innovative g.1me 011 Xbox Live Arcade frOm the creators of Projur Gothllm Rilcillg is Geometry W,lrS. This game is unique and compelling, with gameplay thar involves gravity and weapons that resemble geometric shapes.
1m.
[fyou feel as if I've been leading you along a train of thought, you would be right to trust your feelings. The focus of this book is about programming games llsil1g Java, and we willklrt1 to do just that shonly. Sincc Java is the pioneer language of casual gamc development, I will be emphasizing this aspcct of gaming while creating web-based projects in the chaptcrs to cOme.
Installing and Configuring Java As you might have gueSS«!, Java applet games run in a web browser-Internet Explorer and Mozitla ['irefox work equally well for running Java games. Java programs can also TUn on a deskrop system locally without going to a website.
9
10
Chapter 1 •
Getting Stilrted with Java
These typ<.-saf [,ragrams areealled fill·...
Inst alling Java Java SE 6 is anibble an the CD-ROl\l accompanying this book in the \IavJ folder. You may also ,isit the fa\"J home Pilge al jJ'":J.sun.oom todownJoad the latest ,'ersion of the JOK {s<''C Figure 1.1}. When you install the JDK, the installer will not automatiolly moditY your ~)'Stem's environment variables, which is something we will
... __. __ --_ . """,._-,
"'........ 10 "'" ~,,'_
JaYa(TM)OC~ " I:U6~e2
...,.. ...
............
-"'II"-,,,-,_.,,~
Figure 1.1 Ir>stalliog /alia SE 6.
IrlStalling and Configuring Java
n«d to do so that you can run
w
Jay.l CQIllpiIeT (javac.aL") using a CQIllmand
promp( 01'" sbdI window. The CUfmlt vasion at t!'lt time of this writing is Java SE 6
w install fik is calkdjdk-6u2-windows-i586-p.aL". [f you aR using a othtr than Winc\olo'$ you will nM;I to visit w Java website to do-.nIood the arrropriate ~ lOr )
Configuring Java lava will be installed by default in the f()lder C:IProgram Filesl)ava (on Ih~ Windows plalform; obviously, Ihis will be differen t depending on your system). In this folder arc two folders ~alled jdkI.6.0_02 and jreI.6.0_02, containing Ihe ~eropment kil and runtime environment, respectively. We need to focus our attention on the lirst foldCT ~omaining th~ 10K, in panicular. This fold~r contains a foldCTcallrd bin, in which)'O\l will find all of the Java programs ncedrd to rompilC' and run Java rode. Th~ most imponant programs in this folder are javac.C'Xe (the Java ~ompiICT) aDd appletviewer.C'Xe (theapplt! viewn utility). W~ nmi 10 add this folder 10 the system's environmenl ,.. riables so Ihat we can im'Oke lhe Java compiler from any localion on the hard dri,'C'. I'm going to focus my attention on Windows XP since il is the most widely used operating system. IXpending on the system you're using, th~ steps will be differelll bm the concept will be similar. You need to add the jdkl.6.0_02/bin folder l(l YUllr system path - the list of folders searched when YOIl invoke a program ;It the command line. In Windows, open the Control Pand and run the System utilily. ~[ect the Advanced tab, as shown in Figure 1.2. Her~ you will find a button labeled Environmrnt Variables. Click on il.
Scroll down the liS! of syst~m variables until you find the Path variable. Select it, then didr. the Edit button. Add the following to the end of the path variable: (induding t!'lt snnioolon): ;{;:\Program Filcs\java\jd k 1.6.0_02\bin If you have installed a differen t version. you will need 10 substitute the version shown here with Ihe actual folder name representing the version you installed on rour system. Click the OK button three times to back out oflhc dia logs and s<1VC your scttings. Now let's vcrify that Ihe palh has h..-cn configured properly by tesling the Java installation.
11
12
Chapter 1 • Getting Sta rted with lilvil
S_Fl... . . G. ......I
__
u~
••
H.._
~N.....
.
You """ be lowed M '" .... - . . . . _ 10 moI
v...ae/ltlCl•. proce.... ~_utOlIO."""~c>IIi_
I
~~ )
S!l\W'9
I
S....'4I"""R_ S_ _.tyIleIn l...... ,""" n
OK
Figure 1.2 The
S~lem
Propertie-s dialog box.
II e-
ilC(e-ssi~e
from Windows Cootroll'anel.
To 0pl?n a command prompt in Windows, open th~ Start menu, choosc Program Files (or All Programs), and you will find it in Accessories. Thl? command prompt should appear as shown in Figure 1.3. If you arc using a systl?m like Linux, just open a shell if yOll don't have olle open already, and the commands and parameters should oc the same. Now that yOIl have a command prompt, type the following command and press Ellter: javac -versioll This will illvoke the Java cOlllpiler and instruct it to merely print out its vl?rsion numocr, as shown in figure 1.4. The \'ersion reported here is just what rOll would expect: 1.6.0_02 rcprescnts Java SE 1.6 UlXlate 2.
Installing lind Configuring Java
figure 1.] A (~ prtIfTIpl window has
been
~.
Figure 1.4 TIle Jan oompilef printtd out its wmon numllef.
If you wtrt ablt 10 see lilt vt't'$ion number show up on your Sysltm, thtn you will
know that JaV;l has b«n illSlalltd COlTtClly, and you'rt ready to slart writi ng and compiling COOt! On tht othn hand, if you rectivtd an trror such as "Bad comm;and or fik namc.o,n thtu your tuvironlll('Ilt ""ru.bk has not bttn set corrKtly, as expLainal pr~usIy. 11ltre is an alltmativt 10 tdiling tht syslnn's
13
14
C~apter
1 • Gettiog Started
wit~
Java
mvirooment variable-yOll can iust modify the path (rom the command prompt. However, whm yOll do this, the change is oot permanent, and you will have to set the path every time )·ou open a command prompt. But just for reference. here is how you would do it: set path=%pmh%;C:II'rogram Filcs\Javaljdkl.6.0_02 At this point, you are ready to start writ iog and compiliogjava code. So let's do just that, 10 further test your Java installation. [n a mommt, we'll write a java application that prints something out to the console (or shell). See the S<.,<:tion Ixlow tilled "Your First lava Program."
Java Version Numbers lava's versioning can be confusing, hut it's something you might want to understand. The officiallatcst version of lava at the time of this writing is lava Standard Edition 6 Update 2, or java SE 6. However, the actual version numocr is 1.6.0. Th.. computer industry is an)1hing but consis tent, given the cxtraordinary changes thm have ta ken place on the Internet and in softw'lre development in general. liut one thing has oc'Cn agrCl-d upon in lhe compll1cr industry rega rd ing I'ersioning. The first release of a software product is version 1.0. Often a revision or build number will Ix appended. such as 1.0.8392, which helps technical support or caU ccnter personnel identify the version or sub-revision of software that a customer is using wheo a problem arises. The revisioll lJumber is, in every case. not part of the retail packaging and prod uct name, but rather a tracking tool. Table 1 1 lists the ja\'3 "ersion history.
Table 1.1 mva Version Year , ~
,~,
'"'
'00' ,~
,~ ,~
H~tory
Version
,.. " U
,." "" "
Marketed Name Iav~
1.0 I JOI: 1.0 Iav. 1.1 I J[)I( l.l
~"
lISE 1.3 !lSE ' .4 USE S.O IavJ SE 6 Iav. SE 7
--..
Code Name
.... ~
'"
M."",
~
"
Your First Java Program ~ inlCfl.'Sting thing aoout this table is that it is very '()Jlsistent in the S('(Qnd column (VeTSion), but there are a lot of inmnsisteneies in the third column (Marketed Name). which is not a gnat surp~ sina marketing campaigns sddom makes sense. If you were to follow the progression from Olle' '"CTSion to the nat and tally them, you might note that then have hem K'VCIl major versions of Java (while the eighth veTSioJl is 1.1, and not yet rclcascd). Produa branding is a very C'Xpm.sive and time-
When Sun released Java 2 as a trademarked name, the name caught on. and the version we arc using now, Java SE 6, is still known internally as version 1.6.0. Java funs love these quirks, which are not flalV5 but endearing traits, and it's not a problem once you understand how it has evolved over the past decade.
Your First Java Program I walll to take you through the steps of creating a new Java program (0 test the JOK and a Java appld project to ttst web-browser integration before moving on to the next chapteT_ Let's start at the very beginning so thaI when you ha"e wrinen a full-featured game down the road, you'll be able to look ba,k and see where you started.
Java Application ~ following program, shown in Figure 1.5, is calkd DrinkJava. Type it in and save the file as DrinkJava.java.
illllO rtJ UI. tO .·; cllss Or l nkJna I p ~ b ltc static wo t d .. t nl Str i ng Irgs()J I Sys te•. out. prj nt1n( • [)o you IlkI' to dr t nk Jua 1" ) ;
p~bllc
Now let's compile the program. You'll need to open a Command Prompt window ag
1S
16
Chapter 1 • Getting Started with Java
1/ kq' .... 1lV J..,. . : - . ." " _...., 1Ieco....
fI "., Jo_t_ S. _ _ II
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_
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ue e l _ D<.dJ..,. _He nat'" YO.d _ •• IS« ......... 111 l Sn..... o••••n ... '.I·"" "","IDO <0 "" ... J""?-I,
Figure 1.5 The Drinl
fd i~ IIId
sawd wng
Once in the oorr«1 foldcr, you can Ihen your program:
Nol~.
lI$C
thc javac.oe program to cornpilc
J'.'c Orlnl:JU'.Ju,
lbc Java oompiJcr (ja\'a(.oc) should spend a (cw momcnls compiling )"Our progr.un, and then mum thc command prompt cunor to you. If no ll1C$$lgc' is displaycd, thai mcalU ('\·crything wcnt ouy. You should then find a IlC'W fill' in Ihc folder called DrinkJa\...c1ass.. You can scc thc list of filcs by typing dir al thc command prompt, or just open Windows Explorcr to broW$(' thc foldcr graphically. To run the newly compilcd Drin k/ava.c1ass fiJc, you usc: the java.exc program: J,.,OrlnkJH.
Note that I did not include the .class extension, which would have generaled an error. Let Java worry about the extension on its own. By running this pmgrum, you should see a linc OUlJlUl onlo the command prompt like this; 00 yOY 1He to drink J•• ,?
Perhaps without realizing it, wha t you navc done IKoIl' iscr....te a lava appllm/ion. This is one of thc two t)'J1'eS of la'.. programs you can create. The otlKor type is caJlcd an ppplcf, which describes a program that runs in a .....eb browser and is
Your First Java Program rcally what we want to do in order to create Java games. YOIl Qln certainly write a la"a g.lme as an application and run it on a local syst"m, but the real point of this book is to cr"ate lava applets that run in a web browser.
Java Applet Now let's create a lava applet and note how its code is different from a lava application. This applet that you're about to write will run in a web browser, or you can run it with the appletviewer.exe utility (which comes with Java). Open }'our favorite text editor (Notepad, TextPad, Emacs, or whichever it may be) and create a new file called FirstApplet.java with the following source code. TextPad is shown in Figure 1.6. Before you try to run the program, though, we'll have to create an HTML container, which we'll create shortly.
-'--
"""" """,.
_
oM>
:11:12 11 ~;,!,~<%q:.~
•
•. r";',-"''''-=',,--~~-~---cr,-,--~-----o; l "
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" Figure 1.6 The firstApplet soorce code if,
Te~tPad.
17
18
Ch~pter
1 • Getting
St~rted
with
J~v~
Tip The 11';"1 edilion 01 www.textpad.com.
Te~IPad
is provided on the CD-ROM, Yoo can optionally download il from
I~port java.allt. ", Illport java.applet.', public chss FI rsUppi et extends Applet I public voId palnt«(;raphlcs 9) l 9.draIlStr1ng( "Thls Is lIy first Java Appletj", 20, 30),
The applet code is a lill1c different from the application-based code in the DrinkJava program. Note the extends Applet code in the class definition and the lack of a static main method. An applel program extends;1 class called Applet, which mcans the applet will receive all of the features of the ApplH class (which has tI\(" ability to run in a w!.'b hrowser). Essentially, all ofth{· complexity of tying in your program with the web browser has been done for you through c1'lss inhcritance (you r program inherits the (eatures of th" Appl et class). You C:ln compile the program with this (Onlnland, javac FirstApplet.java Now, if you happen to be using TextPad, as I am (refer to l'igurel.6), you can compile the program from within TextPad without having to drop to the command prompt to compile it manually, As Figllre 1.7 shows, Textl'ad has a macro that will launch the lava compil!.'r for you and r"port th" results of the compil!.'. If there arc no ",rrors in the Java code, it will report "Tool completed successfully." In order to run an applet, you must provide an IlTMl.container. This is a basic HTt.11. web page containing the code to eml>l.'d an applet on th", page. We'l! be creating one of these containers for every program in the book. But don't worry, it's easy to create an I-lTML container, and the eml~'dded arrlet COOl." is shon and sweet. Create a new file called !'irstApplel,htrnl and enter the following code into this file: F I fS tApp 1~t
Your First Java Progrllm
<.ppln codebilSe - ". " code - "flrstApplu.clilSS " "ffrstApplet " wldtb - "640" ~lght - "480"
u.
-
hspace vspace
- "0" - "0"
align
- ".1ddle"
> < / ht_l)
This contai~r -b pa~ cock indudl'$ an C'tllbnkkd tag with paraII'I
'".IK".......... "~ .......~ ......,01v."..p,... v,, ... p.... j.>~1
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• •
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Figure 1.7 Compiling Java
"
19
20
Chapter 1 • Getling Stfrted with Jav
---
_...
--
Figure 1.8
The fintApplft
pRlOpm
is nftIing iMidt lh. Appet
appltt, among other propmics. You can liUso:
~
DOW
uriIiIy.
opm this file with Applet V~
applrt,iewer FintApplet.html The Apple! Viewer "indow appears with the FirslApplet program running, as shown in Figul? 1.8. You can also open the FirslApplrt.html file in your favorite web browser. Using Windows Explorer, locate the folder containing your project and locate the FiTStApplel.html file, then double-dick it to open it in the default web browser. Figu re 1.9 shows the applet running in Internet Exp lorer.
What You Have learned Well, this has been a pmty htavy chapter thai covered a lot of material, but my was to get the Nsics covered so that we can jump right into jaVil game programming in the nat chapter. You learned about:
goal
• Casual gam($, what tl\(y arc, and their importance
Review Questions
_... ...'- -
-
fIgure 1.9 RrstApp"t is IUlming .s an <.'flIbed
,,~
•
, ~.
appI~t
in
Int~mel
ExPorer,
• The Java Development Kit (lDK) and lava versions • Editing and compiling Java code • Standalone Java applications and Java applels
Review Questions The following questions will help you [0 determine how well you have learned the subjects discussed in this chapter. l. What does the acronym ")DK" stand (or?
2. What version of Java arc we focusing on in this book?
21
22
Chapler I • Getting Started wilh Java
J. What is
th~ nam~
of lh~ compa.ny lhal cr~aled la,'a?
4. \\'her~ on th~ web ",ill )'OU lind Inc, lext nlilor c
5, In ",'hal '"Car "''as la"a first rckased? 6. Where on 1M ",-dl is lhe primary download
sit~
for lal...?
7. Whal Iypot' of Ina program do you run wilh lhe ja\";l.Cl'C tool~
8. Whal lypc of Java program runs in a wdJ
bro,,~r?
g. Whal is Ih~ name of the command-lin~ 1001 used 10 run a web-hJsW lal... program? 10, What is lhe name Oflhc paramelCT IMssed 10 lhe paint!) el'elll mdhod in 3n
applel?
On Your Own US('
Ih~
foUo..ing ~nrci~ 10 lesl mur grasp of Ihe mJ.l~ co,'cre
chapl~r,
Exercise 1 Modify th~ FirstAppltt program 50 thaI il displays your own nwssa&~ on Ihc lo(:rC('n below Inc, CUrffnl message.
Exercise 2 See whether rou can figurc OUI "here System,oul.prinlln oUlput goes whcn run from an applel project, SIllCC lhe It"xl is nOl displayed ill tht" applt"1 window.
CHAPTER
2
.JAVA PROGRAMMING ESSENTIALS
/3V:l is a matuu programming 13ngu3ge thai offers many good features 3nd Q.pabilitiC$ that make it p
If you are jll5l getting S1aned as a java programmer. then this chapter will bdp you gain some familiarilywith the Java bnguage. You wiD Ic:un most of the basics in this
chapter that you will need to wrile an applet-Ixucd wm game. There is a Jot more to the lava language than what you willicam about in this sole ch,'ptcr, obviouslyl11,my entire books have been wrillen aboul java. This chapler will help give you a jurnpstarl if you arc new to lava. If you have experience with java, you may find the infonrultion to be: vague, bUl il is more importanl for a beginner 10 understand ooncepts ralhcl"Ihan sundards. In addition. I will not deh~ into any features that are new in Java SE 6. Herr is what you willlc:un in this chapter: • How to wrile Java code using appku • How to usc the java dala types • The basics of object-oriented programming • How to write java classes 23
24
Chapter". Java Programming Eswntia!s
Java Applets Th~
are two dilT..rent types of prograll1$ you can coOlpi~ with Ja....: applications or applets. A Java UPtHicufion is a program compiled to run on a computer asa sLllndaloTl<' application (hma the' naJ1l<'). A Java appl~. on the' othC'r hand, is compiled specifically to run in a web browser. Java applicatiom are lm.llllly written 10 run as ~'er programs, whilC' applm run as client prograll1$ in a Tl<'tworkC'd environment. For enmple. Java Web Server (JWS) is a Java application that hosu wC'b pag.. fila to a .....tl browser (such as InterM1 Explorer or Morilla Firefox). and it is comparable to Microsoft 's Internet Information Server (115) web server and the open-source Apache' web scrv<:r.
Web Server Technology Explained The main d ilTerence is lhat Microsoft's web :server (115) and the Apache web :server were wrilten in C++, while JWS was wrillen in Java./WS can host regul;IT HTML web paga and custom Java Server I'ages (151'), which are custom web server programs written in Java. A Java applet is difTerent: An applet is a "dientside" program that runs entirely in the web browser, not on the web server. A Java Ser...er Pages application literally runs on th.. web server and sends contC'TIt to th.. web browser, whi~ an appl~ runs only in the web browser. For this reason, we say thai SCf\'C!" progranu run on the' "back end," while applm run on the' "front end." Microsoft's 115 web SCf\'C!" has gained in popularity and marUt share in rcce'nt yt'ars, thanks in pan to the' new .NET (prollOUlKC'd "dot n~") technology. The latest ...ersion of 115 hosls Acti...e Ser.....r Pages .NET (ASP.NET) pages. which are similar to Java ServCT Pages (lSP) in concept, but ASP.N~" pages are written in Visual Basic or C# (pronounced uSC<'_sharp"). If you don't know much about web servers and web applications, don't worry- we will only be wTiting web diem programs, not :server programs.
Hosting Java Appfets If you really find that you enjoy Java, then you may W;lnt to consider creating or enhancing your own website' with Java applets. You can build an entire website as one large appl~ or you can embed many different apple'lS inside a standard HTML page to enhance your website. One ofthe' st rong suilS of Java is that you don't need any special t)'p<' of web snver in order to use Java on your wrllsite'. Java has been around since 1995. and web browsers h.a...e supported Java since
The Java language I;l\'a 1.1. Microsoft InteTn.... Explol"eT and Morilla Firefox support lhe blesl version ofJava. To update your browser, simply install Java SE 6, and lhe installer will add a plug-in 10 your web browser aUlomatically. This is nc<:essary if you wanl 10 run the exa mples in lhis book-mosl web browsers come wilh an older \·crsion of Java, such as 1.4.
Compiling Java Code The e;\sicst way 10 compile a lava progrJm is by using lhe command-line compiler. A5 you may recall from the previous chapler, you usc the javac.cxe progrnm 10 compile a .java file inlo a .class file. You lhen usc IheappletviCW(:r.cxe program in conjunaion with an .htm! conlainer file with;lJ\ embedded applct tag to run your Java applet in I~ applct viewer program. ¥ou an also open this HTML lcsl file in a web browser to run the applet. Rather lhan using a complex and large Inlegraled Development Environmen t (JOE) 10 build and compile your Java code, I recommend using a simple leXI edilor and t~ command-line tools instead. In l~ previous edition, we' used Borland IBuilder as our IDE of choice. This lime around, we're using just simple lext editors (with TcxtPad bring my cboice in WindoW$). This will impm~ your programming skills and make you a more useful progrnmmeT, since you will nOI be lied 10 any specifi( platform or IDE (such as JBl.lilder). A good texl editor thai I recommend is TcxlPad because il is small and hus the abili ty 10 (ompile (Ctrl+I):;Inc! run (Orl+3) your lava programs. The cost oflhe fuUy regislered version of TcxlPad is II pallry sum compared to the (ost of a full IDE sudl as lBuilder. Of counoe you can also usc any frtt lext edilor as wdl, lbough most do not ha~ Ihe nice buill-in support for lava that TexlPad has. Anolher pair of ahemalives thaI you may (onsider is Net Beans (www.nelbeans. org) and Eclipse (www.cclipse.org). Bolh arc free IDEs wilh varying levels of complexity :;Ind fcaluTC$ Ihal you may want to upgrade 10 whm your Java projects become too brgc to manage wilh a simple file system.
The Java Language There arc lhousands of classes in Java, bUl we will only be using a few oflhem 10 build web :;Ipplets. Now then, I suppose el'en a word like "class" might be a mysteT)' if you arc new to programming. A <:bss is a Klrt of container thai holds both dal:;l and funaions. Do you ha~ any experience with the C++ bnguagrl
25
26
Chapter 2 • Java Programming
Essential~
)~,........as based on C ., by "borro"'·'ng" all of the best features of C~ + and dropping the more difficult ~spects of the langu~ge. The Sun Microsplmls progrJ.mmers who dewloped the 'a\d specifiCltion Crelted a langwge thai is more of an evolution th~n something created. C ~ + is a powerful l~ngUilS<' ~ to build e'\'el),hing from cell phone g;t1l1e:$ to operating S~mlS to super· computeT simulations.. The poWeT of C+ ' makes it diffieull for ~nJ1('Q to grasp, and ("\en profl$Sionals ....ho 1u\"C" spenl many vears "'orking with dJ.tabasn and web applications rna)' be st)mied ....hen confronted by C.,.....-. It is a world· class l~nguage, and there 3re doz.em of compilers for it on ('\'ery computer s)')u'm. Ilere is a list of software buill in C., ~:
• Microsoft Windows
• Microsoft Office • Microsoft Visu31 Studio •
Microsoft Internet Explorer
• !.inux • Mac OS •
Sobris
• Mozilla Firefox • Star OprnOffice I
~ould
go on and on, listing thOUSillJds of operating systetm, producli\ity Cimf d('\'ice dri\ers. compilers. .....semh!ers. interprel...rs. and on and on. ~ppli,at;ons, ,ideo
Now consider )3va. lnere is jU5t one compiler for it, the lava Development Kit (JDK), which;5 available f(lr the most popular c0111l'uler SyStenlS. Java is innovative enough to be calk'd a new languagc, but it was heavily innucllced by c ++. Java is much easicr to program than C++. Java aUlomaticaHy handles memory management for you-all )"OU do is allocate memory for new variables alld objects, and thcn you don't reall)' need to wolT)' about freeing up the memory afterward. ""':1 uses a t«hnology aIled garbou coll«rioll to remove unused things from memory th,u }"Our program no ionS<"" ll<'OOs. To gh"C")"OU an analog)', in the rnIm 0001\"3, )"ou don't e'\"m need 10 Cilrry lhe tr;lS/Kan out to lhe SIred for
The Jowa
LJngu~e
pickup beo!US(' the pro...ge colltclor just picks up all the trub thrown about in your hoUS('. TIlt pro...y roIltcl.or is son oflike a link robot thaI seuma about the hoUS(' st:It(hing for lrash to pick up. Whtn you an: done with your Chinest takrout, just pilCh the container and your napkin, and the lillie trash robot will find it and dean it up for you. This co"ltIlead to sloppy progra mming if you spe nd many years programming in Java and then swi tch to a more demandi ng language like C++, so Java makes it possible for you to write solid rode Ihat dea ns up after itstlfif you wish to use il. There is a dra~ck to garbay coU«tion, though: You can't tdl it specifically 10m" to pick up the trash ( nriables and ob,itct.s that an: no longer used), only that then: is trash 10 bt' pKbd up (as with the real-world ga.m.gt coIkctors J1lO$t of the timt!).
Java Data Types Let's now learn about the basic data types avaiklblc in Java, because you will be using these data types throughout the book (and presumably for the rtSt of your programming ca re-er). Int~Numben
Jan supports many data types. bUI probably the most basic data [)'pC is tM illltgtT. Integers rtprtSol"nt wholt numbers, which an: numbt'rs thaI have no d«imal point. There are several types of integers that you may usc depending on the size of number you need to store. Table 2.1 shows the types of integers you can usc and their attributes. Since Java programs alii run on a wide variety of computer systems (th is is called cross-plnrfomr suppon), you might bt' wondering whether these data type values
Table 2.1 kttegel' Oata T)'Ill'S
...".
Sift in Bits
byte ~~ort
'"
10"9
32 bot> 64 bios
-12310121 -32.768 lO 3l.161 -2, W,483,64lIlO 2,141,483,647 -9,223,3n,036,~.I7';,808 lO 9,223,371,036,854,775.801
27
28
ChaplE'f 2 •
Java Programming Essenlials
will b<.-Ih~ S3m~ on <:v~ry sysl~m. Aft~r all, a Java program can run on a litll~ c~ll phone or it can run on a supe rcomputer, such as a Cray Red Storm system. Tip
irlIomIilIon abouI ~ dled ad. _q600.arg Jar a ill: cI tht lOp SllO on lhe ~ At Ihr tme 01 \hi. wntng. lhe net powerful a:np.rte" on tht pIaIwt is IBM's B~"'" ~ a 1IWd-~ 280 lrillion apo
for
moll!
~
Java gelS around the dau type inconsiSlency in C++ by defining that data types will be exactly the Arne. regardless of the compuler syMmI on which the Java program is rulllling. Ifs lhe job of Ihe Java Runtime Environment ORE) 10 d~termjne at runtime how th~ current computeT syst~m will handl~ the data types your Java program is trying to use, and it docs this scam lessly beh ind the scenes.
Floating-Point Num~ There are t.....o da ta types available in Java for .....orking wilh f1oaling-poi nt num bers. A floating-point r~'Prcsents a decimal value. 111e float data type stores a 32-bil single-precision number. Th~ doubl~ data type stores a M-bil doublepr«is.ion number. Table 2.2 shows th~ spOOfic.s of these two data types.. Th~ easicst .....ay to det~rrnine th~ rang~ for a numeric data type is to usc th~ MIN_VALUE and MAX_VALliE properties of the base da ta type classes. Alt ho ugh we usc lowercase to specify Ih~ type of a nu m~fic vamble (byte, short, Int, long, float, and double), these base numeric types arc aetu.ally instances of Java cla.sKs (Byte, Short. Intl'ger, long, Flott, and Double). ThCTdore, .....~ can lake aped: insid~ these base classes to find som~ goodics, Th~ MIIUAlUE and IlAX_VAlUE properties will give you the range of values fo r a particular data type.
I have written a program caIIe1:I DataTypes Ihat displays these values in an appl~t window. "Ilu.- output is sho.....n in Figure 2.1, and the source code listing follows.. This program is on Ihc CD-ROM in Ihe \sources\chaptcrll2\DauTypcs folder.
Ta ble 2.2 Floating-Point Dilta Types
'''' .......
SizE' In Bits ,.-S
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UE-l24 10 1.7'I169ltl4a6lltS1E+lO!
The Java language
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i_j)Ort Ju •• "t.·: i_port ju. applH •. publlC chss Da taTypu extends
~pplet
(
IIpaint on tne applet window p4lblic void painUGraphics g) I IIselKt a nice 1000t g.setFont(llft FonU ' Courier lew ' . Font.PUII. 12)); Ifdisplay .ini_ and .. d _ walues for n.-ric data types g.drawStrin,( · 81te . ... 81te.MIILYALUE +. to • ... 8yte.II....CVALUE.~. 201; g.drawStrlll9( · Short • + Short.IIIILYALUE+ · to· ... Short ..... x.-VALUL 5. 35); g.dra"Strlng( ·lnt • + Integer .M IM_V ... LUE+ · to· ... Integer.MAl_VALUE. S. 50l : g.~raw5tr1ng( · Long • + long .MIN_V...LUE+· lO· ... Long.M... x.-V"'LUE.~. 65); g.draw5lring(-flolt :. + Float.IIIILULUE +. to·
29
30
Chapter 2 • .laYa Programming E5sentials
... flou.Il.I,l...V.oI.lUE. S. 80); : . ... Oouble.WIN_VALUE"'· to· ... Ooub\e.MA~_VALUE. 5. 9Sl;
~.dra.Str1"qt· Double
Characters and Strings
There are two data types in Java for working with character data; char and String. Note that char i.s a base data type, while String is au tomatically r«:Qgnizable u a class (due to the uppercase fiT5t ldtn-), JaV3 tries to make programming easy for C++ programmers by using many of the same basic data types in order to make it easier to converl C and C++ programs to Java. So we have a base char and a Strlnq class; of course, as you now know, every data type in Java is a cl:lSS already. You define a chu V3riable like this: cll.. stude"tgrade; chlr exa.score· ' A'; Thc char data type can only handle a single cha racler, not an cntire stri ng. Note that a character is idmtifi~ wim single quotes ( ' A') ramer than double quotes, oecrssary for strings. The String data type (or rather, class) i.s vny easy to uSC,' and is used by many of the Java library methods. (Remember, a method is a (unction.) For instance, you have seen a lot of the Graphics class $0 far in this chapter becau$C it is the main way to display things (such as tal) in an apple! window. Here arc a couple of differmt ways to crrate a string; String fuorlte~a. - ·Sld Meier's CiYll1utlon IV·; String usernl.; userMlit - 'Joh n·"'· R. .... · OOe"; In addition to supponing the phu operator for combining strings (something that C programmers look upon with mvy), the String class also comes rquipped with numerous suppon methods for manipulating strings. I won't go over ~'ery property and method in Ihe String class here because thai is the role of a Java reference book-to cover every single detail.
The Java Language Tip If yoo are enjoying Java <0 fa< and you thin\:. you will stid: with it you wi ll definitely need a UlffiIl""!lensive lava language reference boolc.. lreoommend Herbert Sd1 ildt's ava: 11le Complete Reference. Seventh Ediricrl (M<;(jraw·HiII C\$bome Media, 20(6). A good inl'oductoly boo!< for beginners is IoIIn Flynt's Jilva Progrilmming fOf rile Absolute Beginllef. Se
linked
documenta~on
at iava.sun.coml,efereocelapi,
One good example of a function we've been using in this chapter is Graph; cs. drawString. This function has many overloaded versions avaibble (overloading is expbined later in this chapter, in the section entitled "Objeet.Oriented Progmmming") that give you a lot of options for printing text to the applet window, but the main version I usc is this: dra"String(String >tr,
Int x,
1nt,)
Note
We have just watched the surface of the Graphics class (and the Graphics2D inheritl'
Method
Description
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31
32
Chapter 2 • Java Programming Essentials
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• figure 2.2 JBuilde< displays the CO/lll'/ltl of a dass witI1 a I"'IH'P window. Possibly lhe single greatest advantage to using an IDE is the built· in help system. whkh is available in tools such as lBuilder and Eclipse. If you aren'l using an IDE that provides context-sensitive help and class member lists, then you will need a good rderence book or website. Tip If you ilfe looking for help 00 a specifk )a"a language term or class, the easiest way to 100<. up that inf<>rmation is by U'i ing Google. $earth ' java
boolean gameover· fll se ;
The Java Language HeTt is a short method lhat r,",urllS a Boolean value based on whtlher a value is within a boundary of a minimum and maximum value: publ te boo leln eheelollounds(1ong n I. IOIHJ IOller. long upper) I If lYil (lo..u II ¥II ) uwer) return filse;
ehe return true; Here is an example of using the checkllollnds method 10 detmnine whether a sprile's position on lhe scr~n (in the horizontal orienta tion) is within the screen's boundary: sprHeX· spr1 leX + I; H (eheekScunds(spritex . O. 639) -- true) sp r HeX - 0; This short e~ample assumes lhal the sprl te Xvariable has already been declared eulier in lhe program. The spri te's X position on the screen will wrap around to the left edge anyt ime Ihe spri te moves off the rig.ht edge of the screen. This Boolean method an also be wnt1en like this, where lhe·· true is assumed in the If S1alnnent: If
lellteklloundslsprl teX. O. 639))
Note that [havt: Id't out the -- trlle in this line of code. This is possible because lavaevaJuates the Tl'Ium vaJueofthe ehe<:kSollnds method and replaces the method call with the rdum value when the program is running. Thus if the ch«UOllnds method Tttums lrue, the 1r S1alement becomes this: HIV",t)
This is why we can leave the -- trlle oul of Ihe equation. On the converse, when you want 10 tcst for a false relurn value, you can inserl •• h i se in the if statelllent or you can usc Ihe logical nl'gativc operalor (!) in the statement; 1f (IcheckSounds(sprlteX. O. 639))
The result is that if cheekSounds returns false, lhe I f statemenl will ex«ute lhe code that follows; otherwise, lhe code is nOI ex«uted. Speaking of which. you may include a single line of code after an 1r slalemenl, or you may include a code block enclosed in curly br.KCS il$ follows. This is especially
))
34
Chilpter 2 • lilvil Progrilmmiog Essentiills helpful if you "'alll to do more than one thing after a conditional statemelll relurns true or false: publ!c boolean check8oundsllong val. long lower. long upper) jflval
The use of curly br,ICes in this new version of chedBounds might not change anything, but it docs allow you to add more lines of code before each of the return statements. (For instance, you may want to display a llleSS
All army is a collection of \';)riabJes ofa specific data lype that arc organized in a managcab\e container. lin array is created usiog one of the base data types. a Java libra!)' class, or one of your own classes. To tell Java that yOIi want an arra)', allach brnckets to the dala type io your variable declaralion: I nt[] hlghScoreL! st ; But there are 1,,"0 steps to creating an array because an array must first be defined, and IlleIl memory must be allocated for il. First, )'011 define the data type and arra)' variable name, then you allocate the ana)· by specifying the number of elemcllls in the arl
ThE' Java LanguagE'
ofscrolling backgrounds and spaceships and llltlicrs and explosions, all of which arc made possible with armys. But lhe real power of an army is made obvious when you start iterating through an array with a loop. If you need 10 updale lhe values of lhis army, you mighl access the array elements individually like this: HudentGrades(O]
~
90:
HudentGrades(29] - 100:
If you truly need to set each element in ,m army individually, then an array can still help to cut down on lhe clutter in your program. And an army will always benefit from proct'SSing in a loop when it comes to things such as prinling out lhe coments of the array or storing it in a data file, or for any other purpose you may have for lhe array. leI'S sel all of lhe elements in an array to a slarling value of zero (this is good programming pmclice); long(] speed· new )on9(100J: for(lntl-0: t <100: !++) I
speed[l1- 0: There is another way to creale an array by seuing the initial values oflhe array righl al the definition. This army of five floals is defined and initialized in memory with starting values al lhe same time. float[ 1 rad1 oStattons - { sa. s. 91. 3. 97.7. 101. S. 103.0 ):
You can also creale multidimensional arrays. An array with more lhan one dimension will have a multiplicative number of dements (based on the number of elements in each dinl('nsion) becausc for every one dement in lhe firsl dimension, there arc N e1emenls in the nexl dimension (based on the size of lhe next dimension). In my own experience wriling games, I seldom usc more than one dimension for an array because it is possible (and more efficient) 10 use a single-dimellsioned array, and then index into it creatively to deal with multiple dimensions. Here is an example of a two-dimensional array that Slores lhe values for a game level. The pound characlers (Il represent walls (or any olher object you want ill your game) while lhe periods (.) represenl dirt, gmss, or any other type of image. I presume that this is a level for a lile-baSl.-rl g.'me, where each character in the army is drawn 10 lhe screen 'lS a tile from a bitmap file. ChH[H] gaaeLevel - I
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36
Chilpler 2 •
{",
{.,
,
Java Programming eS5enlials
,
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Another common practice is to create a game level with just numbers (such as 0 to 9). Some programmers prefer to use character-based levels because they son of look more like a game level. and arc. therefore. C
2,2 .2. 2.2.2 . 2.2.2.2. 2,1.1.1.1.1.1.1. 1. 2. 2. I. I. I. 1. 1. 1. I. 1. 2. 2.1. 1. l. l. l. l. l. 1. 2. 2. J.I.I. 1.1.1. I. l.2. 2.1.1.1.1.1.1.1.1.2. 2.2.2.2.2.2.2.2.2.2
n, , t - induclfd ~ . . . . bcd's CD-ROM. Ltd ... m. ~ ~ You un Inl
out more ~ Dlut this gfUI IeveI-«liting IOOl at _~co.,*- HclweoIet m. SlIbject 01 tilHlasfd saolling is ~ m. WlPt 01 this bod. IIIl' dil=~ ~ ~ ~ memy to show you what is posslile. for an txhaostiw guidt to the subiKt I reI.... yoo to VIWiII Basi< ~ Prograrnmjng fry TtctIS, Sccood fdirioll (llIomsoo Course Ted>rdogy PHI, 2(06), Although this book fOCl/l.tS on \l8.NH it is one ot the ttw bookl that fJqllairtl how to build a tilf. biill!d ~ from watth, and the concepts can be lIpplird to JiNa, should you wish to o:mte such
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.,....
Un you I11ake out the simibrity bctwcm the two game Icvds shown hen? It's all the same data, just rcpresmlN differmtly. When Mappy aports a 1n-e: Iikc this, il sends !he dau 10 a text file that )'OU can then opm and pute into )'OUr game's source cOOe. To make it work. )"Ou would dd1nc an array 10 handk the d.lla Iik£ this: tnt{][) gl.eLfyel·1
{2.2.2.2.2.2.2.2.2.21. 12. I. I. I. I. 1. 1. 1. 1.21. 12. I. I. I. I. 1. 1. 1. 1.21.
The Java Language 12,1. I. I. I. l. 1. 1. I. 2l. 12,1.1.1.1. I. l. 1,1. 2l. 12,1.1.1,1. I. 1. 1. 1. 2), 12,2,2,2.2.2.2,2.2.2) I,
Tip Ooo't forget the semicolon at the end of an array dedaration, or yoo wi ll get some vel)' strange
errorl f,om the Java compiler. However, I prefer 10 treat a game level (or other array-based da ta .sequence) as a single-dimensional array because data like this is easier to work with as a onedimensional array. Here is how J would define it: lnt[] gameLevel - 1
2. 2.2.2,2,2 . 2. 2.2,2, 2,1.1.1.1.1.1.1.1. 2, 2. 1.1.1.1.1.1.1.1. 2. 2. 1.1.1.1.1.1.1.1. 2, 2,1.1.1.1.1.1.1.1. 2, 2.1.1.1.1.1.1.1.1. 2, 2. 2.2.2,2.2 . 2. 2.2.2 I,
Do you see the subt le difference between this lD array and the 2D array defined before? AliI need to know are the width and height of the array data, and then I don't need multiple dimensions. In this example, this game level is 10 tiles wide and 10 tiles deep, for a total of 100 tiles. (A tile is a small bitmap used to build a game world in a 2D scrolling game, and it very closely resembles the analogy of noor tiles in the way it is used .)
The Essence of Class In case you haven't noticed, I've been talking about classes a lot. That's because you can't really get around the subject when writing a Java program. The main part of a Java source code file itself is a class. You might have seen a C program before and you might already be familiar with the maln() function. Here is a simpleC program: intlllain{1nt argc, char argv[]) { printf("1 alll a C progralll . In ' ): return 0:
37
38
Chapter 1. •
Java Programm ing Essentials
Let's take a look at the same program written in pure C-t + : 'I nclUde 1ntru in (int argc, char argv{]) l std , :co ut "I a. a C++ prog ra ll. " c: s td: :end l : return I : Now take a look a\ the same program written in Java: importj ~ v a. io .·: p~b l ic C\HS S~lIp le Java
r
public st atic void m~jn(Strin g ar gs[lll Systell .out. pr int In("1 all a Jav a program ") :
lXl you Sff any simibrities among these programs? You should, because they are listed in C"o]ut;on;uy order. Now, I don't want to get into an argument with anyone about whether Java is truly an evolutionary leap ahead of C++ lJ«ause I'm not sure if I believe that in the strictest sense (with a feature comparison). Hut I do like to think ofjal'a as the next logical step above C++; it is easier, less prone to error, but not as powerful. I)ocsn't that describe ;lny system that tends to evolve ov{'"r timd Take the compuwr industry itself, for instance. The earliest computers were built with thousands of vacuum tubes, which were difficult to maintain 'lnd very prone to error; and as far as power consumption goes, 1think the computers of old definitely usro more power than the computers we commonly usc today- but let's not talk about performanc{'", which is no contest. The C program is quite simple and llIaybe even readable by a non-programmer (who may nOI underst,md anything other than the pr l ntf linc, alld even then with much confusion ). Thl' C++ program is so much gobbll'dygook to anyonl' but a programmer. But those of us with a C++ background often describe C+ + code as beautiful and elegant, with a powerful, perhaps even imimidmillg, lure. The Java program is very similar to the C and C++ programs. Likl' the C+ -t program, the Java program must ·'gt"t solllething" frolll "solllewhere else" in the form of the illport j ava, 10,' statement. This java.io is a library that provides access to the Sys tem. Qu t class, which is uscJ for printing out text (as you probably guessed ). But the biggest difference is thatlhe java program is located inside a cl"sl. This class is called SaJlpl eJa va, and inside this class ('nclosed with
The Java laonguage curly brace$) i$ a main function very similar 10 the main funclions found in the C and C++ programs. Whal is this SallplNan class, you may a.sk~ The troth is. n'e?1hing in la\1I is a class, and it is not possible todo anything usdUl in Java withoul using a class. AU source code that you write in Java will be enclosed inside a class definition.
The .a1n Function The core of a Java application is Ihe Hin function. (Note Ihat applrts typically don't have a lWin funclion, as I'll explain shortly.) The lWln function has this basic format: pUblIc Hltle voId -.aln(Strlng i1rgs[]l 1 I
The parameter (String ugs[]) allows yOll to pass information to the Java program and is only practical when devclopinga Java application (rather than an applet) to which you can pass paramel('rs, pre$umably from a command prompt or shell. You alii pass parametCTS 10 a Java applel, but that is not done very often. I once worked for a company that built vchicle tracking systems using GPS (globlll posi/ioning ~mn), and my job was 10 maintain the: la'.. progra.m that displayed a map with all the vchicks in the Slate of Arizona n'l()\"ing along their routes. This Java program r«eivtd "chicle tracking informa.ticm from a $CrYC'<, and then displayed it in an apple!. Caution Jar
1ft
sewnI _rs tNiI 1ft Jound III
in
Let's dissect the lWin funelion 10 help you better undCTStand what it does. The term pub! ie specifies that this (unction is visible outside the class. (Remember, every JaV,! program runs inside a class.) The static tcnn specifies that the function definition never changes and is not to be inherited (borrowed for use in another fUlletion). The stHle keyword is optional and 1I0t often used in an applel. The void term means thatlhe function docs not return a value. Every Java application you wrile will have a Hln funCiion, just like every C and C++ program. However, a lava applet, which runs in a web brOW5CT, conlains events instl'ad and is not in complete control in the same way that a siandalolll' Java application (...i th a main method) is..
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40
Chapter 2 •
Ja~a
Programming Essentials
However, you eml write Java classes that dOII'1 have a m~1 n function. Why would you want to do that? A class is usually created to perform a spedfk task, such as the handling of sprites in a game. You might write a sprite class that knows how to load a bitmap fik and draw a spri te on the screen; then the main Java program (with the m~t n function) will COl/Slime or use the sprite class, which itself has no "'ain function. A class has its own variables and functions, SQme of which are hidden inside the class itself and invisible outside the class. What I'm describing here are some of the key aspects of object-oriented programming, or OOP. In some cases, as when developing an applet, you may just usc the pai nt event rather than using a Ilain function. (More on that later.)
Object-Oriented Programming There arc four main concepts involved in OOP, though you may not use all of them in every class you write ,
• Data hiding • Encapsulation • Inheritance • Polymorphism I'll briefly talk about each of these concepts because you will bedealing with these throughout the book. I don't spend a lot uft ime discussing advanced concepts like these while writing lava games, and this book is not int....ndcd as a primer on the Java language. Hundreds of books have been written about Java programming, includ ing some very complex textbooks on the subjed used in college courses,
Data Hiding
Onta hidillg is a key concept of OOP because it provides a way to protect data
within an object at rumime from direct manipulation. Instead of providing access to certain pieces of data, a class defi nition will include functions (oft....n called methods or arcessorslmmllfors in OOP lore) for retrieving and changing data (often called properties) that is hidden within the class definit ion. An accessor function retrieves a hiddel1 variable; a mutator changes a hidden v:uiable.
The Java Language
This way, the programmer can specify exactly what changes can be made to a private variable through the built-in mutator functions and return customformatted data through the accessor functions. For instance, if you W'lnl to make sure that a birth date is valid, the mutator function can restrict changes to a certain range (such as 0 to 120). The following source code demonstrates the concept of data hiding. [ have intentionally kept the code listing simpler by not induding any comments. publlc class vehlcle { prtv~te Strln9 lI~ke: prtnte lnt nUlIIWneels; publlc String getM~ke() { return . ~ke:
I publIc boolun setM~ke(Strlng newake) I if (newlOake. length() ) OJ I luke - newm~ke: return true: I el,e { retucn fa I se;
public Int getNumWheelsO ( return nu....hee l s;
I public boolean setNumWheelS(lnt count) I If (count) 0 U count <20) I nu....heeh - count: return true; ) el se I return false:
Encapsulation £IlCllpslIlllrioll is related to data hiding in that it describes how information and proce&SCs are both handled internally by a class. These two concepts are often Ilsed interchangeably, depending on the opinion of the programmer. (l prefer
41
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Chapter 2 • Java Programming Essentials to use the term rllC/lpSlIlariolt rather than dara hi/liltg,) I would suggest that encapsulation invol,'es mod-ding a real-world entity. while data hiding describes the ability to U5e private variables in a class. It's common to en(;lpsulate a realworld entily by writing a class thai describes the data and functions for working with that data. In the vehicle class example:, I haveeocapsulattd the specifiC-limns for a basic "ehick inside a class with hidden (or private) dala members and public functions {or methods}.
Inheritance Inheritance describes the ability to reuse dass definitions and to make changes 10 a subclass that relies on a base dass. For instance, the vehicle class might Ix used as a basis for many subclasses covering a wide range of vehicles, from two·wh~l motorcydes to IS·wheel semi trucks. When you are writing the code (or a dass, it is best to pili each d;]ss inside its own wurce code file. Java allows yOll to inherit from a single base dass. Not . A/though C++ ~ you III WlfriIIrom ~ ba5e dMses,. dlis leaun oftfll CiIMS_ problems tharl ~ soMs. so it IS wIdom tMd. ~1Nd 01 nUople inherilarn. J;wa * - you 10 1lIerf~_ ~ far thl' ~ and methods that shcUd be IoI.nI WIIhin " partjaUr dtis.
.... nUupIe
For inslance, the SimpleClass program in Uources\ch"ptcr{)! on the CD-ROM includes the source code listing for the wehlcle dass. and it is stored in a file called vehidc.ja'-a. Also included in the SimpleOass project is the main source code file (;llltd Simpl~ass.,iava-:andthis file "consumes" or uses the wehlcle d"ss defined in the vehicle.jalO1 file. Additional classcscan be: written and $31'td in their own source files. TIp To add a new dass 10 your prlljK~ just ae.te. new text file with" .java eXleflsion and compi~ ~ s.eparately from your main program f i ~, Th;s;s vet)' easy 10 60 using TeXlP<>d by prenirog Ctrl+\ to (ompile)'OUr J••• code,
A "O'lSlmClOr is a method that is called whenever you creatt> a new class in your program. I'm nQt lalking about typing in a new claM, but when a class is instan· tiated into an object at runtime. When a new class is created (with the new operator). the class dmnition is wed to construct an object, ~ where the keyword comes in herr. 111<' new object is "constructed" when it is being crated at runtime; the class is a blueprint wcd to build or construct the ob:i«t at runtime.
The Java Language Definition 1lJjldl1lid~ means to CA!ate or to coostruct Within the cootext of objKt-oriented programming. new obj«ts a
When I click the OK button on the Class Wizard dialog box, a new file called truck.java is added to my project, and it contains this source code: pUb lIC chs, truck extends vehicle I public truck() I I This is a nice, clean 'tarting point for a new class. Note that this class inherits from the veMcle class (extends vehicle), and it include, a simple constructor (pUblic truck()). Thi, constructor is called whenever you use new to create a new truck obje<:t, using code like this: tru ck silverado - nell truck(): The constructor i, ,pecified after the new operator in this line of code, and this is called an emply COIlSlnlClor. If you want to pass parameters to a constructo r, you can do so by defining another version of the constructor, which is a topic that needs to be covered in the next section on polymorphism.
Polymorphism Polymorphism is a complex word that, when broken down, equates to poly (" many") and morpl! ("shape"); therefore, polymorphism refers to having "many shape" or "many shapes." Java allows you to write many versions of a function (or method) with different sets of parameters. When you write more than one version ofa method, you have overloaded that method. Overloading is a te<:hnical programming term that describes polymorphism at work. Tip I haw been Iffing tile terms fulKlioo and mell10d togetl1e( up to this point I wi~ refM to mell10d ffom th i, point forward. Just note that a method i5 the same as a function. and thi5 applies to accessor/mutator functions (terms that are used by C+ + programmers). Just r""",mber: A property i5 a variable. while a method i5 a function.
