Making 8-bit Arcade Games in C

225 Pages·2017·3.79 MB·English

by  Steven Hugg

MAKING 8-BIT ARCADE
GAMES IN C
An 8bitworkshop Book
by Steven Hugg
Making 8-Bit Arcade Games in C
Copyright©2017byStevenHugg
All rights reserved. No part of this book may be reproduced
withoutwrittenpermissionfromtheauthor.
Firstprinting: April2017
Disclaimer
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ofthisbook,thepublisherandauthorassumenoresponsibility
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Making 8-Bit Arcade Games in C is an independent publication
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Contents
Preface . . . . . . . . . . . . . . . . . . . . . . . . . . . . . ix
Whyreadthisbook? . . . . . . . . . . . . . . . . . . . . ix
Whyfocusonarcadegames? . . . . . . . . . . . . . . ix
Whichhardwarewasmostinfluential? . . . . . . . . . x
WhyuseConan8-bitplatform? . . . . . . . . . . . . . xi
1 CPUBasics . . . . . . . . . . . . . . . . . . . . . . . . . 1
1.1 Bits,Bytes,andBinary . . . . . . . . . . . . . . . 1
1.2 HexadecimalNotation . . . . . . . . . . . . . . . 2
1.3 Signedvs. UnsignedBytes . . . . . . . . . . . . . 3
1.4 IntegerOverflowandArithmetic . . . . . . . . . . 4
1.5 TheCPUandtheBus . . . . . . . . . . . . . . . . 4
1.6 CPUInstructions . . . . . . . . . . . . . . . . . . . 6
2 TheZ80CPU . . . . . . . . . . . . . . . . . . . . . . . . 8
2.1 Registers . . . . . . . . . . . . . . . . . . . . . . . 9
2.2 ReadingandWritingMemory . . . . . . . . . . . . 11
2.3 FlagsandBranching . . . . . . . . . . . . . . . . 12
2.4 Stack . . . . . . . . . . . . . . . . . . . . . . . . . 15
2.5 LogicalOperations . . . . . . . . . . . . . . . . . 16
3 Hello8-bitCWorld . . . . . . . . . . . . . . . . . . . . . 18
3.1 PreprocessorandCompiler . . . . . . . . . . . . . 18
3.2 Assembler . . . . . . . . . . . . . . . . . . . . . . 21
3.3 Linker . . . . . . . . . . . . . . . . . . . . . . . . . 22
3.4 ROMImage . . . . . . . . . . . . . . . . . . . . . . 24
4 SomeCExamples . . . . . . . . . . . . . . . . . . . . . 25
iii
Contents
5 The8bitworkshopCIDE . . . . . . . . . . . . . . . . . . 30
5.1 DebugWindow . . . . . . . . . . . . . . . . . . . . 33
6 TheVICDualHardware . . . . . . . . . . . . . . . . . . 34
6.1 History . . . . . . . . . . . . . . . . . . . . . . . . 34
6.2 MemoryMap . . . . . . . . . . . . . . . . . . . . . 35
6.3 Video . . . . . . . . . . . . . . . . . . . . . . . . . 35
6.4 Colors . . . . . . . . . . . . . . . . . . . . . . . . . 38
6.5 Typedefs . . . . . . . . . . . . . . . . . . . . . . . 40
6.6 AMinimalMainFunction . . . . . . . . . . . . . . 41
6.7 CRoutines . . . . . . . . . . . . . . . . . . . . . . 43
6.8 Controllers . . . . . . . . . . . . . . . . . . . . . . 44
6.9 Z80EntryRoutine . . . . . . . . . . . . . . . . . . 46
7 SiegeGame . . . . . . . . . . . . . . . . . . . . . . . . . 47
7.1 DataStructures . . . . . . . . . . . . . . . . . . . 48
7.2 MainFunction . . . . . . . . . . . . . . . . . . . . 49
8 ShiftandRotate . . . . . . . . . . . . . . . . . . . . . . 57
8.1 ShiftOperations . . . . . . . . . . . . . . . . . . . 57
9 TheProgrammableSoundGenerator . . . . . . . . . . 60
9.1 TheAY-3-8910PSG . . . . . . . . . . . . . . . . . 61
9.2 InlineFunctions . . . . . . . . . . . . . . . . . . . 65
10 Binary-CodedDecimal. . . . . . . . . . . . . . . . . . . 66
11 Pointers . . . . . . . . . . . . . . . . . . . . . . . . . . . 68
11.1 APointerisaTypedMemoryAddress . . . . . . . 68
