Game Development in Eight Bits

Presented at Beer City Code (Grand Rapids, MI, June 1, 2019).

Transcript

1. GAME DEVELOPMENT 
 IN EIGHT BITS Kevin Zurawel | https://famicom.party
3. A.K.A.
 “STUPID NES TRICKS”
4. WHAT IS A “NES”?
5. NINTENDO ENTERTAINMENT SYSTEM (1985)
6. DONKEY KONG (Arcade, 1981)
7. ATARI VCS / 2600 (1977)
8. COMBAT (ATARI VCS, 1977)
9. $871.00
 + labor 
 + shipping (~$2600+ in 2019) MISSILE COMMAND (ATARI, 1980)
10. TARGET PRICE:
 ¥9800 $40 (1980)
 $120 (2019)
11. NES TECH SPECS ➤ MOS Technologies 6502 CPU (1.79MHz) ➤ Custom Ricoh “Picture Processing Unit”
 (256x240 resolution, 64 colors) ➤ Custom Ricoh “Audio Processing Unit”
 embedded in CPU (five tone generators)
12. NES TECH SPECS ➤ 2 KB work RAM +
 2KB video RAM ➤ No permanent storage ➤ Read-only cartridges;
 32KB code, 8KB graphics data
13. WHAT IS “8-BIT”?
14. “Bit: a binary digit,
 representing either a 0 or 1.
15. Number of bits Possible values 1 2 2 4 3 8 4 16 5 32 6 64 7 128 8 256
16. “8-Bit: A CPU architecture based on registers, address buses, or data buses of that size.
17. As far as the NES is concerned, everything is a number between zero and 255.
18. LET’S DIG IN!
19. DRAWING GRAPHICS
20. 256 pixels wide
 × 240 pixels tall
21. 256 pixels wide
 × 240 pixels tall 61,440 pixels
 per screen
22. 256 pixels wide
 × 240 pixels tall 61,440 pixels
 per screen ÷ 4 pixels per byte
23. 256 pixels wide
 × 240 pixels tall 61,440 pixels
 per screen ÷ 4 pixels per byte 15 KB
 per screen
24. 256 pixels wide
 × 240 pixels tall 61,440 pixels
 per screen ÷ 4 pixels per byte 15 KB
 per screen (!!!)
25. PROBLEM #1 How do you draw a screen of graphics
 in less than 2KB?
26. SOLUTION: GET ABSTRACT
28. BACKGROUND SPRITES
29. BACKGROUNDS
30. BACKGROUNDS
31. BACKGROUNDS 32 x 30 grid of tiles 8x8 pixels per tile 960 tiles per screen 1 byte per tile
32. BACKGROUNDS 32 x 30 grid of tiles 8x8 pixels per tile 960 tiles per screen 1 byte per tile 960 bytes
 per screen
33. PATTERN TABLES (“8KB GRAPHICS DATA”)
34. WHERE’S THE COLOR?
35. 64 POSSIBLE COLORS
38. SPRITES
39. SPRITES 256 bytes of sprite RAM
 ÷ 4 bytes per sprite 
 (tile #, x/y, palette #) 64 sprites at a time
40. …AND ONE MORE THING No more than 8 sprites
 visible per scanline
42. PROBLEM #2 How do you show a lot of action
 with only 8 sprites per line?
43. SOLUTION: FLICKERING
44. SOLUTION: FLICKERING
46. GOING BEYOND 
 ONE SCREEN:
 LEVEL STORAGE
48. 14 screens of graphics
 × 960 bytes per screen ~13 KB graphics data
49. 14 screens of graphics
 × 960 bytes per screen ~13 KB graphics data … for World 1-1 alone
53. ×4 !!!
54. PROBLEM #3 How do you store a big game
 in 32KB or less?