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Chapter 2 • Java Programming Essentials The complete truct c1a5$ $Ource code listing demonstrates polymorphism. Note the construdor, truckO, which has hem overlooded once with an alternative version with the following syntax.: publIc tructlStrlng .. ke. Strl.... .ooel . StrIng engine. Int towIng) You wiD probably not pus all of the data to a cbss in this manrocr all at once, U it is not usually "cry practical. You may pus any vallle$ to the constructor tlut you think will hdp with the initiawtion of the object that is being instantiated, but keep in mind that t~u au methods avaibble for reading and clunging thoSC' variables (or properties) u well. Do you see how the default constructor includes $C\Ieral method calls to sellhe private variables to some initial values? This is a good practice to do when creating a class definilion, because it eliminates Ihe chance of a null.pointer runtime errOT from occurring-which is common when working with strings Ihal have not yel been sellO a value. I've decidtd not to include a string lenglh check in the set functions to make the source code easier 10 read, but this sort of built·in error handling is a good idea. publlc chss truck utends vehIcle { prlnte Strlng .ooel; prlute Strlng engIne; prlnte lnt towlngClp.clt,; publlc truckO I setMitfl "..ke"l; seU"""ee!sl41; selllode11"lIOde1• ); setEngl nel "engl ne"l ; set T0111 ngCopicl t,tO) ; publlctrucklStrlng_i.e. StrlngllOdel. String engIne. lnt tOil Ing) I se tlla.e(uke); setllode1(lIOde1) ; seUngl nel engl ne) ; set T0111 ngCipiC Ity! towl IIg) ; publ1c StrIng getllodeHI { return .ooel;
The Java language )
public void Ictllodel(String newDdel) t -ode I • ntdOde I :
public Strlnt tetEntlr>eO t return tn9lne: )
public .old ICUll9lntl Strl ng IItWt1lglnt) I tllglnt· ~Int: ptlbllc Int getTowlngCipiclty() I return towlngcipaclty: )
I*bllc void setTowingCipiclty{lnt ulue) ( towtngcapiClty· ..lue:
Now Itt's make some changes to the main source code in the SimpleC1ass.java file. This is the part of the program that consumes, o r uSC$, the vehicle and truck classes. Here is the complete listing: 101portjna,lang,": 1.port java.a ppl et,"; 1.port jiva,a"t. "; publlc clUS SI~leChss utends ....pplet 1 vehlcle car; truck llthtntng; ptIbllC void InitO t lIinl thl he i vehicle object Cir - new vehiclel); Clr.utMahl ·ford· ): clr.seU~heeh(4):
Illnltlallze. tlvck object "II", I constructor llthtnlng - new trvcuoford SVYo. · f ,ISO lIthtnlng·. ·S,4l Triton '8 ' . 7700): )
4S
46
Chapter 2 • Java Progr
g,letfont(new foot('Verdana", foot.BOLO, Ill); fldhphy the car lofo
9.drawString( 'Car luke: • + car .getMake(). 20. 20) : 9.drawStrl ng( 'Number of IIheel s: " + car. getNulllWheel s(). 20. 40): Iidisphy the truck info 9.drawSt r1 nq( • TruCk Ma ke, "+ 11 ghtn 1nq. getMakel ) . 20. 70): 9.drawSt r1 nq( • Truck MOde I: " + 11qhtn 1nq .qetMode l( l. 20, 90), 9,drawSt r1 ng( •Truck engl ne: • + 11ghtol ng .geHngi neO. 20, 110); 9.drawSt ri nq( •Truck talll n9 capacHy: " + 1Iqhtnlng.getTolilngCapacltyl). 20. 130):
What is the most significant part of this program lhal might seem unusual or surprising? Well, take a look at those last fe'" lil1es of code where the lruck information is displayed On the screen, The truck is using a method called getHake() thai is 110t evell defin~xl in thl" trud class; lhis isa 11lelhod found only in the vehiCle class, from whkh the truck class was inherited. Thai is the real power of inheritanct'-tht' abilily to reuse fUl1clionalit}" while enh:mcing existing c1a~.
I ha"e added the truck class to the Simpll"Class program, which is where the vehtcle class may also be found. You can open the Simpll"Class project from Ihe CD-HOM in the \sources\chapterQ2 folder. Figu re 2.3 shows the oulpul from the current version of the program up to lhis point.
What You Have Learned This chaplCr providt."d an o,'ervi...w of th... b"sks of Jav" programming. You le"rnt."d about th... differences between a Java :JpplicatiOl1 "nd" J"v" applet, and how to write programs of e"ch type and then compile "nd run them. You kMl1ed the basics of object-orienled programming "nd many other J"va programming issues th"t will be hdpfuJ in later ch"pters. Sp«ific:Jlly, this dmpter co\"ered: • How to write a Jav" application • How 10 write" J"va applet • How 10 compile a Java program
Re~jew
-..........
Questions
_,_..
c.......,. ... ~
' ..........."
".
'"
,''''''''_'',>0''''_ ..... ,
,,_<_, "00
--
figure 2.3
The SimpleClass program now demonstrate! inheritartCe with the
tr"c~
(lass.
Review Questions The following questions will help you to determine how well you the subje<:ts discussed in this chapter.
ha~e
learned
I. What is the name of the JDK tool used to compile Java programs? 2. Which JDK command-line tool is used to run a Java application?
J. Which ]DK command-line 1001 is used [0 run a Java applel? 4. What are two good, fret: Java IDEs recommended in this chapter? 5. Encapsulation, polymorphism, and inheritance are the keys to wha t programming methodology? 6. What's the main difference between a Java application and an applet? 7. Which method of the Graphics class can you use to print a text message on the screen? 8. How many bits make up a lava integer (the int data type)?
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Chapt~
2 • Java Programming Esst-ntiab
9. How many bits are thf're in a Java long in leger (th~ long
10. What progr:amming language was lava OOSW o n1
On Your Own Use Ih~ follo...;ng aercises to test your grasp of th~ material chapter.
CO\~
in this
inh~rited class 10
try out
Exercise 1 Writt your own la"" class and then use it to almd an tht concepts of inhC'ritana and mapsulllion.
Exercise 2 Modify your new dass by addingsomc methods Ihat dcmonstratc the concepl of polymorphism by wriling sever-II versionsofth~ SOIm~ mdhod with different sets of panmders.
CHAPTER 3
CREATING YOUR FIRST .JAVA GAME
This chapter will give you a glimpse of whal's coming in the ne:xt few chapters while teaching you some of the basia of game creation. The gam{'" featured here was inspired by the classic Atari game of A5leroids. My first video game syslem wa, an At ari 2600, and [spent many hours with il. In this chapter, you'll learn how to creall' a varimion of this classic game, which will be th{'" basis of a more advanced game later on when we get to Part 111. Here arc the key topia in this chapter: • Creating an A5leroid5-slyle game • Writing key classes: BaseYectorShape, Ship, Asteroid, and Bull et • Writing Ihe main source code • Calculating velocilies on the fly
About the Game Project Our game project in this chapter will rlln in a web browser window wi lh a resolution of 640 x 480 and will be done entirely using vector graphics. It will h,we some features that you have not yet learned aoout, bu t the exposure to this code will be helpful to you. I want to introduce routo some of the concepts early on, before you have learned all oflhe prerequisiks (otherwise we wouldn't be able to creale a game until about halfway through the book!). You may not
"
50
Chapter 3 • (reating Your First
Ja~a
Game
figure 3,1 This Asteroids done is the basis for a much more .lITIbitious game.
understand e~erything in the soun:e code for the game at this point, but you will learn how it works in time. Figure 3.1 shows the completed game you will build in this chapter. As mentioned, the game is cntirely based on vc<:;tor graphics. The player's ship, the asteroids, and the bullets are all rendered as polygons, as shown in Figure 3.2.
Definition Vector graphics dis.plays are diff~Nlt than ou, modem monitors in that t!Ie'I d,aw s~ based OIl enlire lines. On the othe' llaod. 01"" mode,n displays (i"aw f35ler grifPhics based On pixels.
All of the objects in the game are moved using an algorithm that calculates the X and Y velocity values, which are used to update the object's position on the screen. All of these' values use tloating.point math, and the result is tluid 2D rotation animation and realistic movement (see Figure 3.3). Each of the vector shapes in the game has a built-in bounding reclangle that is used to simplify collision testing, which is a crucial aspe<:t of the game (see Figure 3.4). Without it, the bullets would not destroy the am'roids, and the ship would be invulnerable! Collision testing is what makes gameplay possible in a game.
About the Game Project
Fi'ilure 3.2 The objects in the
~ a«'
all
~ed ~ ve<;l()l' gr~pl1ks.
Figure 3.3 FIOlIting-point IT\o1th algorithms give the gam.
~ 'f~l;sti<:
look and lefl,
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Chapter 3 • Creating Your First bv" G"me
f igure 3.4
1lQurdnl.! reaangIes _
lMd lO delKl
when to/lisiclm
O((UI".
The goal is to modify this game concepllatu on to come up with a high.quality, polidlm game wilh a 101 of inlfie$ting gamepLay fe:ltures (such as POWeT\lPS) by the time you've finidlm the book. The fiNI version ofGabctic War isan aradc:styk game with JTWly diffuent type of ;l5teroids, mimoltm aplosioTl$, and poWttups for the playn'5 d1ip. Whm "'-< 5t3rt working in earnest on Galactic War, well nuke a tnnsition from ,·ector graphics (based on polygons) to nsluized graphics (based on bilmaps). But befote you can run, as the old 53ying goes. you have to learn how to walk. Thischapter teaches you how to walk, and you will gl'lldually improve the game a little at a time, starting with the next chapter.
Creating the Game This game is d ivided into five classes. Does tha t seem like ... lot of classes for just your first game? [ thought about thai for a while, consideri ng this might be too much code all at once. But I think you will enjoy it. This is ... complete game, for thll! most part, so you ClIn aaminll! it-pore OVeT the lines of codll! in Holmesian Slyle (with a magnifying glass. if you wisb ) -IO learn the secreu of how a game is made. You are presmtm with a m~ayof sorts-a complete game. Your task is
Cruting the Game ITVersc-engineeT the situation to determine, Step by step, what ~ents led up to the romple1e game. The main cbss, Asterotds, contains Ihe main source code for lhe game. Four additional cbsses are usai:
10
• lueYectorSh.pe • S~lp • B\llin
Creating the Project You can type in the code for each of the dasses (a nd the main sou rce code file, Asteroids.java) and then compile each file into a .dass file using the Java Development Kit (lD K) command-line tools. The compiler is called javac.exe. You can compile a file by simply typing: javac Asteroids.java and IiUwise for the 01heT source co& files. I recommend using TatPad if you are a WindoW$ ustT because of its very ron>"C'nitnt support for the JDK.. ....'here you ClJl compile your Java program with QrI+1 and run it with Ctrl+3, Just note that in order to run an appkt-bued prognom, you must creale an HTML ronlainer file, as described in the fi1'$t chapter,
The BaseVectorShape Class The three main objects in the game (the asteroids, the bullets, and the player's shi p) are all derived from the BueYectorSh.pe class. I origi nally wrote this game without the base dass, and in the end, all three of the game objects (the player's ship, the bullets, and the asteroids) ended up sharing most of their properties and methods, so the 8ase~ectorSh.pe class was a way to clean up the code. In the end, I put a lot of usefu l methods in this class for handling the needs of thi5 vector graphics game. lIy doing this, I have usai the object-orienled fealure called inhtritllnu."The Asteroid, Ship, and lullet classes are all derived from 8i1se~ectorShilpe, which contains code thai is sham! by all three. As a result, the co& for the three su~ is quite shon in each C2St.
53
54
Ch apter]. Creating Your Fi rst Java Game This g:lme detects w llisioll s betwee n the a~teroids. bu llets. and player's ship, so each vecto r shape in the game includ es it s own bou'lding rectan gle. While the getBounds() method is not found in the BaseVectorShape class for reasons I'll explain in a moment, this method docs use the geU< l and gety() methods from the bas<' class to cakulate the boundin g rectangle. Thi s class basiGl ll y w ntain s all Ihe variables Ihat will be used to move the ObjfftS around on the scr~....n, such as Ihe X and Y position, the vel ocity, the fa cing and mo,-ing angles, and thc shape itselr (which is a polygon ). Tip What il booooing 'cd
i llport ja_a .awt .Shape ;
f·····················..··..···..···..··..···..·..···..···
.......................................................... • hse vector shape class for for pol)gonal shapes
pubHt class 6~seVectorShape I f/varla bl es private Shape snape; prIvate bOol ean al i ve ; private dOub l I' x ,J ; prIvate doub l e _elL velY ; pr Iva te doub l e IIOveAngl e. faceAng 1e ; I f ~ ccessor Ile t hods public Shapeget5hape(} I return shape; ) pu bl Ic boo l ean IsAlheD I return al1ve ; publ i cdoublegetX() (returnx ; 1 publ ic dou ble getY() I return) ; 1 pub1 ic double getVe1l0 I return vell ; publ it doub l e getVelY() I return velY ; I pub1i c doub l e getMoveAngl e(} I return IlOveAngl I' ; pub1i I' doub l e getF aceAngl e(} I retu rn f aceAng l I' ; f/~utator ~nd
nelper IIIl'thods public voId setS h ~pe(Shape shape) 1 this . shapee shape ; l pUblIc void setAllve(boolean alive) I this alive - al he ; publ1t voi d setX(double xl \ thls. x - x; \ public void IncHdauble. j \ l ttlis ,J> .... j ', \
/
Creating the Game publ i c void setY(doub l e y} I thl S.1· y: I publ i c void lncYCdoubl e i) I thl S.1 <- i; I public void setVelX(double velX) I thls.vel~ - vel~: public void IncVelX(double 1) 1 thls.velX <- I; I public void setVe)Yldoub1e velv) I thls.velY - velY; public void incVelv(doub1e 1) I thls.velY <- 1; I public void setFaceAngle(double angle) I this. hceAngle public void IncFaceAngle(doublei) I this.faceAngle<-i ; pub11 c vol d setlloveAng1e (double ang1 e) ( this .lIOveAng1e public void lnclloveAngle(~ouble I) l thls.lIl()veAngle <- 1:
angle: l angle; I
IldHault constructor I se t Shape(null ): setAllve( fal se): setx(O.Ol: setYCO.Ol:
6He~ectorShape()
seUel~(O.O):
seUelHO.O): setMOveAngle(O.O) : setFaceAngle(O.O) :
The Ship Class The Shl p class handles the shape, position, and velocity of the player's ship in the game. It includes its own bounding rectangle, which is calcu lated based on the custom polygon shape for the ship. The Ship class inherits all of the public properties and methods from the 6ase~ectorShape class. I. port java. awt. Po lY90n: Illport j aVI •awl. Rectangle:
I·····················································.... ..........................................................I
pub! Ie class Ship extends BaseVectorShape I IIdeflne the ship polygon private lnt(] shlpx-I - 6. 3. O. 3. 6. 0 J: private lnt(] shlpy· ( 6. 7. 7. 7.6. -I ): IIbounding rectangle public Rectangl e get8ounds{)
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Sf;
Chapter 3 • Creating Your
Fi~t
Java Game
Rectangle r; - 6. (int) getr() - 6. 12.12);
r - neWRect~ngle((lnt)getX()
return r; ShlpD ( sel5hape (new Polygon (Shi px. shl py. sh Ipx. Ieng th) ) ; se tA1ive{ true) ;
The Bullet ctass The Bullet class defines the bullets fired from Ihe ship. II is also derived from the BaseVectorShape cbss, so most of Ihe functionality of Ihis clar.s is provided by the base clar.s. All we r.::ally ne<.'d to do for bullets in Ihis game is to define a rectangle that is one pixel in widlh and height. This small shape is used to calculate the bounding r~'Ctangk returnt'd in Ihe getBounds() method. While we're only drawing a rectangle the size of a single pixel, we will still Ireat it as a r«tangle, but when it's time to ched; 10 see whether the hulle! has hit ,m aSleroid (using collision delcction), then we'll do it slightly differently than the way in which we compare collisions belwttn the player's ship and the asteroids. Instead of checking for an intersection, we'll see whether the bullet is "contained within" an asteroid. I_port Java ~wt.·; Illport Java awt.Reetangle; /
. .......................................................... , • Bull et class - polygonal shape of a bull et
publ Ie class Bullet extends BaseVectorShape I IIbounding rectangle public Rectangle getBounds() I Rectangle r; r ~ new Rectangle( (Intlgetx(). (lntl getv(). I. return r;
BulletO (
Ilcreate the bu\ let
sh~pe
1);
Crellting the Glilme setSll.pel_ RKhll91elO, O. l. Ill; selJ,.11nthlsel;
The Asteroid Class Tl1e Asterol d class also inl1erits from easeVectorSn ape and provides three of its own new methods: gelRotnlonVelocity, setRotltionYelocity, and geteounds. The rotation vclocity value is used to rotat e the asteroids (whkh is a cool effect in the pme). ~ get8O\lnds method returns the bounding rectangle for the asteroid and is similar to the $;lime method l'ound in the Ship and 8ullet classes. Il11POrt Il11POrt
jiIY jiIY
t.'olygon; t.Rectingle;
.... ···································..··..···..··..··..····f
f· ·······~············································ • Aste ro1d c1lss . for polygonal asteroid snlpH
publlc c!lSS AsterOid extends Bl$e~ectorShlpe I fldeflne the asterOid polygon shipe prhlte Int[) Istx - ('lO, ,13. O.lO.22, 20, 12, 2, -10, -ZZ, -161; prlute Int[) ISty - ( la, U,I7 .211.16, ,20, ,22, ,14, '11, ·lO, -5J; fI", tltlon speed protected double roUel; ,",bile doublegetRotatlon~eloefty()I return roUel; I public .old setRotatlon~eloclty(doubley) (roUel - y; flbo undlng rectangle publ1c Rectan~leget8ounds() I Rectlngle r; r-MWRectingle((lnt)getiO' 20, lint) geUO· 20. 40,(0); retUNi r;
IIdeflul t constructor AsteroldO I setShlpe(new Polygonllstx. Isty. Ish. leng t h»); seUlhe(true); SHRotat lon~e loc l tytO .0);
57
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Chapter 3 • Creating Your First Java Game
The Main Source Code File The Ol3.in SOUf(e code file for this game is found in 3. file ",lied Asteroids.p..... I 3.01 pro,·iding the eomp~e source code listing hen' so you C3n eumine it in dcuil while re:tding mv el:pLanuioll$ of each ~hod:tlong the W3.y. I recommend you study the source code to get 3. good fed for how this S"mt works.
i..,or~ j •••.• pplet.·' 1..,ort j.v•.•wt.·; I~ort j.va .• wt.event.·, laport j.va .• wt.geoa.·: I.port j •••.• wt . 1a.ge •• : I.portj •••. utll. · :
/
. ..................................................... • Prl .. ry chn for
t~e
gaat
/
public class Asteroids utends Applet
l~plMeflts ~urnable.
Ithe .. In ~hrUd be<:_$ the glat loop Thrnd gawloop, /use this a$. dcuble buffer Buffer!'dl..ge backbuffer; flthe ..1n drawIng object for the bact buffer l>r.ptlfc$2Dg2d: fltoggle for dr.wlng
bou~dlng
bOU$
boolean sho"Bounds· false: /fernte the astero1d arr.y Int ASTEROlOS· 20: Anerold[) .st • new ,l,$teroid[ASHROIDS1;
bullet arr.y Int 8lJUHS· 10; Blll1et{] bul1e~. _ Bu'let(BUltCS): 1nt clirrent8ll11 et • 0; flcrute the
Keyt'Hener I
CrUl ing the G.""", IIt~e pl.yer'S s~lp 5111p skip - nev 5blpO;
Ife r ntt the Id ent ity t ..nsfor. 10.0) M f lneTr ans f Orll Ide" tl t y - newAfflneT r~ nHor.(} ; Ilerntt a ran dOil nu~r generator hndOil rand - newRand.:-():
Applet i nit(} Event ~
appkt tnttO f'Vm l i$ run wbm the appkt fi rst sian s up and is us.ed 10 initialize the game. The code first crcatda double buffeT. upon which all gr.lphias will be rendered in order 10 produce a smOOlh screen refresh WilhoUl flicker. The player's ship and the asleroids are iniliali'£Cd, and then the key listener is st:lrtcd.
I·····················································
....................................................., • apple t Inlt nent
public wold InitO I /luntt ne bilek buffer for s_t~ grapllics baekbuffer - nev hfferMINge(6'lO. 480. hffer~INge. TYPLUCRGB): g2d - backbuffer .createG , a ph Ics( }; Il set up t he shi p shlp . seU(310) : slllp . setY<2 ( 0):
/lset up the bullets for (Int n -0: n(lUlLHS: n++) I bullet[n] - nev B"lletO;
li ereate th e asteroids for (lnl n - 0; n(ASTE ROIOS; n.... ) I an[n)- ne. ASlerold(); as t [n). setRoUt IonYeloci t,( ralld. nutlnt (J)+I ) : an{n). setl{ (double )rand. nut Int (600 )"20) : as t{n). set'l (double )r and. nut Int (UOj .. 2ilj : an{ nI. setltcveAngl e( r and. nut Int(31iO) ) : double ang- asl[n] .getllcveAngle(}· 90: as t[n} .se t VI!! I X( ea \(Ang I e llc~el{ ang) ) ;
59
60
Chapttr 3 • Crt.ting Your First Java Gamt ut[n] . nUtl He. IcAn91 dIowtY( Ing') ;
{lHut tht ultr Input Iisttner Idd~tyLl$ttntr( tM $);
Applet updateO Event 1M appltt's Ilpdttt() e\'mt is triggered whenever the 5CrttIl needs to be rrlrrshed. This game does not call the updlttll method from the game loop yd, although a future version of the game will make this change, which provides better <:ontrol over the scrten refresh process. This met hod docs aU of the drawi ng to the applel window by first drawing graphics to the back buffer. This buffer is then copied to the applel window during the pil nt() event.
The identity tnnsform is ttl<: stllrting point of a vector-tMscd transform that allows vector-based shapes to be rotated and IIlOVrd around in the game. First, you start at the idmrityand then move the shape and rot.1t it from there. If you don't start off with the identity bcforr manipulating a shape, then it will be moved with the previous shape rather than on its own. /
. ..................................................... • Ipplet updlle
t~tnt
to rtdr,w tht scr een
{
publiC wold upd gld. lttP,I nt( Co Ior .8LAC() ; gld . f111RecttO. 0, getS1ze().wldth. getShe() he1ght) ; {lprlnt so-e Stltus 1nfo.... t10n g2(l.lttColor(Color .l/llll[); g2d.drawSttlng( 'Shlp: .......th.rour>dhhlp.getxO) .... . .. .... tll.«!un(ltllllp.'etH}l. S. 10); t2d.clrawStrlngt ' Mawt Ingle: " .. Kath.round! slllp.gtUlo.t....,gleO)+90. S. 25); g2d dra.Strlngl "Flct Ingle:' ......th.roun(l( slllp .gtHlctAngleOl. 5. aD};
Creating the Game
IIdr'll t~e g•• gr.phlcs drawShlp( I; drall6ulleh(); dr'llA.sterolds( l;
II rep.a ln t the .pplet 1l111llow p.alntlgl;
Drawing the Player's Ship Tht drall$hl p() mtthod is callffi by the updatel I tvent to draw tht player's ship onlO Iht back bufftr altht COITtCI X and Y location. !kfore drawing, tht idtntily trall$fonn i$ stt so thattht $hip's local coordinalt syuem i$ usN, rathtr than tht prnious v«tor'scoordinatts. Remember, a tnnsfonn afftcts an obj«t's X and Y position. The idtntity is tilt staning point {O,O}. When the ship is first dnwn, il is actuallyctntered at tht origin, with tht shape of the sh ip being drawn from --6 to +6 in the X and Y axes, So tht ship is abou t 12 pixels square in size. If you don't draw a vector around the origin, then rotation will nOI work al all, becau.soe rolatioJ1$ occur al the origin-or rather, at the idmtity Ioation.
.
/
• dr.IlShlp called by .pplet upd.te ewent
.....................................................
/
publ1cyolddruShlp(11 g2d. set Trans for.( Ident I tyl ; g2d. tr.nshte(shlp.geUI I. shlp.getll I); gld. roUtelllulI. tllRlidl ans (5111 p. 911!tfaceMgl e( ) II ; g2d. setCa Ior(Col or .OIWlIiE 1; g2d . fill (sill p. getSII.pt!:( II ;
Drawing the Bullets Tht drawllulletsO method goes through the array of bullets and draws any ~ that nted to bt drawn. Thi$ only occurs if a bulkt is alivt using the hA.llveO mtIhod. Then tht bulla is transfolllltd to iLS position on tlit Kt'ttfI, and tht shape {which is a tiny rt'CIangk} i$ drawn.
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Chapt"r 3 • Cr"ating Your First Java Gam"
I········
• drawB" 11 ets ca II ed by app 1et upda te event
.
............................................·········1
public void
dr~1I6ul
lets() (
Illtera te th rough the ~rray of bull eh for (Int n - 0 ; n < BULLETS ; n++l I Ills thh bullet cu rrentl y In use? If (bullet["].1s~live()11 Ildra w the bull et
g2d. se t Trans f or.( Ident i ty) ; g2d. trans late(bullet{n],geU() , bullet[n]. getY(»; g2d. setCo 1or (Co lor, MAGENT ~) ; g2d . drall( bu l let {n], getSh~pe( ) ) ;
Drawing the Asteroids The dr allAsteroids() method draws all of the asteroids in the ast[] array. depending on whether they are ali,·c. When the playcr fin'S a bullet and it hits an asteroid, that asteroid's alive variable is set to false, SO the asteroid is no longer drawn to the s<:reen-and it is also ignored by the bullets after that. An interesting option in this method will draw the bounding r~"<:Ctangle around the asteroids if you have toggkd bounding on by pressing the B key.
I····
.
• drall~sterolds called by applet update event
....................................···············_·1
pub1 ic voId draw~steroids{} I ffiterate through the asteroIds array for (Int n - 0; n < ~STEROIOS ; n++l l Ills this asteroId being used? if (ast[nJ. ls~lhe()) {
Ildraw the asteroid g2d .setlra ns fon( 1dent1ty); g2d . trans1 ate(ast(n] .geU(). ast[n] . gety(») ;
Creating the Game 92a.rOUte(lIitll. toR.!dlJnslnt[n) veUlonAnvle( II); 92d. setCo10r(CoIor . DAtlLGAAYl ; V2d. flll (ut[n).vetSh.pe( I);
Screen Refresh The p.intO lVent occurs when the applet window needs to be refreshM. This mdhod is calkd by the: IIpditeO mdhod and simply serves the purpose of drawing the back buffer to the: applet window.
I···················..·························.. ····~ ..................................................... • Ipplet 1I1lldow ,elUlnt event· -dr," tbe !lact buffer
/
public void pllnt(Gr.phlcs V) l Iidraw the back buffer onto the applet Window g.draw!lUge(blckbuffer. O. O. thts};
Thread Events and the Game l oop 1"hc'n-an: thrtt thread events that an' pan ofa program ..ilm you impkmmtthe Rllnn.ble interface in a lava applet. Runnlble tdb Java that your apple!: will support mon: than one thread. A thread issort ofa mini program that can run on its own. You create a new thread in the stlrtl I lVent, and then destroy that thread in the stop() event to keep things running smoothly. The most interesting thread lVent is called run(). This event method contains the code for the game loop, which is a while loop that son of powers the game and keeps it running at a consistent fnme nte. This even t calls the V.....Updlle() method, .... hich processes the current frame of tbe game by moving obje(u around on the screm. testing for coUisiol1$, and so on.
I···········..··..······..···..···..··..···..······..· • thrnd surt eYent . st.rt the VI. loop rllnn1ng
.....................................................,
pllbl Ie void stirt() l fferute the gUleloop thre!d for vneloop· new Thread(thtsl; VI.1 oop.start();
rUl·tl~
IIpdltes
63
64
(h"pter 3 • Creilting Your First J"¥" Ga.mt
.
{
• thru d run e.ent ( ga ll\' loop)
·························..···..·····················1
pUblic wotd run() I lIilcqulre tM current thread Thread t - Thrud.currentThrud{ I:
l!keep goIng as long as the thrUd H .1he wh11e (t -~ ga-eloop) I try I /{updilte the g•• 10
I ~pillnt();
t··········..········..······························· • thrUd $lap event
·····················································1
public .otd stop{) I IIklll the gil.loop tnrud g••loop-null,
Game loop Update The g•• Update{) m~ is alIed by the gilme loop thread when iI's lime to proces.s tl\(o game for the Dat appkt window rdTc:sh. The game loop is timed to hit around 50 frames per $«Ond (fps), and the window refresh occurs "her 91.Update is run. Nomlally lhe game loop will run as fast as possible and only lhe screen refresh will be til-d to a specific frame rale, bill in th is first game. thai difference is nOI imponant. {
.
·····················································1
(rnting the Gilme prtute wold 9•.upd.te() I update5hlp(l; updateBu II eh( I; updateAs terOI dsl 1; checkCol1 hlons( l;
Updating the Ship The update$hl p() method updates the ship's X and Y position using the velocity variables. This method also "W3rps" the- ship around when it crosses an edge of the' $Cf«fI (in which case lbe sha~ is moved 10 the opposite side of the scrrc'n). This is a technique used in many classic art2dC' games.
I················..··..·········..······..······..··.. • Update the ship position bllsed on weloctty •••••• ** publ1c void updHeShlpO r f/update Ship'S X position Ship. inCX(Shlp.get~el X( l);
,
IIl1np irOul'Id left/rlght If (shtp.~tI() < -10)
sht p. sell(9etSi le( ) .1I1dth + ID); else If (shlp.\IetIO >getSlleO.llidth + 10) shtp.sell( -10); f/upd.te shlp's YposH Ion ship . 1ncHshlp. gelVeIH)}; (Illrap around top/bottOll If (shlp.\IetH) ('ID)
shl p. sen( getS Ilei J. hel lIht + 10); else If (shlp.9etY() lIetSlzeO.helllht. ID) shtp.setH-ID);
Updating the Bullets The updateBull eh() method updates the X and Y position for each buJ1etthat is currently alive USillg the velocity variables. When a bullet hits the edge of the scr«n, it is di5abled.
65
66
(hilple, 3 •
(,eilling You, First JilViI Gilme
I' ••••••••••••••• • •••• • •••••••• • •••• • •••••• • ••••••••••
public voId upCHehl1ets( l I lI.ave uch Of 1M bulleh for tInt n - 0: n IUl US: ".....) 'lis th'$ bullet l>t11'l9 u~ed? f (b"lletln).I~ ...lhelll flupdUe bullet ' $ x 1'0$1 llon bullet(n]. lncl( bulltt[n] .get Vtllll) : II bullet dlsappeHs at lef t /right edge If (bull et(n ].gttX() (0 II bulltt[n] .geU() ) getShe() .wld t h)
lIupdate bullel's J po$ltlOfl b"llet[n] . tncYlb"l·et{nJ.getYelYl I: Ibullet d sappun at top/llolt.. tdge fibullet:n).geU()ullet[n J.geU t) ) getS1ltt) .lIelg~t) bJllet[n]. HtAl het hheJ:
Updating the Asteroids The updateAs terol ds() mdhod upda les the X a lld Y position of each asteroid lhat is currently alive based on the vel(>(it y variables. These X and Y values and velQCities are all sel to rnndom values when the game slans up. The asteroid§ are wuped around the edges of the screen. One inlcresting thing about Ihe ;lStcroids that differs from the ship and bulJeu is tt.;.t the ;lSteroids are rotated b) d r.mdom
Creating the Game
number of degrees cach frame, causing them to spin 011 thc sen."cn. Th is is a prrtly nice effe.::t that adds to the quality of the game.
f····················································· ..................................................... • Update the asteroids based on velocity
/
pub I i c vo; d upda te~. terol ds () { fhl
I/ warp the asteroid at screen edges if (ast(n].geU() < -20) ast{n]. setHgetSi ze() .wldth + 20); else if (ast[n].getX() >getSlze( l.wldtn + 20) Ht[n]. seU( -20); /Iupdate tne asteroid's Yvalue Ht[n] . IncY(ast(n] .getVel Y()); Ifwarp the asteroid at SCreen edges <-20) ast[n].setY(getSize( 1.height + 20), el se if (ast(o].geU() ) getSize( l.hei ght + 20) asUn].setY( -20); 1f (ast[nl.geU()
Ilupdate the asteroid's roution asU" 1. I ncMove~ngl e(a st [nl, getRota t i onVe loci ty( )1, II keep the angle wHhln 0-359 deg r ees if (ast[n].getMoveAngle() < Ol
ast{nl. setMoveAngl e( 360 - ~st(n] ,getRotati onVelocHy(»; else If (ast(n].getMoveAngle() ) 360) as t [nl. selMoveAng Ie( as t [n], getRou t i onVe Ioc Ity( ) ) ;
67
68
Chapter]. Creating Your First Java Game
Testing for Collisions We haven't discussed collision detection yet, but I think you will gctthe hangont hcre broiuSt this chectColll slonsO mcthod is str:aightforward, First, there is a loop that g
.
{
...................
• rut uter(llds f(lr C(lllislons with shlp(lr
b~llets
, public voId checkCol1islons() {
IIlter.te through the asteroids arrlY for (Int _·0; _
if
/
.
• (he(k f(lr (llll$lon with bullet
./
for (Int n - 0, n < BUllETS: "....) t III s till s bullet \leI nq used? if (bullet{nj,l$Alht()) I llperf(l'" tile colli st on ttst I f (IS t(_J ,9Ct8tNndS( I. contal ns(
,
C'eating the Game bulleHnl getXCl. bullet[n] get1())) bullet[nl. setAl lYeCfal s~): Ht[1II1 .setA) lYe( fal se), co"tlnue:
/
.
• check for coll i s Ion with shIp
./ 1f (a st [_l. getSounds ( ). intersects Cs hi p. getSou"ds ( ) )) 1
aHC_l. setAllveUal se}: sh1 p. seU (20) : sh1 p. set1(240): shl p.setFaceAngle(O); sh1 p.setVel X{O): shlp . setVelY{O): continue,
Keyboard Events This game uses the keyPressed() evem to detect key presses. while keyReleased{) and keyTyped() are ignored (although they must be in the source code listing because of the KeyL 1stener interface). The most important parts of this method are found in the code following the thrust and fire keys. which arc mappe-1'S ;n the expression to dlange in a consistent w/tf. Amovement algorithm causes. for instance. the. vanat>e 00 a" x - ~ <;<,>ooj;nate plane to change SO mat it consistently ;ncreases in value, rnc.wing whatever object it represents horizontally across the saeen.
69
70
Chapter 3 • Creating Your First Java Game An advanced movement algorithm is used to move the objects in the game, which is covered in the n<:xt seclion. Movin g the ship muSI look as realistic as possible- so you can apply thrust to the ship, rotale to a new dire<:lion. then apply thrust, and Ihat new angle or movement is added to the current velocity va lues. The result is a "ery realistic zero-gravity motion for the ship. Some progralllmers like to use a mass/acceleration algorithm to mow a space ~hip. That is a good method, where the mass (or weight) of the ship affects how fast it can mOI·e.1 have simulated this effect using a velocity algorithm illste:ld, which. again, is covered in the n<:xl sec tion.
I·····················································
..................................................... • key lIstener e ven t s
/
public voId l:eyReleased( KeyEvent k)! pub l ic voId l:eyTyped( KeyEvent k) { I publ ic voId keyPresse d( KeyEve nt k) I int keyCode - k. getKeyCode() :
case KeyEven LH....lHT: //left arrow rot ~ tes shIp left 5 degrees s hip . jneF~ceAngl e ( ·5) : If (ship . getFaceA ngle() <0) shl p.setfaceAngle(360 ·5) ; break:
II
case KeyEvent . VICR1GHT : r Ig ht ~ rrOlr rotates ship right 5 degrees s hi p. ineFaceA ngle(5) : If (ship.getFaceAngle() >360) ShIp setFoceAngle(S) ; brea k; case KeyE vent .VK_UP ; Ilup arr Olr odds thr ust to sh Ip (1110 nOfll
break ; Sp~ce con be used t o fj re KeyE yent . VICCOHTROL ; KeyEvent. VICENHR ;
I /Ur I . Enter . or c~se c~se
lre~po"
Creating the Game clSe KeyErent. VI(..SPAn: IIflre i bullet cllrrent811)) et....: If (cllrrent81l11et ) BUtLETS I) currenlhllet - 0; bill Iet(cllrrentBllll et l. seU) i ~e( Irlle l ; IIpolntbullet In sa. dIrection ship is facIng bu II et[ curren t Bu11 et l. seH(ship. getU ) ); bullet[currentBullell. sHY( ship. getY( l); bu II etC currentBu II el l. sellloveAngl e( sh Ip. geH aceAng1e (l . 90 l ; IIf1re bullet al IMle of the ship double angle - bullet(currentBulletl.geUioreAngle( l: double su - sh1p.getYe1J1 I; double s¥y - shlp.geltelYl I: bllllet(eurrentBulletl. stUelI(su" eil(:An9lello~eI(an9Ie)• 21: bulletlcurrentBulletl. seUe1Y(svy" eilcAn9lello~eY(angle) • 21; break:
Calculating Realistic Motion The most fasdn:lting part of this game is how the mo\'ement of the pbyn'$ ship. the bullm., and the asteroids a~ all coni rolled by two methods thaI mum lloa.ling-point values for the X and Y update for the object. O.flnition
The ea l eAngleMo~eX() method uses cosine 10 cakulate the update value for X, returned as a double. The clleAngle"o~eY(l melhod uses sine 10 calculate the update value for Y. also returned as a double. These small methods accept a single pal1lmder (the angle IMt a game object is facing) and rdum an cstimalN X and Yupdate value in pixels based on tlut angle. I can't S1rcss enough how wonderful these two methods are! In the past, I M\"C miN mainly on the brute force (and imprecise) method to move galm objects (usually called sprires) o n the SCr«fl. I would set the ¥elocltyl to I and ¥elocltyY to 0 to cause an object to mo\'e 10 the right. Or, I would SCI ~elocltylloO and ~cloeltyY 10 -ilocause the game obje<:t to mo\'c up on the screen. These veloci ty variables, along with an object's X and Y values, would cause the objeclto move around on the S(rl'Cll in a certain way.
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Chapter 3 • Creating Your First Java Game I have writun many games that llSol'd this type' of movement code. Invariably, these: games include: a lot of switch statements to account for each of the directions that an object might ~ being. For i/Utance. if a space-ship sprite has right direo:tio/U of travel. then J would ....rite a switch statement thitt considered the case for each direo:tion (0 to 7. when 0 is rxmh and 4 is south), and then update the X and Y values based on the ship's direo:tion. No longer! These: wonderful methods now akulate the vdocity for X and Y based on an object's orientation as an angle (from 0 to 360). Not only does this result in a more realistic game, but the source code isaetuallycleaner and shorter! As far as realism goes, this code supports every angle from 0 to 359 (where a circle is composed of36O degrees). You can point the spaceship in this game al an angle of I, then fire a weapon, and thai bullel williravel JUSt slightly offfrom due north. The biggest difference between this new method of sprite movement from my previous game is that I previously used integers, but now I am using floatingpoint variables (doubles).lbis allows the velocltyX and velocltyY V3riables to refled anyofthe 360 degrees of movement. For an angle of 45 degrees, velocltyX is Sd. to 1 pixel, while vetoel tyY isSd. 10 O. The cardinal dir«tions (north, south, easl, and west) are similarly predictable. But when dealing wilh an angle such as 17 degrees, the velocity variables will be Sd. to some very unuswJ numbers.. For instance. welocltyX might be 5d to something like 0.01, while nloct tyY is 5d to something like 1.57. These: num~n don't equate to actual pixcl-Jeo.'eI Il')()\'('ments on the scum in a single frame. but ....hen you consider that the game is running at SO fps or more, then these values add up, and the ship or other game object is moved O\'er time in the correct diTedion. Since the v«tor transform method eJlp«ts floating-point values for X and Y, these velocity values work just line with the part of the program thai draws things on the screen. It is fascinating to watch, and we will be using this te<::hnique throughout the book. Now, without further ado, here are the velocity calculation methods in aillheir simplistic glory:
I·····..······..·······..··.. ..·····..····..······ ···~
• calculate X-.:Iv_nt value based on dIrection anvle
··········..···············..························1
public double ulcAnVlellovdldouble anvleJ r return (double) lllath.coslall91e 'Ilath,PI/I80IJ:
Review QUf!Slions
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,
...................................................../ p~bltc
double CllcAnglelloveT(double Ingle) I (double) (llilth. sin(lngle • IIiIth. PI 1 ISO)) ;
~turn
What You Have learned This chapter threw a lot of new concepts your way withoul fully explaining all of them, bUI with the goal of giving you an opporlunity to euminc a nearly romplcte game and Stt bow it was craled from Sian to finW!. This Asttrouustytt gaITl(' will bt ('I\hanccd in substqutnt chapttrS into an exciting arcade-Slyle gamt with a scrolling background. Specifically, you learned: • How to usc: the Graphics20 class • How to usc: a thread as a game loop • How to draw vector graphics to rnakt gamt objects • How to move an objca based on iu velocity • How 10 tt$! for collisions bct",-cm gaITl(' objKts
Review Questions The foJlowing qU~'StiOllS will help you to determille how well you have learned the subjects discussed in lhis chapter. The answers arc provided in Appendix A, "Chapter Quiz Answers." I. What is tht
n.3IT1('
of the mc-lhad Ihat e.tlcubles the velocilY for X?
2. Wbat is the base class from which Ship, Asteroid, and Bullet are inherited? 3. Which dassic Alan gam.. inspired th.. gaITl(' df'VC'iopcd in this chapttr? 4. \\!him typt of collision testing does this samt ust? 5. Which method of th.. Shipe class does this game uSC for collision tesling?
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Chapter 3 • Creating Your First Java Game 6. Which geometric shape class do the Ship and Asteroid classes use? 7. Which geometric shape class does the Bull et class use? 8. Which applel event actually draws the screen? 9. What is the name of the interface class used to add threading support to the game? 10. What math function does calcAngl eMoveX use to calculate the X velocity?
On Your Own Although this game will be enhanced in future chapters, you will learn a lot by making changes to the source code to add some of your own ideas to the game right now. Use the following exercises to test your grasp of the material covered in this chapter.
Exercise 1 If you apply a lot of thrust to the ship so that it is moving very quickly across the screen, and then rotate around backward and fire a bullet, that bullet will seem to stand still or move very slowly. This is be
Exercise 2 The ship tends to rotate rather slowly when you press the left or right arrow keys, making it difficult to hit asteroids that are closing in on the ship from all directions. The rotation angle is adjusted by 5 degrees each time the keys are pressed. Modify the game so that the ship rotates much more quickly without changing this 5-degree value. In other words, you want it to rotate by the same value, but do these rotations more quickly.
PART"
..JAVA GAME PROGRAMMING
This5«ond pnt oftht book will cover the important lopia you need (0 know in order to write an appln-based game in Java. including graphiC$, sound. music. Uybo.:Ird and ffiOUSl' input, timing. and so 011. Hen: ne the chaplCTS in Pan II: • Clapler 4: Vector-Based Gnphics • Chapter 5: Bilmap-Rased Graphics • Chapter 6: Simpk Sprites • Chapler 7: Sprite Animalion • Chapler 8: Keyboard and MouS/: Input • Chapler 9: Sound Effects and Music • Chapter 10; Timing alld the Game Loop
CHAPTER
4
VECTOR-BASED GRAPHICS
The previous chapter really pushed the limits as far as the amount of information cover«! without thorough explanations beforehand. I wanted to immerse you in the source code for a game right up front before fully explaining all of the concepts to give you a feci for what is involved in cTt'llting a real game. The Asleroidsdone was not a greal game, and nOI ewn vel)' good-looking, but it was functional 'ava has a robUSI and feature-rich set of classes for working with 2D V«1or graphia and bitmaps (cxplaiDed in the naI cmplcr), making il pos.sible to draw rectangles, polygons, and olhcr shapt:S very easily. Here are the key topia in this chaplcr: • Drawing and manipulating vector graphics • Using the AfftneTnnsforll dus • Applying the lranslation, rotation, and scaling of shapt:S
Programming Vector Graphics You have already been exposed to a significant number of features in Grapht cs20 and other classes in jn.. ~wt (the Abstract Window Toolkit), such as RecU"gle and Pol,go". Thc core of Java's 20 graphics engine is the Grlphl cs20 class. This class is incredibly vCTS3tile for working with I'ector graphics and bi tmapp«l graphics. For il1$tana, Graphlcs2D has 10 methods for drawing images in a variety of ways! In my opinion, this is somewhat of an o\'crkill just to draw
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Chapter 4 • V«tor·Based Graphics
ilrulgcs on 1M screen. But Java is wdl known for its ven;,atillty and wnvmitncc. This class knows how to draw m:tangla and many othtr shapts. But it can do a lot mort than just draw-it can abo 1l'lOVt. roUtt, and scalt shapes!
Working with Shapes Ltt's writc a shon program 10 dcmonstrate. The RandomShapes program is shown in Figure 4.1, and the sourct code listing follows this paragraph. r have highlighted all of the imponant lines of code in bold text, and you'll learn about the classes, properties, and methods that have been highlighted.
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/
..
...................... tllpOrt jua ....t.·; tllpOrt jua .• ppl~t.·; tllpOrt jua.a>lt.~.·; IlIpOrt jua.llttl. · ;
public class
Rande-S~.pes utends Appl~t
lI~er~'s t~~ s~ape
private
I
used for drawIng
S~.pe lh.p~;
fi9ure 4.1 The
~
Jlf09rJfII ilusums Iht 'NplIlcslD ~
/
Progr,mrrung Vector Gr,phics fllpplet hit e>ent pUblit >old init() l shipe-new Rectlngle20.00uble(·1 O. ·j .O. 1.0,1.0): fllpplet paint e>tl\t p"blit >oid palnt(Grlphles gl I Ifereate In instlnee of Grlphits20 &rlphles20 g2d - (&rlphle s20Ig: lisave the Identity tr~n$for. Aff1neTrinsfol'llldent1t1 - new Affindrlnsfol'll(); Ilcreite I rlndo- n~r gen.eutor Rlnda. rind - nl!W R.l1\dooI1 I: IIsue the window wldthlheight lnt width · ge tS lu( l. wl dth: i nt hel ght • getS he ( ) . hei ght : IfUll the background with blld ,2d.utColor(Color.Iucrl: ,2d.f111It1ctlO. O. wI4th. lltl,htl: for(lntn-O:n<300:n++)1 IlruU Grlphlcs20 t o the identity trlnsfor. t2d. SllTrlnsfol'll( ld ent l t1 1: IIWI_e. rotlte. Ind sule the shipe rindoaly t2d. trlnshte ( rln
This program uSfil Ihe Grlphics20 class to translate. rOlate, and scale a Shape object randomly. which retulu in the screen being filled with random rectangles of v;lrying sizes and orientations. This simple program illustrates lhe basoe roncept bdtind lhe Asraoids-sty!e game from lhe previous chapter-dlat Java
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Chapter 4 • Vecto r- Based Grilphks provides the toolset for manipulating 2D graphics, and it's up to you how you will use these versatile tools. The R.lndomShapcs program defincs a Shape object (called shape) and then uses that basic obje<:t to create a Rectangle2D like so: shape - nell Rechngl e2D. Double( -I .0. -!.D. 1.0. 1.01; This works, even though the shape objox:t was originally created as a Shape be
Working with Polygons The Polygon class is a bit different than Paint and Rectangl e be
Figure 4.2 The aste
Programming Vector Graphics
••
... e.•
••
figure 4.3
n. ~ Jdl9ln wi tit lllOClflrd in 1M ltailclc'h~lS
pn:l!JiI!Il.
~
two arrays define the X and Y points for the polygon. We caD a point a and the plural form is I'I'rtices. When you are creating a polygon in this manner, keep in mind that the X and Y arrays must pair up, since every X must go with a Y v'llne (0 make a vertex. YCTtl'x,
When you're ready to draw a shape, whether it is a rectangle, a polygon, or something eJs,e, you have two choices. You can usc the Ill} () method to draw the shape with a filled-in 00101". Or you can usc tnc dr,.() method 10 draw !he outline or bonier of the shape in the CUTTmt color. ~ color is set with the setColortl method beforehand. Sometimes il can be confusing ...t1cn)'Ou are Irying 10 define the shape of a polygon using tbe two arrays of X and Y point$, so you may want to design the polygon on paper or in a graphics C'ditor first. Figure 4.3 shows the design of a five-sided star-shaped polygon. Seeillg a diagr.lm of the image can really help, especially when yOll have a complex polygon in the works. Here arc the arrays for defining this polygon. Note how the poinu directly cOlTC$pond to the values in the figure.
prt.,telnt[]xpolnh-l 0.10.-1. 1.101: prhate intO ypolnh· 1·10. ·t. 10. 10. ,2 I: Let's write a program to demonslrale how 10 create and draw polygons. The IbndomPolygoru program will usc the five-sided slar polygon with random rolation and scaling. The output of the progrnm is shown in Figure 4.4.
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.......................................................... • Ran~olllPolY90ns progra ..