11.2 APointerisaReferenceToAnotherVariable . . . 69
11.3 APointerisaString . . . . . . . . . . . . . . . . . 69
11.4 APointerisanArray... SortOf . . . . . . . . . . . 70
11.5 APointerisanExtraReturnValue . . . . . . . . . 71
12 TheMidway8080Hardware . . . . . . . . . . . . . . . 72
12.1 History . . . . . . . . . . . . . . . . . . . . . . . . 72
12.2 MemoryMap . . . . . . . . . . . . . . . . . . . . . 73
12.3 Graphics . . . . . . . . . . . . . . . . . . . . . . . 73
12.4 Drawvs. Erasevs. XOR . . . . . . . . . . . . . . . 75
iv
Contents
12.5 DrawingText . . . . . . . . . . . . . . . . . . . . . 77
12.6 Pixel-AccurateSpriteShifting . . . . . . . . . . . 78
12.7 WatchdogTimer . . . . . . . . . . . . . . . . . . . 80
13 Game: CosmicImpalas . . . . . . . . . . . . . . . . . . 81
13.1 GameData . . . . . . . . . . . . . . . . . . . . . . 81
13.2 TheGameLoop . . . . . . . . . . . . . . . . . . . 83
13.3 CollisionDetection. . . . . . . . . . . . . . . . . . 86
13.4 AnimatinganExplosion . . . . . . . . . . . . . . . 89
14 Interrupts . . . . . . . . . . . . . . . . . . . . . . . . . . 91
14.1 Interrupts . . . . . . . . . . . . . . . . . . . . . . . 91
15 Randomness . . . . . . . . . . . . . . . . . . . . . . . . 95
15.1 GaloisLFSR . . . . . . . . . . . . . . . . . . . . . . 96
15.2 Entropy . . . . . . . . . . . . . . . . . . . . . . . . 97
16 InitializingMemory . . . . . . . . . . . . . . . . . . . . 98
16.1 Initializedvs. Uninitializedvs. Const . . . . . . . 98
16.2 InitializingMemory . . . . . . . . . . . . . . . . . 100
16.3 InitializingStringsvs. Arrays . . . . . . . . . . . . 101
17 TheGalaxianHardware . . . . . . . . . . . . . . . . . . 102
17.1 History . . . . . . . . . . . . . . . . . . . . . . . . 102
17.2 MemoryMap . . . . . . . . . . . . . . . . . . . . . 104
17.3 OtherSpecialAddresses . . . . . . . . . . . . . . 108
17.4 GraphicsROMs . . . . . . . . . . . . . . . . . . . . 109
17.5 Sound . . . . . . . . . . . . . . . . . . . . . . . . . 109
17.6 WhenNottoUsememset() . . . . . . . . . . . . . 110
18 Game: Solarian . . . . . . . . . . . . . . . . . . . . . . 111
18.1 DrawingTilesvs. Sprites . . . . . . . . . . . . . . 113
18.2 Attack! . . . . . . . . . . . . . . . . . . . . . . . . 115
18.3 DirectionsandTrig . . . . . . . . . . . . . . . . . 117
18.4 AlienBehavior . . . . . . . . . . . . . . . . . . . . 119
18.5 ReturningToFormation . . . . . . . . . . . . . . . 120
18.6 Missiles . . . . . . . . . . . . . . . . . . . . . . . . 121
18.7 BlowingUpAliens . . . . . . . . . . . . . . . . . . 122
18.8 GameSound . . . . . . . . . . . . . . . . . . . . . 123
v
Contents
18.9 KeepinginSyncwithInterrupts . . . . . . . . . . 124
19 MakingMusic . . . . . . . . . . . . . . . . . . . . . . . . 126
19.1 HittingtheRightNote . . . . . . . . . . . . . . . . 126
19.2 LayingouttheScore . . . . . . . . . . . . . . . . 127
19.3 SwingingwiththeTempo . . . . . . . . . . . . . . 128
19.4 ComposingtheMusic . . . . . . . . . . . . . . . . 130
19.5 NeedSomeMIDIFiles? . . . . . . . . . . . . . . . 130
19.6 Scramble/FroggerSoundBoard . . . . . . . . . . 131
20 IntegersandYou . . . . . . . . . . . . . . . . . . . . . . 132
20.1 PowersofTwo . . . . . . . . . . . . . . . . . . . . 132
20.2 UnsignedComparisons . . . . . . . . . . . . . . . 134
21 TheAtariVectorHardware . . . . . . . . . . . . . . . . 135
21.1 History . . . . . . . . . . . . . . . . . . . . . . . . 135
21.2 HowVectorMonitorsWork . . . . . . . . . . . . . 136
21.3 AnalogVectorGenerator(AVG) . . . . . . . . . . 137
