Learn RASTER SHADERS on Commodore 64

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You will learn:
1. How to use two most important assembly instructions - [REDACTED] and [REDACTED]
2. How to draw Raster Bars?
3. How to stabilize the raster interrupts?
4. How to open borders?
5. How to draw under the border?
6. How to display more than 8 sprites?
7. How to play sid music?

Video cards can execute small programs whenever a pixel is displayed on screen.
Commodore 64 can execute small programs whenever a raster line is displayed on TV.

Pixel shaders can be used to create realistic lighting, special effects and even compute physics!
‘Raster shaders’ can be used to split screen, display more sprites and even play sound!

Transcript

1. “RASTER SHADERS” on
2. I keep old computers alive mehowte Michał Taszycki on
3. I can teach you to program Commodore 64 one bite at a time h tt p:/ /64bites.com/
4. I have bad news for you…
5. Commodore 64 belongs to the past…
6. Today
7. Back then
8. Today
9. Back then
10. Back then
11. Back then?
12. Wait!
13. Today!
14. Today!
15. HOW?!
16. Pixel Shader varying vec3 N; varying vec3 v; void main(void) { vec3 L = normalize(gl_LightSource[0].position.xyz - v); vec4 Idiff = gl_FrontLightProduct[0].diffuse * max(dot(N,L), 0.0); Idiff = clamp(Idiff, 0.0, 1.0); gl_FragColor = Idiff; }
17. “Raster Shader” irq: lda #$ff sta $d019 ldx #$05 d: dex bne d ldx #$00 c: ldy #$08 a: lda colors,x sta $d020 sta $d021 inx dey beq c txa ldx #$07 b: dex bne b tax cpx #$8c bcc a
18. Enough with theory!
19. Let’s code!
20. A minimal program :BasicUpstart2(main) main: rts
22. The most important instructions
23. LDA adress LDA #value RAM ➞ A register STA address A register ➞ RAM The most important instructions
24. rts main: lda # sta background_color lda # sta border_color GRAY DARK_GRAY Border & Backgound Colors .label border_color = $d020 .label background_color = $d021 :BasicUpstart2(main)
25. Macros rts main: lda # sta background_color lda # sta border_color GRAY DARK_GRAY
26. rts main: lda # sta background_color lda # sta border_color GRAY DARK_GRAY .macro background(color) { } Macros
27. lda # sta background_color rts main: :background( ) color lda # sta border_color GRAY DARK_GRAY .macro background(color) { } Macros
28. lda # sta background_color rts main: :background( ) color lda # sta border_color GRAY DARK_GRAY .macro background(color) { } Macros
29. lda # sta background_color rts main: .macro border(color) { } :background( ) color lda # sta border_color GRAY DARK_GRAY .macro background(color) { } Macros
30. :border( ) .macro background(color) { } lda # sta background_color rts main: .macro border(color) { } :background( ) color lda # sta border_color GRAY DARK_GRAY color Macros
32. Meet Raster Bars
33. What’s the secret behind Raster Bars?
34. Doing nothing!
35. Raster Bars // long delay :background(BLACK) :background(DARK_GRAY)
36. Delay :background(BLACK) :background(DARK_GRAY) nop
37. :background(BLACK) :background(DARK_GRAY) nop nop Delay
38. :background(BLACK) :background(DARK_GRAY) nop nop nop Delay
39. :background(BLACK) :background(DARK_GRAY) nop // ... many more nops nop nop Delay
40. :background(BLACK) :background(DARK_GRAY) .for (var i = 0; i < ; i++) { nop } 230 Delay
41. .macro nops( ) { } .for (var i = 0; i < ; i++) { nop } :background(BLACK) :background(DARK_GRAY) 230 count Delay
42. :nops( ) .macro nops( ) { } .for (var i = 0; i < ; i++) { nop } :background(BLACK) :background(DARK_GRAY) 230 count count Delay