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81
S2
Chapter 4 • VKlor·BaSt'd Graphics
lllp(lrt ll1pOrt 111port 1.port
jau.a"t.·: jna.applet •. java .utl 1. ': j ava.awt. geOll.· :
pub11C c]on hndo_Polygons
e~tends
Applet ( O. -10. ·7. 7. 10): prlute lot[] )'polots· (-10. -Z. 10. 10. -21:
prlvatelot[]~po1ots·1
lI~ere's t~e s~ape used for d.."log prlvate Polygoo pol)':
lI appln lott ueot p"bllc void lottO I pol)''' netl Polygon(xpolntli. )'polnts.
xpolnts.lengt~):
lIapplet paInt nen t p~bllc void palnUGraphlcs g) I IIcrute an 1nstance of Graphlcs20 Grlphlcs20 g2d· (Grlphlcs20) g: llsove the Ideotit)' Iransfo.. Afflndrlnsfo.. Identlt)' - nelf AfflneTrlOsfo..( I:
Programming Vector Graphics
IIcrute , r,ndOll nu-btr gener,tor IIndllII r,nd - n~ IIndOll(): Ilsue the "'ndOll "Idth/helght lilt " Id th - getSla( I. " Idth: lilt kl ght - getSlze( ). height; 1/ fl II tk backgraund " I th blick gld. 5~tColaf (Ca1ar . IUCI) : gld.f111hctfO. O. wldth. heigH):
farlilltn-O: ,,<300: n++) r II reset Graphl cs20 to the i dent Ity trlns far. g2d. sHTran$far.( Identl ty): IlltOve . ratate. and scale the shape randa.ly g2d. translate ( rand. nutlnt() I "I dth. rand. outlnt{) I height) : 92d.rata te(Mlth . taR, dllRs(360 * rlnd.nutoa~blel)) I; 92d. SCll el 5 * rand. nutOaub1e{). 5 * rand. nutOaublee » :
IIdr ." the shape " I th I randOll cal ar gld.setCala r(_ calarlfllld.nutlnt( »); 9ld.filHpalYI;
Rotating and Scaling Shapes The preceding programs have used vedor rotation to rotate r«tangk$ and polygons by a random value. Now I want 10 give you a little more direct exposure to Ihis feature by writing a program thai rolates a single polygon on the screen using Ihe arrow keys and, alternately, the mouse buttons. The scale factor is set to a fixed value of 20, which you can change if you want. Figure 4.5 shows the output of Ihe RotatePolygon program. There arc a couple of notable differences betwccn this program and the last one. This program jU$1 draws a single shape, so Ihcrc is no need to SCI Inc identity tr.msfonn before drawing. This program implcmcnl$ tnc ley LI stener and House' ll$tener inlerfaces, which mans thai lhc program must U5C all of the methods dcfiiW in these inlerfau dasoses, even if you don'l pbn 10 U5C them. II's an odd quirt thai is inhcrmt to how intcrfKc cb:sscs worlc. bcaU5C they an abstract..
8l
84
Ch
Figu,. 4.5 TIlt P.olaIef'dItgon prow... _
,) Wr-Wpod
~
. ..........................................................,
,
• RoUUPolJgon progra•
l-slort I.port l-slcrt illpOrt ll1pOrt
java .awt .·; java,awt.event. Jav a.a pplet.·; J av,) . ut 11 . ' ; JaW,). , .. t. geOll, • ;
pubHc chn Rot,)uPolygon utt1lds Applet ll1plmenu leyllsteMr. Mo"uLlsteMr
I prlutelnt[]xpolnU-{ 0,-10, -1, 1,101; prlute lnt(] ypolnts - (-10, ,2, 10, 10. -21: Ilhe r e 's the snape used for dralling prlute Polnon poly;
lipolygon rClt,tlon W,)rhble lntroUtlO1l-0; Ilapple t inlt event public void lnltl) I Ilcrute tne polygon
Progr(lmming Vector Gr.phks
Ill nlth l la th e l lHene rs Iddltrlhunlr{thh l : Iddllolltell st_r(tll1 s ):
/lt pp le t pt ln t eve nt pu~1ic ~ol d pt l nUGr aph1cs g) I /lcreUe an ins ta nce of Gnpll1cs2D Grapll1cs2D gld.· ( &rtpll1cslD ) 'I: /lsue th e Iden t ity trans fo r. AfflneTransfor1l Identity· new AfflneTransfor.():
IIsue the window wldth/lleight Int width · getSlze( ).wldth: Int height· ge t Slze( 1.height; Ilfi 11 t he bac kg round with bla ck g2d.setColor(Color.BLACK); g2d..tlllRecUO. O. width. hel'lht);
/IrIOn . rotlte . l lId selle the shape rlnde-ly gZd.transhu(wldth I Z. height 12); gN.sclle(20.20); g2d. rohU(Nlth. tobdl Ins ( roht1 Oft) 1;
IIdr .. the sh.pe wi th. r.ndo- color gZd.ntColor (Color .RED): g2d. til Hpoly): g2d.ntColor(Color.ILUE1; g2d.drlw (poly l ; II hand le keyboard events publ Ic voi d keyReleas ed (KeyE vcn t kl ( public void keyType<:!tlcyEwent k) I ) public void hyPressMlKcyEwent k) I switch n.'lctteyCod.eOl I cne KcyEvcnt.U...LErT : rotation--; If (rotltion <0) rotltlon - 359:
8S
rep.l ntO; bre.k; (lse le,E_ent. n ... RI6HT: rOtitlolt++; If ( rotitlOf1 ) 360) rot.tlon" O. rep.lntO; break;
Ilhandle lIOuse ewents public ~o1d lIOuseEntered(Mouse E~ent.) l I public ~old lIOuseE~lted(llouseE_ent.) t I public ~old _seRt)eased(lIouseE_ent.) I I public ~old WlusetllckedtllouseE_ent.) t I public void WlusePressed(HouseEvent.) ( swl tch( •. getButton()) I cue lIousehent. BUTTONl: rotltlO11··: If (rotltlO11 <0) rotatlOf1" 359; repalnt O; bruk; cue HounE.ent.BUTTON3: rotitloP++: If (f1ltatlO1'1) 360) rotation" 0: relllllnt(): break;
What You Have learned This c~pter provided a bridge from the materia.! in which you wae immtrsed in the previous chapler 10 the new oonccp15 you will learn in the next chapter, covering the basics of vector-graphics programming. The next step in graphics is to draw bitmaps, and then regular sprites, followed by animated sprites. We have much 10 learn in upcoming c~plers! Here is what we covered in this chapter. • How to use Ihe 6raphlcsZD class 10 manipulate vector graphics • How to transla te, rota te, and scale veclor shapes
On Your Own
Review Questions The following questions will hdp you to determinr how ..'til you havc lcamnl lhr subic'cts discussed ilt this chapler. n.c answers are provided in Apprndix A, "Chapter QUil. Answers." I. What is the primary class we'vc been using '0 manipulate vector gl"J phics in this chapter~ 2. Wha, is lhe name of the Appkt (''I'cnl Ibat rd"rrshcs 1M scrm? J. W1I<1I is the name of the Gr3phialD mclhod lltat dm..s a filled r«ungld
4. Define the words comprising the auonyrn A'NT. 5. What class makes it possible to perform transb,ion, rotation, and scaling of shapes! 6. Which 6raplllcslO mclhod dr;lW5 a polygon?
7. \V1lich tr;lnsform mclhod moves a shaJ)(' to a nrw location! 8. What method initializes the kryboard listenC1 inlerface! 9. What method in the value!
R~ndo.
class returns a double-precision floating-point
10. \V1lich KcyLhtcner evcnt detects kc-y presses?
On Your Own U$C' thr following exercises to tesl your grasp of the malerial covered ilt 'his chapter.
Exercise 1 ThC1C arc nu.ny cnmple progranl$ in Ibis chapter lhat could be modified and aperimmted upon. Ld's tweak the RandornPolygons progr.lm-modify Inc program 50 thaI it dr;lWll IWO different polygons instrad of jusl a singk onr.
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Chapler 4 •
Vector-Based Graphics
Exercise 2 Modify the ROlalePol)'gon program .'iO Ihal it "'ill rotale based on mou5C.' mo"enwnt instead of llUlIon clicks. You will rwed to implement the House· IIottonl1stener interface (and events) and call lhe addHouseHotlonltstener method 10 gain access 10 lhe .ausel'\ll.ed evenl. In Ihise'enl, )'ou can lrad: mouse: nto,·ernenl and rolate lhe polygon accordingly.
CHAPTER
5
BITMAP-BASED GRAPHICS
Jan. has a robu5l aDd fature-rich 5d of ~ for working with 2D bitmap~ gnphics (also known u mstrr grtlphics), allowing you to load and draw bitmaps vayeasily. Bitmaps are the k
Programming Bitmapped Graphics I mentioned before thaI there are 10 methods for drawing bitmap images in Java. Actually, six of tho$e methods are found in the but Graphics dass, while the remailling four are found in Graphics2D.1 think you will lind the four Graplltcs2D rmthods more useful, 50 WI' WOIl't spclld any time working with the legacy \·ersions. The moSI amating Ihing about the Graphtcs2D dass is how its methods for manipulating 2D graphics work equally well wi th vectors
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90
Chapter S • Bitmap-Base
as you ha\~ manipuLltM \~or gl'ilphu thus far. This awaome functionality will tnlllsble well into tM subsequent chapters on sprite and animation prognomming. The real difference when working with images il; that you will ntoed to create a separate AfnneTr~"~fo ... objcctto manipubte the INge obj«t, rather than going directly through Graphlcs20.
loading and Drawing Images You can ~ me get I..ge( I method to load a bitmap Ilk stored in manydiffcrmt fOrm.llt$, with the most common being PNG (Ponabk Network Graphics) and BMP (Windows Bitmap). This method il; found in the main App l et dass and can be usffllO load a bitmap file for usc as anwork in your game. The method for drawing a bitmap is similarly straightforward: It is called drawl. agel l. Let's write a program that demonstrates how to load and draw a bitmap image. We can usc the getl . age O method to load an image file, and then usc draw· lllolge( ) to draw it onlo the applet window. FiguR" S.l shows the OUlput from the Drawlmagc progr<1m. I have highlighted the important lines of code.
Figure 5.1 The DrlWlmage progo-am loads a bitmap file and drirW$ it.
Programming Bitmapped Graphic;
This ~ily castle image was rendtfed by Reiner "'olein using Caligari trueSi»Ce. He oIlm a large amount of roya1ly.fref game artwor'<.. such as 1M ust\e, at tos website. www,rffierslileetde ~
Gelman site wiIh an English ~.
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,
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"
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,
,
11lport JUI awt.': I~o rt Java appIU. " : I.rt Jan lift. ' : public chss DrawllUge utends Applet I !lluge nr1able prlnte luge luge: prlnt! Dill getUlll(Strlng fl1enl. ) I Ullu rl-null: try ( uri - tht l.getClus() getResourcelfl lenil.):
I catch (Exception e) (l return uri: lIi1pplet Intt !Went public .old Init() ! I.ilge - gUIr.age(getuRl("ciistle
png~)}:
lIi1pplet pllnt !Wfflt public .ald palnt(lirlphlcs g) I IIc reate In lnsunce af &raphtcslD GraphtCllD gld _ (GrilphlcllD) g: 111111 the bilctground with bhct g2d. utto Ior( Color .al.ACll: g2d. fl IUKU D. D. getSlle(). wi dth. getS Ile( ) .lItl gM) : IIdrn the luge g2d.drawluge(1.lge. D. D. this):
{
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Chapter S •
Bitma~6ased
Graphics
Figulll S.2 The RaodomlmigfS program driJWS imigfS at laOOom Iotatioos. with random rotation and lUling.
Applying Transforms to Images Now I'U demonstrate how to apply a transform to a simple bitmap image. Remcnl:lC'r, a transform is a pnxesli that manipulates the position, rotation.. or scde f.actor of:l shape or image. This will makt- our sprite code in the upcoming ch:apttn rnlly fun bKause the sprite images will be manipulated with thtst transforms :as well Sioce this code is similar to the (Ode for manipulating vtctors. it should look at least somewhat familiar, ~n if you don't fully understand it. One differenee when working with an image is that yo u must d efine a separate Affi neTr,nsform object for manipulating the IlIIage object b«ausc the Gr,phl cslO transforms are designed to work only with vectors. Figure 5.2 shows the output of the Randomlmages program, showing a space-shi p image l:IC'ing moved, rotated, and sc.aJed.
, . ......................................................·······f I . r t J,v, .,lIt.·;
IlIp(Irt J'u, 'liP1et. • ; 1_1I0rt .utll.·; I_port J,.,.,wt.geo- •. i_port J,v,.net
j,.,
Programming Bn.n.pp('d Gr.phics pub11 c c 1a ss RlndOlllllages extends Appl et I 1I1.lge variable prlnte luge Illage: IIl dent1t7 trlns fOl'Sltl on Affllll!Trusfora Iclentlt7 · new AfflneTransfora( 1: prhlte URL;etU RL(S t rlng flle nl M) ( UR L uri· null ; try I uri • Uls .gnClln( l.'ietResource(fllenIMl :
I cnd lhceptlon e) ( I return url ; Iflpplet lnlt nent public wold ln1tll ( Illage - oetillage (,nURl( -spa cnh1 p. pn,- l l: IIlppl et pllnt u enl pUbl1c wold pllnUGrlphlcs gl ( IIcrtite In Instince of Grapll1 cs2D Graplll cs2D , 2d - (Graph lcs2D ) , : llworkln, transfol'll object Af11 neTrlns10r. trlns • new Affl nelrlnlfor.( ) : /I rlndOll nullber generltor Rlndoe rand ~ new IlIndOll( I;
II IPIll et vi ndow wldth / hef gilt lnt width - ;etSlze( ) .wldth; lnt height · getSlzel) ,height: llfill tile blIckgNlund wi th bllck g2d.selColorlColor.SLAU): 'i2d.flllRect{O, O. getSlzell.wldth. getSlze/l height);
/ldrlw the ililge lIu1tlp1e tlMS fo r (lntn-0:n<50 ; n.... )( trans. setTrusfol'll l l dent l t7 ) : llaowe. rotate. sClle the hMge rudOlll7
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94
Chapter 5 • Bitmap-Based Graphics tra ns. tr anslate ( ra nd .next Int ( )Swl dth . rand . ne~t Int{ )Shel ght) ; tra ns. rotate( Math .to Radl ans (360 • rand .nextOo ub1e( ) » ; dou ble seaIe· ra nd .nextDo ub1e( )+1 ; trans.scale(sce1e . scale); IIdraw the ll1J.age 112d . drawlla ge(llalle. trans . this);
Transparency Although you can load and draw a bitmap at this point, lhe code you've seen so far is very limited. For one thing, the get Imilge(} method can't load a bitmap file out of a Java Archive (JAR) file. JAR files will become very important later, in Part Ill, when we build the Galactic War game. Since the game is so large, with so many bitmap and sound files. it takes a Jong time for the game to load over the web (unless you have a broadband connection). You'll learn how to create and use a JAR file soon enough. All I'm concerned abou t right now is that we are using code that will be compatible with a JAR, so that Java can read files out of the JAR as easily as it reads the raw files from the web server (or the directory in which your program is located if you are running it locally). The Abstract Window Toolkit, known as AWT, provides a class caBed Toolkit that knows how to load a bitmap file . It's smart enough to look in the current URL path where the applet is located (something that you must pass to the lleti llage{) method) . You can usc loo l~\t in your own programs or you can instantiate a global 10011:.1t object and then Uf>C itthtoughoul Ihe game; there are many options. Let's take a look at how this class works; Toolkit tk - 100lkit .1letDefaultToolk lt() ; I.~ge
shl p - tk. getl lllage( ·sur_destroyer. png'):
First, I created a Toolkit object by returning the object passed l>3ck from Too Hit.getOefau 1tToolkitO . This method returns a Toolkit object that represents the state of the Java program or applet. You can then usc this Toolkit object's getlm~ge() method to load a bitmap file . Since we want our applets to be JAR-friendly so games will run on the web as efficiently as possible, I will use the getURL() melhod again; l.~ge
shIp - n.get llllage(getURL< ' star_destroyer .png·)):
Traospareocy
Opaque Images L.et'$ $Ian with what you have already ltamed up to this point-how to load and draw a bilmap wilhout any tralUpolrmcy. At this poinl il doesn'l mailer whether you use the Applet or the Tool kt t 10 load a bitfll
.
/
..................................................... • BltaapTeH progra_
/
lI.po rt I_port I_port t.rt
java.allt,· , java.applet,·: java. ut t I. ': java ,net,';
publ1e clan BttaapTest extends ,""pitt tlll)le_mH Runnable I Int screenlltdth - 6(0; Int screenlletght - (81);
9S
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Chapter 5 •
Bilmap-Based Graphi(s
l..ge1..ge: Thread g._loop: RlOIdOli rind - new RaOldOll{): prlute URl getURUStrlng fllenil ..) 1 URlurl-nul1: try I ur I - this .get(lus ( ) .9I!tlleslKlr(e( HI enil_) ; I ciltch (hcepUon e) I I return uri: public void Inl10 I Tool kit Ik - Toolk1t.getDdilUltToolklt( ) ; I .. ge - tk.geU..ge(gnURU-i1Suroldl.png-));
pUblic Yold ltutCl ( gil_loop - n"" Thrnd(lhh); gil.loop.stut() ;
publlc ~old stopCl { g...eloop-null;
publlC ~01d runO { Thrnd t - Thread .currentThrnd(); wMle (I - gUleloop) { try ( Thrnd .s l up(lO) ; }
Ciltch (!fturrupted£Xception e) ( e.prlntStilctTrilce() ; }
repillnt():
publ1c void updilte{GrilpMcs gl p.llIl(g );
C
Tr(lnsp;trency po,lbllc yotd INtnt(6r'llhtcs 9) t 6r.p~tes2D g2d 16uphtes2DI,: tnt "tdtb - scrnnWtdt~ . tIlllge.getWidt~(thtsl - I; jnt hetgM - serunHelg~t - j,qge .getHetght( U,lsl . I; 6
Q2d.dra"I~Qe(1.ge.rUd.nutlnt(.1dt~l. r.nd.nextlnt(he19~tl.
th1s):
This shon program loads the bitJrnlp image shown in Figure 5.4. In many pmgnmrning bngu;oges and gnphia; libraries, you must specify.ll transpamlt pil;d ccMor to ~ uxd for tnll1SJQrmcy. In the aamplc shown here, the bld rqion around the edges of the astm>id would ~ considered the Utranparmt ZO~" of the image. This trnll$parmt color is black in the exampleshown here (with an RGB value 0(0,0,0), but other colors can be used (or the transparent color too-the color pink (255,0,255) is often used for the transparent color b<.'cause it stands Out so well. la.... uses a more advanced method to handle trall$parmcy, as the next section
apbins.
Transparent Images Java is a sman language that handles a lot of things for the programmer automatically, including the drJwing of t ransparent images. This really makes life easier for a Java game progmmmer because many game librJries use a transpuent pixel for transparency ill$tead of a mask layer. So instead of dealing with transparency in code, it's handled in the source anwork.lf you supply lava with a transparent bitmap file, it will draw that image transparently.
f igu re 5.4
This
op;>QOe
b4tmap Image contains no
tr~~rl'l'q
i1tormation.
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Chapter S • Bitmap-Based Graphics
Most Jav;l progr
..
• _ _~ .. - - -- _. •• ~~~~ D"'.bY. 1 . _ _ ' '"I "' . " t~"',...
. '\ ~. ••
,.
".• •, •,
Figure S.S 1lle iSterold Image IIoJS been !to'tn a tr~1 mask t....
--_
.
-
.
Tranwarency
Figu.. S.6 An ilpha dwJnellayer
~ ~..xl«IlO
d>r
~teroid
in"!Jl' 10 Ijit i1l1'ampa~.
Ln'stau the same program you just typed in for BitrnapTesl and run it again. Only this time, it will load up a new \'et"Sion ofthe asteroid I.png fik that has bttn ediled to support lranspareocy. Figure 5.6 shows tht OIItput from Iht TranspartnlTest program. 1be soura rode has not ehanged (refer earlier 10 the BitrnapTesl program listing), oollht PNG fill' has changed, which accounlS for the difference!
Working Some Masking Magic Ltt's take a look at how you actually crtate a masked PNG image. I'm using Paint Shop Pro becausc it's very easy to usc. If you want to usc this program, you can down load the trial version from www.jasc.com.SinceCorelacquired the company that created I)aint Shop Pro, the link may be forwa rded to www.co rel.com.[.ve used Corcll'ainter too, and it is alSQ a useful tool with similar fu nctionality. Let's take a look at the asteroid image loaded into the program (see Figurt 5.7). To add a transparency layer 10 an imagt, you need to locate tht Magic Wand tool available in masl graphics editors. Afttr SC"lccting Ihe tool with your mouse, dick somewhere in the black region (or on any pixellhat isn't p.art of
99
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Chapter 5 •
•
Bitmap-Ba'led Graphics
.... ~ w.·
r -
..-.
-
Figu re 5.1 A 3D rt/ldilion of a dumpy asteroid (coorlesy of Edgar Ibarra).
the game object). This should loom the edges orthe game object and highlight everything around it (Stt Figure 5.8). Now tha t you have a sdmion available, you need to inven it b«
The next step is to create a new mask Layer in the image to represent the transparent portion. You can tell Paint Shop Pro 10 generate a mask based on the
Trilnspilreocy
.' ,
Figure 5.8
The cuter edge of Iht ~leroid ilflo1!ll'
-
- .... .~
Figure 5.9 Pl'!piriog to inven Iht wlection.
~
been ...lected willi Iht M. Wand IClOl.
101
102
Chapter 5 • Bitmap-Based Graphics
"':' . """ , ,;";,,,'~~~--- -- '''4 ~ "
III
..
r
- .,-.
J
.~
•
'------~ " .~
.... _.
."' Figure 5.10
- .....-
The boond.Jry of the asteroid is IlOW Sl'lected.
selection you've made in the image. To do this, open the Layers menu, select New Mask L1yer, and then Show Selection, as shown in Figure 5.11.
>I, Although I am basing mis Morial on the ex(ellent grapl1k ed~or, Paint Silop ~ most professional graphic editors support layers and prol'icle similar fcatur,..; to mose found in PSP. The GIMP, for instance, is a freeware griljlhk editor wim (omjlilrable features and is available on many platforms (Windows, linux, and 50 on). Download The GIMP (GNU Image Manipulation Program) from www.gimp.org.
In Figure 5.12, the transparency has been created based 011 the masked selection, The result looks very nice; this asteroid is ready for primetime! You can load this image into your Java applet and draw it, and it will automatically be drawn with transparency so the outer edges of the image (where the black pixels used to be) will not overwrite the background of the screen.
Trarnparency
.....
.
•
. .. •
f igure S.11 CrNting ~
new mom IIy8 out of !he wIection.
figure S.12 The flteroid image now lias a masffil
tr~ency
1Iy8.
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Chapt~'
5 • Bitmap-Based Graphics
What You Have learned W~ \'Iill wnlinue to \'I~rl \'lith tr;lIlspu~nt imagu from this point fO""'3rd. so you ha\'~ Ieuncd a \Try irnponant tool in thisdupterthat will make it pol&ibl~ 10 crC'at~ utrmlely atll'3eti\'~ pffieS. Spt'CifiooIl\'. you kamed:
• How to dl'3w bitmap images • How to trJnsJal~, rotal~, and scale bitmap imagl!S • How to draw bitmaps with transparency
Review Questions Th~
following questions will MIl' you 10 determin~ how well }~U ha\'e Ie:lrned subjccu discussed in this chapter. n.e answ~rs u~ provided in Ap~ndil[ A. "Q,..aptCT QUil AIlSI'I'CTS." th~
I. What is the primary clus. wc'\'~ bttn using to manipulate bitmappcd graphics in this chapt~ 2. What method initializes
Ih~
keybo;!rd listener interface?
3. What Graphics20 method is used to draw an image? 4. Which Ja\'a cia$:> contains the get!luge() metho·d? 5. What cia" makes it possible to perform translation. rotation, Jnd SClling of imagesl 6. Whi<;h Gr.phlcslO method dra\'l"S an ima¢ 7. Which Innsfoml mnhod mo\'es an image to a '-'Ior;;otion? 8. What isttM-
n.an~
ofthc "transparency" channel in a J2-bit P:-lG im;a¢
9. "'Jut is the Applet class method used 10 load a resource from 10. Which keyLI stener e'em
d~te(\s
JAR!
key prtoSSes?
On Your Own Usc the following exercises to test your grasp of the materi
On Your Own
Exercise 1 ThcTc are IIklny example programs in this chapter thaI eQuid be modified and expeOlTlt'ntM upon. TwtoIk tht Randomlllklges program. Modify the program so lhat it !ooids and dnws two diffeTmt im.1ga nndomly instead of just a single im.1ge.
Exercise 2 Modify the Dnwlmagt prognm so thaI it will scale the imagt largtr or smaller with tht uS(' of the keyboard plus (+) and minus (- -) keys.
lOS
CHAPTER
6
SIMPLE SPRITES
Up to this point you have learned about a lot of jaVll classes that are useful for m;lking a game, particularly the Graphl cs20 class. The previous two chapters provided the groundwork for this chapter by showing you how to tap into the Graphlcs20 class to draw vectors and bitmaps.. At this point, the source code for evm a simple bitmap-based game will tend to be too compliated and too difficuh to manag<- without a better way to ~ndle the objects in a game. What you need at this point is a new class that knows how to work with gameobjectssomething known as an /ICt(Wor a spri'''. The goal ohhis chapter is to develop a Wily to handle the game objec1s moving around on the sclftn. Here are the specific topics: • Programming simple sprites • Creating a Sprite class • Learning about collision testing
Programming Simple Sprites A sprite usually represents an animated graphic image that moves around in a game and is involved with other images. The difference betwccn a regular image and a sprite is often that a sprite will encapsulate the image data as well as the methods needed to manipulale it. We will creale a new class later in this chapter
'"
108
Chapter 6 • Simpl", Sprites callfil laagHnt I I" which will ~ able to load and draw a bitmap, and we will then cre:;!!e a new Sprite class that will use laageEntlt,. I would !ike to build a p,air o( cbsses to simplify sprite programming. We will Sprite cbs.s in this chapter aDd ~n add d~ Anlaat~Sprlte cbs.s in the next chapter to haDdIe animation. lbe new SprHe cbs.s that I'm going to show you herr mightlw de5Cribed as a lam"" dus. What do I mean by "heavy"? This is not a simple, abstract class. Instead, it is tied closdy to the Applet and Graphics2D objects in our maiD program. You would not ~ able to use this Sprite class on its own in a Java application (a standalone program) be<.:aus-e it relies on !he prescntt o( the main apple!: to function. Although it is possible to write a Java game that runs as an application rather than as an applet, our focus here is on web games. So, our new Sprite class will work well in this environment. c~te ~
A spri te cannot draw itself without the Applet and Graphles2D objects in a main program. Although the Sprl t e class could usc methods such as getGraphl cs() to pull information from the main apple!, our examples use a double buffer (a back b uffer image used to update graphics smoothly, without nickering the 5O:r«n). The 8iSeGa_Entit, class will handle aU of the position, vdocity, rotation, and other 10gislkaI properties. while laageEnt I t, will mallt use o(them by providing mrthods $\Ieb as tr.nsfo,..( J and 4rav( ). 1want to simplify the Sprl Ie cbs.s 5(l it doesn't expose all oftbese propttties and methods., but provides a simpler means to load and draw images. This simplification willlw especiaJIy helpful in the IJCl[t chapter be<.:au.se animation tends to compliOlte things.. A useful sprite class should handle its own position and velocitydata, ralher than individual X and Y vaJut$ (or these propttties. The sprite's position and velocity will be handlfil by the 8iSeG._Entlty class. The Sprite class will not inherit (rom llaageEnt I t,: instead, it will use this class internally, like a regular variable. I also want the accessor methDds to resemble simple properties, while the llIutator methods will be in th e usual "set" format. For in stan",~, I want the Sprite class to have a position() method that returns the position of the Sprite obj ect, bu t it will use a setPosltion{) melhod to change the X and Y values. For instance, I want to lw able to access a sprite's posi tion and velocily by wriling code like (hi$: sprite. pes it i on( ) .Il ) sprlte.pesltion().l( I
Programming Simple Sprites On top of these requirements, we should not be concerned with numeric data types! I don't want to typecast integers, tloats, and doubles! So, this Spr i te class will need to deal with the differences in the data types automatically and not complain about it! These aTE! minor semantic issues, but they tend to seriously clean up the code. The result will bea solidly built sprite handler. First, let's take a look at a support class that will make it possible. Tip
AA Mcessor method is a method that returns a private variable in a das~ A mutator method is a metllod that dlaoges a private variable in a dass.
The PointlD Class The Point20 class is a helper class with the sole job of storing and providing X and Y values in a variety of numerical formats. There is a lava library that also contains a POlnt20 class, but it w;IS unsuitable for our purposes here. However, there should be no conflict because that other class is contained within a package.
1·····..
*0 . . . . • . .
• Point20 Cl ass
·**..••••••••..•••••••••••••••••••••••.. •
·····..·······....··..·········..····..···..·..····..·····1 Polnt20 utends Object l private doubi e ~. y;
ChS5
lIint constructor int y) setX(x); seU(y); I Ilfloat constructor Point20(f1o~t x. flo~t y) setX(x); sety(y); I Iidouble constructor Point20(doublex. doubley ) { setX(x); setY(y); Polnt20{int~.
IIX property double X() { return x;
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110
Chapter 6 • Simple Sprites public yold SHI(double x) ( thls.x ~ x: I public yold SHllflolt xII thls.x~ ldoublel x: I ""bllc yoid sHI(lnt x) I tbis.x ~ (double) x: I ' " prolH!rty double HI (rebrny: I public yoid setHcIoub1e yl I this., ~ Y: I public yold seU(flolt Yll thls.y ~ ldOliblel y: J public yold seU(lnt yl I this., ~ (doublel ,: I
Basic Game Entities The 8He~ectorShape class was introduced oock in Chapter J for the Astemu/sslyle game. We will uSC: a very similar class for sprite programming in a fulure version of Galactic War (beginning ill Chapter II, "Galactic War: From Vectors 10 Bitmaps"). Here is the code for Ihis class. public cllss 8neGa.eEntttJ utends Object l IInrl,bles protectell boolun,l he: protected double x.J: protectell double Yell. Yell: protecte
Programming Simple Sprites
pub11 c voi d setFace~og1 e(double public void incFace~og1e(double pub11 C voi d setHove~og 1e( double public void incHove~og1e(double
aog1e) I ~h1 s . fa ce~og1 e - aog Ie; I) I thls.hceAogle .... i; l aog1e) I thi s . lIIOve~ng Ie - ~ngl e ; I) l thls.MOve~ngle .... j; I
Iidefault constructor BaseGameEntlty() ( set~1 Ive{hl se); setX(O.O) ; setHO .Ol; setVeIX(O.O); setveIHO.O) ; setHove~ngle(O.O) setface~ngle(O.O)
; ;
The Image Entity Class The ImageEn t i t y class gives us the ability to use a bitmap image for the objects in the game instead of just vecloT"based shapes (such as the asteroid polygon). It's never a good idea to completely upgrade a game with some new technique, which is why some of the objects in the first version of Galactic War will still be vectors, while the player's ship will be a bitmap. When you reach Chapter II, you will have an opportunity to examine the progression of the game from its meager beginning to a complele and complex game with sprite entity management. I always recommend making small, incremental changes, play-testing the game after each major change to ensure that it still runs. There's nothing more frustrating than spending two hours making dramatic changes to a source code file, only to find the changes have completely broken the program so that either it will not compile or it is full of bugs. The ImageEnt I ty class also inherits from the BaseGameEnt I ty class, so it is related to VectorEot i ty. This class is awesome! It encapsulates all of the functionali ty we need to load and draw bitmap images, while still retaining the ability to rOt'lte and move them on the screen!
1·········0*·..•........·····················..·····..··..
.......................................................... • ease galle I_age cl ass for bi t _apped game ent I ti es
import Java.~ ..t.·; 1mport java. a..l. Gra ph Ics2D;
/
111
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Chapter 6 • Simple Sprites jllpCrl jiIYa.awt.t_.·: jllPOrt jan.app1d. · : IllPOrt jan.nd. o: polIbllc class IIliteEntlt7 u tend s &as e&a_Ent1 t7 I Ilnrlables
pl'1ltecte
l.ateEn t lt7(Applet a) I applet-a : setl.age{ nu1 1 l : setA l 1ve{true):
public Illite tet1Ilite() ( return lllige: public vo1d sellllite(Jllite Illite) 1 this. Illite - Illite: double ~ - applet .tetSheD .wldtM2 width( 112: double 7 - applet .tetSlzeD .Mltht/2 heltht( )12: at· Mf1I1l!Transfonl.9l!tiranslatelnstance(l. 71:
\lllbilc lntw1dthO ( If (Illite I-null) return lllige. tellli dth( applet) : el se return 0:
I public lnt height( l { If (1.age I-null) return l.age.getHelght(app1etl : else return 0:
public double tetCenterlO I rdurn geU( I + width() I 2:
Programming Simple Sprites
pubHC double gUCtnterYO I return gUYO + \l.tlgMO / 2:
public yo1l! sU6r.lplllcs(6r.lphlcs2D,ll ,2d· g:
prlnh URl getURLISlrlng fllenallt) 1 URlurl·null: try I uri ~ thls.gttClass{) getRuource(fl1enallt): I catch (hcepl101\ ell return uri;
Pl/bllc yold lo.ldCStrlng fHena ..)I llIa~e· awlu.gulllage(guURl( flltnalltl): II~lle(getillage().gulildth(applet) (. D): double ~ ~ applU.getSI ze() .II1dth/2 - "ldth( 112; double y - app let. getS I ze( ) . hel ght/2 hel ght( lI2 : at· Affl ne Trans for•. getT rans la le Instance( x, y):
public void transfor.() ( aLsetToldent Ity(): at. translale( I IntlgetiO + "ldthO/2, (Int)getY() at. rotate( IUth. toRadlJns( guFueAng IeC ) I) : at . translatel ·"Idth()l2, ·htlgM( 112):
+
helgM0l21;
P\lbllc wold drawl) I g2d .drall lllage( getlllageO, at, .Ipp1et) :
IIboundlng rectangle publIc Rect~ngle gel8ounds() I Rectl ng le r: r ~ new Recling I e( (I ntlgeU (), (\ ntlgttY ( ), ,,1 dth() , hel ght ( ) ) : return r;
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Chapter 6 • Simple Sprites
Creating a Reusable Sprite Class Following is the source code for the new Spri te class. This class includes a 1011 of features! In fuct, it's so loaded with great stuff that you probably won't even know whattodo with it all at this poin!.1 am not a big fan of inheritance, preferring to build core functionality into each class I usc.
Collision Testing The Sprite class includes several methods for detecting collisions with other sprites, and it also provides tests for collision with Rect~ng l e and Poi nt20 objects as a convenience. Remember that I wanted this Sprt te class to be intuitive and not cause the compiler to complain abou t silly things, such as data type con· versions? Well, the same is true of the collision testing code. There are three versions of the CoIl i desW1 th() mcthod in the Spri te class, providing support for three different parameters: •
Rect~ngle
• Sprite • Polnt2D This should cover almost any game object that you would like to test for a collision. Since these mcthods arc built into the Spri te class, you can call them with a single parameter, and the internal data in the sprite itself is used for the SKond parameter that would normally be passed to a collision routine.
Sprite Class Source Code This new Spri t e class does not inherit from anything other than the base Object, although it uses Im~geEntlty internally for access to that class's excellent support for image loading and drawing. Why doesn't this class inherit from B~seGameEntlty or ImageEntlty? Those classes followed a logical inheritance chain but also included a lot of features that do not need to be in the core of the Sprite class, that's all. We still have access to those properties and methods if we want to use them, by using an ImageEntlty as a private variable, but we get around the problem of having to deal with private/public access and inheritance. Inheritance is a beautiful concept, but in practice too much of it can make a program too complicated.
Creating a Reusable Sprite
I·········································
C~
.
.......................................................... • Sprite tIns
/
<_por t jUI .I Mt .·: IllPort JUI.applet.·: p~bllc
clau Sprite utends Object I prlnte IN9l'£nt1t1entlt1: protectell Polnt2D pos : protected Po lnt2D vel: protecte d double rotRHe : protected lnt cu r rentState:
Ilconstructor SprlteCAwlet a. Graphlcs20 g2dl [ entHy ~ new IflIgeEntltyCa): ent 1t y .setGra ph Ics( g2d) : enl1 t y. se Ul l .e( fa l se) ; pos· new POlnUDlD. OJ: weI • new Polnt20(D. 0): rot~te ~ 0.0; currentState·O;
IIl ol d blt_a p ' 111' publlc void IOldCStrlng fllenUle)I etltlty.1oadl H lenalle):
Ilpe r fonlaf'l ne trans fOnll t Ions pu bllc Yol d t rans for_C) ( ent Ity. seU ( pos. X( l) ; ent1ty . setHpos . Y( 1); en t 1ty . trans fOnll I :
IIdrlW tke hlilge public .oldd raw(J ( ent1 ty .g 2d.dra M[_ageCutl t y get I_agel l .ent l ty .at .ent1 t y.appl et); IIdrawbounding rec t angle around sprite PIlbllc vold draw8ounodslColor cl I
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Chapter 6 • Simple Sprite5 entfty.
liS
the positIon besed on ~eloclty public vold updltePosltlonO 1 pOI . setltpos.X() + vel.XO); pos.setY{pol.Y() + vel.H» ;
lIupd~te
rellted to .ul,..tlc rOUI on heeer public double rOUtfonbte{)1 return rotbte; I publlC ~old setRotHlonRiteldoub1e rite) roU.te- rite;! public ~old updlteRot~tlon() 1 set F~ceA"g1el f ~ceAn
II-el~ods
IItenerlc sprIte sUte url.ble (~1 he. 6ud. coil 'ded. et c.) publIc Int sutel 1 I return currentStlte; I pub1Ic ~oid setSUte( i nt s t~ te) ( currentSt~ t e - stl te ; Ilreturns I bounding rectlngle public Reclugle getBounds{)! return entlty.getBoundsll ; I/sprlte posttlon publlcPolnt211pos'tton lreh"'pos;! publIc voId setPos; t iOllIPolntlll post I thl s.pos - pos; II spr I Ie lIO.e.ent vel oc tty
pub1 ic Polnt20 velocIty!) I return vel ; I pub1 ic vo id se tv elocHy(Pol nt20 vel) I t his . vel - vel; Ilreturns U.e center of l~e sprIte IS' Point21l publ c PD'nUll certer( return( ntll Pol nUll( ttl: ; ty. getCenterl( ). entity. 9ttCtflterl \ I)
IIgeneric ur1lble for selecthel, usln
pu blic .oid se tAlhe(boo l ean .li.ell entlty.leUlhe(a1i.e) : llface angle i nd i cates ..hi c~ 4i reet1on ~pr i te is fac 1"9 publ ic double fUeAl>gle( I I return ent itl.tetFaceMgle( I: I publ ic .oid setFace gle(double anglel I ent Itl . setFace gI e( ang Ie) : I public . oid se tFaceAngle(float angle) l ent! tl . setFaceAng let (double) angle): I public .oid setFace.....gle(lnt angle) I ent1 t, . setfaceAngl e( (double) angle):
11.,.e angle l/ldicates direct lOll sprite Is .,.'ng
publl c doubl e .a.eAng1eO I return ent Itl .getllo.ung1 eO : publ i c .oi d setHoweAllgl e( double Ingl e) I en t lty. sHMoweAngle(angle) :
I public . oid setllo.e gle{float angle) I ent Itl .seUlowe gle( (double I al\91 e):
I public .oid setHoweAngle(lnt angle I I ut I ty .setKo>eAn gIe ( (double) ang1 e) :
llrehrns the source Illige Ifldt~//lelg~t pub lie Int Illigellldt~() I return ent It)' .If' dt~(): I public lnt ladgeHeightIJ (return entlt)' . ~elg~t(J: for coil islon If l tn a rectangul ar shape public boolean collideslli t h(Rectangle rect) I return (rect. Inter~ectS(get80u/lds(J II:
Ilt~eck
I I fc ~ etk for coli i sion with another sprl te pub11 c boo1e. n co1li des ll l Ul (Sprtte spd t e) I return (getBou"lls( I. Intersects (sprl te. getBounds ( ) 11 :
I IIcheek for coli h i OIl with a poi nt publ ie boolean coil idnll HMPolntZO point) I retu rn (getBo un d1( ). con t ai nl (poi n1. X( ). poi nt
Y()) 1:
118
Chaplft 6 • Simple Sprites
publiC ~pplet IppletO 1 returne"tlty.lpplet; 1 pub II c Graph 1cs2D grlph I cs(} I return e"t 1ty . g2d; publIc luge l..get)I return entity. luge; 1 PIlbl1c wold setlu9t( luge 'ugt" I ent 1ty. set lugetluge);
Tip 6 II feJtI.ft nssing &om I!le Sprl te diss..: this pcwot we wiI 90 _lhil next dIIpIer.
.........._
.. _
sW!ecl
Testing the Sprite Class Let's gi\~ 1M Ill!'\'> cbsl;cs ..~\~ dc\"dopro in ltus d1iptn I tal run. The follo..ing program (shown in Figurt' 6.1) dr;tws a badcgmund inlaU:and then driwS a ~pril{' randomly on the screen. This tcst progrlUlI uses a thread and the Runnable interface in order to draw a sprit{' repeatedly on th{'SCIl'('ll without user inJluL W{"U study this kalurt' more lhoroughly in Olaptn 10. "Timing and ttlt- Gaml' loop." when w{'
r19uA! 6.1 1hlo SpitloTest
~ogram
demonstrates haw to 1M lhf
Sp'H~
cliss.
Creating a Reusable Sprite dass
kam more about threads and the pmt' loop. Sl:udy this short demo prosnm wdI, bcaUK it ckmonstrates ~ps the lim high-speed enmplt you.~ $em thus far.
I ····································· · ··· ·~·········· p rg gr~•
• Spr l teTnt
•••••••••••••••• u
/
1l1port j~u . llf t.·; tllPllrt JUI.llIt. i-.lge • • ll11Pl1rt jUI,lppleL ' : '.rtjul,,,ttl, · : tlllPllrt jlu.net. · : publlc cllst SprlteTest extends "'PIll et 1.,.1e.ents Runnable ( lnt scree nll id t h - 640: l nt sc ree nHe19ht - 480: IIdouble buffer objects hffertdl-.lge bACkbuffer; 6npkics2D 92d; Sprite utero1d: 1-.l9tht1tJ' back!lround: ThrUd IIll1t l oop: Rand a" rind - new Rando-() ; public voId i nit() { IIcrute the back buffer for s.xlth gr aphics INlckb
publiC void stlrtO I gillt loop - newThreldlth is) :
119
120
Chapter 6 • Simple Sprites galll('lOop.s t~r t(l ;
publicvoldstop(){ gall\l'loop - null;
public void runO I Thread t - Thread.currentThrudl J; while (t - -qallleloopl I try ( Thrud .sleep(301;
I cnch (JnterruptedE~ceptjO"e) ( e. prl ntStack Tracel ) ; I repalnt();
public void update(Graphlcs g) l Ildraw the backg round g2d .d ra",lllge(background.getl.uge(J . O. O. screenliidth I . screenHeight'l. thlsl; int",ldth - screenliidth . asteroid. 'llagelildth() . I ; int height· screenHelght Hteroid. IlIIageHeiqht{} • 1; Pol nt2D pol nt • new Poi nllO (rand. ne~t Intt "'I dth 1. rand
"e~tlnt(helght)l;
as tero Id. setPos It' on( pol nt) ; as tero j d. transforM( 1; as tero Id.drawl }; paint{gl;
public voId palnt(Graphlcs 9) ( Iidra wthe back buffer to the screen g.draw!luge(backbuffer. O. O. this) ;
R~~iom
What You Have learned This significau l chapler produced a mQnum~ntal new version of Gaklctic War that is a foundalion for Ihe chapters to come. The final vestiges of the game's \"CCIor·based roolS ha~ hem discarded, and the game is now fully implemented wilh bitmaps. In this chapter.)'Ou learned: • How to create a new, powerful Sprl te class • How 10 dl'll'<:t sprite collision • How to write ~ble methooh and classes
Review Questions The following questions will help you to dctermine how well you have learned the subjects discussed in this chapter. I. What is the name of the suppo" class created in this chapler to hdp the Sprl te elass manage position "nd ~Iocity? 2. During which keyboard event should you disable a key-press var iable when
detecting multiple key presses with global
variables~
3. Which thrtt types of parametCTS a.n you pass to Ihe collldesVltM J method~
4. Which Java class provides an alternate method for loading images that is not tied to the applct~ S. Which Ian package do you need to impo" 10 use the GTlpll1cs20 class? 6. Which numeric data type ~ the POl nt20 class (creatoo in Ihis chapler) use for internal storage of the X aud Y VOllues? 7. Which data typt$ can the Potnt20 class work with allhe constructor 1evel~ 8. Which sprile property dC'lennines lhe angle at whieb the sprite will
mov~
9. Which sprite property determines at which angle an image is pointed. regardless of movement dirl'<:tion~ 10. Wh ich MftneTransfor. method allows you to translate, rotate, and.scale a sprit~
III
122
Chapter 6 • Simple Sprites
On Your Own Use the following exercises to te51 your understanding of the malcrial cO"erc
Exercise 1 The SpriteTesl program demonslr:ues the usc of the Sprite dass. Modify the program so thaI it draws multiple instances ofthe asteroid sprite on Ihe .screen, each moving and animating differently.
Exercise 2 Modify the SprileTest program C'o'en further by adding collision testing, such Ihat Ihe asteroids will rebound off one another when they collide.
CHAPTER
7
SPRITE ANIMATION
This chapttT adds a significant new feature to )'Qur box ofJa.... tools-the ability to load and draw animat~ sprites and apply thai knowkdge to an rnhancrd new sprite clau. You willieam about the different wa)'510 store a sprile animation and how to acc~ a single frame in an animation strip, and you will s« a new class called Ani.atedSprite with some S('rious new functionality that greatly extends the baS(' Sprite class. Here are the key topics: • Sprite animal ion techniques • Drawing individua.l sprite frames • Kccping track of animation frames • Encapsulating sprite animation in a class
Sprite Animation the years I have seen many techniques for sprite animation. Of the many algorithms and implementa tion$ I've sludird, I beliC'V(' there an: two CSSCTItial ways to animate a graphic object on the screen-by loading individual frames, each stored in its own bitmap lile. or by loading a single bitmap containing rows and columns of animation frames.
()o,-er
124
o..pter 7 • Sprite Aoim;,tion
Animation Techniques First, there is the ~"or
The second sprite animation technique is the tiled method. This type of animation invol,·cs storing an entire animation sequence inside a ~ingle bitmap file, also known as an 1I11;rWI/;otl Slr;p. Inside this bi tma p file are the many frames of the animation laid out in a single row or with manycolumllSaod rows.. Figure 7.2 shows an animation strip on a single row, while Figure 7.3 shows a larger animation with multiple columns and rows.
Drawing Individual Frames The key to drawing a single frame from an anillliltion sequence stoTt'd in a tiled bitmap is to figure out where each frame is local.-d Iligoritllmiallly.lt's impossible to manually code the X and Y posit ion for each frame in the image; the very
Figure 7.1 An ri'nation
~ wiIh
figure 7.2 An animation
~trip..,,;m
I t _ SlOItd ..
a 'iingit row.
~ bmnap
filrl.
Sprite Animation
Fi\Jure 7.3 No iIIIimatiotI 5ll1l.mh ..... cdurMi il'Id two rows.
thought of it gives me hives. Not only would it take houn to jot down t~ X,Y position of every frame, but the bitmap file oould easily be modified, thus rendering the manually c:akulated poinl$ irrelevant. This is computeT scienc:e, alter all, $0 theTe is an algorithm for almost everything. You can eakulate the column (that is, the number of frames IlcrOS3) by dividing the frJme number by the number of eolumns and multiplying that by the height of each frame. frllleYe (frllieHullber I colU1II15) • helghl; This will give you the correct
row down into l~ image where your d~ired frame
is located, but it wiD not provide you with the actual column, or X value. For that, you need "similar solution. Il1$Iead of dividing me frame numoo by oolumns, we will use modulus:
frjlltl· ( fralleHuilboer 1 col.-5 ) • II1dth; A5 you might have noticed, this looks "Imost CX3C1ly like the fonnula for calculating fralleY. Now we're multiplying by width and using the modulus character instead of the divi$io" character. Modulus returns the remaitrder of a division, rather than the quotient itself, If you want the Y v,llue, you look at the division qllotient; if you want the X value, you look at the division rt'maimlrr. Here is a complete method that draws a single frame OUI of an animation sequence. TheT(' arc a 101 of parameters in this method! Fortunately, they are "II
12S
126
Chapter 7 • Sprite Animation clearly Iabel"d with descriptive names. It's obvious Ihat we pass it Ihe source lilag e, the destina tion Gr aph l cs2D objecl (which docs Ihe real drawing), the destination location (X and V) , the number of columns across, the frame number you wanl to draw, and then Ihe widlh and height of a single frame. What you g<"t in relurn is the desired animation frame on the deslination surface {which can be your back buffer or the applet window}. pub II c yol d draw Fra lle{ lu ge source . Grap hf n2D dest . Int destx . In t desIY . Int C015. int fraae . Int Width . Int hel ghtl Int f ra ll('X - (f rame S co l s) • widt h; Int fra ae~ - (frallC I cols) ' heigh t; des t . drawi llage( source . desIX. dest y • des t u.,.1 dth . des tHhel ght . fraOle X. f r alle~ . f r all e~ .....ldth . frarne V+height . t hIs) :
Keeping Track of Animation Frames Acquiring the desired animalion frame is just the lirsl step toward building an animated sprile in Java. After yOll have figured out how 10 grab a single frame, you muSI Ihen decide what 10 do wilh it! For inslance, how do you tell your program which frame to draw, and how does the program update the current frame each lime through the game loop? I've found that the easiest way to do Ihis is with a simple upd,lle method that increments the animation frame and then tests it against the bounds of the animation sequence. For instance: eu rren t f ra ae .... anhu t IenOl rec tI on : (eur rent Fralle) totalFrame5 -Jl I eur ren t FrallC - 0;
if
I
else If (cu rrentfr alDC <0) { eurrentFrame - totalFra:ne5 I ,
Take a dose look at what's going on in lhe code here. First, the current frame is incremented by all arbitrary value stored in a variable called anlJla t 10nOI reet Ion. This will always be either -lor t to animate forward or backward. Then. the next line ehed::s the upper boundary (tot a IFr allles· J) and loops back to 0 if the boundary is crossed. Similarly, the lower boundary is checked, ~lting
Sprite Animation currentrra-e to the upper boundary value if necessary. The end result is thaI three VlIIriables are needed: • currentfra-e • totalfra-es • Int .. ttonOtrectton You would WlInt 10 call this upcbte cod... from the Ihread's run( l ~t method. But, speaking of th... thread, tMt does bring up an important issue-timing. Obviously, you don't WlInt every sprite in the game to animate at exactly the same rate! Som... sp rites will move very slowly, while olhers will have fast animations. This is re;lllyan issue offine.tuning the gameplay, bUI you mllst have some sort of nu:<:hanis1l1 in place for implementing liming (or each animated sprite st'pamtdy. You can accomplish this by adding a couple more variables to the mix. First, you will net
1f (fr••Count) fr._OellJ) ( fra..count.o(l;
currentrr•• _ ant ..ttonOt rectlon; If (currentFra.... ) tot.1fr••s·\) I currentrra. - 0; I else If (currentfra-e < Ol { currentF ralie - tolal fra.s·\;
Testing Sprite Animation I'd like to go Ihrough a compktl' enmple wilh you so thesl' COI\Ce-p1$ will fed more md to you, .. nd so that you can see thl' dramatic result when a sprite is
127
128
Chapter 1 • Sptite Animation
Figu re 1.4 All animated blIII with 64 11"-.
animaled. ~ AnimalionTest program loads a massive &I-frame animation St'quenct (shown in Figure 7.4) and animates it on lhe streen while moving the sprite :1Tound at the sallie time. Since we are slicking to lhe subj«l of animation in this chapter, the program doesn't attempt to do any transforms, such as rotation. But can you imagine lbe resull of an animated sprite Ihal can IlOO be rotated? This program will help 10 determine ....tLat we need to do in the upcoming animation class. The output from the program is shown in Figure 7.5, where the single animated sprite is bring drawn over a b."kground image. Following is the cooe listing for the AnimationTesl prognm. I havc highlighted Uy portiol15 of code (Ihat are new to this chapler) in bold lexl.