55. 1. MAKE USE OF DEFAULT COLOR 228
 non-default 
 tiles
 
 (23.75% of
 the screen)
56. 2. MAKE USE OF REPEATED META-OBJECTS Instead of 24 tiles, store “pipe, height 6” and write code that draws pipes
57. 3. USE BASIC COMPRESSION (RUN-LENGTH ENCODING) Instead of storing 96 tiles, store “brick tile repeats 32 times” for three rows
58. SUPER MARIO BROS.: GET EVEN MORE ABSTRACT "set decoration” (3 screens wide)
59. { {
60. ;level 1–1 
 L_GroundArea6: .db $50, $21
 .db $07, $81, $47, $24, $57, $00, $63, $01, $77, $01
 .db $c9, $71, $68, $f2, $e7, $73, $97, $fb, $06, $83 
 .db $5c, $01, $d7, $22, $e7, $00, $03, $a7, $6c, $02 
 .db $b3, $22, $e3, $01, $e7, $07, $47, $a0, $57, $06 
 .db $a7, $01, $d3, $00, $d7, $01, $07, $81, $67, $20 
 .db $93, $22, $03, $a3, $1c, $61, $17, $21, $6f, $33 
 .db $c7, $63, $d8, $62, $e9, $61, $fa, $60, $4f, $b3 
 .db $87, $63, $9c, $01, $b7, $63, $c8, $62, $d9, $61 
 .db $ea, $60, $39, $f1, $87, $21, $a7, $01, $b7, $20 
 .db $39, $f1, $5f, $38, $6d, $c1, $af, $26
 .db $fd World 1-1… in 101 bytes! "I AM ERROR", p.131
61. ;level 1–1 
 L_GroundArea6: .db $50, $21
 .db $07, $81, $47, $24, $57, $00, $63, $01, $77, $01
 .db $c9, $71, $68, $f2, $e7, $73, $97, $fb, $06, $83 
 .db $5c, $01, $d7, $22, $e7, $00, $03, $a7, $6c, $02 
 .db $b3, $22, $e3, $01, $e7, $07, $47, $a0, $57, $06 
 .db $a7, $01, $d3, $00, $d7, $01, $07, $81, $67, $20 
 .db $93, $22, $03, $a3, $1c, $61, $17, $21, $6f, $33 
 .db $c7, $63, $d8, $62, $e9, $61, $fa, $60, $4f, $b3 
 .db $87, $63, $9c, $01, $b7, $63, $c8, $62, $d9, $61 
 .db $ea, $60, $39, $f1, $87, $21, $a7, $01, $b7, $20 
 .db $39, $f1, $5f, $38, $6d, $c1, $af, $26
 .db $fd World 1-1… in 101 bytes! Header Footer "I AM ERROR", p.131
62. ;level 1–1 
 L_GroundArea6: .db $50, $21
 .db $07, $81, $47, $24, $57, $00, $63, $01, $77, $01
 .db $c9, $71, $68, $f2, $e7, $73, $97, $fb, $06, $83 
 .db $5c, $01, $d7, $22, $e7, $00, $03, $a7, $6c, $02 
 .db $b3, $22, $e3, $01, $e7, $07, $47, $a0, $57, $06 
 .db $a7, $01, $d3, $00, $d7, $01, $07, $81, $67, $20 
 .db $93, $22, $03, $a3, $1c, $61, $17, $21, $6f, $33 
 .db $c7, $63, $d8, $62, $e9, $61, $fa, $60, $4f, $b3 
 .db $87, $63, $9c, $01, $b7, $63, $c8, $62, $d9, $61 
 .db $ea, $60, $39, $f1, $87, $21, $a7, $01, $b7, $20 
 .db $39, $f1, $5f, $38, $6d, $c1, $af, $26
 .db $fd World 1-1… in 101 bytes! Header Footer Byte pairs (screen location, metatile) "I AM ERROR", p.131
63. Byte pair Column/ Row Description $07, $81 0, 7 (start new screen) 
 "?" block w/ coin $47, $24 4, 7 row of bricks, length 4 $57, $00 5, 7 "?" block 
 w/ power-up item $63, $01 6, 3 "?" block w/ coin "I AM ERROR", p.133
64. A DIFFERENT APPROACH: PITFALL! (ATARI 2600, 1982) 256 screens 4KB cartridge size 128 bytes RAM
65. “RANDOM” LEVEL GENERATION Use a random number generator algorithm with a fixed seed value
 to generate a predictable
 (and reversible!) stream of bytes Algorithm + seed: 50 bytes
66. https://www.youtube.com/watch?v=MBT1OK6VAIU
67. 8-BIT PHYSICS
68. THE “STANDARD” 2D JUMP ALGORITHM Height at time t = 
 vertical velocity + (acceleration from gravity2 / 2)
69. MATH ON THE 6502 CPU ADC SBC ASL LSR Add (with Carry)
 Subtract (with Carry)
 Arithmetic Shift Left
 (“multiply by 2”) Logical Shift Right
 (“divide by 2”)