43. This will draw the bar… Somewhere :(
44. We need to start drawing at a specific Raster Line
45. We need to invoke a “Raster Shader”
46. We’ll get there but first…
47. Take a look at the cursor
48. Take a look at the cursor WHY DOES IT BLINK?
49. Meet Interrupts Small routines (let’s call them “shaders”) invoked by a signal (CIA TIMER, VIC CHIP)
50. Here’s our “Shader” raster_bars_irq: jmp irq_handler :nops( ) :background(BLACK) :background(DARK_GRAY) 230
51. // Disable IRQ handling sei // Enable IRQ handling cli Now we need to attach it to a signal
52. // Disable IRQ handling sei // Enable IRQ handling cli Disable interrupts while we do it
53. // Disable IRQ handling sei // inject the handler lda #<raster_bars_irq sta irq_vector lda #>raster_bars_irq sta irq_vector + 1 // Enable IRQ handling cli Inject interrupt handler
55. // inject the handler lda #<raster_bars_irq sta irq_vector lda #>raster_bars_irq sta irq_vector + 1 Let’s Use another type of IRQ cli sei
56. cli sei First delete the injection
57. cli sei // Disable the interrupt generated by timers lda #%01111111 sta cia1_interrupt_control_register sta cia2_interrupt_control_register // Negate already scheduled interrupts lda cia1_interrupt_control_register lda cia2_interrupt_control_register Disable Timer IRQs
58. But Enable Raster IRQs cli sei // Disable the interrupt generated by timers lda #%01111111 sta cia1_interrupt_control_register sta cia2_interrupt_control_register // Negate already scheduled interrupts lda cia1_interrupt_control_register lda cia2_interrupt_control_register // Enable raster interrupts lda #%00000001 sta vic2_interrupt_control_register
59. Let’s Choose Raster Line cli sei // Disable the interrupt generated by timers lda #%01111111 sta cia1_interrupt_control_register sta cia2_interrupt_control_register // Negate already scheduled interrupts lda cia1_interrupt_control_register lda cia2_interrupt_control_register // Enable raster interrupts lda #%00000001 sta vic2_interrupt_control_register :request_raster_irq(106, raster_bars_irq)
60. .macro request_raster_irq(line_number, handler) { } How to Choose Raster Line
61. .macro request_raster_irq(line_number, handler) { } lda #<handler sta irq_vector lda #>handler sta irq_vector + 1 Inject the adress of the handler
62. .macro request_raster_irq(line_number, handler) { } lda #<handler sta irq_vector lda #>handler sta irq_vector + 1 lda #line_number sta vic2_rasterline_register Choose Raster Line
63. .macro request_raster_irq(line_number, handler) { } lda #<handler sta irq_vector lda #>handler sta irq_vector + 1 .if (line_number > 255) { :set_bits(screen_control_register, %10000000) } else { :clear_bits(screen_control_register, %10000000) } lda #line_number sta vic2_rasterline_register It might not fit in a byte
64. .macro set_bits(address, bit_mask) { lda address ora #bit_mask sta address } .macro clear_bits(address, bit_mask) { lda address and #255 - bit_mask sta address } Helper macros to toggle bits
65. Raster IRQs need to be Acknowledged jmp irq_handler raster_bars_irq: :background(BLACK) :nops(230) :background(DARK_GRAY)
66. raster_bars_irq: :background(BLACK) :nops(230) :background(DARK_GRAY) lda #%00000001 sta vic2_interrupt_status_register jmp irq_handler By touching special register
67. raster_bars_irq: :background(BLACK) :nops(230) :background(DARK_GRAY) :exit_irq_handler() .macro exit_irq_handler() { } lda #%00000001 sta vic2_interrupt_status_register jmp irq_handler Let’s put it in a macro
69. We need stabilization :exit_irq_handler() raster_bars_irq: :background(BLACK) :nops(230) :background(DARK_GRAY)
70. But stabilization is… complicated :exit_irq_handler() raster_bars_irq: :background(BLACK) :nops(230) :background(DARK_GRAY)
71. Let’s fake it ;) :exit_irq_handler() raster_bars_irq: :nops(14) :background(BLACK) :nops(230) :background(DARK_GRAY)
72. We’ll hide jittering under the border ;) :exit_irq_handler() raster_bars_irq: :nops(14) :background(BLACK) :nops(230) :background(DARK_GRAY)
74. Let’s make more bars! :exit_irq_handler() raster_bars_irq:
75. :nops(14) :background(BLACK) :nops(4) :background(DARK_GRAY) :nops(29) :background(GRAY) :nops(29) :background(LIGHT_GRAY) :nops(29) :background(WHITE) :exit_irq_handler() raster_bars_irq: Let’s make more bars!