. ..................................................... /
/
IlIpOrt JilYi. i.t . ': IlIpOrt jiIYiI.i1pplet.·: IlIpOrt JilYiI .ut 11.':
I.port
jIVII . awt
. I.age
pUbllc clin AAI ..ItIO~Tut ute~ds .l.pplet stitle l~t SCRHIlIIIDTH ~ MO:
l..,l_~ts
RuMilble I
_, _. ....
figure 1.S 1hlo AAunationTel program. stattc tM SCR[[NHElGHT - 480; Thrud gllle1 oop; Rando. rand· new Randall(); IIdoubh buffer objects Buffered I.age blckbuffer; Graphtcs2D g2d ; I/background tllolge lllolge background;
IIsprtte nrllbles IlIolge blIll: 1nt balll· 300. blIllY" 200: 1nt speedl. spHdY: lIutllolttOll nr11bhs 1nt currentfrl." D: tnt totalfr. .I" 54: tnt u1l1olt1onD1rKttOll- I: tnt fr..count .. 0: tnt fra.tlell, .. 5:
Sprite Animation
129
130
Chapter 7 • Sprite An imation private URl
Rlget"Rl(Str;~g fllen,W)
I
~rl a n~ll;
'" urI -
t~h.gftCllSsl)
.9ftllesourcelfl 1e
J Cilte~ l{lceptton el /I return ~rl;
public yotd tnHll 1 Tool ki t n · Tool ki t. getlli!fau l troo l. t tl ) ; I/crul! the bilCk buffer for sllOO t h grilphlcs b,ckbllffer • nelf 8ufferfdllUgel SCREEII1l!OTH. SeRE' 8~ffere~:II.ilge. TTP£_:U_R&8I; 92d· bilnbuffer .crenfCrilp~ic$(): IlNd t~e Nckgro~nd ilU~ Nckgrouno· tk.ge" :ugl (~t Rl ""oOOgrilin.png" I/l0ild the billl ilnlailtlon strip billl • tk. getilUge( gftURLl aXb' 11. png· )) : speedX. r,nd.nutlnt(6)+l; speedY . rilnd.~utlnt(6)+1:
public void surtl) 1 gil'lle 1ClOP • n.... ThrUd~ til Is' : 9,w100p . stirt():
publlc votd stopl II gilwloop·n~ll:
public yold runll r Ihreild t · Thrud . cu r re~tlhreild() ; lfht l e{t-gilll-e l oo p) ( try l ThreilO. $1 eep: 20) ; cnch
f ~ntfrrUjlad£.cept len
el I
~.[ I G~l .
Sprite Animation
e.prlntStacHrace() ;
I glieUpd.tet); fellllntl);
publlC wold ga.UpdlteO I II$H: If It's tl. to ani ..te frlle(_t++; If (frl.cOUllt > fr••Oell1) { frUII(OUlltooO; lIupdlte the ,nl..tlon fn. currptfr. . . . I"i ..ti ollOi rKt f 011; If (currentFr•• > totllfn.s • 1) { cllrrentfr•• ·O;
J .1st If (currentFre. (Ol ( current Fr••• totll frl.S • );
lIupdate the ball pO$!tion ballX .... $peedX; 1f «(ball X <0) II (ba 11 X > SCRHMWIOT~ • 64)) I speedX '- ·1 ; ballX .... spudx; I balU .... speedy; If «billY (0) II (bill T ) SCREEN~E1GtlT • 64)} I speedY '- I; bllly .... speedT;
public wold IIpd'te(Grlghln gl { IIdr," the blctgro~lId gld.drllll..ge(bickground. O. O. SCRWIIIIOTH I. SCRE[llH[lG/lT-1 . this); IIdr," Ut current fre. of 1"1 ..t1011 drillfr,..tbll!. g2d, bllll . b.llY. 8. curr.ntFrl., 64, 64); g2d .$ft(olor(Color .BLAell;
131
132
Chapter 1 • Sprite Animation ,2d.dr."Strlll9("PosltlO11:· tbllll1t . . " tbllilT, S, 101: g2d.dr.vStrln9( "Yeloclty: " + speedl + "," t speedY. S. 2S): 92d.dril"Strln9("AnllNtlon:" tc"rrenHr.... S, 401: pil1nt(9):
p
Now, after reviewing this code, you mighl be wonderi ng why we aren't using lhe lU!ileEntHy and Sprite cluscs from lhe previous chapler, since they would WI down on so much oflhis code. That's a good question! The reason is this: I don 't like 10 build 100 m3ny dependencies into class definitions. As I explained in lhe previous chapter, 100 many links in an inheritance chain om lead to problems, This progr:am is completely Idf-contained, withoul n«d of any atra classes.. A single, self-conlained example is far more educalional than a short program filled Wilh object variables dl'Clared from (Uslom classes. Al a certain po inl, we wi ll do thaI. BUI righl now, let's focus on just one subject withoul any dependencies.
Encaps ulating Sprite Animation in a Class There arc some significant ncwpia:es of cock in the AnimalionTesl program Ihal we'll definitely n«d for Ihe upcoming Galactic War projed (in Part III), All of the properties can be slllffed (lhat's slang for rnalpsullllM or wrappdJ into a class, and we can reuse thaI heautiful dril",frillleO method as well. One really
Sprite Animation great thing about moving drnFrllle{) inlo a class is thaI moSI of the paramelers can be eliminated. as they will be pulled out of Ihe class in lernally. Selting up an animation will require a few steps up fronl when the game Slarts up. but aflet lhat. drawing an animaled sprile will be an automatK process with just one or IWO melhod ails. Note. also. that we're inheriting from the basic Sprite class from the pl'n'iow chaplet! I'D highlighl the important code in bold.
, . ....................................................., • AlilutedSprl te ellss
l-.or, l-.oH 111ll0rl laporl
Jan.awt. ·; Jan.applet .·; java.avl.luge .'; Jan.net. ·;
class AnlaatedSprlte extends SprIte { /ltnls Il1ige holds the large II led bHaap print!! luge an1.'.age; Ifte.-p luge passed to parent draw llethod Bufferectluge tMPluge; liiraphlcsZD tMPSurfaee; /leuuOll properties prlnte lnt eurrFr••. tatF,..,; print!! lnt anl.olr; print!! 1nt frCount. frOeIl,; prlnu lnt frll1dth. fr1llllght; prlnte 1nt eah;
pu~lle
public AnluudSprlte{Ajlplet aPlllet. 6rJphlcs20 g2dl ( super(applet. g2dl; eUrrfriUle - 0; totFralles - 0; anl.olr-I; frCount - 0; frOelay - O; frWidth - 0; frHelght - 0; eols - 0; prlnte URl 9l!tuRUStrll>g fllen_1 1 URlurl-null;
133
134
Chapter 7 • Sprite Animation tryl
uri· thl s. getC Iass () geUesource( HI enalle1: )
citch (Exceptlc.n e) II return uri ;
publtc lold load(Strlll9 fllen••• Int col ...s. Int rOOlS. Int width . Int height) J/IOid the tiled .nINt1on bll.llap Tooltlt It - Tooltlt.9t!tllefi\lltTooltltO; anl~Noe· tt.oeUN,e(9t!tURl(flleni.ll; ntCal ...s(cal.-s); setTaulfra.s(colu.ns·rows); setfr••1l1dth(wldth) ; seU ralleHel,ht (hel oht l; flfr• • IN,e Is pissed to parent class far dra"lng t"pIN,e - nelf BufferedIN,e(,,14th. height. Bufferedlaage. TTPE.JIlT..AR6Bl; tNpSurhce· teepINoe.crnte6r.phlcs(); super .utlaage(teIlpINge):
Intcurre ntF rillle() I return currfraltt : ) Claid setCurrentFra.( Int (ra.) ( currFralle· frallf';
p~bllc p~bll
public Int fra.1l14thO 1 return fril l 4th: I public lold setfra.llldth(int "Idth) r frllidth - "Idth: publiC Int frilleHelght() I return frHelght: I publlc lold seU. . .Height( tnt height) 1 frHelght -height: publtc Int totilFra.s() I return totf..lles; I public lold setTaulFr_s( Int tot.l) I totfra.s • toul; publiC Int inl..t1onOirectlon(} I return ,nllOlr; I public laid setAniutlonOlrect lon( Int dl r) I anllOl r· dlr; I public Int fra.-(ountO I return frCount: I public lal4 setF...-(o~nt(tnt COllntl t frtaunt· COllnt; I
Sprite Animation public Int fra~eDelay() I return frOehy; I public vOid setFra~eDe1aY(Int delay) {frOehy - delay; public 1nt columns() I return cols. I public void setColwllns(1nt IIU ~ ) {cols - nu... pub1Ic vol d updateAn lll~ t Ion(} I frCount++; I f (frameCountl) ) fr~IIleOel ~y()} setFrallleCounHO) ; Ilupdate the ~nl.~tfon fraille setCurren tF rame( currentF rame () + anlllM t Ion01 rect Ion ( ) ) • if (currentfr~IIleO ) toUlFramesO - 1) I setCurrentF rame (0) • I else if (currentFrameO (0) ( setCurrentFrame(to t~ IFraooes() - 1);
public void draw() I /lc~lcuhte the current fraDe'S X~nd Yposit10n 1nt fralleX • (currentFraeO S co IullllS () * fra_eWldth () ; lnt fralleY· (currentFraDe() I colu..,sO} * fraIleHelght(); /lcopy the frallle onto t ne tellp
i~age
O. O. fraIleWldth()-l. fr n eHelght( )'1. fralleX. fralleY. fUIleX+fraIleWldth(). fraIleY+fr neHel ght(). applet() 1:
te_pSurflce.drawlnge(an\.1~ege.
/lpass the temp I!lage on to the parent chs\ and draw It super. set Inge(te_pluge) : super. transforll(); super .draw();
Testing the AnimatedSprite Class I'm not going to list the complete source code for the AnimationCla;s exa mple program, because it is essentially the same as the AnimationTest program, except it uses the new AnlmatedSpr1te class. There is one difference, though. By
13S
136
ChapI~r
7 a
Spril~
Animation
_. -'.'.
figure 7.6 Testing lht AntalttdSprite daiS.
inheriling from Sprite, the Anl ..tedSprlte class allows yo u 10 rolatc Ihe animated sprileS ...itik Ihq arc drawing! This is duc to thc functionalily provided by l..geEnt 1t)', a core support d~ for sprite drawing. I will show you the key portion of lhe program that differs from the AnirrulllionTCSI program (covered cartier in the chapter). Figure 7.6 shows the output of the pr~m. which you can open up and run from the CD-ROM if you wish. Hcre is a list ofall the dasses used in the AnimationClass program. You can copy theSt: files from the previous chapter. The new projttt is called AnimationClass.
• Anl.. ttdSpri te.jeva •
Anl.. t ionClns.java
• Basee;..Entt t)'.jeva • '..geEnl II)' .Java •
PoinllO.Jau
•
Sprl Ie . java
What You Have LearnlJ'd Here is the source code for the fnlt() event method in the AnimationOass program. The TC$t of the program is similar to the AnimationTcst program, so I won't repeat the entin: code listing hen:. The important thing is that you undcrsland how to load an animatkm using the An1 .. tedSpr1te class. Go ahead and open the Animal>OnOass.java file: to sec the complete code listing. Illp rfte urhbles Anf ..ttdSprltt' tNll; publiC yo1d hftO I IIcrute the back buffer for s..oth grapll!cs tNckb\lffer - new Bufferedl..ge(SCRHIIVIDTH. SCRE[.I+EI&HT. Bufferedlaage. UPE....lNT_RGB); g2d - back buffer . ereateGraph! cs t ); If\Md toe background huge Too 1~ it tk - Too \kit . getDeflu I tTao 1kIt() ; b,,~ground - t~.getl ..ge(getURLt ·.oadgra!n.png·); IIload the ball an1..t10n strip ball. new Anl..tedSpritelthis. g2d); tN 11. lOld( ·xb.l l. OIIg". 8. 8. 64. 64); tNll.ntPoslt10l1(new Poht20(300.200); tNll.SltFr.lIeOch,(l); tNll.SltYelocit,("", Potnt20
What You Have learned This chapter tackled the difYkult subject of sprite animation. Adding support for animation is not an (';ISy undertaking, but this chapter provided you with the knowledge and a new class called Ant_.tedSprite that will make it possible for you to write your own games without reinven ti ng the wheel every time you need to load an image and draw it. Here are the key topics you learned; • How an animation is stored in a bitmap fi le • How to load and draw an animation strip from a single bitmap file • How to animate a sprite with timing • How to put il :all togdhcr into a reusable cWs
137
138
Chapter 7 • Sprite Animation
Review Questions The following questions will hdp you to detnmine how well you h
2. From which class docs Ihe new animation class inheri!?
3. How many frames of animalion were Ihere in Ihe animated ball sprile! 4. \\Ihm do you call an animation thaI is stored inside many files?
5. What do you call an animation thaI is all stored in a single fil~! 6. Whal type of parameter docs Ihe MI.. tedSprl U. utVelocHy method accept? 7. What arithmdic opcntion is used to calculale an animation fntJ1ll"S Y position? 8. Whal arithmetic opmtlion is used to calcuLale an animation position!
fram~'s X
9. What is a good class to use when you need 10 creale a bitmap in memory! 10. Which Anl.atedSprl te method dr.lws Ihe cu rrent frame of animation!
On Your Own l1lC: following exncises will hdp you 10 det.ennine how well you h
Exercise 1 The AnimalionTesl program is really LaJ1ll'. I ml'3n, whit.. balls paslw wilh a red X, being drawn ov..r a strange W
On Your Own
Exercise 2 Now that you Cln do fuU-biown animllkm. it's timt 10 rombint thai awtSOmt Clp,ibility wilh timt-provm rollisian dC1td.ian in ordtr 10 add SOmt aaual functionality to tIM: AnimationTm pmjtct_ Modify 11M: program and Clust tht animalro sprite 10 dt$troy each othtr whtn thq rollidt. ntW
139
CHAPTER
B
KEYBOARD AND MOUSE INPUT
1lJe ktyboard and mo~ are tM only rWistic devices for usn input in a wdr based game developed as a Java appkt. But even when oonsidcring a standard Windows-based game developed in DirKtX or another library, the keyboard and mouse are by fu r the most oommon forms of user interaction in a game. This chapter covers the important subject of handling user input. lll.'rc arc the key topics you will learn in this chapter: • listening for keyboard events • Testing keyboard input • Displaying ke'y presses • Reading mouse motion • IXtecting mo~ bUllons • Testing moux input
listening to the User Java provides an interesting way to intemct with useN through a series of lisreller methods. You tell Java that you would like to listen to keyboard input events, and then Java sends keyboard events to your own listener methods, at which point you can check tM key codes to figure out which keys have b«n pressal. or released. TI'C W1Iy lava tdls your prognm that a key has b«n pressed {or that the
'"
142
Chapter 8 • Keyboard and Mouse Inpu t mouse has moved) is through an interface that your program uses-or rather, implements. Your program musl use the l..plemen t s keyword to use an interf.1ce class. This is a type of class that just includes methods your program needs to usc (or implement); the class doesn't really have any funct ionality on its OWTl, This type of class is called an illlerfirce becausc it rqm'scllls a blueprint of Ihe methods your program must usc.
Keyboard Input Th,· KeyL1 stener intl.'rface Iis\('ns for l.'Vl.'llIS gl.'llcrated by the keyboard and sends those events to the callback methods implemented ill your progr;lI\l, Th~ methods are called keyPressed, keyRel eased, and keyTyped, and these thn"C ml.'thods all haw a singlc parametercall&l KeyE~ent. When wriling a program to uS!' the Keyll stener, you modify the class definition of your prognml Il.ing the l..plelllents keyword: public class KeyboardTest extends Applet 111l11e.ents KeyLlstener Tip The interesting thing about the Implements feature of lava dasses i,!hal you
(3/\ implMlenl multiple interlaces in yoor program by sepa
You may rC'C31l seeing thl.' l oplements kl.'yword used before wit h the Runnab1e il\lerface (which added threading support). When you need 10 add more than onl.' in\l'rfacl.' class, you can separate Ihem with commas.
listening for Keyboard Events Your program Ill't'dS to then all the addKeyL1stener mcthod to initiali].e the keyboard listen~'T SO that key evcnt5 will be M'nt to your program by lhe )av-J Runtillle Environment. 11,<: soil.' 1"1I1Ulletl.'r of this llle1hod is Ihe itlSWlCe of YOllr program's class. represented by the I«,..yword this. You use thl s as 3 ""y to identif)·thc current class in a block of code wilholll rderrinillo that class sp«ifially bynamc. II is lbUaUy best to call addKeyll stenerlthlsl in the Inl t me1hod within your program. (nC'C31J that lnlt is alltolllat'C"Jlly called when your app1ct-b.tsc
Keybwrd Input
Table 8.1 VIrtUal
krt Codes (Partiallistl
KIr)' Code ,~
(IT
'tLRIGII" p
' ....U
''-'"''
U..O••. ' ....9
IV... 'U Y(.fl •.. U..Fll ItL(P_l£FT I(.~P_RIGHT
v(.xp..up VUP_OOWN VtLnr£R ~(.8ACtLSPAC(
V(.TAB
.......----.--............... Description
_\:I!ypodlefl H.-.ic 'ooypocl riottl H......nc I:e,pad"" H......nc kfWild dowrl
...... . '" '" [nm key
Thert' art' two ways to drtenni~ thr kry that has brrn p~ or rdused using the KtyEnnt paramdrr. If you want 10 ck1:rrminr thr charact.... codrofa key, you can usr thr gtUtyChu mrthod. which mums a char. If you want 10 know whrthrr a key has brrn prrssrd t-rd on rnr key codr irutrad of thr charad..... you an usr thr gttKtyCodt mrthod irullrad. If your program is listrning to thl' krybo;trd and you press the A kry. thrn geUtyChlT will mum "a" (or "A" if you arr holding down Shift), while getKeyCode will return a virtual key code called VK.....A. AJI of the virtual key codes are wntained in a class called KeyEYent. Table 8.\ shows a partial list of virtual key cooes for the most commonly used keys for a game. Not. WIlen roo want 10 get the 1leys beill\l!ypo'd for "", ;n. chat mes~. lor insl
Testing Keyboard Input lLI's wrile a program to Itst krybo;trd input so you will have a compkteaample of how this works with Ja~ code. I have highlighted 1M important conde in bold. You can .see rnr output of Ihis program in Figurr 8.1.
143
144
Ch
-.
Koy.- 81
...
ll1port Jav, alll,'; illllOrt JUI Iwt.nent.*: l~ft jlYI Ipplet.·: p~ol
111
ltytKl,rdl
~t
utend, AW1et
I~l.ents
llQ'Llstetter I
nt ItyCOdt; char ktyChar; p~bl
IC YOld In1t!) 1 addleyL1ltener( this) ;
public Yoid p,lnH6r,ph;c 9 g.drlwStrlll91 "Prns I ker ... ". 20. 20); 1.c1nWStrt",("ker code; • + te)'Cocle. ZO o 50): 1.c1nWStrhl("ker char; " + te)'Char . ZO o 10):
public voId kerPrusMtlerEvent e) {
Mouse Input klJ'Cocle • e .,etKerCode() ; klJ'Chr •• r tp4lnt{);
IIklJ'llelnsed Is not lIeln, used pu;blll; wold k'rbhued(kerEwent e' { } pu;blie wold kt7T)'lItd( rerEwent el { kerCh,.. e.,cUe}'Ch.r( l; rep,lntO;
This is the bare-minimum corle you need to provide k~ybo;lrd support to yOllr Java programs. so you might want to jot down this page number for future reference (or save the code in a file that you can easily find).
Ti p A VIItUII Ry o:ode is • plttIoo:m-nMrai . . . b • Ry. Whfn you wnte
Tip The I nl t() IIItlh
Mouse Input Tapping into the mouse handler in lava is similar to the process or programming the keyboard. as you might have suspa;ted. Java handles mouse input using evenlS that arc generated by the Java Runtime Environment ORE) and passed to your program when you implement a mouse listener, Tip Tht ~ Runt-nr Uh.'..'...... or . . IS • Sllbsef 0/1Ile .... ~ l(jt (D::J 1het 1$ ~ to iImt you 10 IItw ~ to .. ~ wi 0/ dllIo.ses 1htl you (In l6l! to lUll ...... ~
80Ih 1ht . . tnd ft ME
Ire
inducled in ...... V. 6,
Jlr1l"'ided on 1ht ~
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146
Chapter 8 • Keyboard.nd Mouse Input first step you must taltt to incorporate moU5t t\'mt handling in your program is to call two functions that will tdl the IRE to begin se:nding your program mouse: events, Since we'll bt dealing with two interfaces for the mouse, you must initialize both mouse: handlers, Th is is similar to the function you learned abou t for initiafuing the ktyboard handler, You put thcK functions in the "ppltt's Illlt t\'tnt mtthod 50 Ihat thq- art sure to ~ called when tilt program starts up, You'll rte:al.I from the keyboard KCIion eariier in this chapter that the this keyword represents the current program: in mort t«hnicaltCTll'ls, this represenls the primary obj«1 thaI was created base:d on the _aln class definition in your program,
"fhc,
Tip No abjKt is nat I d8s; il: is tlw rtSWl 011 dIss. Thri 011 dMs IS I bloepllII: b' I procMt. ifd ., abjKt IS tlw product itself lhal !'IS bftn oonsIrIICIed.
publiC ~old In\tO 1 IddMouselhtfne r (thls) : Id dllouseHot tonll stener( thIs I:
Reading Mouse Motion Java provides an interface class for mouse motion and bullon press events that is similar 10 the keyboard interface, The Housell stener class is an IlbSlrlletciass that provides your program with an interface, or blueprint, with five methods that you must impkmmt in your program (rcgilrdless of whether you will U5t all of them): • public void ..usetllcted(llo"seE~enteJ • public void
-ouseEntered(HouseE ~ent
eJ
• publlc void ..useE~ited(lIou5eEventel • public void ..usePruse-d(llousehent eJ • public void -ouseRelused(llouseEvent eJ The HouseL Istener interface keeps tTack of the mouse: buttons, the mouse: position in the applet window, and the moU5t loc.ation when the mouse cursor mo,'cs i"to and 0111 o/the appltt window,
Mouse Input There is another, completely different interface class for mouse mo~'emem. You can read the mouse's position during a bullon or enter/leave event with a HouseListener, but re<:eiving events for actual mOllse morioll on the window requires another interface. To receive events for the mouse's movement across the applet window, you must use the HouseHotionL1stener interface. There are two events in this interface: • public void llO useOraqqed(HouseEvent e) • publie void
mo~seHoved(HouseEvent
e)
Detecting Mouse Buttons Some of these events report when a mouse bulton is clicked, pressed, or released. The only methods thm do not deal with the mouse buttons are lIIouseEntered, mouseExited, and mouseHoved, all of which deal with the mouse's position and motion, regardless of button status. The remaining events (. ouseCI icked, llousePressed, mouseRe1 eased, and mouseOraqged) all have to do with the buttons. As you might have noticed, all of these events have a single parameter called HouseEvent. This parameter is actually a class, and the IRE fills it with information for each mouse event. You can look inside this class to get the mouse's position and button values. For the mouse's X and Y position values, you can use HouseEvent.getX() and HouseEvent.getY(). The parameter is usually defined as (House[vent e), so in actual practice you would use e .getH) and e.get¥() to read the mouse's current position. Likewise, House[vent tells you which button was pressed. Inside HouseEvent is a method called getButton() that will equal one of the following values depending on which bullon is being pressed: • BUTTONl • BUTTON2 • BUTTON3
The getButton() method b lIS<:fUJ if you unly care about detecting a single bUllon press. If, for whatever reason, you need to know when two or three mouse buttons are being pressed at the same time, you can use a different method in the
147
148
Chapter 8 • Keyboard "nd MOU5e Input HounE.ent dus called geUlodltlers( 1. This (unction will repon multiple e\'mlS in th~ MouseE.ent dass, such;l$ tm, (ollo..ing; _
8UTTOMUUS~
•
6UTTON2_NAS~
• 8UTTON3.J\ASk
Thtrt art I1Uny mor~ 1ll
Testing Mouse Input I wouMlikt to show rou a program ulled MouseTest that demonstrates all o((~ mouse tvmlS that )'Ou Iu..t just lamed about. To build this program, ~'Ou should creatt a ntW "'eb applet proj«t ulkd MouseTest, :;md ther! remo"t all o( the automatically gencrated cod~ to })(' rq>l.1ced with tht (ollo..ing rod~ listing inst~ad. This program uses the Graphics dass' d'''wStrlng method alld a bunch of variables to dispkly the status of all the mouse ~"Ven(s individually. Figure 8.2 shows what the program output looks like. Note the important p.arts of the code listing in bold. Tht first part of tht program includes the applet's dass ddinition (with the needed int~rfaces (ollowing tm, 1..,Ie.ents keyword) and ... riabl~ dfdaratiol1$. -ousttest: IlIPOrt JUI.awt.": l.,mrt JUI.awt.event.", I_port Ja... applet.":
packl~
publiC cl iSS HouseTut utends Apple! IlIIll_nts MouseLhtlMr. MousiYlDtlonltstener I l6echre s.-e a:l~se e,ent v..hotes lnt el1cb'.. cllck:f: lnt presu. pren:!,: lnt relusu. releuey: Int enurx. entery:
Mouse Input
:::=";:~m _ _ II:lllO,301 _lftOOOd _ _ 1I11:'1.156 II: J ICI,.Z)l _ < t__
II:'I~
_ _ 4l161.Z!17
lftt ultJ'. exltJ';
tnt drlgJ'. drlQJ'; lnt ... vex. -ov.,; lnt llOustbutton;
The lnl t( 1 ('Vent method is the first method that gelS run in an applel. So .his is where)'Ou would initialize )'Our game objectsand variables, and this isalso where )'Ou add !he listeners lOr any input devicf$ 1M prog.ram ~ to ~. If your program f:¥er seems to be ignoring the ~rd or moUK, check 1nIt( 1 10 make sure you have added the appropriate listener. III.HIlllle the applet pUbl1c voId lnHO I
IddMoueLlstener(th1s) ; IcldJIoIIselkltl onL1stener ( UIs):
The pllntO
~t method is CotIled whrnevCT the appkt needs to refresh the window. Since pllnt() comes with a parametCT ( Grlphics gl, we can usc this
149
ISO
Chapter 8 •
Keyboard and Mouw Input
Objecl 10 draw onto the screen. 'Ibis program uses the Graphics dr!wStrlnli() melhod 10 display texl on lhe applet window. IIrednw t~e applet wlr>dow wotd Pllnt(GTlp~ics g) t 9.drnStrtn'l( "House clicked " • -ousebutton .. . at " • c)tckx. ". ·.clicky. 10. 10}; 9 d.. "Strtng("Ilo~se entered It ... enten. ".· .. enter)'. 10. 251; g.drlwStrtl\9( "House exited It " .. exlh .. "." . exit)', 10 . 401; g.drawStrtng(·IIO~le pressed". -ousebutton •• at •• pressx. ".•• press)'. 10. 551; g.drlwStrtng( "House relelSed " • -ousebutton" " at ... relelSu" ".... relelSe)', 10. 70); g.d.."Strtng("House dragged at ... d..gx . ". · .. drag)'. 10. 8S); g.dra"String( ·House -owed at . .. -owex .. . ... -owe)'. 10.1001;
p~b1ic
The next portion of code includes the checkButton() method, which I have wriuen 10 support lhe mouse event handler in lhe program. This c~eckButton() method chcclu lhe current button that is being pressed and KlS a variable (-o~sebutton) to a V;t.1ue representing the pressed button. IlcustOll .ethod called b)' -ouse ewents to report but ton status private wotd checkButton(MouseEvent e) ( lichee! the -ouse buttons swttch(e. get8uttOllO) { Clse HouseEwent.BUnOMI: -ousebutton -I; bruk; Clse lIouseEwent. BUTTON2: ..unbutton - 2: bruk; CI se lIouseEwent. BUTTON3: lIOusebutton - 3; brUk; default: ..llSebuttool - 0:
Moose Input The -ouseCl icked() event is part of the ~ouseLtstener interface. When you implement this inlerface, you must include all of the mouse events defined in the interface. or the compiler will generate some errors about the missing events. This evenl is called whelK'VeT you click the mouse bUllon on the applel window-in which case both a press and rdease ha.s OCCUfTed. This event is nol usually needed when you program -ousePreued() and -ouseRelused() yoursel f. publ ie yoid 8OusC'Cllcked(lIousehent el { IIsne the 80ua position y'luu el1eu. - e.getI() : el1ekJ- e .geU(): Ilget ,n updlte on buttons
e!IKkButtOll(e): IIrefrUh the
5cr~n
(call the paint eyent)
repli ntO: The ncxl two mous.e event methods, mIlseEnteredO and 8lluse£J.ltedO. an" called whenever the mouse (Ul'$Or f'rlteTS or leaves the apple! window. Th~ events arc nol often needed in a game. public votd
8Ou5eEntered(~euseEYent
e) (
- e.geUO: entery - e.getnl: relNl1ntO: enter~
I publ ic Yeld lIIOuseE~lted(~euseE.enl e) I ulh-e.gelX(l; ulty-e.9ttY(l; reINl1nt/): The lIOusePressed() and lIlQuseRelused(} evenl methods are called whenever you cl ick and release the mouse bulton, respectively. When these (vents occur. you can get the CUlTf'rlt position of tile mouse a.s well a.s the bullon being prascd or released. publ1c Yeid 8OusePrused(lIousehent el I pruu-e.geU(); pressy - e.getYO:
151
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Chapter 8 •
Keyboard and Mouse Input
ehtekButton(e): replht(}: I pybllt vOId llOuseRelused(llouseE.ent el I rellun - e.geU( I: relnuj' -1.geUO: clllckBulton(e) : rlpahtO:
1hcl'lousdiot lonllstener inlerf.1a defines the next lwocvcnes-useClugged() and lIOuseKoved( l. 'These ...·mtsan helpful when you just want to know when the mouse: is moving o"cr the apple! window (and when it is moving while the bUllon is being MId dmo.n). public void llOuuClriqqedlMotlseE.ent el I drag.- e.geU(}: dragy-e.getY(): repaht(}: I p~b 11 e vol d llOuseHored(ll(lu~eE.e"t e I I llO.u-e .geU(): IlOvey- • .geU(); repalntO:
What You Have learned This ehapterexplaincd how to lap inlO the keyboard and mouse listeners in order to add user input 10 )"Our Java programs. • You lC'arncd how 10 detect key prascs.
• You learned about kcy cod~ and character values. • You lC'arned how 10 mid the mouse's motion and buttons.
On Your Own
Review Questions The following questions will help you to doetermine how wt'll you have learnM the subje.;ts d iscussed in this chapter. The answers are provided in Appendix A, "Chapler Q uit Answers." I. What is the name of the method us.ed to enable keyboard events in your prognm~
2. What is the name of the keyboard event interbee? 3. What is the virtual key code for the Enter
key~
4. Wh ich keyboard event willldl yOIl Ihe code of a pressed
key~
5. Which ke}-board event wiD tdl you when a key has been
rdeased~
6. Which keyboard event will tell you the dW'2CtCl" of a p~ key? 7. Which XeyEyent method returns a key code value? 8. Whal is the name of the method used to enable mouse motion
events~
9. Whal is the name of the d;lS$ used as a parameter for all mousc event methods~
10. Which mouse event reporu the actual movement of the mouse?
On Your Own Use the following exercises to test your grasp of the material covered in this chapter. Arc you rearlylO put mouse and keyboard input to the test in a real game yd~ These exercises will dWlenge your understanding of this chapter.
Exercise 1 Modify the KeyboardTcst program so that pressing numeric keys I to 9 will change the font site used to display the key code and character values. To do this,
IS3
154
Ch3pter 8 •
Keybo3rd lind Mou~ Input
U5e the Gr.phlcs class in the plint event, which has a method called sttFont that you can impltmmt like thi$: g. $etFont( new Font( · Ar leI'. Font. NOJlllAl. iiI ue II , I will gi\'e you a hint: The ktyoode for I i$49, so you can subtrac! 40 from tht" k~ coot" to arrive at a good font site.
Exercise 2 Mooify tht" MOUKTest program so thaI a point is drawn whenever the user presK$ a lllOU5e button. You can U5e tht" Grlphics e!au's ftll Reet Jm1.hod and tht" lllOU5e position ",n..bles. (Just draw a r«tangle ..ith four oomtl'S that au one pixel aran.) If you au {ming confidml with your llC'W }a", programming skills. try using the setColor method to change the oolor of the points.
CHAPTER
9
SaUNa EFFECTS AND MUSIC
java has a rich sct of features for recording, mixing, and pbying sound sampk-s and MIDI sequences using a variety of classes that you will learn about in this chapter. You will learn about Java's rich set of sound support classes for loading and playing audio files in a variety of formats through Java's sound mixer. You will then learn about MIDI files and how to load and play them through Java's MIDI sequencer. Here is a rundown of the key topics in this chapter: • Loading and playing digital files • Loading and playing MIDI files • Writing some reusable audio classes
Playing Digital Sample Files Java's Sound API provides a package for working Wilh digital sample files, which has methods for loading a sample file (AIFF, AU, or WAY) and playing it through the sound mixer. The package is called javax.sound.sampled and includes numerous classes, most of which we will ignore. Some of these classes provide support for recording sound and manipulating samples, so you could write a complete sound editing program in Java that is similar to full-blown sound editing programs. One good ex-lmple is Audacity-a freeware, open-source
,ss
156
Chapter 9 • Sound EHe<:1S and Music
.. , ..._----_ •
,..,.-= .... .•-
. ..
'.".: - -, ' ~- - ~
.
,
I:
Figure 9.1 Audacity is ~n ex
sound editor that is available for download at http://audacity.sourceforge.net (see Figure 9.1). The Java Sound API supports the three main audio file formats used in web and desktop applications: • AIFF
• AU • WAY
The digital sample files can be 8-bit or 16-bit, with sample rates from 8 kH:t to 48 kHz (which is CD quality). Java's Sound API includes a software sound mixer that supports up to 64 channels for both sound effeds and background music for a Java applet. Tip for tile latest information about the Java SOOOO API, poinl\'O"r web br0WS8 10 java.sun.com!
produttsljava·medW"",OO.
Playing Oigital Sample Files
Getting Started with Java Sound The fim step to writing SOInt Java sound code is to include Ihe javu..sound. sampkd package:1I !he 101' of your progr:am: lllpOrt Jun. ~ound.$",pltd.·: If you are using JBuilder, you will see a pop-up Intnu to ~Ip you narrow down the claM names wilhin J' .n, which can be very eduCltional. You 'U see Wt when you type in lllpOrt jun.$ound .• JBuilder will show you the two c~ availabk in jun,sound., which are u.pled and .ld1. By adding ," to the end of the import statement, you are telling Ihe Java compiler to import every clas.s within javax.sound.sampled, of which there are many. In fact, when working with the sound system, you will need access 10 severol classes, so it is convenient (0 imporl the associated packages at the start of a progrorn so those classes are easier to use. For instance, without importing javax.sound.sampled. you would need 10 create a new sound sample variable using Ihe full class path, such as: JUU.SOtond. ullPltd .A.udlol~put5tru.slllllle· JUU. sound. slllp 1td .AlIClloSy5tM.')etA.ud 1ol~llUtStru.t ~ew Fi lel "_hoo.
II"·');
Could you imagine: what it would look like if you h
Filet ·_hoo.
1I. . " l} :
AudloSy5tM and Audlolnl)lltStre,. are classes within the javax.sound.sampled package and are used to load and playa sample in your Java applet. Later in this chapter, when I show you how to do background music, you'll gCl the hang of using some classes in a pack.1ge called javax.sound.midi. Cll u tlo n You may run into a problem w;1h Iht audio portion of your g.l
-
10 be well
If the program's flow runs through the UnsupporadAudloFll ~[xc~ptlo" block in your error handler. Ihen the audio file may be encoded ...ith an Ul1$upported
157
158
Chapter 9 • SOund Effects and Musk
r_._ _ ---... ,,--_._1._-
_~I_
"'-1-1- _1_1_1 3
f---r---' ~ .
Figure 9.2 ~
!he IligiqII
~
ionrIIt settwlgS WI Auo:Iicity.
file format. The other, more obvious, problt:m is truu the lile it~lf might ~ mis.sing. You em dlt<:kand oonvtrl audio fiks using the fn.tw;tre Audacity program that I mentioned earlier. Just load up an audio filt !lut you suspt<:t is mc:oded in a weird format, and then savr the lilt to a new format. Figure 9.2 shows the File Formats tab in the Audacity ~ diaJog box. Here you can dwJgt the dt6.u1t lilt fornut for aponing audio lilrs from the Filt: mtnu. If you choo5l:' the Other option from the drop-down list, you will ~ presc:nted with evell more audio formats, but most of them are obsolete. ( For instance, you can save to Creative l.abs' old VOC format, which was popular in MS· DOS games many years ago.) Some of the custom formats require an additional download of a plug-in for that panicu lar sound forma\. The key to sound prog~mming is a class called .I.udlolnputStrea.. This class is used to load a sound lile (which can be an AIFF, AU, or WAY lile) from either a local file on the current ~ ~n~, ....' htre the applC1 is located, or from a remote URi U1ywbere on the InttmC1. An input stl'Cillm is a source of data. You can cl'Cillte a new iruilanCt' of the cbss like so: .I.udlolnputStru. UlllP1t:
Playing Digital Sample Files This statement is usually spedfled as a global variable within the class, defined up at the top of the class before any methods. You can define this variable as private, public, or prote<:ted. (The default, if you do not specify it, is public.) In objectoriented terms, pllblic specifies that the variable is visible to other classes outside the current class, privtl/e means the variable is hidden to the outside world, and prO/ccred is similar to private, except that subclasses (through inheritance) have access to otherwise hidden variables define
1e - Audi oSn tell. getAud i 0I"putSt re~lI ( new Fil e( •numbug. wav" )) ;
Note that the return value of this method is an AudiolnputStrealll. Also, since getAudiolnputStrNfII does not offer an overloaded version that just accepts a String for a filename, you must pass a Fi 1e object to it instead. This is easy enough using a ne... File object, passing the filename to the File's constructor method. If you want to grab a file from a URi., your code might look something like this; URl url • new un ( "http; I /W>N. j ha rbour . comItes t. wa v' ) ; s~ ..pIe - Aud ioSys tem. getAudi 0 lnputStrealll( ur 1 ) ; Either way, you thell have access to a sound file that will be loaded when needed. However, you can't just use an AudiolnputStream to playa sound; as the class name implies, this is just a source ofsample data without the ability to play itself. To playa sample, you use another class called CI i P (ja~ax.sound. sampl cd .CI jp). This class is the return value of an AUdl oSystem method calk-d getCI ip: Cl i P cl i P - AudioSyste... getCl lp(); lOild ing Resources The code "",-"",nte will load a sound file correct!y when your Javil program is running either 00 ygJilms will afrl'adr be ready tOf
1S9
160
Chapter 9 • SOund Effects and Music th t s .getC Iusl J • getRnourcel J MIJ'IIlIlf .,.,., need 10 builcll UllL Kfle is I method ~ ~ goo!:
roe
...,.;., INI
prtnte URL getURLIString fllen •• ) t URLurl-ftull; try ( urI - tht s.getChss( l.getRuource( fl1 eftl.); I catch (E~ceptton e) l ) return urI;
1'Ilfn. ~ .,.,.,gellO ChIptfr 16, !tIl'flnllII'IIl'6.,.,.,'ft_will belNdr lao MIl ~ in I ~ avl ~ (JARJI ~ '1'N' eoq:blOCflS ol1he.lloa IinguIge 'MIIWlg g;wnes MIl 0Ih0r fI'I9M\l, .,.,., wi! ~ COIIII! ' " WIlh II'IIfly usri.J _ _ sum ;os getURL ( ). You l'IIIJ WIIl1 10 store tIwm in IIfIlSII* pICbge ol 'fOUl 0WIl clesignIlIon.. The rooI pICbge ~ be CIhd jharbour. IOd \hen I wooJd Idcl ~ 10 lI"Os, sum IS jhlrbour.graphtcs. Jharbour.utll. MIl SoD OIl Since getURLO is !til' ooIy custom retIlabIe method repeaIe(Iy used .. 11M! book. h is more COll\Itflienl 10 jllSl include h .. ~ das~
""*
Since we don't need. to pass a par:am\"ler to getCI t p, you might be wondering how this obj«t knows whal to play. Thne:'s aetuaUy one: mor\" step involvtd becaU5C al this point, aU you have: is a sound dip obj«t wilh the: cllJHIbility to Iood and play an audio file: or S1r1"am. This method actually rdurns a sound dip obj«t from the: default s~lc:'m milCT.
Loading
th~
Sound Clip
At this point, you have an AudtolnputStre•• and a Cll p, so you just need to open the audio file and play it. These steps;\rC bo th performed by Ihe CI 1p class. First, let's open the sound file; cllp.open( ullple);
Pfilying the SOund Oip Next, there arc: two "'Irs to playa dip, using the Clip class. You can usc: the start() method or th\" loopC) method to playa sample. The stirtC) method simply plays the sound dip. narrator .stnt<);
Playing Dig ital Sample
Fil~
On the other hand, the loop method provides an option that lets you spedfy how many times the dip will repeat, either with a specific number of repeats or continuously. Here is how you might playa dip Drre rime using the loop method; exploston. l oop
download ween with a progress bar when you use a of its medla files.
Ja~a
arm". (JAR) to store the apple! and all
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Chapter 9 • Sound Effects and Musk
Stopping the Sound Oip Most of the time you will simp ly forget about a sound clip after it has started playing. After all, how often do you nl'l'd to stop a sound dTl'Ct from playing when then:'s a sound mixer taking care of all the details for you? Seldom, if ever. HOwe\'er, if you do netd to stop a dip during pbyb;tck. you an use the stop( l method. I SU5pect: the only time you will need this method is whm you aR' looping a sample. kaboo•. stop(): Handling EfTOt'S
One interesting upect of the sound cb= is that they reqUiR that n-ror5 be a ught. The rompi ler will refu50e to build a program using some of the sound classes without appropriate try. catch error.handling blocks. Since this is a new concept, ['lJ quickly explain it. Java errors are handled with a sp«ial error-handling feature called a try..(;Itch block. This featun: w;I$ simply borro.... ed from the C++ bnguage. on which Java w;I$ based. Here is the basic syntax of a try..cnch block.: try ( I
lido sOll('thing bad catch (Except ton el C
I \¥hen you add error handling to )"Our program. you an: "wrapping" an error halldkr around your cod e by literall y wrapping a try. ,catch block around a section of code that you need to track for errors. The Java sound classes require try. ,cltch blocks with specific ~ of error checks. The generic [_cepllon class is us.ed to catch most errors that ace not aught by a more specific type: of error handler. You can ha''(' llIany catch blocks in you r n-ror handln-, from the more specific down to Ihe llIore generic in nature. Ti p In some casH, I try .catch _ hardtr i§ ~!II tade -:eptian _ INt a part;cuI¥ rrleIhod Ilwoows (on pwposeI. In d\ose C3I5oI!:I" yow PJ09'3IIl _ ~ !hi
lIJIllIlIIlfi* em.- hardtr (sudl;jl$ IOExcept ton). Another available version of th e error handler is called try ...catch ..final1y. This type of error-handling block allows you to put code inside Ihe finilly sect ion in o rdn- to perform any cleanup or dosing of files. The code in a IInllly block will
P1-ring Digital sample FilM
be run rtganflnsof wheth~r an CTTOr occurred. II gelS ex~uted if there "r(~rrors nnd if lh~re are
110
errors.
For instance, if you are load ing a file, you will firSl check for an IOElcept 1on bdou providing a gnxric Exceptton handlcl". The A~dioS,ste-, A~dtolnp~t Stru.. and Clip cbsses requiu the following CTTOr haodkn: •
IOE~ception
• Lt neUnava 11 ab 1eExcept ton
•
UnS~PJlOrtedA~dl
oft 1cExcept ton
Let me show you how to implement;In CTTOr handln for
w
audio code you're
about to write for lhe PLaySouod program. The following cooe is found in the Applet. tni t( I evenl: publ Ie ~old tnH() 1 tr, I Ifsource code lines cl ipped I CI tch (Ill I forwedURlExcept Ion ell I cltch (IOEaceptlon e) I I cltch (L jneUnO¥allibleE~ceptlonel I I ca tch (UnsupportedAud IoFl1 cExcept Ion c) I I 111 be the first p¢fSOll to admit that this is some ugly COOl.'. Error handling is notoriously ugly ~ust it adds all kinds of unplrasant-looking mal1;Ig~ment melhoosand f'Venls around your beautifullywriucn sou rce COOl.'. However, CTTOr handling is necessary and prevenlS your program from crashing and burning. I like to think of aIry ...cltch block as a rev limiter thaI prevents n cnr engine from blowing itsdf up when a foolish driver hilS lhe accel~rator too hard.
Wrapping Sound Clips Since error ha nd ling is a necessary evil, it supports the nrglllllent lhat you mny walll 10 pilI some oft-used code inlO reusable methods of your own. A couple of methods 10 load and playa sound ftle would be useful (and thaI ~rror-handl ing code could be bottled up out of sight). It would be logiaJ to Cf\<3j>5Ulue the AudlolnputStru. and Clip objccU inlo a new cbss of your own deign with your
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Chapter 9 •
~
Sound Effects and Music
• . - 1'1'..,-
__
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I !I-'" Ik _ _ _ I
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to lD«l ind
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own melh0d5 10 load and pL.\" .. sound file or URI..I...tcr in Ihis dupter)'OU '.,,11 find source code for a class nlln! SoIl~dCllp thu does just that.
Playing Sounds lbe Java sound classes are not quill.' a "turnkey" programming solution, because )'011 muSI perform several sleps to load and playa sou nd file. I think it wo uld be convenient to wrile a c1as~ lhat has a collection of sound clips you can load and pby at any lime from thaI single class. bUI I hesit ate to "wrap" any la\'" code inside another class when il is such a heavily ob;ect-oricnk'd language in the first place. let's just wrile an example program to Set' how to put all th is code to work. Tht resulting program, called 1>l.a)"Sound, is shown in Figure 9.3. The rt"IC"o·anl code 10 Ihis chapter is highlighled in bold IIIJI'O't java.awt. ·:
'.'t jJYa.applH. ·: .'tjua.lo. ·:
Playing Digital Sample Files
i mport j a v ~. net .'; I. port juu.sound.sa.pled. *; public c l ~ss PlaySound extends Apple t 1 St r l ng f 11ename - "gong .wav " ; Audlolnp~tStrell sllpl e; pr1vate UU ge tUR L(Strl ng fi1en~me) { URLur l -null : try I uri· this getC1ass(} getResource(f ll ename) : I c ~ teh (Exceptio n e) I I return uri :
I /finltlal1le th eapplet pub lic void in1t() 1 t ry I sa.p Ie _ Audi OSyst N .geUudl olnputSt ru.( getURL( fi 1enae) ) ; lIerute ~ sound buffer Cl1p el ip - AudioSyst N .getCI ip(); fl1o~d t he audio flle cl ip.open(ulIPle); flphy the sound clip clip.start(); I catc h (M~ I forRledURL£Xcept i on el I catc h (to£Xceptlo n e) 1 t catc h (l i neUnava il able£Xception e) I t ca tch lU nsupp or tedAudi of 11 eExcept I on e) t t catch (Exce ption e) ( t
lithe pa i nt event ha ndl es the screen re f resh pubUc void p ain t (Gr ~ phlcs g) { i nt y - 1; g .drlwString('Sampl e file; "+ f ilenalH! . 10. 1S' Y++); g. drawStri ng( • '+ S~lIp Ie. getF orm~t( ) . toS tr i ng ( ). 10 . 15' Y++}; g .drawStrlng( ' S~ lI pl in g rate ; • + (in t )s~", p\ e . getForm~t() .getS~ mpl eRate(). 10 . IS ' y++}; dr~wString{ ' S~lIple cha nnels , ' + sallpl e.getForllat().getChannels(). 10. lS ' y++) ; dr~ ..St rjng(' Encode d forllat, " + sam ple .getForllat ( 1.getEncodi ng( ) . toStr i ng( ) . 10 . 1S·y++ ) ;
16S
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Chapter 9 • Sound Effem and Musk 9.drawStrlll9( " Sallple slzt: " ~ slllple.9etForaat().getSalipleSlzelnBIU() + '·blt'. 10. 15')'++); 9.drawStrIll9(" Fra.. Silt: " + sallplt.guForaat().getfra..Slzell. 10. )5')'++);
Playing MIDI Sequence Files Although using MIDI is not as popular as il USl'd to IJ.c for background soundlracks in gamcs, you ha,·c an OppOTlunily 10 savc a 101 of b.andwidlh by using MIDI files for oockground music in a web-based gamc delivered as a Java applet. On the web. bandwidth is crudal, since a gamc Ihat lakes 10(l long 10 load may cause a potential playeT 10 abandon the game and go elsewhere. For this reason. I would liU to r«ommend the use or MIDI for in-game music when ddivering a game through the web. java supports Ihrl.'(' types of MIDI formats;
• MIDI Type I • MIDI Type 2 • Rich Music Formal (RMF)
loading a MIDI File Loading a MIDI file in Java is just slightly more involved t han loading a digital sample file because a MIDI file is played Ihrough a Kquencer rather than ~ing played directly by the audio mixer. The Sequence class is used 10 load a M IDI file: sequence S0fl9 - IIldISystl.'ll.gets.equencelnev FlIt! '.,slc .•ld ' l): A11hough this code doG pnparr a MIDI file to be played through the sequmeer, .....e haven'l ;\dually created an instance orlhe Kqumcer yet, so let's do thai now: sequeneer seq - 1I1dISystl'll.getSequencer! 1: NOll.' that the Sequencer class can ~ accessed through MldlSySleti dirrctly. but it requires less typing in of code to creale a local variable 10 handle the sclup oflhc MIDI se
Playing MIDI SequentnO: u·q.$UrtO;
At lhis poinl, 1M MIDI sequence.should Slart playing when the apple! 'Hindow
comes up.