70. PROBLEM #4 How do you handle jump physics with only addition and subtraction?
71. SOLUTION: DON’T USE PHYSICS ➤ When player presses jump button,
 check if player is on the ground ➤ If yes, move player up n pixels per frame ➤ Stop moving up when default jump height reached ➤ Then, move player down n pixels per frame ➤ Check for collision with the ground
72. MORE PHYSICS: ACCELERATION
73. MORE PHYSICS: ACCELERATION
74. PROBLEM #5 How do you give objects realistic
 acceleration without physics?
75. SUB-PIXEL POSITIONING (“8.8 FIXED-POINT” FORMAT) Represent sprite positions with two bytes ➤ Actual pixel position on screen (0-255) ➤ Fraction of a pixel offset (0-255) Two bytes for X, two bytes for Y
 Calculate X and Y movement separately
76. if (on_ground) { if (button_a) velocity_y = -500; // jump if (dpad_left) velocity_x -= 5; // accelerate left if (dpad_right) velocity_x += 5; // accelerate right } position_x += velocity_x; resolve_horizontal_collision(); position_y += velocity_y; resolve_vertical_collision(); velocity_y += 10; // apply gravity http://forums.nesdev.com/viewtopic.php?f=2&t=12434
77. EVEN MORE PHYSICS:
 COLLISION DETECTION
78. CONSIDER CONTRA (1988)…
81. https://ericleong.me/research/circle-circle/
82. PROBLEM #6 How do you handle collisions 
 between lots of objects in real-time?
83. Image by Allan Blomquist,
 http://tomorrowcorporation.com/posts/retro-game-internals-contra-collision-detection
84. “A POSTERIORI” COLLISION DETECTION WITH WALL EJECTION
85. “A POSTERIORI” COLLISION DETECTION WITH WALL EJECTION
86. RANDOM NUMBERS
91. “Math.floor(
 Math.random() * 255
 ); - JavaScript
92. Math.random() Call the operating system’s
 random number generator
93. THE NES DOESN’T HAVE A RANDOM NUMBER GENERATOR.
94. PROBLEM #7 How do you make random numbers
 without a system-wide RNG?
95. THE TETRIS SOLUTION: DO IT WITH MATH 16-bit Fibonacci linear feedback shift register 
 (LFSR) (XOR bits 1 and 9, store in bit 16, shift right) https://meatfighter.com/nintendotetrisai/#Picking_Tetriminos
97. NASIR GEBELLI http://allincolorforaquarter.blogspot.ca/2015/08/nasir-gebelli-and-early-days-of- sirius.html
98. THE FINAL FANTASY SOLUTION: USE A LOOKUP TABLE AE D0 38 8A ED 60 DB 72 5C 59 27 D8 0A 4A F4 34 08 A9 C3 96 56 3B F1 55 F8 6B 31 EF 6D 28 AC 41 68 1E 2A C1 E5 8F 50 F5 3E 7B B7 4C 14 39 12 CD B2 62 8B 82 3C BA 63 85 3A 17 B8 2E B5 BE 20 CB 46 51 2C CF 03 78 53 97 06 69 EB 77 86 E6 EA 74 0C 21 E2 40 D4 5A 3D C7 2B 94 D5 8C 44 FD EE D2 43 00 BB FA C6 1D 98 A0 D3 54 5F 5E DC A8 00 AF 93 A1 E1 6C 04 DE B6 D7 36 16 C5 C8 C4 E4 0F 02 AB E8 33 99 73 11 6A 09 67 F3 FF A2 DF 32 0E 1F 0D 90 25 64 75 B3 65 2F C9 B0 DA 5D 9F EC 29 CE E3 F0 91 7A 58 45 24 1C 47 A4 89 18 2D CC BD 6F 80 F6 81 22 E9 07 70 FB DD AD 35 A6 61 B4 A3 FE B1 30 4B 15 48 6E 4F 5B 13 9C 83 92 01 C2 19 7F 1A 1B 71 B9 3F 4E 9B BF 9E 87 0B 10 57 F2 26 79 9A 05 C0 E0 F7 4D 7D CA 52 9D F9 BC AA FC 8D 7E D1 A5 42 E7 D6 76 A7 84 8E 66 7C 23 88 37 49 D9
100. “Contra has a single global 8-bit value that it uses as the source of randomness throughout the game. …[T]he next random value is generated by spinning in a tight loop during the time that the game is idle and waiting for the next display frame to begin. -Allan Blomquist THE CONTRA SOLUTION: DO SOME REALLY FAST MATH, ALL THE TIME