21.4 Z80MemoryMap . . . . . . . . . . . . . . . . . . 140
21.5 AVGCRoutines. . . . . . . . . . . . . . . . . . . . 141
22 3-DVectors . . . . . . . . . . . . . . . . . . . . . . . . . 144
22.1 3DTypes . . . . . . . . . . . . . . . . . . . . . . . 144
22.2 SineandCosine . . . . . . . . . . . . . . . . . . . 146
22.3 WireframeModels . . . . . . . . . . . . . . . . . . 148
22.4 Transformation . . . . . . . . . . . . . . . . . . . 150
22.5 TheMultBox . . . . . . . . . . . . . . . . . . . . . 150
23 Game: CrowdedOrbit . . . . . . . . . . . . . . . . . . . 152
23.1 ShapePrerendering . . . . . . . . . . . . . . . . . 152
23.2 Actors . . . . . . . . . . . . . . . . . . . . . . . . . 154
23.3 DrawingActors . . . . . . . . . . . . . . . . . . . . 155
23.4 MovingActors . . . . . . . . . . . . . . . . . . . . 156
23.5 AllocatingMemorywithmalloc() . . . . . . . . . . 157
23.6 LinkedLists . . . . . . . . . . . . . . . . . . . . . . 158
23.7 FunctionPointers . . . . . . . . . . . . . . . . . . 160
23.8 DeletingObjects . . . . . . . . . . . . . . . . . . . 161
23.9 CollisionDetection. . . . . . . . . . . . . . . . . . 162
23.10TheMainLoop . . . . . . . . . . . . . . . . . . . . 163
vi
Contents
24 ThePOKEYSoundChip . . . . . . . . . . . . . . . . . . 166
24.1 MemoryMap . . . . . . . . . . . . . . . . . . . . . 167
24.2 AUDCTLBitMap . . . . . . . . . . . . . . . . . . . 167
24.3 AUDCxBitMap . . . . . . . . . . . . . . . . . . . . 167
24.4 SettingAUDFFrequency . . . . . . . . . . . . . . 168
24.5 POKEYMusic . . . . . . . . . . . . . . . . . . . . . 169
25 MiscellaneousCTopics . . . . . . . . . . . . . . . . . . 170
25.1 Unions . . . . . . . . . . . . . . . . . . . . . . . . 170
25.2 BigNumbers . . . . . . . . . . . . . . . . . . . . . 171
25.3 AdvancedLoopHandling . . . . . . . . . . . . . . 171
25.4 OperatorPrecedence . . . . . . . . . . . . . . . . 172
26 WilliamsHardware. . . . . . . . . . . . . . . . . . . . . 173
26.1 History . . . . . . . . . . . . . . . . . . . . . . . . 173
26.2 MemoryMap . . . . . . . . . . . . . . . . . . . . . 174
26.3 BankswitchedRAM/ROM . . . . . . . . . . . . . . 175
26.4 VideoFrameBuffer . . . . . . . . . . . . . . . . . 175
26.5 Palette . . . . . . . . . . . . . . . . . . . . . . . . 176
26.6 BitBlitter . . . . . . . . . . . . . . . . . . . . . . . 177
26.7 BlittingtoPixelBoundaries . . . . . . . . . . . . . 182
26.8 OtherHardwareLocations . . . . . . . . . . . . . 182
26.9 WhenNottoUsememset() . . . . . . . . . . . . . 183
27 WilliamsSprites . . . . . . . . . . . . . . . . . . . . . . 184
27.1 KeepingTrackofObjects . . . . . . . . . . . . . . 184
27.2 GettingRidofFlicker . . . . . . . . . . . . . . . . 185
27.3 CollisionDetection. . . . . . . . . . . . . . . . . . 187
27.4 Clipping . . . . . . . . . . . . . . . . . . . . . . . . 189
27.5 GettingByWith8Bits . . . . . . . . . . . . . . . . 189
28 Run-LengthEncoding . . . . . . . . . . . . . . . . . . . 190
29 WilliamsSound. . . . . . . . . . . . . . . . . . . . . . . 193
29.1 TheSWAVESystem . . . . . . . . . . . . . . . . . 194
29.2 TriggeringSoundsfromtheMainCPU . . . . . . 196
30 ImportingAssets . . . . . . . . . . . . . . . . . . . . . . 197
30.1 Installing8bitworkshopTools . . . . . . . . . . . 197
vii
Contents
30.2 GraphicsTools . . . . . . . . . . . . . . . . . . . . 200
30.3 SoundTools . . . . . . . . . . . . . . . . . . . . . 201
30.4 Third-PartyTools . . . . . . . . . . . . . . . . . . 201