Playing Music The following program listing demonstrales how to load and playa MIDI file in a Java apple! window. The PlayMusic prognlm is shown in Figure 9.4. As you can sec, there are some minor details about the MIDI file thaI are displayed in the applet window, which is basically just an easy way to determine that the MIDI file has bttn loaded correctly. The key portions of code are highlighled in bold.
__ __
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167
168
Chapter 9 • Sound Effects and iI'lIort l"POrt l.rt l.rt illPOrt
Mu~k
jl......t.·; jln. 'PIll et. • ; jln. Io.• ;
jl".net.·; jnu.sound •• ldi. *;
public class Playlluslc utends Applell 5tr1 ng ftl enUN! l tt Ie.us Ic .•1d" ; Sequence song; W
•
prhlle URl getUlL(Slrlng ftlenl.) I UIlL uri- null; try I urI - thls.getCllssl) .getResourcelf11eol.); )
cltch lhceptloo e) r I returo url;
{{loHI II he the Ipplet public wold lolt() l try I soog - MldiSyst••getSequeoce(getUIlL(11 Ifill.)); Seqllfllcer sequencer· Midi Systfll. getSeq\lf1lcer() ; sequencer. utSfquence(songl; sequencer. open( I; seqllencer. stl rt/ ) ; 1 Cltch (Inwal IdllldIO~t,E~ceptloo el I 1 eatch (1I1dtunlv~ilableE~ceptiooell I cUch (IOhceptlon el I I
{{repllnt tile IPplet .. Irtdov ""bile void palnt/Grlphics,) I lot ~-IO. y-I; if (soog !- oull) I q.dr'vStrln,( ·1I1dl File;'" fileo,•• 1. 15' y++l; g.dr,lfStrlog(·Ruolutloo;· .. song.gelRuolutlon(). 1. 15' y++l; g.dr, ..Strlng(·Tick length: • * song.getTteklength(). 1.15' y l: g.dr,wStrlng( · Tr,cls;· + soog.getTracks().leogth. 1. IS' y ); 9.drawStrlng( 'Patches; • +soog. getP,tchl 1St( l. length. 1. 15· y++l: )elsel
Reusable (laue
g.drnStrlll9( "!rror
lo.dj~g
stquetlCe file""
flle~••.
10. IS);
Reusable Classes Now that you understand how to lood and play sound clips and sequence files, leI'S pUl aU of this useful (but SC3tlered) code inlo two r~sable classes that can be easily dropped into a project and used. Insle;Jd of d~ing with all of Ihe Java sound c~ and packages, you will be able to simply create a new object from 11K- SO~ndCllp and Mtdtseq~e~ce classes, and thm load up and play ri~ a sample or sequence with a couple lines of code.
r should
disclaim the userulllC$S of the:\(' c!uses for you, so you will know ",hat to expect. Java's Sound API has a sound mixer lhal works very well, bUl we can't tal' il1to the mixer directly using the Cltp class that I've shown you in lhis chapler. The sound fi les thaI you load using lhe Clip class do support mixing, but a single clip will inlerrupt iudf if played repealedly. So, in the case of Galactic War. whm your ship fires a we;Jpon , the we;Jpon sound is restarted every time you play the sound. Howt'VCl". if you Iuve anolher dip for explosions (or any other sound), then it will be mixed with any other sound dips currently playing. In Olher words, a single (1 ip object cannot mu wi,II it~l[. only with otMr- $(lurid$. This process works quite well if you usc short sound effeds, but can sound odd if your sound clips are one second or more in lenglh. (They sound fine at up 10 about half a second, which is typical for arcade"g.lme sound effects.) If yOIl want to repeatedly mix a single clip, there are two significant options (and one other unlikely option): • Load the sound file into multiple (I tp objects (such as an array), and then play each one in order. Whml'Ver you need to play this specific sound, JUS( ilerale through the array and locate a clip that has finished playing. and then start playing it apin. • Load the sound fi le into a single (lIp obj«l, then copy lhe sample bytes inlo mulliple C1 t II objecls in an array, and lhen follow the general lechnique Mscribed in the first option for playb;lck. This saves l ime from loading the clip multiple times.
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110
Chapler 9 • Sound Effeas and Music • Wril.. a thmtd.-d $(lund pbyba<:k class lhat cmt.-s a lH'W thr.-ad for eo,'.-ry sound lhal is played. TIt.. thrad willlermilAt.. whm Ih.. sound has compkt.-d playing. This r.-quir.-s $(1m.- pr.-lIy complex cock, and thue is a 101 of ov..m.-ad involv.-d in cr.-aling ;lnd destroying a Ihr.-ad for .......ry singl.. sound Ih;lt is pl;l)'td. On........y 10 g..t around this ov..m..ad is to cr.-ale a ,lrr..lld pool at th.. start of the program and th ..n reuse Ihreads in Ihe pool. Again, Ihis is some "ery advanc~-d code, but it is how pro(C$,lional Java games handle sound playback. If you write a great Java game suitabl.. for publishing (such as Galactic War, which you will start in th... n...xt chapter and dev..lop throughout th.. book), [ would m:omm..nd on.. ofth.. first IWO options as good choices fOf a simple gam.-. You don't W3.nt to deal wilh the ovcrbcad (or weighty coding r.-quircmmlS) of a threaded solution, and an array of lh·.. or so dupliones of a sound clip can be played 10 good effect-with mixing.
The SoundClip Crass The SoundCIlp class em:apsulates the Aud1 oSystelll, Audlol nputStruIII, and CI ip classes, making il much easier to load and play an audio file in your appl els. On the CD-ROM there is a project called Soundd.ass that demonstrates this class. This class simply includes all of Ihe code _'v.. covered in th.- last f.-w pages, combined inloa singl......ntity. Nolelh... key portions of Codelhat I'vediso.tssro in this SCCIion, which are highlighled in bold. Tip A ~ projKt dflnoninmg this elMs Is wailable on the ([).R{)M in the Isol:ucesId\aplelO'Jl SourIdClMslokle<.
i.po r t javu .sound. u.pled. *: illportjan.lo.·: lllpOrt jan.net.·: publlc clan SoundCllp 't~e source for audio dna prlnte Aud10lnputStrea. supie; 1/ sound eli p properly 15 reid· only here
prl ute Cl 1p clip : public Clip getCltpO I return clip: I
Reusable ClaSSl!'l 1I100p1ng property for cont1nuou$pllyllict prhitt boolun 1000plng· hi se: public .old setlooplnglbooltlln _looplngl I looping - _Iooplng; public boOleu getlOOlllngCl I return looping: I IIrel"!ll1 prOl"!rt, U5e
prhllte String fllen•.,.- 00; pub11 c .01 d setF 11 en•.,.( Strl ng _fl1 enillt) I f 11 enllllt - _f I Ientllt; publlc String getfilenll.,.O I return filenllrae; I Ilproper t y to verlfYllhen Hlnple 15 rudy public boo) elln Islolded() ( return (boolunHUllple I-null):
Ilconstructor public SoundCllpO I try I IIcrult i 50und buffer cllp - 1.IlcI10S,ltell.getCl Ipl I. I c.tch lliMtJnn.II.lIle[ueptlon eJ I
IItMs onrlolde
II
Illlrllltter
prlute URL get UR L{Strlng filen!.) ( URL url- null: try I uri - thl s.getClus( l.geUuource( f l lenll.l: I citch (Exception ell rthrn uri;
171
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Chapter 9 • Sound EffeCtl and MUlk I/Ioad sound file pUbi ic boo1 un 10ad(String audiofi Ie) I try I Ilprepue the Input stre•• for an .lIdio file
utFllena.(alldlofil.) ; I/set the ...dlo strea. source u~le· 1.lId10Systl!ll.getAudloln""tStr.... (~tUIl{fllena.»; I/Ioad the aadl0 file cllp.opH(sallJl l el: return !rue;
I catch (IOExceptlCHI el I return false; I catch (UnsupporttdAudloFllebceptlon el I return false; I catch (LlneUnnallablehcept Ion el I return false;
publ1c ~old play() ( flex1t 1f the snple hasn't been loaded If (I hLoaded( II r eturn ; IIrelet the sound clip cl ip, setfrallePosl t ion(O); IIplay u.,le wah opt lonal looping If (looping)
cllp,Ioop(Cl1 p,LOOP_COITI MUOUSLYl: else
ell p, loop( repnt) ;
public wold stopO I cllp.stopO;
The MidiSequence Class l1lc "idl~uence cI.ass is another CUSlom cI.ass lhat Il'IIUs it nsier 10 work with tM Java sound code. This cI.ass malpsulates 1M IlldlSyste., Sequencer, and
Reusable Classes ~uenct
classes, making it much tuie:r to load and playa MIDI file withjusl lwo
IiI'lC$ or code inslead of many. Take nole of the: kc:y portions or code:. which ha~ bc:c:n highlightN in bold_
--
Tip
ACIIl'Ilpifte pnljKI ~ flsdlss is . . . . . OIllhe (I)-l()M illhe ~
IlIJIOrt JilYl. Ia. " ; IlIJIOrt jiIYl.net."; I~art JilYu.saund,.1dl,-; public class M1dlSequence I IIprlrury .I ~ I sequencer object pr1v.te Seq uencer sequencer; flprowl~e Sequence 15 • reld-anly property prlvatt Seiluence song; public SequenctgetSong() I return song;
IIfllen•• property h reld·anly prlute Strl", fllen ; publlc Strl", getFil O I rehrn fil ...... ; 1I100ping property for lOOpl1l9 contlnUl;l\lsly prhlte boolu" looping - fllse; public boolun getlaoplng() I rehrn looping; I public void setlooplnglboolun _looping) I looping
~
_100pln9;
IIrepe.t property for looping. fl~ed nu.ber of tl.s prlute Int repeat - 0; public void setReputl Int _repe.t} I repeat - _repeat; publIc 1nt getRepeat(ll return repeat; I IIreturns whether tne sequence h readjr for actIon public boole.n hLo.ded() I return lbooleanllsequencer ,I sOpen(»);
IIprl ..ry constructor publlcMldlSeqllencel)I try t IIfire up the SeillIef\cer
173
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Chapter 9 • Sound EHero and Ml>sic sequencer · MldlSystea.lIetSeql>enctr( I : I cltch (MldlUnnal1ablehceptlon el ( I
I ((over 1olded constructor accept s al dl fl1 enallf public MldISequence(Str1n'l aldl file) I thls(): f/cill debult constrlOctor first 10ld(aldlfl1e): f/load thealdl file
prlnte URllletURUStrlnll tll""a.) I URlurl-nul1: try I uri • thi s .IIHCI iSS( ) .lIeUesourcel fll ft'allf): I cltch ([ueption e) I return url:
f/l Old a aid 1 fl1 e 1nto
I seqllence public boolean 10adlStrlnll .ldlfl1e) 1 try ( Ilioad the.l dl file Into the seq~encer filenaltf· .idl file; sonll • IIi dl Systfll.lIttSequenct( lIetURl( fil enaltf I ) ; stq ~ encer . setSeq~enc e (song) ; seq~encer •open ( ) ; r etur n t rue ; I catch (lnvalldllidlDahhceptlon ell r eturn hhe: I catch (1I1diUn"ulhbleE:
f/play the aidl seq~ence public wold playO I If (!seq"!ncer . IsOpetll) I ~turn; If (Ioopi"lll I sequencer. setloopCou.t (Stqllfnctr LOOP_COITllOOIISLY) : sequencer.surt() : lehe(
Review Questions sequencer. utLoopCount( repnt) ; sequencer. start( ) ;
fl st op the 81dl sequefl(e pub li c wol d s tt:lp () I seqllf1neer .SUlp( ):
What You Have learned This chapter explained how 10 incorporate sound dips and MIDI sequences into your Java app lets. Game audio is a wry important subject because a game is just nu fun without sound. You learnw; • How to load and playa d igilal sound file • How to load and playa MIDI sequence file • How 10 encapsulate reusable code inside a class
Review Questions The following questions win help you to determine now wdI you have learned the subjects discussed in this chapter. The answ=; are providw in Appendu A, "Chapter Qui:t Answers. " I. What is the Il3me of Java's digital sound system dass~
2. What is the name of Java's MIDI music system dass? 3. Which Java dass handles the loading of a sample
file~
4. Which Java dass handles the loading of a MIDI file? 5. What type ofexception error will Java generate when it cannot load a sound
file'! 6. Which method of the MIDI system returns the sequencer object? 7. ''!hat is lhe main Jan class Menrchy for the audio system
class~
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176
Chapt~
9 •
SOund Effects
~nd
Music:
8. What is the main Java class hierarchy for the MIDI system class? 9. What three digital sound file formats docs JaV
On Your Own Use lhe following exercisc:s to Icst your g:rup of the mat~al oovcrC'd in this chapter. Are you ready to put sound and music to the test in a real game yea These exercises will challenge your ullde~tanding of th is chapter.
Exercise 1 Write your own sound-effects generating program to try out a large list of sound fi les. You can acquire sound files of various types by searching the web. Have the program playa specific sound file by pressing kC)'5 on the keyboard.
Exercise 2 Wrile a similar progrom for playing back muhiple MID I music sequence files by pressing various kC)'$ on the keyboard. For an even greater challenge. try combining this program with the one in Exercise I so that you can try out playing music and sound effects at the same time!
CHAPTER
10
TIMING AND THE GAME Loop
You havc learned how 10 uSC' thc Graph1cs2D class to program graphics using ve
m
178
Chapter 10 • Timing and t he Game Loop
The Potency of a Game loop The key to creating a game loop to facilitate the need$ of a high-speed game is la\"3's multithreading capability. Threads;IU sIKh an integra.! pan of Java thai il mUt$ a special thread available to your program jusl for this purpo$t. This speciallhread is called Ru"n,ble, an inlerface class. However, il'smlirdy possible 10 wrile a Java game "',thout th reads by just using a simple game loop. I'll show you how 10 do this first, and then we1l take a look at threads as an even bener form of game loop.
An inttrf«f am ~ "" <>b5tr"" dM5 wn!I propenies and meIhods lhM 3Il! definfd but I'lOl . . . m«JIfd. A P'O!1'" thM """ an inIfff~ dM5 ;.; ~ 10 aIflSOfIlf it. and must i~ lIlI of !he pobIic rnttf>o(t in !he inlerfKe. lypciI namples indu:le [fyL t s tener aod Runn,b 1e.
A Simple Loop ~
Runn.ble interlace gives your program its own awareness. I realize lhis concept sounds a lot like anifida.l inleUigmu, but the term
• f;9U~
10.1
The~propn.
The Potency of ao Gaome Loop caon~,
this program doesn', do aonylhing in ruJ time; it waits until you press a key or dick the IDOliSe' bero~ d"'wing a r«langk.
,
. ·······f
.............
~
lllpOrt JUt lllpOrt j lllpOrtj l.po r tj
aollt.·: aollt.nent.·: app lu .·: utl1 .·:
pu blI CChH SlaplHoop extends Applu lapleMents Key U stener, MouseU stener I R.ndo- rand
~
new RalldOll():
publiC YOld in!tO I .l1dh,ll stener/ thl s I : aoddllCl~sellst_rttlllsl
:
publie fold p.llnUGraophlcs gl I Gr.phlcs2D g2d· IGraphles20l g:
Ilcreate a randOIll reetangl@ lntll - rand.n extlnt( 100 ) : lnt h· rand.nutlnt(100): lnt x - rand.nutlnt(getSizeO lI idth . II ): inty·rand.nutlnt{getSlze().helght· h): Rectangle reet • new Reetangle(x,y,II,h): JIg_rate a randce color 1nt rN! • raolld. next [nt (2!16) : lnt green· rand.nutlntI2~l: lnt blue· ralld.nutlnt(2!>6): g2d . s@tColor(ne-ColorlrN,grnn,blue)l: Jldrallthe rectangle g2d.flll(reet):
Jlhandle keyboard nents public foid keyRelused(hyEfent kl I publle fold keyTyped(KeyEwent kl I I
179
180
Chapter 10 • Timing and the Game Loop public void keyPreneilCKeyEvent kl I rep.lntO;
IIhandle ..use uents public void ..useEnter!'dlllousehefll _, t I public void ..usehlteilUlouseEnnt _, I I public void -ouseRelus!'dlllousehefll _, ( } publl c void -ouse( 11 ck!'d{lIouseE,ent _, I I public 'old -ousePrnseil{lIouseEvent _} I rep.lnt();
Tip The Ra ndom dass ;\ loeatt
This program h.as no loop whalSOeVn", so it cannOI process anylhing in rtal tim~nol sp.au ships, asteroids, jumping Italian plumbers. yellow dot -tatCT$, or fe
Not . I've t-n thinUng about. w~ to use;ll 01 thew interiiKe OOses (such ill Runnable and l!le input listeners} by lUCking tIlrm MIl into a class ~ of tIlII' main~. This 5I4'POfI class -..:I pn:I'Iide ""f main progfanl wilh rY lMIIlS when IIWlgs ~ sudl as bJ fft15eS, fI'IOtM ll'ICIWlI'I!I'I II'Id CIlher _ ~ this is dle biIdl 01 an idN lIwl wiI beame some SO"! 01 game ensJilIel l.e'I's wait II'Id see wIIat Part .. "The Galactic war 1'nljKt,. has in S'n.
The Potency of a Game Loop
Overriding Some Default Applet Behaviors lbtre in $Crious problem with this program b«2use it was supposed to just adda new rectangle every time the user presses a key or 1llOU§C' bUIIOn, not rtdraw tM entire appld window-with a single r«Ungle left OVtt. lbtre is definitely some-thing odd going on b«2U§C' this program shoWJ J.D,,!, worUd as cxpro.cd. Well, it tul'JU out that Java has b«n ~ng with the screen without pennissionor ~thcr, by difaw( The Applet class, which is the basis for the SimpleLoop program (rec:aIl that it ati'7UU Applet), provides many default cvmt methods that do artain things for)'Ou. You don·t even nm:Ito implement pllnt{) if you don't wanl to, and theApplet baseclass will provide il for your program. Granted, nothing will be drJwn on the window as a rcsult, but the compiler won't give you an error. This differs from an interfuce class (such as Keyll stener) that IIUl1IdllleS that you must implement all of its abstruct methods. So it's prelly obvious by this difference in functionality Ihat Applet is not an interface class, but a fully functioning class. What happens. then, whrn you implement an Applet clasli method such as 1nlt(} or p.intl l? These methods aT(' essentially empty inside the Applet class.. ah, they exist and are not abstract, but they don't doanyrhing. The Applet claS$ defines Ihese md.hods in such a way thai you can O'Wf'T"i,kthl'lTl in your ..ppld.. For instance, in the SimpleLoop progr.un, SimpkLoop is aaually the RanK' of the class, and it inherits from Applet. 1lJnrl"0f"C', Simpldoop has the opportunity to override any ohhc methods in Applet that il wa.ni.S to. including hilt( I and pllnt( I. Howt'Ytt, tMre's anothtt method that we haven't wed)'l!'1 aUed upodate(). Aha! No. I wasn't holding out on you-you've aaually wed Ihis method before. in the game project back in Chapltt 3. 1bt updlte() method actually II«s do something as coded in the Applet cbJs-i t caIls replintO 10 refresh the appld. window. (Light-bulb momen!.) Since the default upd.teO method has been refreshing the sen"en for our programs, we have had ab$Qlutely no c01l1rol over this process. That explains why only one rectangle was being drawn at a time in the Simplel.oop program updlle(} was refreshing the sereen on its own. In a sense, your Java program is a slUl'e to the master Applet class until you override the functionality by rewriting its methods. It's time 10 break tht bonds of objoxl-Oritnled slavery. Let 's add the update() method to the program: puMlc void updlte(Grap~jcs 9) I pa 1nt(t);
18\
182
Chapter 10 • Tim ing and the Game Loop
Figure 10.2 The SimpleI.oop progrilm now dlaws rna." ~Ifs.
As you can 5C'C, the: upchte ( 1 mdhod is bearing a single: line: of cOOc:, a call to the:
pal nt ( 1 mc:thod. This giVt:$ you compk1e: control over the: scrttn rdroll bc:causc: the default updH ell would root just rqxtint the: scrttn, it woukl abo dmr 1M scr«n. Now you can run the: SimpleLoop program and Stt a bunch of rectangles as originally expected, as shown in Figure 10.2. I think this example makes it pretty ckar that any serious game ...~1l nte:'d to override the update() method as wdlas paint( 1. But that doesn't rally address the subject at hand- what about the loop? I've been calling this program SimpleLoop when no loop is even being used. Let's gettD that now.
Feeling loopy There are quite a few Applet methods available that we haven't implemented yet, in addi tion to the standard methods you've snon.so far. I'll go over the remaini ng kq Appl et methods at the end of this S«tion to make you aware of them, For now, I'd like to introduce you to the: next Appl e t mdhod: stutO , The sUrt( I mdhod is invoked in your Java appltt by the web browser right after calling
The Potency of a Game Loop
in1t( l. So, you can use in1t() to get the game ready to go, and then use Hart() to get thing!i moving. Now you finally haY< an opportunily to add a real loop to this progr.tm. BUI just for kicks, what do you think would happm if you added a III1i le() loop to the In1tD method? I tried it, so you should try it too. Doing this will lock up the applet, which will not evcn be disp layed. Why! Ik<:ausc inl t( l is ealled before the applet has evcn brought up thc web browser or applet viewer, so putting a loop he-re preve-nl$ the- apple! from drawing. Howeve-r, this is not the- case with the stutl) method, which is calkd afte-r the applet has hem initialiud and is ready to go. lbe engine has hem started and is just waiting for you to press theaccde-rator at this point. You can build on this game loop, too. The-caUto re-pa int the-window isonly the last in a gaml". Firs!:, you move your game objects around on 1M SOttIl, pttform collision testing. and so forth. You can ptrform all of these steps in the- start() event and then call re-paintl) at the very end. Here- is a suggestion. This is 1I0t actual code that you should add to the- Simpld.oop program-it's just an eltample. .st~
void stJrtO I lithe 91. loop vIIlh(trlle) I II.,;).., the 9111e objects upd~ teObJ ects( l ;
p~bl1c
llperfo", collision testl/l9 testeo!! hlons( l; !lredraw the window repa1"t();
Recovering long-lost Apptet Methods Learning about the start() and ~pdHe() events was intriguing. Let's take a look at some morc helpfulrntthods in the- Applet class lhat will Ix useful. The- ShowStltllS( 1 method is used to print some te-xt in the bonom status har of the- bro~r window or apple! viewer program: showStaluslString 1S9l
183
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Chapter 10 • Timing and the Game loop
The IsActi Yet 1 method delermines whether the applet is a'tive, which is marked just before the stut() event method is ailed: boolun isAtthel) Tbe st.rt() method is called after InttO arK! il; often usN to resume the apple! after the usn Iw; b ~ away from the applet page and then returned. YOld sUrtO Tbe stopl I method is called by the web brows.er when the web signifying that the applet is about to be destroy«!.
pa~
changes,
Yold stop() The destroy( 1 method is <:ailed by the browser when the applet is about to be destroyed (removed from memory). void destroy()
Stepping Up to Threads We use the Runn.ble interface class to add threading support to a game. This inttrface has a single tvent method called rill'll) lhat represents the lhread's functionality. We can cmllle this rune 1 method in a game, and thaI will act like the game loop. Tbe thread just calls rill'll) once, $0 you must add a willie loop to this method. Tbe"hlle loop will be running inside a thread t.ha.l il; 5CpaTllle from the main program. By implemenling Runn.ble, a game bKomes multithreaded. In that sense, it will su pport multiple processors or processor,ores! For instance, if you have an Intel Core2 Duo or another multi-core processor, you should be able to $Ct' the applet running in a thread thai is 5CpaTllte from theweb browser or appltt viewer program.
Starting and Stopping the Thread To gel a thread running in an applet, you have to create an insta nce oflhe Thread class, and then stan it run ning using the applet's st.rt{) event. First, let's crcale the thread object: Thre.d thrud: Next, create the thread in lhe surt{) event method: PIlbllc Yold sUrtO t
Stepping Up to Threllds thrUd ThrudCtll1s); thrud.SllrtC); &
_
Then you an write the "ode for the thread's loop in the run() n't'nt method (pan ofRunn~bh).We'll take a look at what goes inside runC) in a moment. First, let's take a look at the stop() event. This method is provided by the Applet dass and can be overridden. It has no functionality bydcfaull. This is a convenient place to killthc thread, so let's do that: public woid stop() ( thrud-n~ll:
The ThreadedLoop Program Let's take a look at thCl'ntireThre:adedLoop project, and Ihm I'll nplain the loop for the thread inside the runC) method. The key ponions of code have been highlighted in bold.
I·········
• ThrudedLoop progr••
....
.
,
l-eMlrt j.n.'wt.·: lllpOrt j.n.I.,..,. · ; l-eMlrt j.YI"wltt.·: IlI(IOrt j.n.utl1.·;
pUblic class ThrudedLoop ntends Applet 1111l1rllrnh Run".bl, I I/r."da. n~llber gener.tor Randolll ra"d new Rand01llC ): &
Ilthe ..i n thread Thrud thrud; IIcount tllr n.-ber of rectangles dra.... longcount-O; flapplet Init ennt public wold Inlte) 1 Ifnot needed this ti-e
18S
186
ChapiN 10 • Timing and the Game Loop !llpplet surt tvfllt pub11, void suno ( thread" new Thrna{th1s); thread .stut{) ;
Ilthrnd run eyent publl' void run{) I 1000g stut ~ Systeoo"urrentTI ...II1!s(), lIa,qulre the ,urren! thrnd Thrnd 'urrent '" Thrnd."'rrentThrnd( I; {Ihe r e's the new gaM loop wtl1le ('urrent-- thrndl { try ( Thrnd ,sl eep(O); }
utcll1lnhrruptedExuptlon d ( e.prlntStadTra,,() ;
IIdrlw s_th1ng repl1ntO; Ilflgure aut hOll fnt 1t's rUll/l1ng 1f (start + 1000
Jllpplet stop event publ" Yold stopO I thrnd .. null;
JlapplUIlpc!lte eyent publl, void upc!lte(GraphlCI gl I pllnt/g);
Stepping Up to Threads II'W1et p.lnt elent pI.Ibllc lold p.lnt(Gr.p~IU g) I Gr.p~IU20 g2d· (Gr.phtu2DI g: IIcreHe' r.ndOil rectangle 1M II • qnd .nextlntOODI : lnt h· r.nd.nutlnt{lODI: tnt ~ • r.nd.nutlnt{gHSlu() .lIldth .• ,: tnt J . f'nd.nntlnUgHStu( l.~etght . h): Rectangle rea· new Rectangle( •. J .1I.h): IIgeMute I r.nda. color tnt red· rlnd.nutlnt(256): tnt IIreen· r.nd. nutlnt(2561: int blue· rand . nutlnt(256): g2d. setCo l or( nell Cclcr(red.green .bl ue)): IIdr.1I the rectangle 92d. ftlll rect): lI.tid .noUer to count... :
t~e
counter
Now let's eX3mine this ru MI event that is called by the Run nab l e interface. There's a lot going on in this method. First, a variable calle
lbe core of the threld loop includes a call to Tllrud.sIHp(OJ, whkh is a place-holder for slowing the game down 10 a consistent frame n le. Righi now it's running as fasl as pos.sibk because the sleep( ) method is bting passed a O. This single method call requires an ClTor handler because: it throws an [nterruptedE.cepticn if the
187
188
Chllpler 10 • Timing and the Game Loop
fi9ure 10.3
The 1'hrNd..t.oop pnIpll
tr, 1 TMud.sleepIOl; I
cltcM Interrupted(Kcept I(ln el 1 e.pr\ntSuckTr~ce(
l:
After this call 10 sleep (which will slow 1M g.t1Tle 10 a consistenl frame rate), Ihm we can call game-rebttd methods to updatt ob;tcts on the Kr«n, perform collision taling, perform g.tme logic 10 interact wilh enemies, and $0 on. In the block of code thai follows, you can ~ $Ome liming code inside an If stalemenl. This code prints OUI the number of rectangles thai have been drawn by the pll nt() event during the pasl 1,000 milliseconds (which equals 1 second). IIdrill
s_thtng
rep~tnt(l:
What You I/fl9~r~ o~t
_
I t (su rt .. 1000
Ha~
Learned
tnt It·s runnl"9
I sUrt e S,5ttll. current TlIlelli111 S( ) : sh""Status( ·R~ctan91 u per second: . .. count): counteO:
The single call to repaint() aClually makes this program do soml'/hilrg; all of the rest of th~ code helJl5 this ml'1hod all to do its job cfl"a:til·ely. Here inside the run() event, whkh houses the: new thrnded game !oop.l've used one of the: new .&.pplet ITIl'1hods. 1lIe shC¥Status() ITIl'1hod printsoul a string 10 tbe status har at the: bottom of the Web broW$l"T or appld viewer.
Examining Multithreading Aside from the sample g;une in Chapter J, this program might h~ve been your first exposure to multithreaded programming. Java makes the process very easy wmp;lred to other languag('S. I've used a Ihread library cilled pthread to add thread support in my C++ programs in unux and Windows. and it's not very taS)' to USoC at aU wmp;lral to Java's built-in support for threads.. We will wntinue to USoC Ihreads in every subsequent cbapter, 50 you will bave had a lot of exposure to this subj«t by Ihe lime you complde Ihe book. Nole ~ Third Edirion (Thomson (oorse PHI. 2006l 00YefS the pthread and rnatl'f other ouss1Ntform game ~ \Opics. and is bawd .-.::I the AIltgro IiiInry and the ( ...... ~
Game ProgtMllflling All 1/1
~brary
What You Have l eam ed This was a heavyweight chapteT wt wvnal some very difficult subjl'cts. But the idea is to get up the most difficult part of a hill so you can reach the peak, and then headon down theotheTsidc. That iswhat thischapterreprcsems- thc last few steps up to the peak. You have now learned the most difficult and challenging aspects of writinga Java game at this point, and you are ready 10 start headingdown lhe hill at a more leisurely pal? in the upcoming chapletS.. This chapter aplained: • How 10 create a Ihreaded game loop • How to override default appld mdhods • How to manipulate a bitmap with transformations
189
190
Cnapter 10 • Timing ,nd the Game Loop
Review Questions The foUowing qUe$lions will help you to determine how wdJ. you have learned the subj«t.s discussed in this chapter. 1be answers are providM in Appendix A, "Chapter Quiz Answers.." I. What is the name of lhe inlerface c1as5 lhat provides thread support! 2. What is the name of the thread execution method thai you can code inside the separate thread~ 3. Whal is the name of the class that handles vec10r·ba5ed
U$e
to run
graphics~
4. What Thread mdho
U$e
to store a bitmap ima~
9. Which 6Ullhlcs2D method is used 10 draw a bitmap? 10. Which c1ass helps to improve gameplay by pr
On Your Own The following exercises will test you r comprehension of the topics covered in this chapter by making some important ch.anges to the projects.
Exercise 1 The l breadedLoop program runs at br....akneck sp·eed with no dday. Modify the th read delay value to see whether you OIn slow down lhe numbl.'"r of rectangles being drawn to just 1,000 rectangles per second.
Exercise 2 The ThreadedLoop program jusl draws V«!or graphics. Modify the program so that it draws animated sprites instead.
PART III
THE GALACTIC WAR PROJECT
This final part of t~ book is devoted 10 th~ dtvelop~nt of a compll'1~ gam~ called Galactic War, built entirely in Java as a web appld. By the lime you have finished reading the book, you will have lC'3rned how to create this game from scratch and deploy it to your website. Here are the chapters in Part Ill: • Chapler II: Galactic War: From Vectors to Bitmaps • Chapler 12: G~laclic War: Sprites and Collision Boxes • Chapter 13: Galactic War: Squashed by Spacc Rocks • Chapter 14: Galact ic War: Entity Management • Chapter 15: Galactic War: Finish ing the Game • Chapter 16: Galactic War: Web iA-ploymmt
CHAPTER
11
GALACTIC WAR: FROM VECTORS TO B,TMAPS
The G~I~ctic War proiect will demonstrJte just one type of game that can be created in Java. This game is compln, but that complexity is hidden inside a game engine that, once written, does not n~'\'d to be opened again. You will write an al'pkt that will inherit from the game engine, and then the vast majority of the core code for the game will be handled behind the scenes. We'll build the game step by step, beginning with the simplistic Asteroids-style game from Chapter 3, gradually improving the game until it is finished and ready to be put up on your website. The first step to building Galactic War is to begin converting the original project from an entirely vector-based game into a bitmap-based game. We'll start with a partial conversion in this chapter, retaining some of the vector shapes but replacing the player's ship with a bitmap. Here are the key topics: • Improving the game • Generalizing the vector classes
Improving the Game Chapter 3 gave you an example of a semi-complete A>leroids-style game to show you what would be covered in the upcoming chapters. You have now learned enough about game programming in Java to greatly enhance the game. That original game featured a class called BaseVectorShape, which contained
'"
194
',,",pter 11 •
GiI~k
W"r: From 'leeton to Bitmaps
all of the properties needed to manipulate game obje'C1s on the scm:n (the asteroids, bullets, and ship). In this chapter, we'll make a few changes to add sprite support, and in the next chapter we'll move the game entirely over to bitmaps. By upgrading t~ spaceship to an illl
• Asteroid.jav.ll •
Bullet.jav.ll
• Ship.jaV1l • SoundClip.java •
MidiScquence.jaV1l
Note that I did not include the main source code file, Asteroids.java. There an: a few changes needed to add image support to the game, so [ will just give you the complete sou rce code listing for the main code file, which is IlOW called GalacticWar.java.
Generalizing the Vector Classes In the Asteroids project in Chapter 3, there wen:S("Vera[ dassoes to handle the ship, asteroids, and bullets in the game. Now we're going to gencrolize these thr~ classes and make them mon: general purpose, since a lot of code is shared among these classes. The Ship class will be replaced entirely with an l..gcEntlty (covered back in Otapter 6). Let me show you what wt"n: going to do with the .\steroid and Bullet c~
Improving the GlIme Cre~te a n~ soun:eeooe file(3l1«1 VectorEmity.java. 'l1lis class is verysimpll", ~s the following rode suggests. Note that this class inherits from hse~.Entl t)'!
Holt
.
/
• ¥ector clHS for hindllng gi. ent I ttes
.......................................................... l"IlOrt
/
JIY~.i.. t.·;
public clin YectorEnt I t)' utends BlseGi.Entlty I lIurhbles prhlte Shipe shipe; Illccusor llethods public Shipe getShipe() I return shipe; I lI..tator .thads public void setShipe{5hipe shipe) I t/l1s.shipe· Shipe; I Ildefault constructor ¥ectorEntHyO I set~pe(null ):
The New Asteroid Class
The Asteroid class will be modili«l now to use YectorEntity as a base class. This fred up a lot of code that was previously dupliGitoo in Asteroid and the olher classes. The Aneroid class inherits from YettorEntlty, which in turn inherits from BaseGallleEntlt)'. You eun open up the Asteroid.java file that you copied over from th{'" projfft in Chapter 3, or you can just add this as a HeW dass to the Galactic War project.
I···············..····································.... • Asteroid chss derlYes trOll hseYectorShipe
......................................................····1
publiC ehss Asteroid utftM!s hctorEiltlty (
195
196
Chapter II • Ga lactic War: from
V«t~
to Bitmaps
JI
prlute lnt[] ut,,-1·20.-I3. 0.lO.22. 2(1. 12. 2. -I(I.-2Z.-161: private lnt{] asty· ( 20. 23.17 .20.16. -2(1. -2Z. -Ia. -11. -2(1. -51: II rotation spee~ protected double rotYel; public double 9!tRotatlonYeloclty() 1 return roUel: I public wold utRotatlonhloc1trlcloubh, yll rotVel - y: I llbounding rectangle public Rectangle getBouoos{} 1 Recungl e r : r -newRectingle({lnt)geU{) - 20 . (IntlgetY() - 20 . aO. aO): return r;
lldefault COflHructor AHeroldO I setShapelnew PolnonlulJ:.. aHy. un_length»): setA11we{ true) : set Rotat1 cnVe l ocl trIO . 0):
T"h. New Bullet Oass Much of the code in the previous Bullet daSii has now been moved to VectorEnt 1tr as well , so we can JUSl rewrite th i5class and give ilthe specific information relevant to a bullet object (most notably, that the getBounds() method returns a rectangle thaI is one pixel wide and one pixel high)_
.
/
• bllet class derhes
B.aseYeetorShape
.......................................................... f~
/
lJlllOrl jan .awt. · : publiC class Bullet utends YectcrEntl tr I llboundlng rectangle publlc ~ctangle get60uMs l I 1 Rectangh r; r - new Rectang' el lint loeUO. Ii ntl geIY (). 1. I): return r:
Improying the Game
BulletOI IIcrute the bullet
l~.Pt
letStl~PtlfN!'ll~cu",le(O.0.1.1));
letAlhelhhel:
The Main Source Code File: GalacticWar.;ava The actual gameplay hasn't changed much in this new revision. Figure Il.l shows the game with a new bitmap image being used for the player's spaceship. However, we have upgraded the core classes sign ificantly in this updme. which will be very useful in the nex t chapter, where ImageEntity will sec a lot mOTe usc. 1.,gtEnt tty, which you learned about in Chapler 6. provides a getBounds() mnhod to perform collision lesting. You can stilltogg.le the bounding rectangles
figu.. 11. 1 n.. plIyfr's sp«I'Ship ii ..- I bitmap II'N9l' ..n.. Ih.1n
~
palypL
197
198
Chapter 11
•
Galactic War: From Vectors to Bitmaps
Figure 11.2
The bo
on and off by pressing the B key. Figure 11.2 shows the r«tangle around the player's ship. The collision code is a little too strict for a truly enjoyable game be<:ause the bounding rectangles are slightly too big. We'll corr«t th is by finetuning the collision code in the next two chapters. The majority of the code remains ullchang~-d from the Asteroids.java file b.lck in Chapter 3, so you may just open that file and modify it as indicated. But I'm going to list the emire program again because it's been a long time since we went over that code. I have highlighted in bold att of the lines of code that have changed. If the source code for a particular method has nol changed at all, I simply commented out Ihe code and inserted Ihe statement linD changes needed, so keep an eye out for this comment and then reuse th:l! code from the Chapter 3 proj«l. II is a beallliful testament 10 object-oriented programming that so few changes arc needed to this source code file! /
. .....................................................
• GAlACTIC WAR.
Ch~pter
II
/
I.por t java . appl H.':
Improving the Game
IlIIlCrt I.rt IlIPCrt llIIPOrt llIIPOrt /
jUI.IlIt. ·; jUI.IlIt.Uent. ·; jUI.IlIt.g_. ·; jUI.IIILluge. jUl. ut 11 . ' ;
. ..................................................... , • Prlurr ellss for tl\e gl•
~ull\lc
elln Gll,etWln utend~ """p1H 1l1pl_nu IhInnlble. leylhtener lithe uln thrud Ilec.-e~ tl\e gl.loop Threld gl.loop; lIu$! thh 1$ I double buffer Bufferedluge blCkbuffer; Ift~ uln dnlllM object for t~ blCk buffer GrlpMC$lO g211: IItoggle for drilling bounding bou~ boolun ~hOllBound~· rll~e: /feru t e the u t erold Irrar In t ASTEROIDS - 20: A~ terol d[] IS t - nell As terol d[ASTERO IDS] ; Ilere~U tne bul let array In t 6UllETS -10: 6ullet[) bullet - neIl6ullet[6U llETS) : Int eurrentBullet - 0:
lithe p1iJ'lr' s sMp 'lOIIge[nt1ty ship· new ' Nge[ntltr(tMs); Ifcrute Ue Identl tr trlnsfoMl AffineTrlnsfol'll identity· new Afflnelnn~foMl( I; /fcrute I rlndoe nlllltH!r gellerltor bncloe rind· _ Rlndoe( J; /flold 50un
I··································, . ..................................................... , • Ipplet \nit eyent
199
200
Chapt er 11
•
Galactic War: from Vectors to Bitmaps
pub l lcvo1dlnit()I /I c reate the back buffer for smoo th graphi cs backbuffer • new Bufferedllllage( 640. 480, Buffered Image. TYPE..I NT.JlGB) : g2d - ba ckbuff er . c rea teGNpht cs () : ({set up t he shl p sh1 p. setX( 320) ; sh1 p. setH 240) : sh1 p. 1oad( "spacesh1 pi •png " ) ; sh1 p. setGraph1 cs (g2d) ; {Iset up the bul lets for (lnt n· 0; n
flset up the !steroids for (Int n · 0: n
(l1o!d sound files shoot - new SoundCI1 p( ·shoot ,lIav·); explode - nell SoundC l Ip( •explode lIav·): Iistart the user Input l istener add Key Lis tener( thi s ) ;
I .. ••• • .. •• •• ••••••••••• •• •• ••••••••• ..•• ..•••• .. • • .. •
• app1et updlte event to redraw the screen
........ .................. ............ . ..... ... .... u l pub l iC vo1d updatelGraphlcs g) { liND CHAN GES HERE
Improvin g t he Game
,
.
..................................................... • drawShip called by applet update e_ent
/
public _oid drawShip() 1 fftrUsfor. and draw the sh1p sh1p. t r ans for.( ) : sh1 p.dra w() : //draw bounding rectangle around ship if (showBoundsll g2d. setT rans forll( i dent j ty) ; g2d. setCo1or( Color. BLUEl : g2d. draw( shi p. getBounds ( l ) ;
There are no changes beyond (his point. Please double-check the source code listing in yOuT new Galactic War project to ensure that all of the methods following this point are included (from the project in Chapter 3). If you prefer, you may open the completed project on the CD-ROM in the folder \sources\ chapterll\GalacticWar. /
. ..................................................... • drawBull ets ca 11 ed by
~pp 1et
update event
/
publlc void drawBullets(} I ,/NO CHANGES HERE /
. ..................................................... • drawAs tero i ds ca 11 ed by aPO) et update event
/
publ ie _oid drawAsteroids{) //NO CHANGES HERE /
.. ....................................................., • applet window repaint e_ent· 'draw the
pub 1ie void palnt(Graphics gl I //NO CHANGES HERE
bac~
buffer
201
202
o..pttr 11
/
• GaloKti( War: From Vectors to Bitmap"
. ..................................................... • thrud sttrt
tf~nt
. $tart tht fa. loop running
/
public woid start( I I liMO CHAMGES HERE /
.
• thrud run ewent (ga. 1009)
••••• .. •• .. •••••• ..•• •••••••••• •• ••••• •••• ••..•••..··f
public wold r~"() ( liMO CHANGES HERE
.
/
• thrud $t0)9
tf~nt
.....................................................
/
public w01d slopO I / fNO CH~NGES HERE /
. ..................................................... • ..we al'd ani ute the ObJKts In the ga•
/
prl.Ht wold gUltUpdHt() 1 //NO CHAHGES HERE
.
/
..................................................... • UpdHe the $hlp posit Ion bHK on .eloclty
/
public wold updateShip() 1 //NO CH.IJIGES HERE
..
/
..................................................... • Update tilt bullets based on welocltr
pubHc wOld updUtB~11tU() ( // NO CHANGES HERE
/
Improving the Game /
. ..................................................... , • UlXIUe the asteroids bastel on velocity
public void upd,teAsterolds() I llltO CIIAllGES HER!
I·····················································
.....................................................
• Test asteroids for collisions with ship or bullets
/
pubHc lold chec:kColllsfonsO I IlItO tlLUGlS HERE
I· .. ••••••••••• .. •• ..•• ..••••••••••••••••••• ••••••••••
....................................................., • hyllstener elt1lU
public void keyRelusedlKeyElent k) I public void te)'T)'pedIKeyElent t} 1 I pUblic voId keyPrtssed(KeyElent k) I CHANGES HERE
I NO
I····················································· • cilculate X-o.elltnt "lue based on d1rectlon Int1e
············..·······································1
pub 11 c d(l~b 1e cll cAntl eHo.eX I d(l~b Ie Intl e) IINO CHANGES HER!
I·······················..···························· ..................................................... • Cllcullte y ..,uent IIlue bned on dIrection Intle
public double c,lcA",,,ltllOleHdouble In,le) 1 IINO CIWI6ES HERE
/
203
204
Chapter
11
•
Galactic War: From Vectors to Bitmaps
What You Have learned This was a heavyweight chapler thaI covered some very difficult subjects. Bill the idea is to get up the most difficuh part of a hill so you can reach the peak, and then head on down the other side. That is what this chapter represents-the last few steps up to the peak. You have now learned the most difficult and challenging aspeds of writing a Java game at this point, and you arc ready to start hcading down the hill at a more leisurely pace in the upcoming chapters. This chapler explained • How to add bitmaps to Galactic War • How to support multiple key presses
Review Questions The following quest ions will help you to determine how welJ you have learned the subjects discussed in this chapter. The answers arc provided in Appendix A, "Chapter Quiz Answers." 1. What is the name of the class that handles bitmaps? 2. Which class in Galactic War detects when bullets hit the asteroids? 3. What is the maximum number ofsprites that can be supPQrted by the game? 4. Which method in the Graphics2D class aClua lly draws the image of a sprite? 5. What is the name of the Appl et method that redraws the window? 6. How llJany key presses can the game detect at a single time? 7. Wha t method do you use to track the mouse's movement? 8. Whattypc of graphics entity docs the game IISC for the astero ids? 9. Regarding ship rotation, by how many angles can the ship be rotated? 10. What method prov ides the game with support for collision detection?
On Your Own The following exercise will test your comprehension of the topics cover~-d in this chapler by mak ing some important changes to the projects.
On Your Own The Galactic War game is much more playable now than it was back in Chapter 3, thanks in part to the new keyboard handler. But we are completely ignoring a perfectly valid altemative to the keyboard-your trusty mouse. Devise a way to add mouse support to the game. You could rotate the ship when the mouse is moved left or right, apply thrust when the monse wheel is used, and fire when the button is pressed.
205
CHAPTER
12
GALACTIC WAR: SPRITES AND COLLISION BOXES
The goal o f this chapteT is to develop a way to handle the game objects moving around on the scr~n and to enhance the Galactic War game with some significant new gameplay features using sprites rather than just images and vectors. Here are the $p«ific 10piQ you wililcam aboul: • Upgrading Galaclic War to a sprite-~ game • Adding new artwork to the game • Adding new functionali ty to the g.1meplay
Creating the Project The Galactic War game has so mudl potential that I'm cagn to implement. but the game has been sormwhal hobbled up 10 this point du!!' to i15 being Iimitedfirst byVCC1ol'$, then by $imple bitmap$. Now that we haVl!' this useful ~ Spr t te das.s available with some serious functionality built into it, the game will really start to resemble what 1am envision ing for it. The first thing 1 want to do is enlarge the app let window to 800 )( 600. I rea lize that 640)( 480 provides beller support for users oflow-tnd Pes, but the truth of the matter is that most usen run their Pes at 1024 )( 763. while a similarly larg!!' peruntage U5<' 1280 x 960 or 1280 x 1024. Only a tiny minority of PC ~ run the system at the Iowa nsolutions. A resolution of8OO x 600 will giv!!' the game more breathing room due to the large si:u of the aslC1'Oids.
208
Chapter 12 • Galactic War: Sprites and Col lision Boxes
Figure 12.1 The new ol'l'Siorl ot Galactic War.
As you can sec in Figure 12.1, the game has been completely converted to bilmapped graphics, finally doing away with the vestiges of its vector-graphics ancestry.
The Galactic War Bitmaps There are a lot of high-quality bitmaps in the game now, giving it a sharp, catchy appearance. The first and most significant change to Ihe game is that it now uses a background bitmap instead of a blank, black background. The bluespace.png background image was created by Reiner rrokein and is shown in Figure 12.2. This is one example of many backgrounds, srrites, and tiles you can find in the Reiner's THesel collection at www.reinerstilesel.de. There are five different types of asteroids of the large variety in this iteration of Galactic War. These gigantic rocks wi]] be blasted into smaller pieces in later iterations of the game: at this roint, shooting one of them simply causes il to disappear. I wantc
Creating the Project
f igure 12.2 The badgroood image used in Galactic War.
fig ure 12.3 The five uniqIJe asteroids featured ;n the game. Figure 12.3 were rendered by a talented 3D artist by the name of Edgar Ibarra, who actually created these asteroid models for a project I was working on several years ago. I have converted the asteroid bitmaps to the PNG format using Paint Shop Pro, as well as applied a transparency mask in the process. The spaceship has also been upgraded significantly from the version presented in the previous chapter. I based the spaceship on a design by Reiner Prokein and significantly modified it to give it a more distinct look with a pseudO-3D appearance. (Note the four guns, top and bottom.) Figure 12.4 shows the ship sprite. This is a great-looking ship, if I do say 00 myself. I'd like to add a small fire
209
210
Chapter 12 • Galactic War:
,-
and Collision Boxes
_------ ..
. "' .....l;I"" ll". b
Sprit~
~;::=
1'"
.... _
_j["ijr__
4
!iI._.
---....,
_. .
~ "-f""'=":J
.~ .,
~·iI
••
•. _._........... _-
--"'._-~
fig ure 12.4 The player's spaceship used in Galactic War.