101. SAVING PROGRESS
104. PROBLEM #8 How do you save a player’s progress on a read-only cartridge?
105. SOLUTION: PASSWORD SYSTEMS
106. SOLUTION: PASSWORD SYSTEMS
107. https://tomorrowcorporation.com/posts/retro-game-internals-punch-out-passwords
109. https://strategywiki.org/wiki/Mega_Man_2/Password_Mechanics
112. AN ALTERNATIVE…
113. SOLUTION: STOP USING READ-ONLY CARTRIDGES (1986) FAMICOM DISK SYSTEM
114. MITSUMI QUICKDISK (1986, 2.8”)
115. http://www.famicomdisksystem.com/disks/
116. PROBLEM #9 How do you make writable game 
 media that users can’t easily copy?
117. SOLUTION: ADD BATTERY-BACKED MEMORY TO THE CARTRIDGE
118. “HOLD RESET BEFORE TURNING OFF POWER”
119. PROBLEM #10 How do you ensure that save data
 hasn’t been corrupted?
120. SOLUTION: WRITE SAVES MULTIPLE TIMES ➤ Store multiple copies of
 the save data with a 
 CRC code (checksum) ➤ On load, check saves one
 by one until you find one 
 that is intact Dragon Warrior (1989)
121. “WHATEVER HAPPENED
 TO BABY NES?”
122. DONKEY KONG (FAMICOM, 1983)
123. DONKEY KONG (FAMICOM, 1983)
124. KIRBY’S ADVENTURE (1993)
125. KIRBY’S ADVENTURE (1993)
126. KIRBY’S ADVENTURE (1993), STAGE 2-1 (40 STAGES IN TOTAL)
127. NES-101 “TOP LOADER” (1993)
128. PROBLEM #11 How do you expand the NES’ capabilities without changing the console?
129. SOLUTION:
 CHANGE THE CARTRIDGE
130. MMC1 (1987; 225 LICENSED US GAMES) PRG-ROM: up to 512KB PRG-RAM: optional, 8KB w/ battery CHR-ROM: up to 128KB Mirroring: switchable on-the-fly
132. CPU PPU CHR-ROM (graphics) PRG-ROM (code) NES CONSOLE CARTRIDGE RAM MMC1
133. MMC3 (1988; 195 LICENSED US GAMES) PRG-ROM: up to 512KB PRG-RAM: optional, 8KB w/ battery CHR-ROM: up to 256KB Mirroring: switchable or 4-screen VRAM
134. NINJA GAIDEN II: DARK SWORD OF CHAOS (1990, MMC3) Scanline IRQs
 to modify
 background
 scroll http://www.dustmop.io/blog/2015/12/18/nes-graphics-part-3/ Sprites
135. NINJA GAIDEN II: DARK SWORD OF CHAOS (1990, MMC3) Scanline IRQs
 to modify
 background
 scroll http://www.dustmop.io/blog/2015/12/18/nes-graphics-part-3/ Sprites
136. DONKEY KONG (NES, 1985)
137. KIRBY’S ADVENTURE (1993)
138. NINTENDO / VIDEO GAME HISTORY BOOKS ➤ Altice, Nathan. “I AM ERROR”. MIT Press, 2015. ➤ Bogost, Ian and Montfort, Nick. “Racing the Beam: The 
 Atari Video Computer System”. MIT Press, 2009. ➤ Bagnall, Brian. “On the Edge: The spectacular rise and fall of Commodore”. Variant Press, 2005. ➤ Sheff, David. “Game Over: How Nintendo zapped an American industry, captured your dollars, and enslaved your children”. Random House, 1993.
139. NESDEV.COM (WIKI AND FORUM)
140. HTTPS://BOOK.FAMICOM.PARTY
141. THANK YOU! Get in touch: kevin@famicom.party