76. :nops(14) :background(BLACK) :nops(4) :background(DARK_GRAY) :nops(29) :background(GRAY) :nops(29) :background(LIGHT_GRAY) :nops(29) :background(WHITE) :exit_irq_handler() raster_bars_irq: // ... Let’s make more bars!
77. :nops(14) :background(BLACK) :nops(4) :background(DARK_GRAY) :nops(29) :background(GRAY) :nops(29) :background(LIGHT_GRAY) :nops(29) :background(WHITE) :exit_irq_handler() raster_bars_irq: // ... // ... Let’s make more bars!
78. :nops(14) :background(BLACK) :nops(4) :background(DARK_GRAY) :nops(29) :background(GRAY) :nops(29) :background(LIGHT_GRAY) :nops(29) :background(WHITE) :exit_irq_handler() raster_bars_irq: :nops(29) :background(LIGHT_GRAY) :nops(29) :background(GRAY) :nops(29) :background(DARK_GRAY) :nops(29) :background(BLACK) :nops(4) :background(DARK_GRAY) // ... // ... Let’s make more bars!
80. Meet Sprites Hardware-accelerated bitmaps
81. // Enable all 8 sprites lda #%11111111 sta sprites.enable_bits Sprites on/off
82. // Enable all 8 sprites lda #%11111111 sta sprites.enable_bits .for (var i = 0; i < 8; i++) { :set_sprite_position_x(i, 60 + 32 * i) } Sprites’ positions
83. .macro set_sprite_position_x(index, position_x) { } Sprite position
84. .macro set_sprite_position_x(index, position_x) { } lda #position_x sta sprites.positions + index*2 + 0 Sprite position
85. .macro set_sprite_position_x(index, position_x) { } .if (position_x > 255) { :set_bits(sprites.position_x_high_bits,1<<index) } else { :clear_bits(sprites.position_x_high_bits,1<<index) } lda #position_x sta sprites.positions + index*2 + 0 Sprite position
86. Another “Shader”? raster_bars_irq: :exit_irq_handler() // ... :nops(14)
87. sprite_row_irq1: :exit_irq_handler() // ... raster_bars_irq: :exit_irq_handler() // ... :nops(14) Another Interrupt
88. sprite_row_irq1: :exit_irq_handler() // ... raster_bars_irq: :exit_irq_handler() // ... :request_raster_irq(60, sprite_row_irq1) :nops(14) Schedule 2nd from the 1st
89. sprite_row_irq1: :exit_irq_handler() // ... :request_raster_irq(106, raster_bars_irq) raster_bars_irq: :exit_irq_handler() // ... :request_raster_irq(60, sprite_row_irq1) :nops(14) Schedule 1st from the 2nd
90. sprite_row_irq1: :exit_irq_handler() // Set the y-position, bitmaps and colors :sprites_row(70, 0, 3) raster_bars_irq: :exit_irq_handler() // ... :request_raster_irq(60, sprite_row_irq1) :request_raster_irq(106, raster_bars_irq) :nops(14) Vertical Sprites’ positions