-
...... ...... --~
animation coming out of the engine nozzles when you press the Up arrow key to apply thrust (fulUre enhancement!).
The New and Improved Source Code There's a lot ofsource code here for the new version of the game. Th is is necessary be
Creating the Proje
5tt
the current slate of the project by looking at the list of
files now required by lilt' project:
• 8a5cG
IJllogeEntity.j.wa
•
Sprite.java
Point2D.java
Tip
n-
Two obwIoullJ ~ omossionlo fie 9i'Rr sot.- ' - bHlllOWld tftects iRd IIMic. We wi idd lOWld III the gaml' in ~ 15. ·GaLIctic war. FitIMIng the GMnf.'
The first (ode li5ting here indudes the main d:us definition for the game, along with the global variables. r have highlighted key (hanges to the 1}1111e in bold tex!. {
.
• GALACTIC IIU, Chlpter 12
..................................................... jUI.lpplet. · : jIU.I"t. · : jIWl.I"t.nent JUI.I"t ,1"'ge JIU . ~t 11. ': I~ort JIVI. lang. 5Y51C11 :
/
l-.ort l"POrt l"POrt IlIllOrt IlIllOrt
.
{
• Prl ... ry (lin for the 91 •
......
..
/
pIlblle
211
212
Ch~ptt r
12 • Ga lactic
W~r :
Sprites and COllision
80~ts
I/$prite st.te .. 1ues SUtlc lnt SPlllTUORllAL· 0; lutlc lnt SPlllTLCOLLIDEO-I: lithe IIllln thrUd MC_S tl\t g•• loop ThrUd g••loop: IIdouble buffer objects Buffertdlllllgt b.c\buffer: Gr.ph1cs2D g2d: IIVirl0US toggl es boo I t.n shOllBounds - true: boole.n collh10nTestlng· true: IIdeflne the game objects I. agtfntlty background: Sprite ship: Sprl te[J ast * nt~ Sprltt[ASHROIDS]: Sprl tt[J bulltt · new Sprl tt[BULUTSJ: Int current8ul1et - 0: Ilcreate a randaa n~r gener.tor II..1ndaa ral'ld· _ II..1ndaa(): IIde fine the SOIII'Id Hfects Objects So"I'I
lnt frav.Count - D. frlv.Rltf - 0: , ong s t.rtTille - Sys te•• currentT l11tlll111 s ( ): Thc sho~Bounds and colli s 1onTest I ng va riables arc used to draw some helpful information on ,he scrcen, which is invaluable while develop ing a complex S'lme. Figu re IZ5 shows the game with bounding bo~es and collision testing turned on. When a collision occurs, the bounding boxes of the two objects arc drawn in red instead of blue. You can turn ofT collision testing altogether, if needed for testing.
Cruting tho! Project
Figure 12.5 80lIlding boxe and mIisions are IoggIfd with Ihr Band C keys.
This brings up an imponanl point aboUIIM currenl Slate of 1M game. ~ au a lot of new featu res in the game, and il prt'lty much look$the WoIy it will whl'll il is finished-acept for a scrolling background and a few olhorr tidbits. The game really docsn'ttake any action atlhis point based On a collision. Instead, collisions arc dt'l<.'Cted, and that status information is made available 10 the game through the sprite's state property (which is gmmc enough for use howt'Ver you see lit). Welll't'Visit tilt' prQCt':SS of responding 10 rollisions in Ihe nal du.ptlT. Next up is the In It () t'V<."Il1 mt'Ihod of tM applt'l:.
. ..................................................... /
• applet lnlt event
/
publiC ~old lnlt() I Jlc reate t~t back buffer for s_t~ ,upIl1C$ backbufft.·""", s..fftredlugt(SC REUlIlIDTM. SCRHlOIEiGHT. Bufft.edlugt. TYPL,.r_RGlII: ,Zd· backbllffer .crUltGrilp~ tu():
213
214
Ch apl~
12 • Galactic War: Sprites and Col lision
8o~es
Ifload the bukg round iMge bldg round - IleII IMgeEnt a,ltM J) : bldground.l~dl-blunplce.png-I:
Ifse t up the ship ship· new Sprite(UIs, g2d1: shlp,lold("splcnhlp.png-1: shl p, setPos i t 1onlnev Pol nt20l CENTERX, CENTERY»): ship, seUllve(true): Ifset up the bulleh for (l nt n - 0: n<6U llET S: 11+ +) I bull el(n} - net' Spri t t l thl s, g2d1: b\llltUn]. 1ol d(·p hs.ullot. pIlg-l:
II set up t he I steroids fo r (lnt n - 0: n
IIstirt th, user input lhtener Idd t eyll stener( t hi s) :
Creating the Projea The next sedion of code is the main game update ponion of me game, including the applct updateO ('Yenl, the palntO event, and three methods to draw the game objects: draw$hlp(), drawBull eU(), and draw~~terold~().
.
/
, applet
~p'Sate
ewent to redraw the screen
.....................................................
/ .01d updlte(Grlphlu gIl IIcalculate frlM rHe frIMCount++: 1f (SystM.currentT1MHll1 1$0 >stlrt1,.. + 1000) { stutT1M - Systee.currentT11ol!111111s0: fUMbte· frllltCouot: frl.count·o:
p~bllc
Iidraw the backgro~nd gld. drawluge( background. geUuge( ) •0,0. SCREENWIIlTH-I. SCREENHEI&HT·l. tbls): IIdrlw the gl.. gnplllcs drlwAsterolds( J: drawShlp{): drawBullets() : IIpr1nt stltus lnfoNlltlon on the screen gld .lietColorCColor. WHITE 1: gld.drlwStrlng("fpS: W+ frlMble. S. 10): long X - Mlth.round(shlp.pos1tlon(J .l()): leng)' - Mltb.round(shlp.pos1tlon(). V()): g2d.drnStr1ngC"Shlp: w+x+".w+ y • 5. 25): g2d.drlwStrlng( "No,e Ingle: " + Nlth. round( sh1p ....wgleOl+i0. S. 40): gld.drlwStr1ng(Whee ang)e: "+ Math.roundC shlp.faeeAngleOI, 5. 55): If (showBoundsll gld. setColer(Celor .GltEN): g2d.drlwStrlng('BOUNOING BOXES'. SCREENWIOTH·150. 10):
215
.216
Ch.a ptH 1.2 •
Gal~
War.
5pril~
and Colli$ion !lofts
if (tolll$lOl1Testlngll
gld. setCo1or(Co Ior . 6REERI : gZd . d r~WSt rl ng( 'COll [51 O ~ H5 TI MG' • 5CRE £MII IOTH ' 150. 25) :
IIr~p~lnt
tM
~pplU
.lndow
p~lnt(gl :
I·········· •
dr~wSh 1p C~ 11 ~ d
by
~ pp 1et upd~ te ~vent
.
••••••••••••••••••••••••••••••••••••••••••••••••••" ' 1 publlc void dr~wShlp(J ( II let the tr ~nsfOrll for the lnlge shl p. t rlns fOrll( ) : ship.dr~w(J:
If (showBounds) I 1f (5hi p. stltt( ) •• SPRITl..COLlIOEo ) s hi p. drlw8ounds ( Co lor. REO ) : else shi p. drllf80unds (Co I or . 8LUE I :
/
. ..................................................... • drlwhllets ulled bYlpplet updlte ewent
/
public void dr~ w Bullets() I for (lnt n· 0: n (8ULLET5: II-H) t If (bullet[n).~lln()11 Ildr~w thebull~t
bull et(n]. tnnsforn( ) : bill I etC n) .dnw( ) : if (shadounds) ( 1f (bull et{n]. shte() .- 5PRITl..CoLLloEO) bII1Iet(n) . drawlounds (Col or . 1E0 I: else bu I let[n). drlwBounds( color. BLUE) :
Creating the Project
I······························
.
..................................................... ,
•
dr~wAsterojds c~lled
by
~ppltt
updUe event
publ ic .oid dnwAsteroids() I for (Int n· 0; n < '!'sTEROIDS; I"H) I If (ut[n].llheO) ( IIdr,w t~e uterold ut[n}. tr!nsfor.(); Ht(nl.dr! w() ; if (sbowBovnds) I lf (ut[n].stlU() •• SPIITE-COLLIDEO) ut(n]. drlwBovnch(Co lor .IUD) ; else ute"] . drlwBounds( Co I or . SLUE) ;
. .....................................................,
,
•
~pp)tl
window
rep~lnt evenl-dr~ w
tbe b!ck buffer
publiC .old p'lnt(Gr~p~lcsg) I g.drlwl..ge(blckbuffer. D. D. tbls):
or
The next section code updates the gamc via thc g~lIIel oop thread, which calls g~IleUpdate( l. Th is method, in turn, calls methods to process user input; update the ship. bullets, and asteroids; and perform oollis.ion testing.
,
.
....................................................., • tbrud sun event - stlrt tbt g,llt loop rUMlng public void sllrt() l g'lltloop - _ Tbrud( t hls); gult 100ll. stirt( );
I····················································· ....................................................., publtc .01d run() I
211
218
Ch.Jptl!'l" 12 •
Ga~ic
W lK: Spntes and Col lision Boxes
lI acqu1r e t he cu r rent thru d ThrUd t • Thread . cur rentThreld{); //k«p going IS IO/Ig IS t~ thead 1$ 111 v, " hlle (t·· gl.loop) ! tr1! Threld. s Ieep( 20} ; I CltCh( Inle rruptedhcep t Ion ,) [ e.prlntStlcU r.ce( ), I f/updue the gl. loop gl.Updlte() : repllnt O :
.
/
.....................................................
• t hru d sto p event
/
public voId st op() I gl.loop - null;
.
/
·················..····..··..··..····················f
private void gllieUp dlUO checklnput() : IIpdite$hlp(); \Ipdlte81l1Ieu() ; updateAsterol ds( ) ; if (colli slonTest! ng) checkColl1slons();
..
/
• Updue the shIp pos! tlon bued 00 velocl t1
..................................................... public void updl teShlp() I aM p.llpdltePos Itlon ( I : doubl e lIevlt • sM p. pos ltl OII( I .X( I ; doub11 newr. ship. posl tl OII( I. Y( ) : " " riP Hound leftlrlght If (shlp.poslt l on(). XO < ' 10)
/
Creating the ProjNt _ - SnEOIlIIOTK + 10; else 11 (Ihlp.posltlon( I.I( I nft)[" -10; lI.rlp uound
>SCIEElllllOTH + 10)
top/bott~
< -10) nellY" SCRHMHEIGilT + 10: else 11 (shlp.pOlltl0n(). YO >SCREEMHEIGilT + 10} ntlf)''' -10:
if (lhlp.pos1tlon().YO
s1l1p.let'011t\ontHW '0Int2D(HWlt. ship. utStlte( S.IITEJIOIIIo\L):
1lfW)'J):
I····················································· ....................................................., • Update the bullets blled on veloclly
public Yold updHeBullets() I IIWlYe tile bill I ets for (lnt n -0: n (&uUETS: rt++) I If (bul1et[n!.llhe()}I lIupdate bullet' I x PQs It Ion bull et En]. up.:IItePos1t 1on ( ) : IIbullet dhlppurs at leftlright edge 11 (bullet[n].polltlonl).It) < 0 II bullet [n]. posl tl on I ) .It I >SCREElIVl DTH) bullet[n).uUl1wetfilse) :
lIupdate bullet's y position bull et[n] . up4ttePol 1tl one ) : IIbullet diupptars It topfbottol edge If (bullet [n].pos ltlon ( ).YO <0 II bullet(I].posltlon{ ).l{) >SClEEIlKEl6HTl bul let(n].seUlln{fllse) :
bu I \ et[n] .s'tSti let SPRITUORHAL l :
219
220
Chapter 12 • Galactic Wilr: Sprites and Collision Bo~es
, . ....................................................., • UpdUe the nterolds t>.sed on .elocHy
public .01d
~pdntAsterolds() I
1I~.e
,ncr route the nterolds for (lilt n - 0: n < ASTEflOIOS: tt+ +) I if hst(nl.JlheO) I lI~pdne the n t erald's position Jncr rau l 10n ISt[n]. opdettPos It 1on e); ISt(n). apdlteRout ton ( J :
1nt II· ut(n] .1MgellldtMJ- l; tnt h - ut(n] .IMgtHelghUJ - l; do~ble ntwX· ut{n] .poslt10n( I.I( I: do~ble n~ - ut{n] ./lOsl t10n(). Y(): I/•.,ep t he ~st e r old ~ ro~n d the sc reen edges if (ISt[ n] .poslt l onf).If)
< '11 )
newx· SCRHHWIOTM + w: else if (lSt{n].pos1tionf).X{) >SCRHHIIIOTK+II) newx· ow; 1f (ut[ n].poslt10n O .YO (-h) newy- SCREEWKEI&HT + h: else 1f (ut(n] . poslt1onO. YO > SCREENKEIGKT + II) newy· -h: ut{n].setPosltlon(new PolntlO{ntwX.n~): ut(n] •setSute( SPIIT[JIORlIAL);
I···································
• Test ut'ralds for co III s 1OfIS with shl p or
b~ llets
.
.....................................................,
pobll c .olel checkeo III s Ions Cl I IIcheck fo r coll 1$100 bet ~e n nteral ds end bulle ts for (Int _ · 0: -
(rnling the ProjKt III ter,te
t"ro~g" the bill Ieli for (lnt n ~ G: n (WHETS: ,.... ) I If (bullet[n] •• lheO)I IIcolI Ision? if (ut[_].collldesWltMbull,t[n]l) I bu II't[n]. setSUtfl SPRI TLCOLlI DEG): ut[_]. utStateISPRITLCDLlIDEDl: explode . play() :
IIclled for collisIon ilsterolds ilM sMp for (int _ - 0: -
(i~1p.collldeIW\th(i1St[_j)l(
te_]. setStlte( SPRITLCDLlIDED) : Ih1 p, ietStitel SPRITLCDLL I OED} : e~plllde .pl iI1( l:
iI i
The next SKlion of rode processes keyboard input. The game has prog=sed to the poinl where lhe limp li~ic keyboard input from earli~ chapters was insufficient, so I've added support (0 the game for multiple key presstS now. This works through the use of 5e\lef3l global variables: key Left, keyRight, and so on. 'These boolun variables are set to true during the keyPressedl) event and set 10 false during the keyReleilsed( l event method This provides support for multiple keys at the same time in a given frame of the game loop. 1lIcre is a practical limit 10 the number of keys you will be able to pres at a time, but this code makes the game fluid-looking. and tbe input is smoother than lbe jerky input in the IasI: chapter. / • process keys tllilt line been pressed
.
.....................................................
/
publiC .old checklnputO I if {keyLeftl {
221
222
ChiJpter 12 •
GiJliKtic WiJr: Sprites iJOO Collision
Ill eft arrow rotltes
s~lp
8o~es
left 5 dlgrHS 5):
shlp.utFaclMgle(s~I,.faceAngle O ·
If
(s~I,.faclAngh()
<0) s~lp.setflclMgh(360- 5) :
I e1le11 (h,R1ght) ( IIright urow ralites ship right 5 dl9rlls shlp.utFaceMgle(shlp. flceAngle() + 5): 11 (shlp.flceAngle() 360) shlp.setFlCeAngle{5):
I 11 (ke,Up) ( lI~p arrow applles applyThrutfJ :
thr~st
to shlp
I··················..·..······························ ..................................................... • ke, 1 I stiner nlllu
publlc .old ke,TJpe.dfh,E.enl k) I J publ lc .old kI,Preued(le,r.ent kl I switch (k.getllJtGdeOl { case te,E_ent. Vt..LEFT; ke,left. true: br eak : clse leyEvent.~ICR1GHT: ke,RIght· true: break: case KeyE.ent.Yt..UP: kI)'IIp· trill: break: case Ke,hlllt. Yt..CO.TROl: kI1Flre-tMII: break: case Ke,hent.Yt..B: IItoggle b""rHllnQ reclinoles showBounds·lshowBoundl: brelk: case KeyEvent . ~t..C: flloggle col11slon tutlng colli s 10nTesting - Icol1 I 11onTestlng : break:
/
Creating the Project publtc votd hyReIUStdlleyEvenl~) I switch It.getleytodeO) ( cue KeyEvent. YK.-UFT: teJ'left - hlu: brut: cue [eyE vent .YK.-RI6IIT: teJ'Rlght - f'he: break: cue Keyhent.YK.-U~: keyUp-hlu: break: case KnEvent. ~K.-COHTROl : hyFlre-f,he: flreBullet(): breat:
public vold applyThrustl) I Ilup arrCl'll adds thrust to shtp (1/10 no ....l shlp.setlillnAngll(shtp.hceAnglel)- !MIl:
SJll!~)
IIcalculate lhe I and 1 nloclty based On angle double velx - sht p. velocttyll. Xll: velx +- calcAngleHovd(shlp.lKlveAngle()) • ACCELERATION: double vely - ship. veloct ty(). Yll: vely +- calcAngleHonHshlp ..anAngleO) • ACCELERATION: shtp.seUeloclty(new Polnt20(velx. veI1»: I publ1c votd flrtlulletl) I IJflreabullet e1lrrentBull et++: lf (cur renUul let >BULUTS - I ) currentlul1et - 0; bullet[ currenUullet]. setAll ve( true );
IIset bull et •s start lng pot nl lnt . - bullet[currenUullet].lugelltdth(); lnt h - bull et[currentBullet].lugeHetght(): ~oub lex - sht p. centerO •Xll - ./2: doubley-shtp.centerO.YO - h/2: bul l et[currentBull etl. setpos t t lon( new Pot nt20(x ,y) ) ; llpotnt bullel tn u. dt r«tton shtp t s faclng
223
224
Chapter 12 •
Galactic War: Sprite<; and Collision Boxes
bull et[ cu rrent8ull et] .set FaceAng1e( shl p. hceAng1e( ) }; bull et[ cu rrent8ull et] .setMoveAng1e (shl p. faceAng 1e() - 90); l/fire bullet at angle of the ship double engle - bu11 et[ current8u11 et].-.lveAng1e ( ) : doubl e nx · ca1cAngleMo~ex(angle) • 8ULLET_SPEED: doubl e ny· calcAng1eMoYeY(angle) • BULLET_SPHO: bull et[ cur rent8ull et]. setyelocI ty( new Pol nt2D( lVll. svy)): IIphy shoot sound Shool-play(): The last section of code concludes the main code listing for this new version of Galactic War, implementing the now-familiar calcAngleHoveX() aJld ca IcAngleHoveY(} methods. 1· ..
··**..·····················..·..···....·..··..····
• Angular motion for Xand Y is ca lculate d .................** 0* *0 public double calcAngleHovex(double angle) ( doubl e IlOvex • Math .cos(angle • Hath. PI I 180); return llO~ex :
/
I public double ca1cAngleHo~eY(double angle) ( double llO~ey - Hath. sin( angl e' Hath. PI 1 180): return llO~ey:
What You Have learned This signifi<:cont chapler produced a monumental new version ofCalactic War that is a foundation for the <:chapteTS to (Orne. The final vestiges of the game"s vl.'<:tor-based roots have been diocarded, and the game is now fully implemented with bitmaps. In this chapter, you learned: • How game entities <:can be(Ome unmanageable without a handler (su"h as the Sprl te class) • How the use of a sprite dass drnmatiall1y deans up the sour"e code for a game
On Your OWn
Review Questions The following queslions will help you to determine how wdl you h~ve kamM the subjecls discussed in litis chapter. The answns are provided in Ap~ndiJ: A, "Chapter Quit Answen." I. Which support cbss helps maragt' the position and velocity of sprites~ 2. During which keyboard ~t should you disable a ky.pras variable when dd«ling multiple ky presses wilh global variables~ 3. What is the IlOlInt oflhesprite: collision detection routine: used in Galactic War? 4. Which method in the App1et class provides a way to loo.d images from a JAR fila 5. Which Java package do yOll need to imllQrt to use the Gr.phics2D class? 6. What numeric dat a type docs the Polnt2D cbss (created in this chapter) usc for internal storage of the X and Y values? 7. How does the usc of a class such as POintlD improve a game's source code. \'CT5US using simple variabla? 8. Which pro~ny in the Sprite class determines the angle at whKh the sprile will mova 9. Which property in the Sprite class de'lermincs the angle at which a sprite is pointed? 10. How many milliseconds must the game usc as a deby in order to achieve a frame rate of 60 frames per second?
On Your Own TheGalaetic War game is in a transition at this llQint, after having bemllpgraded significmtly from vector-based graphics. At present, it does not perform any action due to coll isions other than to rCllQrt that a collision has occurred. We want to separate the roJJjJjoll ICJlillg code from the {olliJioll rCJpo"J(" code. Add a mdhod that is called from g.-eUpdau( l that displays the position (x,y) of any object thaI has collided with another objecl, for debugging purposes. You can do this by looking al.ll sprite's state properly.
225
CHAPTER
13
GALACTI C WAR: SQUASHED BY SPACE ROCKS
We'll make a minor enhancemen t 10 Galactic War in this chapter by adding suplXlrt for an animated explosion. To facilitate tbis, we'll have to write wme new code to bandle the timing and state properties for eacb sprite. The goal in this chapter is to add a handler for responding to ship-'lsteroid collisions. When a collision occurs, the game should animate an explosion over the ship, and then put the ship into a temporary invulnerability mode w the player can get the heck out of the way before another collision occurs. Here are the key topics: • Examining possible interactions among the game entities • Adding collision detection between the player's ship and the asteroids
Being Civilized about Collisions Responding to collisions in a civilized manner is the first step toward adding realist ic gameplay to any game. The next step is to add a sense of timing to the responsc code. We'll add explosions to show when the player gets hit by an asteroid! The new animated explosion in the game is a 16-frame sequence, which is shown in Figure 13.1. When the explosion code is addc<1 to the game, the ship will literally blow up when it collides with an asteroid (see Figure 13.2) .
m
228
Chapter 13 • G
o
o
Figure 13.1 The ll;·frame an imaled explosion (courtesy of Re
Figure 13.2
TI>e new Mimaled explosion
~
now part of the game.
Being Civilized about
Colli~ion~
l.cl's lake a look al Ihe changes required 10 update lhe game 10 supporl explosions. There's more involved here than just loading up the animalion and drawing il because we have to accoun l for timing and Sprile Slaw values. The firSI change is in the globol se<:tion at the lOp ofl he cbss-notc lhc changes in bold.
Tip !hi' s Uti c keyword defines a variable thai does nOi change.
pJbl Ie closs Gol act Ic'o'ar extends Applet l",ple..ent~ Runnoble, KeyLI stener I Ilglobol constants stotic Int SCREEH'o'IDTH - 800: stotie Int SCRHHHEIGHT - 600: stotle lnt CENHRX - SCREENWIDTH I 2: stotte Int CENTERY - SCREENHEIGHT I 2: stotle Int ASTEROIDS· 10: stot Ie int BULLETS - 10: stotle int BULLECSPEEO - 4: stot Ie double ACCtLEJU..TlD~· 0.05: Ilsprite state nlues statle lnt STATE.-HDOOL - 0: stltle lnt STATE.-CDLLlOEO - l: stl tl e I nt STATE.-EXPLDOIHG - 2: /ltne ",ol n t~reod beco"'es Thrud gOJIICloop:
t~e
gaM loop
II daub1e bu Her obj eets
Bu f fered I..oge boekbu ffer : Gropnl (s20 g2d: I/variou> toggles booleon s~ollBounds - true: boolean eollhlonTestlng - true: long Colli ~lonT\-er" 0: Iidefine l~e golllC objects laag eEnt1ty boekground: Sprite ship: Sprtte[] aSl - nell Spri!e[ASlfROIOS]: Sprl t ell bull et - nell Sprl te[BULLETS]: lnt currentBul1et - 0:
229
230
Chapter 13 • Galactic War: Squashed by Spa
eftech
sa~nd(llp s~oot;
saO/ndCI Ip fXplOCle: Is111ple "Iy to ~irdle ..,ltlple ~eyprnses bOOlun keyllo1o •• key",.
Makc thc following changes ncar the top of the lnltl f'\ent method to s"itch the background ob;e.::t from an l.. ~e to an 1... ~e(nt1ty. pubHc wold ,nit I IlcreHe Ve back buffer for slIOoth graph1 cs baekbuff er - ntll Bu ffered [",age( SCR[[~ W! OTH. Bufferedl",age . HPCINCRGB): g2d - backbuffer .creHeGraphl cs[) :
SCR[[ ~~[
IGHI •
Ilioad tht background laage backllround .. new l.ageEnt t Iy( thl I) : background. load (~b I utspace. png~) :
1\ext, scroll down inside the Inl t() l"'o'cnt mctbod a bit more until you ha"e found the call to iddl(eyllstenerl thl s) and insert thc follo"ing code in bold. This code lQ;lds a 16·frame explosion animation. 1110.d the upTosloo uploslOll" net' MI ..tedSprlte(thh. 92d): uploslon.lo.d(~e.lflToslon9'x9hl'.JMlg~.i. I. H. HI: upl ollon. utFrI.rN!117(2): upl 011011. uU Tl.tl It I se) : IsUrt Iheustr input listener Iddlcyl Istener ( th \
Being Civililed "bout Collisions ;-
the
boc ~ ground
g 2d . dr~wI,uge (ba ckgro und
getluge().O .O. SC REE NWI OH-I. SCR[E NH EIGHT- I .
this) ; !ldrawthe gUM! gr ophlCS drawAsterolds() ; dr awShi p() ; draw6ul l ets() ; drawhploslons() ; Now, while you're still in the update() method, scroll down a few lines to the part of the method that draws stalUS information on the screen and add the following code to display the ship's current stale. tf (shtp . SUH( )- . STATLNORlV.L) g2d .drawStrlng("Sute : NOll.MAl", 5, 70); else t f (shlp .sute( )"STATLCOLLIDEO) g2d .drawStrtng("Sute : COLLlOEO", 5. 70); else If (shlp .stlteO"STATLEXPLODING) g2d .dro wSt r lng("Sute: EXPLODING", 5, 70) ; Now, scroll down past the three dra w methods and add lhe following O1<,thod after drawAs l erold s(}. This is just IIII' first version of the explosion code, and it only draws a single animated explosion. later, the game will need to supporl several explosions al a time . pJbHc void dr awEx plosiollSO 1 If expIos Ions don't need sepHa t e updne llC thod i f (expl os ion ,a l l ve( }) I exp 1os Ion ,updateAn I-at Ion{ ) ; If (expl osion . cu r rentfr~ me() -- nplos Ion. tot al Frames( )·1) 1 expI os Ion. se t Cu rren t Fr ame( 0) ; explos 10n .set AI I _c( fal sc) ; I else { explos lon.draw() :
231
232
Chapter 13 • Galactic War: Squashed by Space Rocks Next, scroll down a bit more to the gameUpdate() method. Modify it with the additional lines of code shown in bold. void g~meUpdateO ( checklnput(): upd~teShlp() : upd~teeullets() : upd~teAs tero1ds ( ) : if (collhlonTestlng) ( checkCo111 s1on$( ) : h~nd1 eSh1 pCo111 $1 on$ ( ) : hand1eBu11etColl15ions() : h~nd1 eAster01 dCo111 s1 ons ( ) :
prlv~te
Scroll down just past the checkCol1 i si ons() method and add the following new methods to lhe game. The two collision handler rOlllines for asteroids and hullets are not implemented yet, as the goal is first to get a response for ship-asteroid collisions along with an animated explosion. The handl eSh1 pCol11 s1 ons() melhod uses the ship sprite's Slate property extensively to monitor the current state of a collision, and il adds a thr~-sccond delay after a collision has occurred so Ihe player can get out of the way before collisions slart 10 occur aga in. public v01d handl eSh1 pCol115ions() 1 1f (ship. state() ~ ~ STATCCOLLIOEO) ( 1'0111 slonTllM!r - Systelll.current11aeMll l l.1(): ship . setYeloci ty( new Polnt20(O ,0)): shl p. setS tate (S1ATCEXPLOO IKG) ; startExpl oslon(5hi p): I else if (sMp.st~te() -- STATE_EXPLODING) { if (coll1s10nTiaer'" 3000
public void startExploslon{Sprlte sprite) if{!exp10s10n.~lhe())( double x - sprite .posit lon(). X() . spr1 te. get80unds ( ) •wi dth I 2: double y - sprite. posit 10nO .lO .
Review Questions sprl te . getBounds ( ) . heigh I f 2, explosion .setPosl t lon(new Polnt2D(x. y)); exp1os 1on .setCu rrentf rame( 0) , explosion .setAII ve(true l,
public void handleBulletCoI11s1ons() ( for (lnt n· 0: n
public void handleAsteroidColll s1 ons() for (lnt n -0 : n
What You Have Learned This chapter tackled the difficult subject of sprite collision detC<:tion. Adding support for collision testing is not an easy undertaking, but this chapter provided you with the knowledge and explained the collision code in the core classes that makes it possible. You can now dmw two or more sprites on the screen and very ellsily determine when they have intersected or collided. and then respond to such events.
Review Questions The following questions will help you 10 determine how well you have learned the subjects discussed in this chapter. The answers arc provided in Appendix A, "Chapter Qui? Answers." 1. What is the name of the mcthod thm makes collision detcction possible?
2. How many collisions can the game detect within a single update of the game loop?
233
234
Chapter 13 • Galactic War: Squashed by Space Rockl 3. What would happen if the ship were to fire a projectile that "warps" around the screen and then hits the ship? Would a collision take place? Why or why not? 4. What should happen to the player's ship after it has been destroyed by a collision with an asteroid? Describe a better way to "respawn" the ship than what is currently being done. 5. What type of transform could you apply to the explosion sprite to change its size? 6. How docs the ship's velocity affect the result of a collision when the ship is destroyed? Should the ship continue to exert momentum even while blowing up? 7. How can the collision routine be improved upon, so that collisions are more precise? 8. What is the name of the constant applied to the ship when a collision has taken place? 9. What is the name of the method that updates a sprite's animation sequence? 10. What is the name of the method that handles the game loop for Galactic War?
On Your Own Since we are constantly improving the game with each new chapter, there is little you can do now that will nOI be addressed in the next chapter. However, some improvements can be made now that arc not added in future chapters. Here is one such example: Add another explosion to Galactic War so that the asteroids blow up like the player's ship when they collide with the ship.
CHAPTER 14
GALACTIC WAR: ENTITY MANAGEMENT
You have le;mlCd lhe basics of web game programming in previolls chapters, ;lIld you have bem building the Galactic War game here in ParI Ill. The source wde for an applet-based game is becom ing a bi l ledious at this poim. You've seen that there is a lot of code lhat does not change very much from one game 10 lhe next, now thaI you know how 10 write a typical game in Java. Arm'l you gelling tired of steing the kqand mouse handlers io I:'Icrycode listing? [sure am! I don't want to enfolU' too much structure for your own game projects. but I think it will ~ hdpfulto add some organization 10 Inc code.
lkre arc a lot of e--ents and methods that mUSl: ~ caIJed and monilored nogubrly, and sina this code doesn't change very often (if C\o~). it woukI clean up the sourcc ~ considerably if we could move reusable code inlo a separate class. This chapter shows you how to create a base dass for an applet-based framework-or r:lther. a gailit' mgine. You win ~ able to writea game very easily by inheriting from the new-G' 1Ie class. and your game won'l nred to implemenlthe interfaces (such as Runnlble) any longer. Instead, you will be able to focus 00 high-level game design and gameplay. Hcre are the specific topics you will learn about:
• Evenl-driven game programming • Creating a Java applet-based game engine • Interna lizing the sprite handler • Adapting Galactic War 10 the new game engine
236
Chapter 14 • GaliKtic War: Entity Management
Adjusting to Event·Driven Programming The biggesl obstacle 10 the adoption of a game framework, or a game mgine, is that you must give up direct (active:) control of the game and accept an indirect (passive) programming methodology. Adapting Galactic War from a direct In a ~iY(' game: was very challmging. and I woukllikc to share my apcrimce with you so that you will 001 haY(' 10 go through !he pains of developing your own game mgim- the hard way. I could have compk1cd the game two or three times over in the time I'Y(' spmt building the ~. das$ in this chapter, bul the md result is a powerful mgim- for creating additional games for ddi~'Cry on the web.
Exploring the Class Library l.et's take a look althe dasslibnlry as il exists at this point, after the changes made in the previous chapter. Figure 14.1 shows a diagmlll of the four main classC'S we've developed so far. The diagmm doesn't show the YectorEnt I ty class since il is no longer being used. First, BneGulI!Ent I ty contains the basic movement and orientalion variables that are passed on 10 the l. . geEntlty class. This class adds the capability to move, rotate. and draw bitmap images, and it is the core class. From this point, a new
Image Entity
-•• --
---
..... _- ~~~~- • -::":"_!~=;,=-=--
FisJure 14.1
The ku key .liYa ~ b -*ing 'Mlh
Sprite
--,--
AnimatedSprite
giIllt ~
AdjlMing to
~venH)fMen Progr/lmmlng
class nlled Sprite was dtveloped. Now, Sprite does not inheril from llUgeEntity, but r~ther, it uses th is core class to store its internal image used for drawing sprites. That is why the link from I.age[nt I ty 10 Sprite is a doned line. Nat we h:n~ Anh.,tedSprl teo which is the core of the game engine due to iu support for animation. When you look at this diagram and resoIwo the connec:tiol1$ in the l"CVC'l'Se dir«tion. you find that AnllUtedSprl te inherits (rom Spd t e several key properties: an image, width, and height. AnlllltedSprl te also makes usc of an IIlIQeEntity to handle the brge, tiled images containing frames of animation. The Sprite class li~ looking backward, ronsumes an image and its oridth and height propmies. You can use this diagram if you ever stan 10 feel over-..iIrimed while perusing the Gillactic War souoce oodc: ill these: final chapters, because the game is becoming lighter. When an AnllutedSprlte loads its souoce billn~p, that is passed up to the "supeT" or "parent" class (Sprite), which handles the image. This is inherilance at WOl'k. bcause the AnINtedSprite cbss doesn't actually need to handk iu image ...11 [ use the word "tight" to dl'$CribC' the situation in which the source code is not becoming blQtlted, as is often the case when ~ game becomes more advanced . Instead, Galactic War will evolve from a d irect. actively coded model 10 an indirect, passively coded model using the game engine dtveloped in this chapter. The source code listing for the game isabout the Arne length as il was befOrt, but the game has ~n comp/tlely rt:Writtnr. The Ga. ctass is quite complex, but the "front end" or "user" source code file, GalacticWar.java, is much, nIl/ch simpl",. That is the benefit of a game engine-it handles all of the messy details for you, UIowing you to focus on building gameplay. From the engine's point of view, "You art too skilled to be hotherftI wilh $UCh minutiae as sprill' IN.nagement. le1 me take care of that for you, while you focus on making this game u fun u possible!"
Building the New Ga.e Class The purpose of the game engine is to mcapsubte the p/mform code on which the game is developed. In this case, we're talking about a lava applet that runs in a web browser. So, the goal of this chapter is to build a game engine Ihat simplifies. buildi ng web games. with Java. The first step is to creale a new class. I opened the Galactic Warproj«t from the last chapter and began modifying il. Firsl, I crealed a DCWclas.sa.Ued ~1Il'. The 6•• ctass alends (or inheriu from) the Appl@tclass,
231
238
Chapter 14 • Galact.i( War: Entity Managel1lf'nt
as our programs have fOt the last 13 chapters. This new dass will n«d to implmlent the Uybnard and mouse listener intedac:n. 11 wiD also neal to handle the game loop thread on its own, so the derived game will not need to be bothered with mcll details (or rather, logistia, sinee we'n: trying to INmige the Iogistia of an app~). Enapsulating a StiJndatd Java Applet Hen: arc the lNin events that you'n: aCCU$tome(! to stang in a Java app~-bastd program up to this point. I'm including the mouse events because they are going to b< part of the engine, even if we haven't used them very much in Gala(!ic: War. You arc wekome to add mouse support if you wish; I'm iust not sure how you would control the ship with a mouse. pubHc pubHc public llubHe pubHe p~bllc
/lIIblle publlc public IWbllc public jlIIbllc jlIIbllC publ Ie public publ Ie
void void void void void void wold wold fold fold wold wold wold wold wold wold
l nlt() V) palnt lGraphl" Vl sUrt( ) run O stOlID h,.T,.p.e4lke,.Ewtnt k) hJ'PrtnedClt,.Eftnt kl kQ~ltued(lt,.Ef~t kl updlte(Gr~ph lcs
.,usePrtnedlllo~seh~ttl "osf~l.utdlllo\lseEw~t "us.wedlllo~stE
..nt
e)
e)
.,oseDralNedlllousth~t tl .,ustEnttttdlllOusthent tl .,ustExlttd(l!oustEwtnt tl lIOuscClltktd (Househtnt tl
Even if you ignore the mouse listrner events, there are a lot of raw evenls in th is listing Ihat every applet-I);lsw game must implement at a minimum. As for Ihings such as k...'Y events, we wanlto completely repktc:e the stock events with a keyboard handler that supports multiple key pres~ and releases. I experimented with quite a few different ways to do this, and I came up with a solution that is veTS3tile but not totally internal to the Ga.e class. The key events arc passed on to the game, which can then usc a few global boolean variablC$to keep track ofkC)'S needed by the game, The mouse events :;lte parsed, and sever.tl mouse prOllC'rties are made available to provide your game with mouse button and movement infonrnttion.
Adjusting to Ewnt-Driven Programming
Custom Game Events In place of tht- standard applet n'mts., I ""'ant this claM to 50md ~ts to the gamlE' that arlE' directly rela tw to gamcplay issues, such as spri te collision and .s<:r.-m rrtrcsh, The most crucial methods in the GnK~ class usc the ~nl.atedSprl te class, Tl!C' &.w class has thlE' following featurcs: • Performs automOltic double buffering • Maintains a consistent franle ratlE' • Handlcs thlE' input listmcrs • 1\lanages the gJIme loop thread • Maintains an intema.J linked list for sprites • !'erforms an alllomat ic frJmlE' r.lte calcu lation • Automatically mo"cs and dra....s all :Kti,e spriu's • PlE'rforms collision Itsting on all acti"e spritcs • Passes imponant ('\'cnts on to ,hIE' ganlC That's an impressive list of gOOlls for any spri te-based vme engi ne. This engine allows you to build far morc complex gamcs than would be possible with tM simpk arr.l)'S ....IE''>'IE' bcotn using in the prt'Vious chaptlE'rs. Tl!C' kiE"Y to the ~prite handkr is thlE' Jnl,utll,LintedList class. By using a linkw list contOlining ~nj.atedSprJte obje<:ts, you can dynamically add and remove sprites wi thout adHTsely affecting ~rformance. I've managed to get 300 sprites on the .s<:reen at OI1<:e, ""ith full collision tc:sting. and thlE' game stiD runs at ,IK: desired frame ratlE', Keep in mind, the target platform here is a ....d> browser! An}1ime you add some overh('ad to a syst('m, )'OU will inher('ntly imrOllu c(' som(' indficicncy, Thn'e's a tradroff bmoo'ftn simpk sp«d and your dail'(' to ju''IE' an mgaging. complex game with 01 lot of graphics on the screen, I like having the ability to add an explosion to the Vm(' al any point wilhom having to worry aboul that explosion after it has finished animating iliclf. AnlaaledSprlte has a 101 of rropntia and methods that maklE' this possible {soch ;os the llfetl. and 1I (eage vari ables tha t the GUle class uses to terminate a spritlE' when Its lifespa n is completed ). I want to tell thlE' game engine. "II"')', the player's ship has aplodcd riglll I1CTiE' (providlE' X,Y position). PIcasiE' display an nplosion here:'
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Chapter 14 • Galactic War: Entity Management The game engine should nol only animate the explosion at that location, it should also h.:Indle timing aOO then remove the explosion from the linked list Illlrom'lIiC./llly.
n. 1hr iI"'=ed IisI hi hinlIes ip'IIl!S in lilt gnr I'IlginI! iI aglabll di5S ~ calIod Sl'rttes( I. 'bl CMI ~ . . d'I'IC! ~ II,.... ~ when. n - hm &._.
Here arc the ncwC'\~nts introduced in ttH, sprite cngiIY. These C'\'enlsare declared as aDmact hccaus-e the inheriting class must implement them. Thq do not contain any source code in the Ga.e class, ahhough Ga.e does callihem. This i~ what gives the sprite engine the ability to pass events on to the game while still handling all thc rcal work behind the scenes. VOId ga.eStarhp( ) voId gaeTl.edUpdatl() vol d gaeRefresbScreen() voId gaeSbutdown() voId gaekeyOown(tnt \eyCode) vOId ga-eke}'1Jp(lnt keyCode) voId ,a-ellouseOownO voId ,a.ellousel/ll voId ,a.ellousellove vOId sprl tellpdate lAttlNledSprlte sprJte) voId sprltrilnw(Att1 ..te
Adjusting to Eve"'·Driven Programming The Game Class Source Code
Here is lhe complete source code listing for the Ga lile class, which I have been describing 10 you thus far. 1\luch of thi s code should be fa mili ar to r Oil b«a use we've used it extensively in previous chapters. I will highligh t ill bold the crl/ci,,1 code th at is not directJr related to the apple!. While perusing the source code for thl' Ga lle class, pay close atte",ion to all bold lines of code, and then take note of the rest of the code. This should help yOIl 10 grasp exactl y what this class docs.
I········ . ·······..··········..···..···..······················1 • Applet
G~tIe
l .. portJ~ Vl
FrallCllork class
~p pl el .·;
alit .'; j ava. awl . event java .allt . 11IIage java . lang .System; jaVl . lltll .·;
'!II,ortj~va
Iliporl IfIlport Ilport I.port
abst rac t cl ass Ga~e extends App1et j lIIp1ellCnts Rllnna b1e . HouseLlstener . HOllsellotlonLlstener I lithe lIaln gall>E! loop thread private Thread gallle]oop ; IflnternalllH of spr1tes prl ~ate LI nkedL1st _sprl tes: publiC L1nkedL1st spr1tesO ( return _spr1tu, J IIscreen a"d double buffer r elated urhbles private Bufferedluge b~c kbuffer ; prl~ite Graph1cs20 g2d ; prl~ate Int screenllid t h. screenHelgnt ; Ilkeep
of llOuse position and buttons Pol nt20 mouseP os - newP01 "t20(0 .0) : pr Iva t e boo1un lI011 seBut tDns [l - nell boo 1ea n( 4J; tr~ck
p rl~ at e
IIframe rate coun ters and other t111l1ng variables privat e lnt _f rallleeo"nt .. 0; privat e Int~fra!IICRate" 0; prlnte lnt des1 red Rate:
~ey l1
st ener .
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Chapter 14 • Galactk War, Entity Management prtnte 10n9 stirtTl-e. Syst('ll.currentTl-e"lll t s(): l/local ap pl et object public Applet appletl) ! return this: )
Ilgame pause state prt vate boo1ea n _g~lIIeP~used - fa I se : pub11c boo l ean gamePa used() 1 return _gutePaused : pub l ic votd pau$eGa!lE'() I _g!lIIePaused - true: ) publtc vold resullleGalle() (_galliePaused- false; I Iidec I are the game event lI('thods tha t sub· cIa ss . us t illlp Ielllent abstract vol d gaIleStirtup(): abstract vol d ga.eTt IledUpdate( ) : abstract vol d gallleRefreshScreen ( ) : abstract votd gallleShutdownO: abstract votd gallleKeyOown(lnt keyCode); abstract vot d galllel(eyUp( 1nt keyCode): abstract vot d gille"ouseOown(): abstract votd g&e"ouseUpO: abstract votd gallle"ouse"ove(): abstract votd sprlteUpdate(Anl u tedSprite sprlte); abstract vol d sprt teOraw( Ant lIIatedSprl te sprt te) ; abstract vol d sprt teOyt ng (Anl l11atedSprl te sprt te) ; abstract vol d sprt teeo111 s t on (Ani lllatedSprHe spr 1. AnllllatedSprHe spr2): I"
.
• constructor ............. ......... ...............................f
publiC Gallle(lnt fralleRate. intwtdth. int hetght)! deslredRate· fra-eRate : screenWi dth • wl dth ; screenHelght - het9ht;
Ilreturn g2dobJect so sub-class can draw things public 6raphtcs20 graphlcsO { return g2d: II current frallle rate publtc int fra-eRiteO {returnjraeRate:} I/lIOuse button\ and IIIO velllent pub I1c boo lean lIQuseBut ton ( t nt btn) ! retu rn aouseBut ton s( btn]: I
Adjuning to Event-Driven Progr
public
Polnt2DIC~sePosltlon(11 returnlCusePos;
I
I··.. . ·····················································1 ·······~·················
• • pplet lnlt event -eU'od
publlc yold InU!) I /lcrute t"e b.ct buffer nod drnl/t9 surface butbuffer - new Bufferedlllil9f(screenllldth, StteenHelght. Buffered lllilge . TlPCI~CRGBl ; g2d • backb~ffer .cruteCrap hlcs() ; Ilcrute the Internll sprl te I I 51 _sprltu - _ llntedLht
I··················..·······..························ ·····················································1 •• pplet update event -e th od
publIc yold ~pdlte(6npIltCI9) I lIulculite frail! rite _fre.count++; If (Sntetl.currentTl_lIt 'lll() > ItlrtTtlM! + 1000) ( sta r tTIIM! _ Sntell.currentTh,ell l llls(); _fruehte· Jrl.Count; _fra.Count·D; /lonce nery SKOftd all deld sprites are deleted purgeSprltes(); I IIth1s -ethod I. plelltnted by sub cla n gleRefruh$creen() ;
Ildra.. the lnternll list of sprites I f (lgl.',usedO) ( dr.wSprltu{);
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Chapter 14 • Galactic: War Ent,ty Maoagemeot
/lredr,,' the scrun pJlntlg):
,
. ....................................................., • applet windOW
pl~nt
evenl
~lhoo
p~bllc
void pJIAl(GrilpMcs 9) I g.dr ... lllilge(biI'~b~ffer.O. O. thiS):
,
.
• thrud stilrt evenl
stilrt the galle loop
r~nnlng
vold lti1rtl I 9i111e1oop ~ new lhreild Ith I): gille1oop. ~ tnUI:
p~bllc
,
• thrud p~bliC
r~n
void
.
event (g.1Oe loop)
r~n()'
lIi1cq~lre
the current thread
Thread t ·
Thrud.c~rrentThrud() :
Ilprocess the lIiIln galle loop thrUd while It ··gilileloopli
v,
/ISH iI cons1stent frlile rille Thread. sl eep(lOOO , des I redRa te) : I catch( I nterr~pteil[~cept t on e) e.pr'ntHac
lIupdille the Internal list of If (lgIIlePlusedO) { updateSprltes( ); testeo11 hlons();
~prttes
Adjusting to
e~nt-Oriven Programming
".l1ow ailn g• • to upclilte If needed g• • T1IledUpd.te( ):
IJrefresh the streen rep.lnt();
,
.
• thrud
Sl~
ennt
······························~····················'* I
Jl'IIbllC YOld stope) I 111'.111 the g~. loop 9~.IQOp - null;
IIthls IItthod 1Mplelltnted by sub clns g••Shutdown( ):
. ..................................................... , r
,
• key HSlener uents
publlc yold keyTyped(KeyEvent kl I publ1c void keyPressed(KeyEvent 1'.) I g~.KeyOoWll( k. geUeyCode( ) ) :
I publlt wold keyllelened(Keyhent 1'.) gl.KeJtl!l( t. getke,y(ode( I) ;
. .....................................................
,
• thedButtons stores the stote of the MOuse buttons
/
prl vlte wol d checkBut tons (HouseEvent e) swlttMe.getSutton()) ( use Mousehent .8IJTTllIU: MOuseB~ttons[l] - true: MOuseButtons[l]- til se: MOuse!uttOl\s[l]- til se: bruk: cue lIouseEvent. WTTOlll: M<)useBut tons [1] - fll se : M<)useButtons[2]- true:
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Chapter 14 •
Galactic War: Entity Management
WluseSuttons[J] - filse; brUk: elSe llouseEvenLBUTTON3: WluseButtons[l] ~ filse: WluseButtOlls[2] ~ f.lse: WluseButtons[J) ~ true; bruk:
, . ....................................................., • ",use 1t stener events
publtc wold "'usePress~CllouseEvent ell checUuttons(e) ; ",usePos. seU (e .getl( II ; "usePos.setlle .getYC II: g.lltllouseOown( I; J pub 1j c wot d WluseRe 1ea sed(lIouseEwent e) I cheCkBut tons{ e) : IOlIsePos . seU(e .geU() I : -,ousePos . setY{e .getY ()) : gUH!HouseUp() : J
pub 1j c vot d aouseHoved CHouseE went e) chec kBut t ons{ e) : WI.sePos. setlle .geU () I : lOusePos . setHe.geU()); gllltlIouseHove() ; J pub 1t c vO td lOuseOrlgged(HouseEveflt e I I check'ut tOIlS (e I; lOusePos .seU(e.geU( )) ; WlusePos.seU(e.getY( II; g.-'Iollseo-. ( ) ; g'-*'lIseMove( I ; J publ1c votd ..,useEnteredClloouseEwent e) I WlusePos.seU(e.geU( II; ","sePos. seU (e .getY( I) : g.-'IouseMove( ) ;
Adjusting to Event-Driven Programming p~bl
Ie wold 8O~U[~ I ted(lIO~sehf1lt e) I 8OUUPO$.utl(e.geU( Il; "~$ePos . ~ e t Y (e . getH ll; ga.M o~$eM o.e() ;
I Ilthl $ uent Is not netded p~blle
wold ..~seCl lekedOloliseEnnt el ( I
I · .. •••••••••••••••••••••••• ..• • ••••••••• ..••••••••••• • X al'ld Yweloelt)' eale~htlon f~netlOfls
..................................................···1
pr ote ct ed d o ~bl e calcA ng leMov eX{ dou bl e angl e ) I r eturn (doubl e }( Math .cos(a ngle · Mat h,P I /leO)):
I pro t ected dO\lble uleAngleJlOweYldolible anglel I retu .... 160llblel (Math.$lnlan,le · ItHh.PI / l80ll;
I···········
.