30.5 FreeArt . . . . . . . . . . . . . . . . . . . . . . . . 201
30.6 Using8bitworkshopOffline . . . . . . . . . . . . . 202
31 DistributingYourGame . . . . . . . . . . . . . . . . . . 203
31.1 MakingROMFiles . . . . . . . . . . . . . . . . . . 203
31.2 PlayingonActualHardware . . . . . . . . . . . . 204
AppendixA:Troubleshooting . . . . . . . . . . . . . . . . . i
ProgrammerError . . . . . . . . . . . . . . . . . . . . . i
CompilerOddities . . . . . . . . . . . . . . . . . . . . . ii
Bibliography . . . . . . . . . . . . . . . . . . . . . . . . . . iii
Index . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . v
viii
Preface
Why read this book?
1. You want to learn about the internals of Golden Age
arcadegames.
2. You want to experience what it would have been like to
program these games if you had access to an advanced 8-
bitCcompiler.
3. You want to learn C on devices with slow CPUs and little
RAM.
You’ll learn all about the hardware of late 1970s-early 1980s
arcade games, and we’ll create a few simple games with the C
programminglanguagealongtheway.
Why focus on arcade games?
The arcade games developed in the late 1970s to early 1980s
demonstrate a wide range of capabilities that evolved over a
relatively short period of time. Memory and ROM space got
bigger, and video hardware got more sophisticated. Sound
evolvedtoo,frombleepsandbloopstoFMandspeechsynthesis.
These architectures were even more stripped down than per-
sonalcomputersofthetime,insomeways. Thingslikeextensi-
bility and ease of programming were not design criteria. All of
the magic was in the video hardware and sound board, which
wereafewyearsaheadoftechnologyavailableforthehome.
ix
Whichhardwarewasmostinfluential?
All of the system architectures described in this book were
used for more than one title. Some games were developed
by the original manufacturer or their licensees, but some were
developed unofficially — “bootlegs,” in other words. Bootleg
vendorscouldeasilyduplicatethePCB,madeeasierbythefact
that most arcade games included their own schematic in the
servicemanual. Thenitwasamatterofreverse-engineeringthe
originalROMandadaptingtothenewhardware.
Emulator developers have pretty much figured out the hard-
ware by now, but with this book you can experience the thrill
of writing your own “unauthorized” homebrew game for an
obsoletehardwareplatform!
Which hardware was most influential?
We’re going to focus on five distinct arcade platforms — hard-
warethatwasrepurposedforseveraldifferentgames. Eachwas
influentualorgroundbreakinginitsownway:
Midway 8080 (1975-1980): Developed by Dave Nutting Asso-
ciates, this platform’s 7 kilobyte frame buffer not only powered
thehugelyinfluentialSpaceInvaders,butalsoacoupleofdozen
other games. Credited as the first arcade platform that used a
microprocessor.
VIC Dual (Sega/Gremlin, 1977-1981): A tile-based Z80 plat-
form that drove 20 titles, including some of the first RGB color
games. Includedforitssimplicityandhistoricvalue.
Galaxianhardware(Namco,1979-1984): Galaxianwasinfluen-
tialgameforitsvividRGBcolor, smoothsprites, andsparkling
starfield background. It influenced or formed the basis of
severalotherhardwaredesigns,includingPac-Man,Frogger,and
DonkeyKong.
Atarivectorhardware(Atari,1979-1985): Themostsuccessful
vector-basedplatformstartedinblack-and-white(LunarLander)
andlatermovedtocolor(Tempest,StarWars). ItusedaMotorola
6502 or 6809 CPU with custom hardware to draw vectors and
calcuate3Dtransformations.
x