92. By the way
93. WTH is Raster time?
94. A simple way to measure the complexity of a routine Raster time
95. sprite_row_irq1: :exit_irq_handler() // Set the y-position, bitmaps and colors :sprites_row(70, 0, 3) Raster time raster_bars_irq: :exit_irq_handler() // ... :request_raster_irq(60, sprite_row_irq1) :request_raster_irq(106, raster_bars_irq) :nops(14)
96. sprite_row_irq1: :exit_irq_handler() // Set the y-position, bitmaps and colors :sprites_row(70, 0, 3) Raster time raster_bars_irq: :exit_irq_handler() // ... :request_raster_irq(60, sprite_row_irq1) :request_raster_irq(106, raster_bars_irq) :border(RED) :border(GRAY) :nops(14)
97. sprite_row_irq1: :exit_irq_handler() // Set the y-position, bitmaps and colors :sprites_row(70, 0, 3) Raster time raster_bars_irq: :exit_irq_handler() // ... :request_raster_irq(60, sprite_row_irq1) :request_raster_irq(106, raster_bars_irq) :nops(14) :border(RED) :border(GRAY) :border(GRAY) :border(ORANGE)
98. sprite_row_irq1: :exit_irq_handler() // Set the y-position, bitmaps and colors :sprites_row(70, 0, 3) Raster time raster_bars_irq: :exit_irq_handler() // ... :request_raster_irq(60, sprite_row_irq1) :request_raster_irq(106, raster_bars_irq) :nops(14) :border(RED) :border(GRAY) :border(GRAY) :border(ORANGE) WATCH OUT! (SYNCHRONIZATION IS OFF)
99. sprite_row_irq1: :exit_irq_handler() // Set the y-position, bitmaps and colors :sprites_row(70, 0, 3) Raster time raster_bars_irq: :exit_irq_handler() // ... :request_raster_irq(60, sprite_row_irq1) :request_raster_irq(106, raster_bars_irq) :nops(7) :border(RED) :border(GRAY) :border(GRAY) :border(ORANGE)
101. Let’s display more sprites!
102. Wait, what?
103. More than 8?
104. More than 8?
105. Interrupt chain raster_bars_irq: :request_raster_irq( ) :exit_irq_handler() 60, sprite_row_irq1 sprite_row_irq1: // ... // ...
106. raster_bars_irq: :request_raster_irq( ) :exit_irq_handler() sprite_row_irq2: :border(CYAN) :sprites_row(160, 8, 12) :border(GRAY) :request_raster_irq( ) :exit_irq_handler() 60, sprite_row_irq1 sprite_row_irq1: // ... // ... Another interrupt handler
107. raster_bars_irq: :request_raster_irq( ) :exit_irq_handler() sprite_row_irq2: :border(CYAN) :sprites_row(160, 8, 12) :border(GRAY) :request_raster_irq( ) :exit_irq_handler() 60, sprite_row_irq1 sprite_row_irq1: // ... // ... 150, sprite_row_irq2 Let’s add it to the chain
109. Let’s open the border!
110. Thin Green Line… :request_raster_irq(248, open_border_irq) open_border_irq: :border(GREEN) :nops(14) :border(GRAY) :request_raster_irq(60, sprite_row_irq1) :exit_irq_handler()
113. Before reaching the line sprite_row_irq2: :request_raster_irq(248, open_border_irq) :exit_irq_handler() open_border_irq: :request_raster_irq(60, sprite_row_irq1) :exit_irq_handler()
114. sprite_row_irq2: :request_raster_irq(248, open_border_irq) :exit_irq_handler() open_border_irq: :request_raster_irq(60, sprite_row_irq1) :exit_irq_handler() // Enable 25 lines mode :set_bits(screen_control_register, %00001000) Make border thin
115. sprite_row_irq2: :request_raster_irq(248, open_border_irq) :exit_irq_handler() open_border_irq: :request_raster_irq(60, sprite_row_irq1) :exit_irq_handler() // Enable 25 lines mode :set_bits(screen_control_register, %00001000) After we’ve passed that line
116. sprite_row_irq2: :request_raster_irq(248, open_border_irq) :exit_irq_handler() open_border_irq: :request_raster_irq(60, sprite_row_irq1) :exit_irq_handler() // Enable 24 lines mode :clear_bits(screen_control_register, %00001000) // Enable 25 lines mode :set_bits(screen_control_register, %00001000) Make border wide
118. What’s the point? You can’t draw any characters in this area :(
119. But you can draw a bar code ;) lda #%10110101 sta border_pattern
121. And Sprites!
123. Let’s play SID music
124. What’s a SID file?
125. It’s like an mp3 for C64…
126. But the player is included!
127. // Import music from a file .pc=$1000 music: .import binary "music.bin" Import SID file into the memory
128. main: // initialize music jsr music // Import music from a file .pc=$1000 music: .import binary "music.bin" Initialize the player
129. main: // initialize music jsr music // Import music from a file .pc=$1000 music: .import binary "music.bin" play_music: :border(YELLOW) jsr $music + 3 :border(GRAY) :request_raster_irq(248, open_border_irq) :exit_irq_handler() Play a tiny bit of music
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