• updat e U'e sp rite lI H f rOIl U,e g ~lle l oop thread ••••••••••••••••••••••••••••••••••••••••••••••••••• " 1
protected wold IIpda teSprl test I I for (Int n-O; n (_sprites. sinO; n++) I AnllliitedS9rlte spr - IAnI ..tedSprl tel _sprltes,<]eth.); If (spr.alheOll spr .lIpda tePos I t 10n{ ) ; s pr .upda te Rou t 1on( ) ; spr .updateAn l ru t lon() ; sprl teUpdate{ sllr) ; sllr .lIpdateLlfet 1.1 I; If{!spr.alln()) ( 5prl tell)'llll1 ( spr I ;
.
/
·
• perfo,. eollislOO1 ustlng of III Ictln spri t es ~
/
protected wol d testCo Ills Ions( I I !Ilter ate throu,h the sprite list , Ust eaeh sprite agalnst /lever)' oth er sprite In t he lIst
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Chapter 14 • Galactic War: Entity Management for (Int flrst-ll: first < _sprites. sileO: flrstH) C Ilget the fl rst sprl te to test for collision Anllll te
lliook thro~gh .11 sprites .galn for collisions for (lnt secol'd· 0; second < _sprl tes .slu(); second++) C /Illite
s~re
this 15n't the
if (fIrst I· second) (
u.
sprite
IIget the second sprite to test for collision ~nll11tedSpr1te spr2 • (An ll11ledSprl te) _spr Ites . ~et( second) ; H{spr2 .• 11ve()) I If (spr2.collldeslllth(sprl)11 sprlteCol11s10n(sprl, spr2); break:
I else sprl setColl1dedlfahe);
I····················································· • drall all actloe sprltes h the sprlte 11st • spritE's IQfier (n the Iht He drun on top
..·······························..··················1
protected void drlwSprltes() ( IIdra .. sprites ln reverse order (reverse prlorlty) for lint 11-0; n<_sprltes.slze{): nH) I AnJIII tedSpr 1te spr - (Anll11tedSprl te I _sprl tes get (n) : If (spr .•lheC)1 I spr .updatefr••( I; spr . trans fo,..( ) ; spr.dralll); spr1 ttOr.II( spr) ; lI/lOti f1 pllJ'er
£nhancing Galactic War
.
/
• once eve ry second during the (r a_c updHc. U.is _thod • Is ,'lIed to reflOve ,II dud ip r ites (rOIl the 11 "ked 1i st
....................................................., prl VI te vold pur<~eSflrl tes () I for (Int lI'"O; n <_sprltes.slze(); n•• ) Anl .... tedSprl te spr· (An' .... tedSpri tel _sprltes.getln): if (!spr.,lhe()) I _spr1 tes. re.Gveln);
Enhancing Galactic War You will be surprised to learn th:1 t the source codc for Galactic War has remained abou t the same in length , even though the game is dramatically more complex with significant n~ gameplay features. It is truly only a f~ steps away from completion, and mygoal in the nen ChapUT will be to add more gameplay features (such as powcrups). Just play Ii'll' galm' for a few s«ond$, and you'll immediately s« a J>Ced for powerups! This gilme is hard! If you can manage to keep from dcstroying some ofti'll' larger asteroids while working on thc smaller oncs, you migi'll have a chance, but once you start letting bullets ny and asteroids begin to break into smaller pieces, you will have to be quick on the rnaneuI'cring to keep from becoming space dust (which I have just becomeS«' Figure 14.2).
Explo ring the New Galactic War Source Code Rather than go over the source code solely from a functional point of view, I'm going to take you 011 a tour of th e code ,dong with screenshots of key aspects of the game that arc affected by speci fi c sections ofti'll' source code. For a game this complex.630 orso lines o f code is surprising {not counting the support da5.SCS). 1 have highlighted all key lines of code in bokItcxl so they "'ill stand out. If }"Ou pily close atlmtion to ~ bold lines of code, I~ code listings should make more smsc to you.
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Chapter 14 •
Galactic War: Entity Management
LC't's gel st.. rted with the opening atdilS for tht' gamt, where ..JI the initi:l1 variablts ..nd objtcts Ut dmned. 1M most signiflant thing .. boul this code is the short cbss definition! Tht 6I.lIct1cll,. dass just ottnds 6i-e-..nd th
..
/
..................................................... • GALACTIC liAR.
Ch~pter
U
/
IlIp<.Irtj,,,,,"t. ·, IlIp<.Irtj.~,.utll.·:
IlIp<.Irt ju'.lIng.Systell: l..-ort jU, .• vt.uent.·: publIc clln Gahctlcllir extellds G,. I If then ...n be stattc btc~use they Ire passe
Enh.alncing Gal
~
600;
1I_lse global constants flnal tnt ASTEROrOS -10 : fln.l tn t BULlET_SPHO-.; fl~.l double ACCElERATlOI - 0.05: fln.l double SHIPlOTATlOI - 5.0; IIsprlte state v.lues flnal tntSTATE-HORHAL~O: ftnal tnt STATE-COLlID£D ~ I: ftn.l tn t STATE-UPLlIllUIG ~ 2: I1sp rlte types flnlllnt SPRITE-SIIIP -I, flnal lnt SPRITUSTHO ID_BIG - 10; flnll lnt SPRITUSTElO IOJl£OIUIl- 11; fln.llnt SPRITUSTUOI0_WU -12; flnll lnt SPRITUSTElIOIO_TlIY -13; flnll lnt SPRITUUtLET -100; floll lnt SHITE-EXPLOS ION - 200; "various toggl es boolean ShOOlBoullds - false: boolean coll tslonTest tilt e true: IIdeHne the I..yes used tn the g.-e hlageEntlty bl( kgrouod, IlllgeEotlty bulletllllge; 1_lgeEntlty(] blgA$letOld$ • new IllIoe£ntlty[5]: IllIgeEntlty[] ..u.sUtOlds - new IllIgeEntlty[2]; IllIoeEntltJ'[] $_lAsUtold$ • new IllIgeEntltJ'[l]: IllIoeEntl ty[] tll1Asterold$ • new 11lIgeEntltJ'[4] : IllIgeEntlty(] explO$10n$ - new IIlI,eEntlty[2J: IllIgeEnt t ty(] $MplllIge - new 1_lgeEottty(2] : I{(teate a randall n.-tler gener.tor ~ndOOI r.nd - new ~ndOOl( I; {fused to Ill\! ship t"'Porlrtly tnvulnerlble lo ng co 11 Is IonT1l1er - 0 : {fSr»f key tnput tracktng variabl es boolean keyLeft. keyRlght. keytljl. keyftre. keyB. keY(:
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Chapter 14 • Galactic War: Entity Management
,
.
........................
..,
publiC (>,l.cticll.r() I IIcal1 b.se G•• ,1 us' con~tructor iUper(fRAllHATE, SCREEHIIIDTH, SCREEHHEIGHT);
.
/
,
... yold ,1.Startup() 111 old the b.ckground lalge blckground· new laigeEntlty(thl~); blc kground. 1Old( ' b1uesp.ee. pn9 ' ) ; /lerute the ship sprite- f irst in the sprite list ~hiplalge[D]· new laigeEntlty(this); shi plalge(D]. 1old ("Sill cuM p. png-); sMlllalge(l] .. new laigeEntlty (th1s); sh1 Illalge( I]. 1old( "sh1 p_thrust. png") ;
M1 ..teclSprlte ship" new M1.teclSpr1te(t~ls. grlpllles(»; sh1 p. setSprl teT;rpe (SPklTl-SIlI' ) ; sh1 p. set1.ge(sh1 pl.ge[O]. get I..,e() ); shl p. setfra.1I1 dth ( sh1 p. l.gelll dthE}); ship.setfr••Helgh! ( shlp.1 ..geHelgh!(» ; shlp.setPosltlon(new Polnt20(SCREEHIIID1HI2. SCkEEHHU6HT/2); sh 1p. setA11 vee true) ; sh1 p. setState( STATl-MORItAll ; sprltes( ). Idd (sh1 p) ;
111 old the bUllet sprite '.ge !luI letl.ge" _ l.geEntlty(this); bulletlalge. 1old("p las_shot. png"); Illoid the uploslon ~prlte '.ge nploslons[O] .. new l.geEntlty(thh}; e~p I os I ons(O]. \old( "e~p' os, on .png"} ; e~p 1os1ons(l] .. new 1.lgeEntity (this) ; up1os1ons(l]. 1oad( " e~p 1os 1on2 .png-) ;
Enhancing Gala(ti( War IO.d th~ blq tst~rojd I.. ~U 5 tot.ll for 11nt n-O; n<5: Itt+) ( bl9Mt~rolds{n) - new l.. g~Entlt)'(thls): String fn _ Wuterold w+ lll+l) + ".png": b1 gAs terolds [n). laid (fn) : )
Illo.d th~ lledlu. asteroid luges 12 total) for 11nt n -0: n
1I10id the slNll ast~ro'd llNtes 13 total) for 11nt n - 0; n<3; 0++) ( ,.U,sterol ds [n] .. nell [lNg~(nt I t)'(thls ): String fn" ·,.all" + (n+l) + •. png W; s.lAsterol d,(n].l oadl fn) ; )
l10ld t~e tlnYlsterold I.. g~! (4 totall for lint n "0: n<'; 11++) ( tll1.ut~roldsh)" new IIN,~E.ntlt)'(tllls): Strln, fn" -lll\1w", 111+1) ... " .png-: lIl1Astuolds{n]. IOldlfn): lit reate the rando_ asteroid ,pr!tu for (lnt n -0; n
Game Loop Update and Screen Refre$h
Now let's tak~a look at some keyNents passed here from the Game c1ao;s. Remember, these methods were defined as ,,jl$lr(l(/ in Galle so that they would be implcmentl'tl here in th~ ckrh'ed sourc~ code fijI'. ~ ga1leTI-el!Uplllte() method is called from ..ithin the timed game loop thrad. ~ qI1leItefresh:Kreen() melhod is called from the appln updat~l) ('Vmt. I'm 1101 currmdy using g••Shutdownl), but it is a,~ if you IlffiIto dwl ~ befo~ the progr.am tOOs. Now let's take a look at figure 14.3. which shOW'S the game fairly early on in the run. The :wIme toggle'S a~ still available in the game, including collision
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Chapter 14 •
Galactic War: Entity Management
figure 14.3 The largeastereMds brtoak "" intosmallef ones. either when 1heyhit your shipOl'when \'OJ fire a plasma bolt.
testing and bOl.lnding-box display. There are four stages to deslroying an asteroid: • Large, detailed asteroids • Medium asteroid chunk> • Small asteroid pie<:es • Tiny asteroids I)Qn't let the tiny asteroids fool you-they will still damage your ship, and they can be destroyed by your guns. Speaking ofdamage, the game would be more fun if the ship's health were displayed somewhere on the screen-a good featurl.'" to add in the next chapter.
. .....................................................,
,
•
ga~eTjlledUpdate
event passed by gale engine
.old9a.Tlwdllpditt~()1
chKUnput();
' ga.Refr~shScreenevent
.... ",
,
.., , ..
p;1ssed by ga. engIne
,
"
,
..
" /
'Old ga.Refr eshScreen() ! Graphlcs2D g2d - graphlcs() : lIthe shIp Is alwa1s the fIrst sprite In the Hn ked lh t I.IllaatedSprl te $h1 P • (1dl1IWO tedSpr1 tel sprl tes( ) . get( 0) : IIdraw the badgro~nd g2d .drawllWOge( background. get lute( ).0.0. SU[EIIIHOTH·I. SCRHIIH£IGHT· I. this): IIgrlnt status lnforllitlon on the scr«n g2d. setCo1or(Co1or . WHITEJ : g2d.drawStrlng( · FPS: ' + fra-eRitteO.~. 10); long x - Hath. round( shlp.IlOS1 t 10n() .I(): 1ong 1 - Hitth. round! shl p. pos1t 1onO . Y( )) : g~d.d raIlStr lng( ' 5hlp: • + x +'.' + 1 . ~. 25) : g~d. d rallSt rl n; ( 'Hove a n; 1e, ' + Hath.round (ship . JI(I.eAng le( ))+90. 5. 40): gld.dra IlSt rl ng( ' Face angle: ' + Hath.round(sh1p.hcel.llgleOI. 5. 55); If (shlp.state( )--STATLIIORllAL) 92d.drawStr
256
Chapter 14 • Galactic War: Entity Management 92d. seteo Ior (Color. GREEN) : 92d.dr~wStrln9( " (OlLlSIOH TESTING " . SCREEHWIDTH-ISO . 2S):
1-*········..···-*·..··..··..··..··..····..···..····.. ·········..··········································1 • gameShutdown event passed by
void
g~lIeSnutdown(} I lion well, let the
g~rbage
ga~e
eng; ne
collector nave at It.
Updating and Drawing Sprites Next, let 's 13ke a look at the spri teUpd~te() and spr; teDraw() evenls, which are passed on by the Game class. The spriteOr; ng() event is also available here, but iI's not currently being used in the game. You would use this event to keep a sprite al ive if you wanted to keep it around by S<':lling al ive back 10 true . The game engine proces.scs all of the sprit...s in the linked list all10matically (by the gallic loop thread), Aner each sprite is updated, control is sent to sprite· Update() to give you a chance to fool around with the sprile if you n~...x1to. (It is passed as a parameter.) You can make any changes you want to the sprite, and those changes will be stored back in the linked list because you arc working with an object reference-the actual objl.'Ct in the linked list, not just a copy. This is truly where the sprite engine shows its power. You can fir{'" as many weapons as you wam, and they will strike an unknown number of .~pri1(·S, which will each blow up in an animated explosion-and the linked list keeps lrack of all theS<': detai ls for you . All we really have to do is put together a new scratch sprit{'", gil'e it an image from one of our global images, and then pop it off to the sprite lis!. This sprite will then automatically move around on the screen, rotate (if rotation is s<:t}, and animate (if frames exist), This new sprite will also be included in coll ision test ing. The engine allows you to determine whether a collision "sticks" by giving you control at the key point where a collision has occurred, passing both spriles 10 yo ur imp lementation of the spri teColl1 s1on() event. When I was first developing the engine, I thought il \vollld be too limiting to move all ofth{'" sprit{'"s into the list. I kept th{' ship outside the list for a while, and then realized that to truly make the internal sprite handl{'"r work the way it is
Enhandng Galactic War supposed to, you r~ally need to give it all of the sprites it needs to update, draw, and test for collision. When you get tired ofa sprite, just set its a 11ve property to false, and then the game engine will remove it from the list a few seconds later! Furthermore, as yOIl learned in the previous ,hapter, you can make use of the features in AnlliatedSpr lt e for limiting the lifetime of a sprite. By setting the lifespan of a sprite, yOIl can have it automatically krmillate after a c("rtain number of passes through the game loop. For instance, the "flaming plasma" projcrtiles fired from the ship are gi'-("n a lifetime of200 loops. The engine d("te<:ls whell the :lge is beyond the lifespan threshold, and then kills the sprite automatically! Figure 14,4 shows the game after all of the large asteroids h:lve been broken down into smalJ~r ones. The game is truly crazy at this point, wilh close to a hundred small asteroids floating around yuur ship on various random trajc<:tories! It's hard enough just to spin aud shoot frantically, I("t alone move around. I even h'ld \0 cheat \0 keep from getting blown up repeatedly! (I'll share the cheat with you at our next stop in this trip through the source code.)
Figure 14.4
The \h,p
~
OYeIWhelmed by ilIteroidl ilI'ld in need of some we3POfl upglades!
257
2S8
Chapter 14 • Galactic War: Entity Management
.
"
....................................................., , sprltelJpd.te en"t p.ssed by til. e"tlne
pub11 C YOld sprl teUpclilte(AnllOiltedSprl te sprite) I s.l tcM sprl te _sprlteT,pe ( 11 ( ClSe SPRITE-SKIP: IIIrp(sprlte): breilk: case SPRiTLBULLET : IIIrp( spr 1te}: brut: cilSe SPRITLUPLOSIOM: if
lsprlte_eur~trril.O••
sprlte_ toUlFr••sO- l 1 (
sprl te _uUll Yel fillu ) : )
brut: Cil se SPRI n StEROI O_BIG: cilse SPRiTE STEROIOJlEOIUM' cilse SPRln STE ROIO_SIlALL: Cil se SP RIn STERO I 0_T I HY : wilrp(sprlte): bruk:
f " •••••••••••••••••••••••••••••••••••••••••••••••••••
• sprl leOnv ewe"t PiiSSed by til. e"tlne • c.lled by t~e til. c1i1Ss .Her eilc~ sprite 1$ drilWll • to the 1(1~ iI chil"ce lOailnlp~lilte the sprite
....................................................., public yold sprlteOrilW(A"lai1tedSpr!te sp r ite)l if (s~owBou"ds) I 1f (sprHe,collided{) sp r i t e, drilwBou"d s (Co Ior , REO) :
else spri t e, dr ilwBou~ d s{ Co Ior ,BLUE) :
Enhaneing Galactie War
.
/
• sprtttDJtng tytnt puad b, 9u~ tngtnt • cilltd H~trl sprltt's Igt ruchts tu ltftspn • It .... Ich pot nt 1t lit 11 bt kt 1I
.....................................................
/
public .Gld sprlttO,IIIIJ(AnI..t
The m()$t important ""ent in the game is proNbly!he sprlt~GlllStGn() \'\'mt, ..ilkh is passed from the engine to your source eode automaticaUy. "The engine gots through the list ofactive sprites (when' the II tyt property is true) and teslli each one for collision with all the other spri tes in the list (ac""t for the same one-we don't want to have objects blow themselves up for no reason!).
Tah a look at figure 14.5, which shows the ship firing several volleys of flaming plasma bolts toward asteroids. There are several bolts traveling away from the
F;gur. I ..,S I"rojKliIes fired from the Vip ~ get pmed!llrol.9h the ~ __ wIwn they a6»
...........
259
260
Chapter 14 • Galactic War: Entity Management sh ip at various angles and ~ explosions thai are animating on the- S(r('('1l. Figure 14.5 shows sprite collision testing in progress.. Thce-nginc,as implemenled in the 6ne class and inhm led by 6i1hctlcllilr, goes through the- sprites and tests thtrn.a11 for collision-but that's ail it does. Look at the spritt countt"r in this figure-132 sprito! This number includes lht ship, bulku, asteroids, and explosions, and the- nurnbcr ~ and falls dynamically with the- gamtpby. (lbc: mgine- dears out unused sprites that havc " dial" ODCC' C'Vn')' second whm lht frame rate is calculated.) Thcu is no more logic going on behind the S(cn('$ than the- test for collision itself. The engi ne sim ply passes both sprites that have interacted to thc sprl teCo111· s 1on() method. At thi s poi nt, it's entirely up to you to decide what to do with the conflicting sprites. You can destroy them , have them bounce away from each other, or anything else. So all you have to do is figure out what kind s of spri tes have been passed to you through the spr1teColl1s10n() event. You can do this with your own predefined constants (defined as a static int in Java). Forexample, I have defined SPRITE-EXPLOSION for all explosions. Yes, explosion sprites are tC'$too for collision like C'·trything else-but we simply ignore them, let them play out, and then disappear. lbc value of each constant is nOI imponant, as long as each one is dilTerent. 5iIlCC' I defined each oflhe four types of asteroids wi th a stparate constant, I had to write a hdpc1" mnhod called 1s"sterold() to handle them all in tht same way whm they arc pas,soed through tht C'VCIlt handlers. Now, howabout that coot I promistd! WlItn I gt't inlO a lough spot in the-galne.
I hold down the kft or right arrow kty to spin while hitting bolh fire buttons (the Ctrl keys). This launches twice- as many volleys of plasma bolts, as Figure- 14.6 shows. {
. .....................................................
•
~prl
teCo111 s1on eve-nt
p~ssed
by gnt eng Ine
/
pub l iC voId sprl teColl151on(AnllMtedSprlte spr l. AnllatedSpr lte sprZ} I IIjullp out quickly 1f collistons are off if (lcol1 hlonTntlng) return: Iffigure out whilt type of sprite hilS collided swltcMsprl.sprlteTJpot(J) { cilSe SPRITE,..8ULLEi: IIdld bullet hit i1n nteroid? 1f (1 sAsterold(spr2. sprl teTypot( ) J) I sprl .uUlln{hlu):
Enhancing Galactic War
F;gu.. 1•.6 ~ IN>d> lwice
YlIU
a5
many boilS lMlg botIl CIr1 keys!
spr2.utAl he{f,l se): brukAste r old{spr2) : )
bru t; CHe SPRllLSHIP: IIdld Harold crHh 1nto the ship? If (l sJ.ste~l d ( lpr2.lpr1hTYPt()1l { If (spr I . IUh( I -- STATLlIOftIlAll { call1slonTl _r - SystIM.earrffttTllldtlll1l( I ; sprl. seth I11(:1 t1lftew Polnt20 (0. 01 1; doubl e x - Iprl.pollt1on O .Ill • 10; double y - Iprl.poslt1on O .YO • 10; stirtBlgEll.plos1on(new Polnt20 (x. y)l ; sprl. set5u1l (STATLEIP LOOI ~Gl ; sp r2.set.i.lln(hlse) : brukAste rold(spr2) : )
II-a t e ship tellPOrully Invulner' ble else if (sprl.lhh( 1-- STATLEIPLOOING ) { if (call1 l lonTI_r + 3000 <
261
262
Chapter 14 • Galactic War: Entity Management Systell.currentTlMfll111 II II { Ip r l.utSu te (STA n,.. .IlO11Mll ; }
I brnk:
Keyboard and Mouse Events
The keyboard and mouS(' handlers are not always used, but you must still implement them in your program. You might wonder, then. how is this allY better than just using the li$tenen d irectly in the game's source code file~ That's a good quation! Basically, we want to homogenize the ~cnts as much as possible. Note that the keyboard ~enu pas.s nothing but the key scan code, and the mouse evenu pas.s nothing at all- you must access the mouse infom\;ltion through the musePos and .auseButtons variables (wi th their associated acCes.llOr methods). Simply k,no",ing about a ke}t>o;.rd or mouse e-'enl isenough; we don't n«d all of the a1ra information that Java sends the program.
..
/
..................................................... • ;uleKey[)()Wn eoent passel! by gall! \,n;ln\,
public vo1d gaeKeyOolln(1nt keyCod el ( sllitchCkeyCcdel l case KeyEvent. YK.. LHT; key Left· true; brnk: use Keyhent. U ..RIGHT; keyRlght· trc\'; brnk; use KeyE.ent. YK.,UP; keyUp. trut: brnk; eHe KeyE.ent. YK..cownOL : kl!)'Flrt· true : brNk; CiS\' K\'yEv\'nt. VK....B: fltog;l\, boundIng recUn;lu showBound s· tsh0w8ounds:
bruk;
/
Enhancing Galactic War cue Ke,E vent .VILC, JJtonle colli s10n t esting eDlllsloftTntl~" leoll\sIOllTnt1ng; breit;
.
/
....................................................., publi c veld g ~ meXeyUp(lnt keyCodel I swltc Mk eyCodel I cHe h yEvenLVlLlEFT : keyleft· fi15e; bruk : cue Ke,Ev ent. WK.-RIGIH: h,RIgbt· fi15e; bruk: cue hlE ven t. VK.-UP: k.,Up·fi15e: bruk: USI tlyEven t. VK.-CONTROl: k" Flr e.filu: f1re8ullet{): br ei k:
• Mluse evenh PiHe4 by g._ ell
....................................................., ",bile void g.~ou$elloom() I I ",bIle void g.-eHou$eUpl I I I public void g. _ l\I)u$ellO'l( I I 1
Asteroid Manipulation Methods The asteroid$ are the mO$t complicated part orGalactic War. First orall, there arc !Clur types or asteroids in the game, each with several differenl images available ("'hich are chosen randomly when a new asteroid is created ). J have written
263
264
Chapter 14 • Galactic War: Entity Management
figure 14.1 Tht bculding bcae5 MIll «JIIi5oon
~
CMl SIilI be kIggIfd an
CIt
off in the game.
sevenl methods for working with asteroid$, mainly calJed from !he collision ~u thoot occur. The brgtt asteroids an: ~royd and repla«d by SmallCT asteroids, while iIIl apJOSKln is animated over !he old asteroid. Figure 14.7 shows the game with bounding boxe$turned on so you can s« the dimensions of each sprite in the game. Note how even the explosions have a bounding box-they an: included in collision testing as well, even though the game ignores them. All of the or iginal asteroids have been destroyed and replaced with increasingly smaller ones. If you wanl to grab wme powerups (so mething thaI will be added in the next cha pter ), you will have to be careful not to destroy all of the brger asteroids-the smaller ones are next to impossible to get around, and your shi p will get hosed by them in short order if you let the guns go carelessly. As a result of this gameplay factor, this gamt' involves somt' strategy. This section of cOlk marks t~ end of the gaITIt' t'ngine events. From this point forward, all of tht' rrK'Ihods an: custom progn.mmed and provKle tht' real g;tmqIby in Galactic War.
Enhancing Galactic War
.
,
..................................................... • bru t up In IS t erold In t o slNller pieces
/
pr'~lte ~014 b~. U sterol d ( An llN t e
sprit e ) I
sll ltch(sprHt.sprlttTlI.eOII cue SPRITLASTEROI(UIG , 'sp."", .-dhll u tero14s o~er t he old one sp'vnAsteroldlliprlh l i sp'vnAsUr01 d( spr1 tel i sp'vnAster01 d( sprl te l ; Idr," bl~ up10si0ll surUl9UpIos I OII( sprl te. pos Itl one I', brut: cue SPRITE..ASTEROIO_" EO Il.lH , lisp' ,," $all i l .sterOl4s over t he ol d one sp.vnAsterol d( sprl tel; sp'lII\A.s urold( sprl te) : spllIMsterold(sprlte) : II dr," sIN11 explosion s U rtSIH 11 Exp1osl one sprite. posl t Ion ( 1) : bruk; ci se S PRIT USTE ROI D_ SII~ ll , II s p.~n ti ny Ht er01ds over the ol d one splllnAs terotd (sprl te) : 5pllln~s terol d(5prl te) : 5plllnAs terold (5prl te) : IIdr lll slNll expl osion 5tartSIN11£xplos lone sprl te. pos I tl on( II : bru lr.; tlse $PRlTE..A$TE RDID_Tl NY, ISp.,,", r.nda. paver"p SpllmPOIIl!rllp(sprl te I: 'dn ll sull uploslon starts..11 Up1oil 0111iprl te. poil t I011 I I1: brelt:
. .....................................................
....................................................., • sp..... 1 SIlIlle r ISterold bHe
prlnte vol4 sp.....Aster01dIAni ..te
265
266
Chapter 14 •
Galactic War; Entity Manitgement
An1 ..tedSprl te 1St - new An1aatedSprlte(thls. grlphlcs(»: 1St. setA11 vel true) ; f Iset pseudo' randa- pos 1t 1on around source spr Ite 1nt w- sprl te. getBounds( ) .width: lnt h - sprlte.getBounds( I.helght: double x - sprUe. posl t 1onO •XO • wit + rand. nextlnt( 20) -40; double 1 - sprUe.posltl0l10. y() + h/2 + rand.nextlnt(20)-4D; ISt.setPosltlon(new Polnt2o(x,ll):
Ifset rotltlon and direction InglU 1St. setFaceAngle( rind. nutlnU36011 : 1St. sel.lloveAng le( rind. n",tlnU360 II : 1St. seUotitl onlllte( rand. nutlloubl,( II;
IIset velocitl based on IOI. .nt direct Ion doubl e ang - ut.lOleAngle( I - !lO: 60uble veh - calcAnglellovel(lng ): double vell - calcAnglelloveYling l: ut,seUeloc:1t, (new ~lnt20(ve" . v,I, )): llse t s_ slIe'speclflc propertlts sorl tch (sprl te, sprl teT,pe ( I I ( cue SPIIT£j.ST£JtOIO_"&: ut, "tSprl teT1JH!( S'IIT£....AST£IlllIOJl£Oll,ll l : IIplck OIIe of the ra~ astertlld 1.. ~s lnt I- ralld,lIeJltllUll; 1St. set l..ge(.edAsterolds [I). get I..ge( II : ast. setFrallell1 dUl (.eQshrolds [I J.• ldt~() I; 1St. setFralellelllht(.edAsterolds[I]. hel ghtll I : break; case SPlIT£j.STElOloJlEoIUM: ut. setSprl teT,Pt( SPlITUST£IlllIOJMA.LLI : lipid one of the rand.- Isterold 'lIagts I - rand. nextlnt( 31 ; 1St, "tlllage( s.l Alteral ds[1] .getl..g,( II: 1St, "Hr._Ill dtM s.l Asterol ds[ l].wl dtM I I : 1St. seHr._Hel ght (s.Usterol ds(1]. hel ght( II : br eak:
Enh~n(in9 G~lit(ti( W~r
us~
SIIMI Tl.ASHll:OIO_SIIAll : I5t. setSprltfTJ~lSUI Tl.ASTEIlOI O_T i Iff I : Ipic~ on~ of t ~. rarnlo.,ltuold i... g~s t· r. nd.nutlntU): Ist.s~tl.. g~(tnJAst~rolds(11.getlug~()) : 1St. s~tFrl-elfldth( tnJAst~rol ds[ 1] .wt dtM ) ) : ut. s~tFrlMHelght (tnyAstuol ds(l] • h~t ght( ) ) : b r ~ak:
I,:d t h~ new ISter( Id t< sprl test ) ••ddlut):
t~~
sprt t~ lIst
..................................................... • crute a und~ poIlerup.t th~ supplied sprt te loutton • ( t hls will be tllPle-e nted tn t ~ ~ n ~ xt chapter)
....................................................., ~rt
I
....................................................., Il'obl
• id cr•. l~~ ....steroidl new 'sterotd sp r ite . . nt ..tedSprt te 1St - n!'lf ....nt ..tedSprtte(thls. grlphlcs(»: 1St. setAl he(true); ut. setSpr t teTJpe( SPRITUSTERIlIIl..BIG) :
flcrelt~'
Iptck one of the r,nd-..sterotd i.ages int I · rlnd.nutlnUS): ut. set '.,ge( bllobteNltdsI1) .9ttl.. ge( ) I : ut .setFTI-ellt dtMbl90\5terolds[ t ). wi dth( I I : ut. setFruellelghUbl lob terolds[ I). Mlght( ) ): ISH to , und~ pcsl t 'on n the screen tnt ~ _ rlnd.nuUnt(SCUEIIWIOTlHZ8l; tnt J . rond.n.~tlnt(SCREENHEl6iH·IZ8): ut.setPosttlon(new PolntlO(x. J)l: Iset rOUl' on ,nd dt reet ion ,ngles
267
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Chapter 14 •
Galactic War: Entity Management
ut. sethceAngl e( rand. nextl nt(360) ): ut. setHoveAngl e( rand. next1nt(360) ): ut. setRotat t onR~te ( rud .nextOoub1e( » ; /1 set vel oc t ty b~ sed On ~velOf nt dI reet I0" double ang· ut,llOveAngle() - 90: doubl e velx. c~1 eAngl eHoveX(ug): double vely . c~1 cAngleHoveHug): ~st. setve IocHy (new Pol nt2D( ve lx, ve ly) ) ;
lIadd the new astero id to the sprite list sprl tes{) . ~dd(ut):
/
u
••••••
..................................................... • returns true H
p~ssed
sprite type is an asteroId type
/
prhate boole~n tsAsterold(ln t spriteType) ( sw1teh(sprtteType) { cue SPRITUSTEROID.,BIG: cue SPRITUSTEROIOJlEDlUH: cue SPRITUSTEROIO_SHALL: case SPR1TUSTEROIO_T1n: return true: dehult; return false:
Handling Multiple Key
Presses
I spent a lot of time trying to incorporate a multiple key-press syslem into the game engine itself, but this proved to be too troublesome. N, a result, the main game keeps track of key presses and releases using global boolean variables. Since only a handful of keys are ever used in an arcade-style game like this, a more complex form of key handler is not necessary. As il is implemented here, the engine calls a few even!S and passes the key code when a key is pressed or released so thaI you don'l have 10 bother decoding the KeyEvent, MouseEvent, or MooseMotlonEvent class.
.
/
..................................................... • process keys that
h~ve
been pressed
/
Enhancing Gala.cti< War pIobllc Yllld
c~ectlnput()
it .Inys t~e first sprite hll~e lhttd 1 ,t AIllNtedSprltt shlp· l AIlllMttdSprlte) sp rltu l ).gft(O); If (teyltft) { I/left ..rClW rlllltes s~lp left 5 degrHS shlp.setFiceAngle (shlp. hceAngle() - SIlIPROTATlO.); if (shlp.h ceAllg1e O < 0) s~lp.setflceA.llgle(360- SIlIPROfATlO.); It~t t~ip
I else If (keyRight) ( Il r ig~t arrow rlltates th fp right S degrees shlp.setflceAngle(shi p. hceAngle( ) • SHIPROTATlON); 11 (ship.flceAngle(l >36(}) shl p. setFlceMg1e( SHI PROfAT 10.) ;
11 Ue)'llp) ( lup Irrow Ipplles t~ ..... st til ship dt p. set 'lIge( lhl pl..,e[l).,etlllge( II ; IpplyThrustll;
I else Iiset s~ip iatge to noratl non-t~rU~I iatge shl p. set IlIge( shl pllNge[O]. get I., ge( I) ;
Moving the Spaceship
The sp.1uship in Gabelie War is rol3lffi usi ng the lrit and righl Jrrow keys, and thrusl is appliffi by pressing 1M up arrow by_ The IpplyThrust( Illt1.hod handle$
I~
acedenlion of t~ ship while k«ping I~ ship within a reasonabk
,docilY threshold•
...........
,
public ~llid applyl~ru~tl) ( lithe ~hip Is always the firs t ~prite in the 1in~ed li~t AnilNtedSpri te shlp· (AnllNtedSpritt)spri t es () .getIO); Ilup ,rrow add~ thrust III s~ip (1/ 10 nil .... ) speedl shlp.seUlllveAngll(shtp.hciWIgl,()· gO);
269
210
Chapter 14 • Galactic War: Entity Management fl calcuhte thl I aoo Y vel ocltl ba sld on angle double velK - shlp.velocltl( 1.1( I; velK +- calcAnglellovel(ihlp...,eAngleO) * ACCELERATION; If (nlK < ·10) nb.- ·10; lin H (nix> 10) velK -10; double nll - shlp.nlocltl( I. H I ; vel, +- calcAnglellonHlhlp...,eAn9leO) * ACCELERATlOI; If (nl, < ·10) nl, - ·10; IhlH (nl, > 10) nl, -10; sh1p.nUelocltl(new PolntlO(velx. vel,»);
Firing Weapons
The mOSl signifkanl area of improvement for Ihe game is in the weaponry dep.1Ttment, so some lime will be spent in Ihe ne~l ehapler adding powerups 10 the game. You will be able 10 grab powerup icons lhal arc dropped by exploding asteroids, which will Ihen enhaoce the ship in various ways. The (lIfTenl version of the game here has ll(){ changed from the previous chapter, except lhal il now fuJlctlons with the game engine. The Orl key is ~ to fire weapons, bul you can change this 10 ;lll(){!ler key if you want by eumining the key handlers.
.
/
• flrl a bullet trOll the shlp's poslt1011 aoo orlenut1on •• • ••• • •
~
••••u
uuu
"
u ,
public ,old flrellulletO I lithe ship 1s al n ,s the fIrst spr i te In the Il nkiKIl1 H AniutiKISpr1te ship - (AnlutiKISprltelsprltu( ).gltlO); IIc r eate t he new bullet spri te AnlutiKISprlte bUlllt - new AnlutedSprlte(thIS,grapMes(»: bull It. set luge (bull It luge. getluge( ) : bullet. setfrnellldtMbulletluge.wldtM I): bull et. setfruHlHII ght( bullet 'uge .hel gM( l ) ; bull It. sltSprl teT7pe( SPRITUULLETl : bullet. setAllle(true); buliit. sltLlfespan(200); bullet. setfaceAngle( shl p. hemgle( I ): bullet.setlloveAntle(shlp. hemgleO - 90); llse t t he bullet's stlrtll1
Enhancing Galactic War
double , . shlp.eenUr(). Y( I • bullet. 1..geHe19ht( lIZ: IMlllet.utPos1t1on(new Pol ntZDll.1I l: IIsft the IMlll et ' s ye1oc1tT double Ingle - ballet ..enAIl91e( I: dOllble s.. _ ealc:AnglellClnX(uglel* IULLE'CSPEEO: double SfY- ealc:AnglellClnY(uglel* IUlLET_SPEECl: bullet.seUeloelty(new 'OlntZO(SfX. Sfy)): lIadd IMlllet to the sprite list spr1 tts( l .Idd (1Ml1 1et):
Giv~ M~
Something to Blow Upl
There 3re two main methods for sta rling explosions. 1could hnve come up with a craftier way to do this, but I decidcd 10 just write two similar methods: one for initiating large explosions and another for smaller explosions. They usc images stored in the explosions array (of '_lgeEntlt1 objeclJl ). There are currently only two explosion animalio ns. The large explosion is used when you hit a large asltroid. The smaU explosion is drawn when you hil smallCT a5leroids.1 think the result looks prdty good. Because 1!lCTe are Q lot of mWI asteroids and bullets flying evay whidl .... y. you don'l ....nl too oomplex of an explO$ion sucking up lhe game's resources ..nrn Ibm: oould be a couple dottn such explosions animaling at a lime. QIeck out Figure .4.8. The large explosion's frames are 96)( 96 pixels in size and 1!lCTe are
LARGE EXPUlSION
SMALl. EXPLOSION
ftgure 1....
The two eq:hion .-a\lO'IS ~
_
br -.
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Chapter 1<1 •
Galactic War: Entity Management
16 frames; the small explosion has 8 frames, and each one is only40 x 40 pixels in size. The big explosion is used for the ship and large asteroids. This should be used sparingly because it is such a large image.
I····················································· ........................ , • hynch, big uploston It the PIssed loc,tlon ~
publiC "otd stutBiohplosion(Potntl1l potnUI Ilcrute I n
I····················································· • Ilunch, s.,11 uploslon.t the PIssed locltlon
.....................................................
/
pybl1c "otd stlrtwllhpiostonlPoint20 point) I IIcrelte I ne" exploston.t the pissed IOCltton Ant.atedSprlte expl • nn Ant,"tedSpriUltbls .grlpbics(); upl.setSprlteType(SPRITLEXPLOS10Ml; expl.setAI he(true); upl .utAn1.'.age(uploslons[1].geU.lge( ll: exp1. setTotll FraHs I8) ; exp1. setColu..sl.); exp1. setFrallCWl dtM.O) ; exp1. setFrl_HelghU.O); expl. setFrl_Del.y(2l; expl.setPosltlon(polnt); lI,dd the "
What You
Ha ~e
Learned
Additional Game Logk ~
lut method in the gaIl'll' iscalkd warp{ l,and it has l~ duty of making Spriles wnp around the edges of the screen (right, left, top, and bottom). This is kind of a slrange occurrence if you think about ii, but a lot of gal1le$ llSof' this technique. The iOO is that this makes an otherwise Slrnlll playing fidd appe;;tr larger because objects can just travel through etha-J/K'U behind t~ monitor and magically rnppe;;tron t~ Ol~rside, othelWUc' Ul1$Cl.thed. It helps to cont;Iin Ihe pmeplay when a scrolling pme world is not a gool for the gilme. f· · ..•••••••••••••••••••••••••••••••••••••••••••••••••
..................................................... • cause sprite to IlIrp around the edges of the serren
/
public >old wlrp(AnlwatedSpr lte spr) l IIcreHe so-e sho r tc~t variab les Int"· sp r. fra-eWldth()'1; Int h. SpT. fra-rHelght{ )'1: /I"Tap the sprlte around the scrHn edges If (spT.posltlonO.XO CO',, )
spr •pos Itl onl ). seU(SUUIllII OTM); ehe If (spr .posltl onD .XO ) SCREEIllIIOTll) SpT . pos Itl on{). setXI 0-,,); if hpr .posltl0110. YO CO·U SpT .pos I tlon{ J • utYl SCIEEIHE 16HT): ehe if hPT .posltlonO. YO > SCIUIHE IGHT) SpT . posl t lon{ J. utYIO'h):
What You Have learned This W;lS a code-heavy chapter that involved significant changes to the coding modt"l we'~e been following in each chaptt"r up to thi s point. Now that Galactic War is t"~ent -d rivt"n and makt"$ use of a sprite engine, the game has many more upgrade possibilities than it might have had before (where each new sprite had to bc implemented from scratch). Here are the key topics you learned: • How to creatt" an e'\'t"nt-drivt"n gilmt" engiM • How to
llSof' t~
new Ga. class
• How 10 handle all sprites unifonnly, regardkss of type • How 10 adapt Galactic War to an t"Ymt-drivm game
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Chapter 14 •
Galactic War: Ent ity Management
Review Questions The following questions will help you to determine how well you have learned the subjects dis<:ussro in this chapter. The answers are provided in Appendi~ A, "Chapter Quiz Answers." I . What is the name of the new game engine class developed in this chapter? 2. How many sprites can the new engine handle on the screen simultan~"Ously? 3. Which of the four key classes in the game engine handles image loading? 4. How many different asteroid sizes does the game use? 5. True or False: Collisions are handled inside the game engine. 6. What type of object is ani .. I..age, a private variable in ~nl l1atedSprite? 7. Which class is responsible for rendering a single frame of an animation in Ani Ilia tedSpr 1te? 8. What is the maximum velocity value for the player's spaceship? 9. Which class does the game/sprite engine pass in some of its events? 10. Wha t is the name of the support method in An1mHedSprite that returns a properly formed URL for a file to be loaded?
On Your Own The following exercise will help you to see how well you have integrated the new materia! in this chapter with your existing knowledge of Java game programming. There are curreotly two methods used to sta rt an o:plosion-a custom method for large explosions and another one for small explosions. lbese methods do the same thing, but they use a few different properties. How could yOIl revise one of them to handle both cases for a large or sma ll explosion with a si ngle method?
CHAPTER
15
GALACTIC WAR : FINISHING THE GAME
The lhings you have learned in this book all culminate in lhis lasl chapter involving Galactic War. The game will be enhanced, polished, and ready for a production environmenl althe end of this chapter. A111hat will remain to do is 10 package up the entire game, rl"SOUrCCS and all, into a JAR file for dislribulion on lhe web (which is covered in the neXl and final ch'lpler of the book). Here are lhe key topics of inlerest in this chapler: • Adding powerups to the game • Implemenling a global game state wilh a slarl and end screen • Polishing the game and preparing il for production
let's Talk about Pow erups Let's face it; Galaclic War is a difficuh game. !l's nearly impossible to dear lhe asteroids with the weapon we've bcrn using up to this point-a single peashooter, for the most part. I "",nt 10 totally enhance the gamc in lhis chapter and make it ready for primetime- for distribution on the web. To me<.1 thaI lofty goal, lhere are quite a few things to cover in this chapter. I'll itemiu what I'd like to accomplish: • Add powerups to upgrade lhe ship's weapons system • Add powerups to restore health and shields • Add powerups 10 gain extra score points
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Chapter 1S
Galactic War: Finishing the Game
--
_.
'*
'"
F;gu~ 1S.1 GilacIic Wl1f hilS
so: ciftmnI: ~ dill fI'Nno:t Ihe slip Md inaNw JCU iIO:ft.
Figure 15.I.shows the six po.....erup$ that will beadd«i to tlte PI1\(' in this chapter. Tip
The (ompIet! VI'rnon of Ill! ~ is ""ai!able on m, W!'bI.ite. ~_ I am (omjnui"lllC imprtM' Ill! galTll!, it may be SOITIl!'I'I'hal diffmnl by Ill! lilTll! yoo rud this.. Go hffl!: \W/W,jMrboUf.coml BeogiMi~.a.
Ship and Bonus-Point Powerups There are thrl'C' differrot po~p$ that simply inanse your $COK for 250, 500, and 1,000 points.. 'ThcK powerup$ are rdascd randomly when you datroy a liny asteroid-the bst stage of the asteroid's ckterioralion after the large, medium, and small slages. The shield powcrup will increase your shield strength by 1/4 (not Ihe full refill that you wcrt' expect ing!). Likewise, lhe co la can increases your sh ip's health by 1/4, up to the maximum value displayed in 'he health bar at the top oftlte screen. Figure 15.2 shows the Ihret' states the ship can take on duri llggameplay. Wail, the ship doesn't have any shidds! Olt, right; that's a fcatUK we'll add to tlte game in this chapter as wen.
Weapon Upgrades The .....eapon upgrade poowerup is by far the most interesting new feature of the game, and il is very .....e1come given how difficult it is 10 stay alive in this game! Yo u ca n earn up 10 fivc levels of weapon upgrades in this game. I had my son,
Ll't's Talk about Powerups lllRUSTERS
. ,, ,• ••
F"lgun! 15.2 ~ au now Ihrte modts tor lht ship: llOfII\lII, lhR5tels, ind shields.
0
, {;!
...
"
{;!
00. 0' 0 000
• .. ;; ; ;
••
, •
Vu
~
0
{;!
0
J
•
- - {;! - -
{;!
F1i Un! 15.3
The IiYe levels 01 WNJIOfI upgrades for
)'0'.1"
ship.
Jeremiah, help ~&sign thewrapon shown in Figure 15.3.
p;1t1fT1\$
for each
upgrad~, and
the result is
Th~
upgrades w~r~ implemented a little di!Tn"Cntly than our design h~re, bUllh~ result i~ unmistakable. The biggest difft'rcnce i~ upgradt' level fiv~: Rather than firing ~id~ to side, the twO addilionalshot5 go upward at a slight ;lllgle. I made this adjustment whilt' playing th~ gamt' wh~n it seemed to be morc cffe£livt' than firing thcm at 9O-
Standard WHpon Thestandard weapon is shown being fired in Figure 15.4. NOle lhesingle bullet kon in the upper-right cortlt'r of the scrl'en, ~howing the current weapon upgrade level.
WHpon Levef Two Th~
first wtlIpon upg.rack allows th~ ship to lir~ two shots at the Rme time, as shown in Figure 15.5. There aer now IWO bullet icol1$ al the upper·righl. After
277
278
Chapter 1S • Galactic War: Finishing the Game
Figu.. 15.4 The standanI wupon is J WIgle bulK.
Figure 15.5 Two bullets clefinilety 00
J
101 men
~l
lfl's Talk. about
~rups
play testing the g~me for a while, I decided to m~ke this the starting weafXln level. You can stilllo~ this by ge1t ing hit and then drop down to the standard weapon if you aren't careful Weapon Level Three
WeafXln upgrade level three allows the ship to fire three shots at the same time, as shown in Figure 15.6. There are now three bullet icons at the upper~righl. Weapon Level Four
The fourth weapon upgrade gives you four shots at a time, spreading out at slightly wider angles than the previous level, meting out ma"ive damage to the horde of asteroids, as shown in Figure 15.7. Weapon Level Five
Heavy gunner! Weapon levd five is truly ltaggering. delil'ering massive amounts of firepower to the ship. Take care, though-if you get hit, your ship is taken down a notch to level four again. The angles of spread at level five are slightly I'
279
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Chapter 15 • Galactic War: Finiih,ng the Game
Figure 15.7 ro.. shots at a time is good for 'tOO' SfIf-
,.
,
.
•.. , '
..-,.,' ,,
, ,
fjgure 15.8
,.,.
-
'"" • •
, ,. ,
•
..... -.'~
•
••
WNpon U19ide Itvd five res 'tOO' VIp sill: pro,Ktilel
En~rxing
Galactic War
Enhancing Galactic War I'm going to sta rt at the top of the GaLacticWar.java file and note Ihe changes roaM as ...~ move down through the source code. We'll take a look at a few ~ along the way to explain what's happening in the code, As you an mrly see in the pages to follow, the new game engine (via the Ga.... class) makes enhancements incredibly easy \0 add 10 the g.lll1e. Ti p If yau 1m _
yau
ope1\lP
.".
tlle
probkoms updMJng tlle sane code 'MIll the MW in... o.......ool:>, I ~
comPttt GM1Ic W. P'Ol'(l, Ioc".-rI ... lilt CD-ROM .. ~ t,
New Sprite Types The first change to the progr:llm involves adding some new sprite typedefinilions in GabcticWar.p.va. Near the top oflhe pragr.t.rn listing is a set of sprite types. Add the J>eW items shown in bold tUI. IIsprtte t ypes tnt SHlTE.5WIP -I: tnt SP.IH....ASHROIO_RI6 -10, tnt SP.ITE",lSHItOIOJlEDlLAt-ll, tnt SPRlTEJ.SJEIlOIO_SllAtl -12, fl~11 tnt SPRlTEJoSTEROIO_TlNY - 13: fl~ll tnt SHlTL8ULLET - 100: flnll tnt SPRITLEXPlOSION· 200: flnll tnt SnITLPOIfEIW'_SHIELD - 300: fhal In! S'UTLI'OIIEIWPJjUlTM· 301; flulln! snlTLPOVuuPJSO-302: ftnll tnt SPR ITE..-POIfERU L SOO· 303; flul t nt SPR ITLPOIIERUP_1000 _ 304: flul In! SPIITLJ'(lII(lU' _6UN _ 305 :
flnll flnll flnll flnll
New Game States To give Ihe g~ ll1 e Ihe ab ilily to start, play, and cnd (with the option 10 restart), we need 10 add some cond itional gameplay stales and make usc of Ihe pau$C pro~rty in the sprite engiDe (found in the 61.... class). Add the following lines jusl below the J>eW sprile definitions, above tnc toggle V;lI.ubles. ~ J>eW code is shown in bold. Jlgl.... I tltu
fl nil tnt lWlEJtENU• 0;
28\
282
Chapter IS • Galaaic War: finishing the <;,me
I""ogu.. 15.9
11ll' bile
KIftI'I
01 GlUcIic WlIl ~ Iht Uy
fln.11nt IWlUlUnllllt·l: fln.11nt &o\IIE....OJEa·!: /furjous toggles boolun showBounds· hlse: boolun coil islonTest lng - true:
When Iheg:une first starts up. youSttthe titlcscrecn, which ilimown in Figure IS.9. This screen shows 1M k£ys you pre:lli to conlrolIM ship.
New Sprite Images Now let's add some new sprite image definitions llSing the l~geEntltyclass. The ship has a new shield feature, and we have a whole bunch of new images for PQwerups and the updated user interface (such as Ihc hcahh and shield melers). Scroll down a bi t more 10 the block of code showing definitions for all of the laageEntlty obj«ts used in the game. Add til<: fleW (Ode shown in bold. (Note ...tso the minor change to the sh1plaa
/fddlne the juges IIsHl jn the gil., lugeEnt I ty backgrollnd; luge[nt 1ty bul1etlaage:
INgeElltlly{] b1gAsterolds • new INgeEnt 111[5J: INgeEnt1 ty[ J ..edAsterolds - new INgeEnt lty[lJ: lIligeEnt I ty[J s.lAs terol ds • ne. IN;eEnt !tIn J : I~ilgeEnt I ty[ J t n,As te roj ds • ne. I ~i1;eEnt Ity[ 4J : lIligeEntl ty( J uplosions· ne>! INgeEntl ty[2]; IMgeElltlty[] iM plMge· new l..geEntlty[3]: IMgeEnt1tl[] .... rl.. te .. new IMgeEntlty[l]: l..geEntlty blrFril_: l..geEnt1ty powrupSh1eld: IMgeEntlty powel'1lpl!eillU: IN;eEnt1tl pollu up2S0: 1.i1geEllt1tl po.u upSOO: INgeEntlt, poftruplOOO: l..geEnt1tl poftr up6ulI:
Health/ Shield Meters. S<.ore. Firepower. and Game State Variables Now let's add some g10lxll variables to keep tmck of such things as the ship's health, shield power, and game state, as well as more obvious things such as current score, high score, and weapon upgrade level. Add the following code after the image definitions, before the Rilldc.line. New code is shown in bold IIHillth/shleld .ters ilnd score lilt hulth· 20: lilt shield· 20: ll1tseo r e-O: 1lit hi ghs co re - 0 : ll1t f 1reponr- l ; lilt gl.State" GoIJIEJlUU: . . {crute I rind.. nUllber 'lI'neriltor Rilnd.. rind· new Rilnd..():
New Input Keys We need to add support for the new shield abililY. I've defined the Shift key 10 xtil'ate the ship's shield, but you may change Ihis key if you prefer a different one. Locate the key input trxking \'3riabks a few lines below the WI change you just made, and noll' the new \'3rUble added in bold..
284
Chaptff 1S •
Galactic WM: Finishing tt'H! GaIl'Il!'
The collision toggle and bounding box loggle are both still active in the game. Although they were use4 for test ing, they are now known as undocumented hidden CMtlI$ in the game!
I/s_ ~tJ Input tr,eUng urhble~ boolun ~eyLtft. keyRIgbt, ~eJUp. ~tyFlre.
~ey8, ~eyC.
hJSbleld;
Sound and Music Objects Immediatdy bdow the key tnclting variable definitions. ..dd the following code for the sound ..od music objects (or make sure the code looks like this, ifit differs in your souree code listing). Note the changes in bold. I/sortt
~eJ
boDlun
tnput
trllc~lng url.bte~
~eyLeft. ~eyRIgbt.
keJUp. hyFlre. hyl,
~eyC.
hyShleld;
1I10u~ eff~U'~ ....lle
"1 dISequence .us I c .. Mew "I dl Sequenc, ( ) ;
SOUMdCl Ip sboot· new SoundC l lp(): SoulldCl1p uploslOll- ntw SoundCllp():
Loading Med ia Files Unfortunately. all ofthese new feature:5come with a price-lood times. The game loads up very fast on your locIl PC, but can lake 10 to 20 s«onds to load from a wdJ,site, depending on your eonneaion.speed. All the images and sounds used in Ihis game arc fairly small because they are stored in the compressed PNG fomlat. lbe biggesl file is the background, which is about 300 KB, All remaining image and sound files are well under 100 KB, and mosl of them arc in the I to 10 KB range, which is C'X tremdy small indrtd. I suspect thaI without the background image and the large aplosion, lhe pme wouklload up almost iJl5tantly. When packaged into a JAR (wh ich is covered in the next chapter), the entire game is
600 KB. lc1's add all of the new code to garttSUrtuptl to load all of the new images. sounds, and music in tM game. lbcn arealso.some gamcpby-rdated changt$ in Ihis method that you should look out for. All new code and du:nges are high" Hghted in bold, void ga-eStartupO ( I/load sounds and ....Ile
Enhancing Galactic War
.,slc.l0.dl-..slc .•ld-); shoot.lold(-sboot.n-) ; exp I osl on. 1oldl "explode .IU-) ; l/lold the hnlth/sht.ld bars birfr•• " new 'aageEnt1t,lthh ); birfr••. loIdC-barfrl•• png-); blrhMge[OJ· new 'aageEntlt,Cthls); barl..ge[O].lo.dl-barJlnlth.png-); barl.age[!)" new l.. geEntl t,lth15); hrl..gt[l]. loadl"bar_shield. png-I; III o.d powel1olPS powen,pShleld" new 'aaIlIEnt1t,(thh); J/OVtrupShl11 d. load{ "powlrup_shl e I d2. png-) ; powerup~ell th .. new ' ..ge£ntlt,(thls); J/OVerupllnl tho loadl-llO"lrup_coh .pnll"); powerup250 " new 'aagIEnt1tJlthh); powerup2SO. loadl "POOlfl1olp_2SO .jlllg-) ; jIOWlrupSOO" _'aageEnt1t,lthh); powerup500. I oadl "poIffrup_500. png-); poweruplOOO" new l..geEntl t,lthls); powerup l OOO. lOld("powerup_lOOO.png"); powerupGun" new 'aalleEntlt,(thl s); ,-np&un. load( ",-I1oIP-llun. jlIIf-) ;
'Iold the blc
Il~t
""laatedSprl u I~lp" _ A,laattdSpr' tl Itllis. graphlcsC ): ~h1 p. letSpr' teTJP'f (SPRI T[_Sill P) : ship. IH[MIIII(shl plaageIO}.gel[.alle()}; ship. setrrneWldtll(shl p. laageWldth()): sll Ip. set r ra'e~elght( sll 1p. 'aage~I l.htC ) ) :
285
286
Chapter 15 • GaliKtlc War; Finishing the Game Shl p. setPos1t 1on( n!'ll Pol nt20(SCRHll\Il OTII/2. 5CREENIIE IGIlT /2) ) ; shlp.setAllve(true) ; I/Hut ship off IS lnvulllerlble ,hi p. setStlte( Sf UE..U'lOOll6) ; cOl11s1onT1.r - S,st_.CIlrrelltT1RlllI11s() : sprl tes() .•dd( ship) ; 1/10ld t~ b~11et sprite iN9t bul1etlNge - n!'ll INgeEnt lty(thl s): bulletlNge.lold( "plISNshot.png ") ; 1I10ld the explosion sprite lNge nelf INgeEMI ty(this); explos 10ns{0]. 1old{ 'expl oslo" .png"j; exp1os i ons( 1] - nelf 1•• geEnt 1ty (thi s) ; explosi ons(l]. lOld( 'explos lon2 .png ·) ; explo~ions(O] -
1/10.d the big uterold lNges (5 totll) for (Int n - 0; n<5; "..+) 1 bl~terolds(n]
-"til INge~nt1t,{th1s):
String fn - °lSterold· + ("..1) + " .PfI9 " ; bl~terolds(nJ.lold(fn) ; I 1/10ld thoe lledl ... UUrold INges (2 totlll for lint n - 0: n<2; .... ) I -.14tero l ds(n]INgeEntit,(tMs): String fn - ·lIedil.· + (...1) + " .png" : wdAHerolds[n]. 101d( fn); I I/lold the ~Nll uterold lNges (3 totll) for (Int n - 0; n<3; n++) ( sl1Asterolds{n] - nelf (NgeEntl ty(this); String fn - ·sNll" + (n+l) + • . png· ; s.1Asterol ds( n]. 1old (fn) ; I 1/10ld the tlnylSUrold II.ges (( tot.ll for(lntn - O;n(l;n.... )1 tnyAsterol4s(n] ~ nelf INgeEnt It,(thl s); String fn - °t In, " + (...ll .. ". png ": tnyA.sterolds[n]. loud(fn);
"til
Enhancing Galactic: War Jlsurl aff In plUse.ade PIUSe61.{);
Jlde lete th Is lIIod of code. wlt lch h, s beetl .,red to , notller -ethod , •••• .,.ed to resetG, -e /lcrelle the rlnda.l5l erold spdtes far lint n -0; n(AST£ROIOS; nH! ( Crelle,(slerold( !,
./
Game State Issue---Resetting the Game Tht pme us«! to just stan up with aSlt:roids flying at your ship, without any chance to prepare yourself! To avoid this problem, I've addtd all overall state system to the game, which now starts off in G,I.JIE..MENU mode. During normal gamcp lay, the slatc is G,I.JICPLAYlHG. When your ship blows up, the state is GAHL OYER. To make it possible to restart the game after dying (in which case, the high score is retaintd), we n«d a way to reset the key variables and objects- but t~ game should nol rdoad any files! Add the res et Gue {1 rnrthod just below g,.Surt up{J. pt'hiU «Ild rUlt6l.0 (
ffrUUrt tb,.slc saundtrtCk _slc .setlD09lftg{ true) : _slc.pllr{): Ifnwe the ship for tbe rut,rt Anl ..tedSprlU s hip · (Ani..UdSpriteJ sprlUs( ) .Get (O): Jlwl pe out t ilt sprite 115t to sU rt owerl IprlteS( ).clur( J : Jlldd tbe sned shIp to ttle sprite list shlp.sttPasltlon(_ Paln\lD{SCIHIIIIDTIlIl. SCIEElIIIEI&H1ll11 : shlp.s eUllwlltruel: shi p. sttSUtel STATLElPlOOI.G) : Col HslanT1.r. Slste•. currentTl.eII1l Il$() : shl p.$eUelacltl(ne~ PalntZD(O. Oll:
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Chapter lS • Galactic War, Finishing the Game spr1tes() ,add(sh1pl: IIcreate the rando.asterold sprites for (1nt n - 0: n
IIreset variables health - 20: sh1eld - 20: score - 0: flrepower - 2:
Detecting the Game-Over State The next method in the source code listing is galleTl.edUpdHe(), an event passed by the parent Game class. We need to add a bit of code here to handle the GAHLOVER state, which occurs when there is only one sprite left in the game-the ship. Figure 15.10 shows the game in this state after the health mder has dropped to zero.
Figure 15.10 II )'our f1ealrl1 drops to zero. tile game is r:NeI-YOU lose!
Enhancing Galactic War veld gUleTllledUpdate{) ( c~e<:U~put():
If
(lgl.'nsed() 1& sprltn().slzeO --1) { resetGl..(): gl.sute - &AII£.,..OVEI:
Screen Refresh Updates I've made a whole bunch of changes 10 lhe game screen, which is refreshed regularly during the applet's update(} and palnt(} events. I've removed lhe leSling/debugging displays, which show~'d the ship's vitals and Olher lhings. We wanllhe g.1me screen 10 look nice now, withoul any c1u1ter, lkcIuse there are so many changes involved, you may want 10 just delele any commented-oul code and rewrite th is method as indicaled. I will show new or changed code in bold and deleted code in ilalics.. veld
ga.Refres~Screen() Grap~lcs20
I '"
g2d -
1
grap~lcs():
CQWffJlT O/Ir THIS Btocr /IIiif' ship Is ,'.ars tllf' first sprfte fn tile Ifnted list AnINtedSprlte shfp - (Anf.. tedSprfte}sprltes( }.gel(OJ:
1l000~f OR
......,
{{drill t~e backgreund 92d.dr... IIlll9l'(backgrcu~ll.9l't [Iltgl'( ).O,O,SCRHM/10lH· I,SCRUM [00 ,1, this); 011 CQHHfNr our THIS BLocr Ilprlnt HHus fnferllHfen en the screen gU. setCclor(Color.IIHlTfJ: gU.drnStrfng(·(PS, ·.frlllellate(). 5. 10;, leng x -IIUh . round(shfp.pesl! fen().X()): leng y • II. th. round( sh f p. pes I! fen( ). Y( )); gld.dr'/fStrlng('Shfp: ' .. x" ', •• r, 5. l5J: gld. drallStr fng( 'Ho~e ,ngle: ' . Hath. round(sh f p. .,~e.4llg let J )+90. S. 40); gld.drilfStrlng(·(,cUrlgle: '.. Halh.NlIInd(shlp. ',ce.4llg1e( S. S5}; ff (shlp.sUte( )·-STATLIIORNAI} gld.dr'llStrlng(·St,le: IOmL', 5. 10J: else ff (ship. st,te( }--STArc..COHIOfOJ
11 '''llfH()~f
I'
n.
289
290
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~me
g2d.drlwStrfng( ·SUlt: COHIOCO ', S, 70); ..Is .. If (shfp.$l.t .. ()--STArCJXPUXUNG) g2d.drawStrfng( ·StH.. : flPLOOING', S. 70J: g2d.drawStrln'1(·SprH ..s: '+ sprH..s( ).slz..(), 5. 1l0); If (showBounds) f
'12d . s..Uo 10rfColor. '/lUll}; g2d.drlwStrlng("BOOltDfllG BOles ' , S(lIffJtllIDTH'ISO, 101;
i If (collfsfonr..HfngJ I '12d . seUolorlColor .GRUN); '12d. drawStrln'1( ' COLLIS/OIf TESTING', SCRfClfIiIOTH·/50, 25J;
......
/
IIwIIlt Is tile '11. sute! if (gl.Stlte -- 6AIIE../lEJIU) I g2d, ietFOIlt(new Font( "Verdln.-. FOlIt, BOLD. 36) l : g2d, ietCo 1or(Co I or •BUCK) : g2d ,druStrl ng (-&ALACT I CWAR-, 252. 202): g2d .setCo1or(new Color (200.30. 30}) : g2d.drIWSlr1ng(-6ALACTlC WAR-. 250. 200); lntll.-210.,/-15: g2d .setFOIIt(new FOIIt("'lI.sl1ew IloMn" • Font ,ITALIC r Font ,IOLO. 20»); g2d.setColor(Color. YELLOII): g2d.draWStrlng(-COWTROLS:". ll.. ++,*20); g2d.druStrlng("ROTATE - Left/Right ArroMS", x+20, ++,·20): g2d . drlwStr1 ngl "THRUST - Up Arrow" • x+20, ++,/*20): g2d,drawStr1ng("SHIELO - ShHt tel' (no scor1ng)", ll.+20. ++,'*20): g2d,drl.Str1ng("flR[ - Cui ke,-. ll.+20. ++,/*20); g2d, setColor(COlor ,IIHIU): 92d.draWStr1ng(-POII£IWPS IIICIDS£ flREPOWERI-, 240. 480): g2d,ietFont(new Font("Arlel - , Font.BOlO, 24»: g2d. setColor{Color ,OUNGE): g2d,drawStr1ng("Preu EMTER to stl rt-. 280. 510):
I else 11 (ga.State·· &.IJt£.ll:Unlll6) ( IIdraw Maltlllsbleld bars and .ters g2d,drawl.ge(bifFra.,getl.. ~(). SCRE£flllIDTlt - 132. 18. this): for (Int n ·D: n < health; n++l (
Enhancing Galactic: War tnt clJ<. SCaEElIlIlOTH - 13(1 ... n .. 5; gld.d.."llUge(bnllUge[O].getilUgeO. dx.lO. this); }
gld. dr,,, I.age( b' rFrue. get luge( ), SCREENVIOTH - 132. 33. th1 s ); for lint n _ 0, n
IIdrl" the bullet uptrldu for(lntn_O, n
,lse 1f (g••Stltt __ WLOVER) { g2d.sttFoatl_ Foatl'"1'tl'4,n,·. Font, BOLO. 36)): g2d.sttColorlnewColorl200. 30. 3(1); g2d.drlllStrlngl·WE ovn·. 270. loo); g2d.tetFont(ntw Font(·Arl 11·, Font.CEMHIt-8ASHlNE, 24)): g2d. tetCo1ore COlor. ORANGE) : g2d.drl"Strlngl·Pren ENHR to rUhrt", 260. 500);
Preparing to End The galileShutdo"n() event comes next. As you'll recull. this method was left empty in Ihe previous chapter, but now we need 10 IISC it properly. A wellbehaved la\"a program will free up resources before the program .-nds. In the casc of Galactic War, I pmer to rely on/av:l's buill-in g;tr'Ngc colltelor to free up I'OOUrccs automatically. HowcvfT, it is necessary 10 shut off I~ music and any SOIInd ril'tctscurrmlly playing before the applet ends becaliSC' sorndimes a MIDI sequence will keep playing after the game has ended.
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Chapter IS • Galactic War: Finishing the Game '01d gaIl\£'Sh utdown() I .uSlt.stopt): shoot.stopt) : expl oslo" .stopt):
Updating New Sprites Next up is the spri teUpdate( ) event method. There are a lot of new additions hen.' but no changes, as we have aillhese new powerups that need to be handled when they appear on the screen. The most imponant thing to do here is to warp the powerups along wilh everything else in the game. Then, in addition, the powerups need to wobble, or alternate the rotation back and fonh, so they stand out (rom the other sprites. Just as an example, take a look at Figure 15.11. This zoom -in of the ship firing shows how much the sprite engine is handling alone time. In this figure, J count 60 sprites in just this small ponion of the screen (which, granted, is where most o( the action is currently taking place). All of the asteroids are rotating by some random value. The flaming bullets arc rotated and adjusted every time they move along their paths. The ship rotates with user input. Every time you destroy a tiny
Figure 15.11 The
SCfet'O.
Enhancing Galactic War sprite, an cight.fr.ame animation is played. That 's a lot of action! It's a good thing we developed the sprite engine in the last chapter, or nom: of this would have been possible usi ng the old method of handling sprites with arrays. (Oh, and in cue you wen: wondering-the bullet5 have IIOt puscd through any of those tiny sprit~ they have just been SpawnN by the destruction of a larger sprite and wiD soon be annihilated by the incom ing fire.) rKW rode in sprt teUpd.tel), m
The
public yotd spr ItetJpdiltelAlltaltlNlSprl te sprite! , svltchlsprlte.SllrltdY\lf'I» l use SPRITLSHIP, v,rlllSllrtte), breit: ciln SPRITL8ULln, WilrlllSllrtte): brut: eise SPRITLEXPLOSION, t f l sp r t te.currentrriv() e~ sprite. tout Frilllesl)']) I sprite. seUI he(fiIlse), I bruk: cne SPRl TEJ,STEROID_BIG, case SfR ITEJ,S TE RO ID_MEO 1UM, case SfRITEJ,STE RO ID_S"ALL , case SfRITEJ,STEROIO_TlNY: virp( spri te): brut: cue SPRITLPONERUP_S"I ELO: cue SPRITLPONERUP..HULl1l: cue SPRITLl'OllERUPJSO: cue SPRITLP\lllERUP_SDO: cue SPRITLP\lllERtJPJOOO: cue SPRITLPOlIERtJP_6UI: Vill"p (sllrtte): lIalke powerup i1n t altlon wobbl e dOl/b l e ~t - spr t te.rotitlonRlte l), If (sp r1 te. filceAn91e() > 3501 ( sprlte.utlotltlonitllte(~t • ·1): sprl te. utFiceAntl el 350 ) :
cases to the
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Chapter 15 • Galactic War: Finishing the Game else If (sprite.hceAngleO <10) { spr1te.setRotat10nhte(rot· .1); spr1 te. setFlceAngl e( 10) ; }
brelt;
Grabbing Powerups Ncxl in the source code listing is the sprl teCo 11 I Slon() event. All we need to do here is handle all the new powerups that are in the game; this means that only the ship should collide with the powerups. I've moved the test for the collision testing toggle to the top of this method, out of the keyboard handling code, lx.'Cause it belongs here instead. Some new lines have been added to increase the score whenever a bullet hits an asteroid aJld to deal with collisions when the shield is up. Note the changes in bold, as usual. pub11 e vo1 d sprl teCo 11 is i on (An hila tedSpr I te spr1. An1 lIa tedSpr1 te spr2) l Iljullp out qu1ckly if eoll islons are off if (lcollhionTest1ng) return; I Ifi gu re out
IIh~t type of spri te ha s co11 I ded sll1tch(spr1.sprjteType()) l case SPRlTLBULLET, IId1d bullet hit an aster01d? if (isAsterold(spr2.sprjteType())} I bU llpScore(Sl: spr1 . setAl i ve(fal se): spr2. setAl ive(fa1 se): brea kAs te roj d(spr2) :
I
bruk: case SPRIH_SHiP, IIdld asteroid crash 1nto the ship? I f (I sAsterol d{ spr2. spri teType( ) )) I if (sprl.stateO·· STATLNORIIAU { 1f (keyShieldl { shield ·-1: }
el se { colI ls i onTjIller - Systell. current HlleH1 11 j s (1:
Enhancing Ga lactic War
spr1. utYelocitJ(n... Point211Cll. 011: double l- sprl.posHiOll() . IO - 10; double J - sprl.positiOfll) . YO 10; startB ighplosion(Mw Pofnt211Cl . Jll: sp r 1. set5ta t e( STA1E...EX'LOOI NI>l ; ff relluce 5hlp health Ifter a hit health·-l: if (health (0) ( galleStite - WE...OVER; )
Illou f1 repower when)'011 get hIt
flrepower-; 11 (ffreJlllftr (1) f1rej)Olf1!r - I;
I spr2 . setAl heC h l se} : b rea kA5tero i dC sp r2}:
IllOi ke s ~ i p t e"llo r l rl ))' 1 nval nerl b)e else if (spr l. stlteO -- STAiE...EX'LOOI NG) I 11 (coillsionlille r" J.OOO ( S)'ste..currentTi...lllis(») I sprl. setStateCSiATE....llRllAtl ;
I bre~k:
cue SPRITU'OMERU'_SIIIELO: 1f (spr2.sprlteTJpeC )--SPRITE...SIIIP I I shield"- S; If Cshield) to ) shield - to; sprl. setAl I u Cfa I $II; )
break; clle SPRI TE.,POWERUP~HEAL TH: 1f Csprt.sprltlTJpeC)--SPRITLSHIP) ( hulth"-S; If C/Iotalth) to) hulth - to; sprl.$ItAI1u(flhal; )
break:
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Chapter lS • Ga lactic War: Finishing the Game CGSf SPRITLPOWERUP_250: 1f (spr2.spr1teT~ pe{}--SPRITE...SHIP) { bu.pScore( 250} ; sprl.setA11 ve(hlse): )
break; cue SPR ITE...POWERUP_500; If (spr2.spr\teT~pe()--SPRITE...SHIP) { bu . pScore (500) ; sprl. setA1he(hl se}: )
brfGk: case SPRITLPOWERUP_1000: lf (spr2.sprlteType(J --SPRITE...SHIP) { bu.pScore< 1000}; sprl. seUI he
break: case SPRITLPOWERUP_GUN: 1f (spr2.spr1teT~pe(}--SPRITE...SHIP) { flrepower++; 1f (fl repower ) 5) fl repower - 5; sprl.setAll ve(false); )
break:
New Input Keys The game now uses the Shift key to eng:Jge the ship's shields and the Enter key to continue when the g:;nne is in the GAHE-"EN Uor GAHL OVER state. There's also a way to exit out of the game now: When the game is running, you can hit Escape to end the game (see Figure 15.1 2) . Here arc the new key handlers in bold. pu b11c voi d
9~I.eK e~Oown ( 1nt ke~ Code l
sw it cn ( ke ~ Code)
I
c~se K eyEveo t.~K..- LHT,
(
Enhancing Galactic War
F"ogUnI! 15.12 The bupf ~ ... end the game immediatfly and . . . you to
keyleft - true ; break; cue keyEven t. VK.JIGHT, keyRlght - true; br eak ; cue keyEvenLVICUP: keyUp - true; break; cue keyEnnLVICCONlROL; keyFlre-true; brUk; cue keyhenL¥ICB; II toggle boundlnll rKUnll1es $horiounds - ! sllowllounds; bruk; cue hyEwent. 'ICC; IIt0ll91e col11s1on testllll1 (011 hlonTestlnll - !collls1onTest 11ll1: break; CUI keJ'Eunt.VK..SHIFT: 11 (( l tlYUp) &I (sh1e l d ) 0)) hJ'Shfeld· true;
$~ - .
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Chapter 15 • Galactic War; Finishing the Game eln keySh1eld" (the; brelk: cue leyEnnt.VIl.EITER: 1f (gl_Stlu·.. &AltLIIElUl ( reset&l_O: res.-GI_(): glieStite" &AltEJUIIII6:
I lin 11 (gl_sutt! ... W£...OVU) { rentGl_Cl: res~_Cl:
gl_SUte· WLRUUII6: } (1$1
brelk, Klybent. VIl.ESUJ'E: 11 (gl_Stlte·· &AHE.JtuNMI16l I PIUse61_Cl: gl_Stlte· &AHLOVER:
I break:
Now leCs add a single new case 10 the gaJlleKeyUp() even t as well. pUb lIc void g~-eKeyUp(1nt keyCode) { switch(keyCode) ( cue KeyE_ent. YK..LEfT: keyLeft· hlse: brett: clse Key[ _ent. VIl.RIGIlT : teyRigkt - false: brUk: CiSe Keyhent. VIl.UP: keyUp - false: brUk: CiSe leyE_ent. VK..COI'lROL: kerFlre - false: flrehlletll: bre.k: cue ltYhtnt.fk....SHIFT: kerShl,ld" false:
Enhancing Galactic War
Spawning Powerups In the pr~ious chapter _ adckd a ~ method 10 the game ailed SlltlfllPover",pt I. which was kft empty at ttJ.c, lime. Due to that foresighl, _ do not havt to mak£ any dlangt:5to the brea kAsterot d( I mdhod that makt:5thisaillnsltad, here is the fully functional sp,lInPover\lpt I. Attbe lOP of tht codt, a random ptrttnlage: dettnnilltS whether the powerup is act",altyCTtaltd. 1havt it cumondy S('tiO 12 ptTctnt, which providts somt fair gameplay.lf)'Qu want to make Iht game mort difficult, reduce this value. To make il easier, increase it. Even though 12 percent dotsn't sound like very many powerups, keep in mind lh~l every I:lrge asteroid produces three "mediums," each of which products threc "smalls," t~ch of which produces threc "tinys" (see Figure 15.13). That's a whopping 27 tiny asteroids forevcry I:trge one, and since the game starts out with 10 large ones-well, you can do that kind of math. In a single game session, 12 percrnt will grnmlfe about 30 powerops! I think this value should be rtductd 10 about 20 to make the game a bi l more challrnging, but t
The sllallnPOIIerupl I method creates a singk PO"'"CT1lp sprite with 5011'It standard properties Ihat all powerups share, and thrn it $tIS the specilk properties Wiing a random number. Since there are six powerops, this random number determines the type of po_rup.
••
• ••
• •••
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Chapter 15 •
Galactic War:
F;ni~hin9
the Game
prlnte wo16 splllllPlM!rup(Anlute6SprUe sprlte) I lIo~11a fltll tll\1 spritel Iplt out I potterup lnt n" ran6 .nutlnttl00l: If 1ft) 12) return; line tMs powerup sprlte .....1..tedSprlte spr" new Anlute
spr .setRotit IOIIbut8}: spr. nt'oll tton( Iprl te. poll ttOll() ): 60ublt nlx - rIM.llelltDoullh(): 600b1e nl1" rancl.~utDollb1e(): Ipr.setYeloc1t1(new 'olnt20(nb. wely)): spr.setLlfesputlSOOl: spr .setAHn(true): lIentOlllze the sprlte based on potterup type IwUth(rln6.nutlnt(6» { cue 0: IItrnte I new shle16 powrup Iprlte spr. setluge( poolerupShl e16. get luge( l l ; Ipr. setSprl teType (SPRlTE",.POllERUP_SKIELO) ; Iprl test ) .166 (Ipr l ; brnk; tUe I: IItrnte I ~ew hn1th powerup I prlte spr .set luget poweruplleal th. getluge( l l ; spr .setSprl teType( SPRITE",.POllERUP-.HEALTil) : sprltl$t ).ld6{lpr): brnk: cue 2, lIerelte I nltll250'polnt poolerup sprlte Ipr •set l..gftpowerup250 .'lItluge( 1l : Ipr . setSprl teT)1lI(5PIITE",.POIIIERUPJ50): sprl tel () .166( Ipr): brelk; cue l, lIereltf I .... SOD'polnt power"p sprlte spr •set luge( powerupSOD .'lItlugel 1l : spr •setSprl teT)1lI(SPIITE.J'OIlERUP_SODI: sprl til t) .Iddl Ipr): break; eue4, lIerelte I new lOGO'polnt powenlP sprUe
Enhancing Gala(tk War $pr . set huge (powerupl 000 . getl.age( ) ) ; spr .setSprl te Type (SPRI TE.,.POWERUP_1000) ; sprltes() .add(sprl; breal;; elSe 5, I{create a new gun powerup sprite spr .setluge(powerupGun .getl.age()) ; s pr .setSprl teType (SPRI TE.,.POWERUP_GUN) ; sp r 1tes ( ) .add( sPrl ; breat;
Making the Shield Work Ahhough lhe key evenls turn the ship's shield on or ofT, the real work is done in the checklnputO method shown here. Let's l'lke a close-up look at lhe shield in a(tion. Figure 15.14 shows the ship bomb.uded Wilh asteroids, but the shield is taking all of the impact and protecting the ship (at least until the shield Tllns Ollt!), We also need 10 make a change to the new global game state so it will ignore input events unless the game is running-in olher words, it should ignore gameplay
Figure 15. 14 Thi' doloe'up view shows multi~ a'teroids impac1ing the ship', shields (aM bfeaking aparI iOlQ small asteroids Of jusl blowing up).
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Chapter 15 • Galactic War:
Fini~hing
the Game
input changes when in lhe G.o.HE_MENU or GAME_OVER stale. The new code is shown in bold. publ ie void eheeklnput() { if (galleState I- WE.....RUNNINGl return; lIthe ship is always the first ~prite in the linked list Ani lila tedSp rite s hi p - (An i la tedspri te) spri tes ( ) . get (0) ; if (~eyleft) ( Illeft arrow rotates ship left 5 degree~ s hi p. seO' aceAng I e( shi p. faceAng 1e() • SH I PROTATI ON) ; if (shIp . hceAngleO <0) ship.setfaceAng l e060·SHIPROTATIONl ;
I else If (hyRlght) { Ilright arrow rotates ship right 5 degree~ shi p.setfaceAngl e( shi p. faceAng I e (l + SH IPROTA Tl ON 1; if (ship. hceAngleO >360) shl P. setFaceAng 1e( SH I PROTATION) ;
I ifUeyUp) ( Ilup arrow applies thrust to ship shlp.setlmage( shipllllage[11. getlll~ge()); ~pplyThrust() ;
I else if (keyShleld) { shi p, seUlllage (shl plnge[Z]. get Inge( ) ) ;
I else Ilset ship illlage to norlllal non-thtu$! IlIIage s hi p, seUlllage (shl pl.age[O). getl.age ( 1) ;
Making Use of Weapon Upgrade Powerups The new weapon upgrades are aWL'SOllle, as you saw earlier in the chapter~ wouldn't you agree? This is the most interesting new gameplay feature, without a doubt. Each time you get a weapon upgrade, it adds another gun to your ship. However, if your ship gets hit, you Jose an upgrade, so it's pretty tough to keep those upgrades. The goo
Enhancing Galactic War
To support weapon upgrades, the code in nreBullet() has been completely rewril1en, and two ncw support mcthods were needed: adjustDlrectlonO and stodBullet() . The new "bullets" emerge (rom Ihe cemer o(the ship, and then spread out in various pallerns, oosed on the upgrade level (which is in a variable called ftrepower). rll show yo u the new codc for ftreBull et() first pub l ic void flreBullet() ( IIcrea t e t he new bullet sprit e Ani.~tedSpri te[] bull ets - new An t IHt edSprl te(6] ; slf1tch(firellOl'er) { cne 1: IIsingle shot bull e15[ 0] - stoc~Bull et ( ) ; spri test }. ~dd (bull ets(O] ) ; bru ~ ;
cue l: Ifdouble shot bul l e15[O] - stoc ~ Bullet{} ; ~dj ustDI r ect i on( bull ets [OJ, -4}; spri test }. ~dd (bull et$[O] ) : bul lets[l] - stoc~Bul1 e t(} ; adj ustOi r ect i On(bu1lets [1J, 4}; spri test }. ~dd (bull e15D] ) ; brea ~;
cue 3: IItripl e shot bul I e15(O] - stoc kBull et ( ) ; adj u$\Ol r ecti on(b"1Iets COl. spri test }.add (bul 1e15(O] ) ; bull e15(l] - stoc ~ Bu 11 etO ; spri test ) . ~dd (bull ets(l]) : bull e15(Z] - stockBull et(); adj "5101 rec t i On(b"1IelS [ll, spri test ) .add (bull e15(Z]) : break ; cne 4: 114-shot bull e15(O] - stockBu11 etC ) : adj "stOl r ect i on( b"1IelS [0], spri test ) .add (bull e15(O] ) ; bul le15(l] - stockBull et(}: adj "stOl r ecti on( bul IelS [1]. spri tes ( ) .add(bull e150] ) ; bul1et$(2] _ stockSullet(): adj "stOl r ecti on( b" I IelS ell.
-4);
4};
- 5) :
5):
- 10} ;
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Ch.pter 15 • Galaeti< War. finiihing the Game sprlUs( l.addlbulllh[Z]): bullth[3] - stocUullet(): Idjntlllrletlon(bulleu[3) . 10): sprlUs( ) .•ddlbulleu[3]): bruk: cue 5: IIS·shot bull,U[Il] - stoekBul1et(): Idjntlllrletlon(bulleh[Il). -6): sprl US( ). add l bull eh[Il]): bulltU[I] - stocUlIllet(): .djllstlllreetlon(bulleu[I].6); sprl US( ) .•dd(bul1 eh{ I)): buIIIU(Z] - stoeUulleU): .dj utlll reetl on (bull 1'1$(2]. '15): sp r ltu{ ) .• dd(bullets[Z]): bulltU(3] - stodBulletl): .djustOlreetlon(bulleu(3].IS): sprl tu( ) ••dd(bull ets[3)}: bill leU[4] - stocUlIlletO: .dj IIstOl reetl DIll bull ets(I]. -60 I: sprltesl) .ldd(blllleu(4]1: bulleh(5] .. stoekBlIlletO: .dj ustlll reet Ion l bull ets[5]. 60). sprltesl) .•dd(bullets[5]): bruk: }
shoot.pli1(I: Hen's the new .djllslOlrectlonO support I1ldhod. which basically just cuts down on the amount of codc in ftreBul leU) becaU5C this code is repeated for ~ry single bullet launched. This method is new, so you should add it ~low the ftreBullet(} method in your code listing for GalaeticWar.java. prIvate voId adjustOlreetlo n{AnlaatedSprlte sprlU, double Inglt) { .ngle - spr Ite. flceAngle() + Ingle: 11 {.nllle (01 In91e +- 360. 11 se 11 (Inlll' >360) In91 I' - .. 3fiO: sprl te. setF.ewgle( IIIg1 e): sprl te. seUlovWllle(sprl te. f.(Wlll el) -110) : .nllle - sprlte ..auM9le( I: double SYJl" calcAnllleltoveI(.nglel - BULLET_SPHO: double sv)' - ealeAnllleltouHlnglel- BULLECSPEEIl:
Enhancing Galactic War ,prite.seUelocity(new Po1nt2D(svJl, svy)): The Ilellt support method thaI helps ou t ftreBulletOis called stodBulletO. This melhod creales a slocl:: bullel sprite with ,Ill of the standard values need~>d 10 lire a single bulle! from the center of Ihe ship. The cuSlom \lpgrad~-d bulldS arc modified from t his slock build to create Ihl.'" v'lriolls firl.'"powu patterns you see in the game. This method returns a new AnlllatedSprlte objc<:l. prhate Ani.atedSprlte $toetBulletO ( lithe shIp Is always t~e f1ut sprite 1n t~e l1nted list AnllllltedSprite shl p - (Anl.atedSprttehprltu() ,get(O): An1ntedSpr1te bul _ nell An1I111tedSpr1te(t~t" bul . ,etA11 vet true) : bul.setlnge(bulletl.age.getlllllge(» : bul . setFrallCWI dt~ (bull etl.age. wt dt~ ( ) ); bul .setF rallCHet g~t(bu 11 et I. age. ~et g~t( ) ) : bul.setSprlteType(SPRITLBUllETl : bul .setL1fespan( 90) : bul .setFaceAng1e (shl p. faceAngl e( ) ); bul.setMoveAngle(shtp.f&ceAngle()· 90):
grap~lts(»:
({set the bullet's velocity double angl e - bu1.llOveAngl e () : double svx - ealcAngleHoveX(angle). BULLET_SPEElI; double svy - ealcJ.ngleHoveY(angle)· BULLET_SPEED; bul,setYeloclty(new Po1nt2D(su, SVy»; Ifset the bullet's ,tartlng pOs\t10n double Jl - shl p. center( ). XO . bu1, t.agelll dth( )/2; double y - shl p. center( ). Y() • bu1. t.aQeHel ghtl lf2; bul.setposttlon(new Polnt2D(x.y»: return bul:
Tallying the Score The final change to the Galactic War sourcecodl.'" is the addition of a new method calkd bumpScore(). 'Ibis is called in the colli sion routine to increase the player's sco re for every asteroid hit by a weapon. (Collisions with the ship don't Counl.)
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Chapter 15 • Galactic War: finishing the Game publtc ,old bupScorl(lnt h~h) ( score +. "-Icll: If (score> 1I1ghcorel 1I1911score· score:
What You Have learned This hasccrtalnlybecn an eyc-opcningchapter! It's amazing what is possible now that we have a sprite engine with such dynamic sprite-handling capabilities. It's now possible, as you have seen, to add new powerups and ent irely new gamepJay elements by simply add ing new cases to the swt tch statements in the key event methods, as well as adding Ihe few lines of code to load new images. The end result is now a fully polished, retail-quality game that's ready to take on any game in the web-ba5ed casual game market. Here's whal you have lnrMd: • How to add powerup$ to the game • How to enhance gameplay with new features • How to fire a spread of bullets al various angles • How 10 add a game Slate 10 give the game a start and an ending
Review Questions The following questions will help you to determine how well you have learned the subjects dUcus.sed in this chapter. The answns are provided in AppendiX A, " Chapter Qu~ Answen." I. What method in GalacticWar.jaVlll makes il possible 10 add powerups to the
game when a liny asteroid i$
dGtroyed~
2. What construct does lhe sprile engine (in Game.java) use 10 manage the sprites~
3. How many weapon upgrades are available now in Gabetie War? 4. How many differenl point-value powerups are Ihere in Ihe game? 5. What method in GaJaetkWar.java returns a slock bullel sprile ob;«t, which IS Ihen tweoaked to produce lhe upgraded bullet spreads!
On Your Own 6. How many different asteroid images are there in Galactic War? 7. If you wanted to add another weapon upgrade to the game, which method would you need to modify? 8. How many sprites is the sprite engine capable of handling at a time1 9. How many bullets are fired at a time with the fifth-level weapon upgrade? 10. What is the name of the static j nt that represents the game state when the game is running normally?
On Your Own There are so many possibilities with this game that I hardly know where to start. Since 1 consider the game finished in the sense that it is sufficiently stocked with featur~'S and gameplay elemellls to meet the goals I laid out for this book, I will just make some suggestions for the game. I would like to add a black hole that randomly crosses the screen from time to time, sucking in everything it touches. Wouldn't that be cool? Another great feature would be to have an alien spacecraft come onto the screen from time to time and shoot at the player. To keep the alien ship from getting hit by asteroids, the ship would engage a shield whenever it collides with an asteroid; otherwise, it would have to navigate through the asteroid field, and that's some code I would not care to write! Here is yet another idea to improve gameplay, since the game is really hard. The game could start off with a single big asteroid for L<..>vel I, and then add an additional big asteroid to each level the player completes. Although the game can handle an unlimited numocr of sprites, I would end the game at level 10 to keep it reasonable. Since the game currently just throws 10 asteroids at the player from the start, switching to a level-based system would greatly improve the fun factor! For the ultimate version of Galactic War, I refer you to a derivative applet available at www.starnightgame.com. where the team has posted a "space combat demo" of the gameplay in Swrflight: TIle Lost CO/OilY using the source code for Galactic War as a basis. You will find many aspects of this game that are £1miliar after working through the Galactic War project.
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CHAPTER 16
GALACTIC WAR: WEB DEPLOYMENT
This chapter finishes the book by explaining the all-importan t subje<:t of how to deploy your Java applet~based games to the web. I aSSllllle you already have some knowledge about how to usc FTPtocopyyourgame to a web server. I will show you how to prepare the applet so that it will TUn from your own web page! (Evcn if you use a free hosting service, if you can upload till.' files to your website, then very likely the game will run from your site.) You will also learn how to usc the Java Archi,'e 1001 to bundle your entire game (with class files and all media files together) in a lava Arch ive file. Here are the key topics in this chapter: • Packaging an applet in a Java Archive (JAR) • Using the JAR command-line program • Packaging Galactic War into a JAR file • Creating a hoSI HTf.,lllile for the applet
Packaging an Applet in a Java Archive (JAR) The Java Devdopment Kit (lDK) comes with a command-line tool ",lied jar.exe that is used to create Java Archive files. J/\Rs, as Ihey ar(' known, use the ZIP compression Illethod when storing files. JARs can greatly reduce the size of a Java applet- which is crucial for web deployment.
""
310
Chapter 16 • Galactic War: Web Deployment To use the JAR tool, you will need to open a command-prompt window (also known as a slwll in some operating systems), and then set the path to the 10K if it is not already set By default, on a Windows system, the JDK is inslalled al C:IProgram Files\java, and under this folder there will be a folder containing the lava Development Kit (JDK) and the lava Runlime Environment ORE). You need 10 S<.1the path to include Ihe \bin folder located in the 10K. This will differ depending on the version ofJDK you have inslalled. Currenlly on my syslem, Ihe jar.exe tool is located here: C:\Program FileslJava\jdk t.5.0_06\bin You can open the command prompi by going to Start, Program Files., Accessories. You can also run cmd.exe manually using Start, Run. On Linux and Mac systems, the 10K is usually already added 10 Ihe path when it is installed.
Using the jar .exe Program The JAR tool is a bit finicky. If you don't use the parameters exactly right and in the corred order, JAR will complain and fail to create the IAR file you wanted it to create. The order of the parameters should not be significant, but it is in this case. The general syntax ortlle JAR command can be viewed by typing JAR ar rile command line. The output looks something like Figure 16.1.
Crea ting a New JAR File
The parameters in this Help listing are de<:eptive. Not only should you llpt use the dash (-), bUi these parameters must be spe<:ified in a spedfic order. For instance, we use the c parameter to tclllAR to creatc a new JAR file. Bm this parameler I1u,SI be used along wilh f 10 specify Ihe file name. I can'l imagine a situ'ltion where you would want to use the JAR tool without using a IAR file, bUl I guess that's just me. After the cf parameters, you specify the JAR file name, and then the files you want to add. Here is an example: jar cf test.jar '.class This command will create a new JAR file called test jar and add all .class files found in Ihe current folder to the JAR file. Aft er doing so, if Ihe JAR 1001 successfully created the new JAR file, il will simply exit and not print anything oul. (So remember, no display equals no problems.)
Packaging an Apple! in a Java Archive (JAR)
Fi\lllre 16.1 \lerifyirlg mat the JAR program
is il'Iailable al the command prorr>pL
Listing the Contents of a JAR File
To display the contents of a JAR filt,
liSt
the tf par:amettT, like so:
jar tf test.jlr You an also include the • option to display the contents of the JAR filt with dtuils. This option also works when creating a new JAR file. hUI you mUSI he artful 10 include tht v option afttr tht c or t paramtltr. Here's an example of bot h cases: Jar c, f tesLjar '.class Jar tv f tesLjar
EJrtr.tctjng Files
from
a JAR
Fi~
You an extract a single filt or all lilts from a JAR filt using the ... option, like this: Jar xvf test. Jar ',.
Updating it JAR File
You can update a JAR file using the II parameter, Any files you specify will replace existing files in the archive, and any new files will be added.
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Chapter t6 •
Galactic War: Web Deployment
Jtr uot test.Jar HelloWo r td clin M.nifest Files Jav.l archiva an include: a manifest fik !Nt tdIs the' JRE the' ~ of the' .cbss fik it should nm (automatically) when il opms the JAR fik. Since this in fairiyrommon OCCUrTtnCle.:md manifest fiks ~ a cioch. it rnaU$ ~ to include: OM in a JAR fik !Nt wi1I run on the' web. The gmer.tI fortn:.lt of tilt manifest fik Joob JW> this:
.... tn·Clus: Ftlena. You should not ilKlude the .class extension. There are more options for manifest files, but this is the only Olle you neal to be cOlKemed with when the goal is to run an appld stored in a IAR file on the web. Be sure to add a blank line after this single line in the manifest file, or lhe JAR 1001 will complain. To use a manifest file WhCll creating a new archive, you can use the III parameter option. lust be sure that this is the Imt [eller in lhe options you include.
J ar
C~ f.
test . ja r lUn! fest. txt '. cl us '. ?"g
Hou ~ . . J.w.J cormtI.nIY's ~ WIth didlk rm ~!he JAR proopm _1lOt t*d MUG mINd, Un Oflf clol!S IlOt usuaIy drri: a hot be¥!fage ~ • JAR.
Packag ing Galactic War in a Java Archive The JAR program is fairiy easy 10 ~ olKe you grt used to its specific nquirelTICrltS. Now let's ~ this tool to pack.a~ Galactic War inlo a Jav.l archive. This will SOlve a lillle space and will keep the game together in a single file 50 you won·. leave any media files behind when copying the game or uploading illo a _!lsite. C&ution You must load fill'S in a ctftain W/l1 in \'OIK codlo 50 that the JRE
wi~
know how 10 reild t!ltm from
a JAR file when you have drployed the apple! to a ~ite. I·oe s~ you a couple of diffegl'S and other media files in th;s book. The method you must use when a game is deoployed in ~ JAIl uses the J~va. net. URL dass and !he getResource() method to aute a URl that \'011 can pass to !he appropiaIe .... <;f sound loader. The getResou rce ( ) method is available from thi s. getel a55 (J. This mtthod wiI Cll're(tIy puI a rnetilo • hom ttw loaI fiI. 'Y'~ or from ;I JAR fiI. whrn leCUl'Ce5 ;Ire sand wilhin a JAR. 11M is an eumpIe: ~Rl
urI- thls.getClanlJ.j)etResouru{fl1el\;l.);
Packaging an Applet in a Java Archive (JAR) The fim ordl'T of business is to copy your project foldn- to a new location so you don'. a«idenlally mess up the original. Essentially, this ~ foldn- contains the run-time fib for me game-the .class fib and all assc1S. Reviewing the Pr'oj«t Fi/e$ Now let's create a Java archi'l< to con lain the fib needed by this game. l1J<, manifest.lXt file and index.hlml file (covn-ed nat) arc found in the GalacticWar foldtr. I have copied all of the Galactic War media and class files into a folder called GalaeticWar\project. Included are 30 image (PNG) files. two audio files, and one MIDI file. In addition, we have these nine lava class files: • AnimatedSprite.class • BaseG:mleEntity.class • Game.class • lmageEnlity.class • Point2D.class • Sprite.class • GabcticWar.dass • MidiSequmce.dass • SoundOip.class These files wn-e compiled using Java SF.. 6. That's a lot of files for a single game! The last thing I want to do is deploy this gamt to a web stever by copying all 42 files along with index.html, although that is definitely a workable option. In fact, ;fyou just edit the HTML file (which you'll learn to do here shortly), you Cln simply copy these files to a website and run the game over the web. But a Java archive works so much kller, and it saVC$ some space too.
Building the Java Archive Using the CD command in the command prompt, 1''1< changed the current
folder 10 \Beginning Java\chapterI2\G;oI
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Chapter 16 • Galactic War: Web Dep loyment
' ' ' ' _ "', _ ,.""..... ......".. . ,..'......,.,. ,. f..'- t_, 0, --... _ , ."" lm: ::: 11m ."' "",... ",.... ,,,., " -_,, . .. ~'"
.. , _
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-.
.
~'"
>l_• • •• • •
~:::l;;:; .,'1 _ ,,,,,..
_
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....
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• m"o>
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".,... ...,"
-~
.
,-
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figure 16.2 Listiog the contents of the GaladicWar Iokle,. files are located. I've copied all of Ihe class and media files to a subfolder called project to keep things tidy. So, all I h~ve in this m~in G~laclicWar folder are index.htm!, manifesuxt. and the projecl subfolder (see Figure 16.2). The manifesl.lxt file for Galaclic War conlains this line: Mal n·Cl ass, G!la el i cWH This tells the jRE which of the .class files 10 open up and start runn ing after opening the JAR file. (Ik sure to include a blank line after the Mai n·Class property line.) You will need to use an optional parameter of the JAR program that lets you specify a subfolder where the actual files are located. You don't want to just tell it to include .Iprojectl·.· bc<:.lUse that will add .Iprojeclto the internal structure of the JAR file. Instead, you want to grab all the files inside of .Iprojecl, bUI not include the folder name. The option is C (uppercase is important). Here's the command to create the GalaclicWar.jar file: ja r cvflll Ga I ac t I cllar . jar 'un1f es I . tx I . C proj eCI •
This line tells JAR to create a new java archive called GalacticWar.jar, to include the manifest informalion stored in manifest.txt, to use the projeCI subfolder, and
Creating an HTML Host File for Your Applet
Figure 16.3 Cn>.~ng
the deployable JAR role
to add all files in Ihat subfolder to the JAR file. Figure \6.3 shows the output of the command. If thes<' additional steps get on your nerves, just lump everything together in a single folder and fun the JAR program in the same folder as all your Java projcrt's files, without using the Coption, like so: j ar c.fll
G~l acticWar
.jar lIal'll hst. txt •. '
Creating an HTMl Host File for Your Applet HTML is short for Hyper/ext Markrlp ulIIgllIIge, and it is the w;lter nowing through the world wide web. To run a Java applet on the web, you have to ellllmithe applet inside a webpage. This involves creating an HTML file with an 
