Learn RASTER SHADERS on Commodore 64

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“RASTER SHADERS” on

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I keep old computers alive mehowte Michał Taszycki on

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I can teach you to program Commodore 64 one bite at a time h tt p:/ /64bites.com/

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I have bad news for you…

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Commodore 64 belongs to the past…

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Today

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Back then

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Today

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Back then

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Back then

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Back then?

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Wait!

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Today!

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Today!

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HOW?!

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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; }

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“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

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Enough with theory!

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Let’s code!

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A minimal program :BasicUpstart2(main) main: rts

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The most important instructions

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LDA adress LDA #value RAM ➞ A register STA address A register ➞ RAM The most important instructions

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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)

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Macros rts main: lda # sta background_color lda # sta border_color GRAY DARK_GRAY

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rts main: lda # sta background_color lda # sta border_color GRAY DARK_GRAY .macro background(color) { } Macros

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lda # sta background_color rts main: :background( ) color lda # sta border_color GRAY DARK_GRAY .macro background(color) { } Macros

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lda # sta background_color rts main: :background( ) color lda # sta border_color GRAY DARK_GRAY .macro background(color) { } Macros

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lda # sta background_color rts main: .macro border(color) { } :background( ) color lda # sta border_color GRAY DARK_GRAY .macro background(color) { } Macros

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:border( ) .macro background(color) { } lda # sta background_color rts main: .macro border(color) { } :background( ) color lda # sta border_color GRAY DARK_GRAY color Macros

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Meet Raster Bars

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What’s the secret behind Raster Bars?

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Doing nothing!

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Raster Bars // long delay :background(BLACK) :background(DARK_GRAY)

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Delay :background(BLACK) :background(DARK_GRAY) nop

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:background(BLACK) :background(DARK_GRAY) nop nop Delay

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:background(BLACK) :background(DARK_GRAY) nop nop nop Delay

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:background(BLACK) :background(DARK_GRAY) nop // ... many more nops nop nop Delay

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:background(BLACK) :background(DARK_GRAY) .for (var i = 0; i < ; i++) { nop } 230 Delay

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.macro nops( ) { } .for (var i = 0; i < ; i++) { nop } :background(BLACK) :background(DARK_GRAY) 230 count Delay

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:nops( ) .macro nops( ) { } .for (var i = 0; i < ; i++) { nop } :background(BLACK) :background(DARK_GRAY) 230 count count Delay

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This will draw the bar… Somewhere :(

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We need to start drawing at a specific Raster Line

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We need to invoke a “Raster Shader”

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We’ll get there but first…

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Take a look at the cursor

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Take a look at the cursor WHY DOES IT BLINK?

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Meet Interrupts Small routines (let’s call them “shaders”) invoked by a signal (CIA TIMER, VIC CHIP)

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Here’s our “Shader” raster_bars_irq: jmp irq_handler :nops( ) :background(BLACK) :background(DARK_GRAY) 230

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// Disable IRQ handling sei // Enable IRQ handling cli Now we need to attach it to a signal

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// Disable IRQ handling sei // Enable IRQ handling cli Disable interrupts while we do it

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// Disable IRQ handling sei // inject the handler lda #raster_bars_irq sta irq_vector + 1 // Enable IRQ handling cli Inject interrupt handler

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// inject the handler lda #raster_bars_irq sta irq_vector + 1 Let’s Use another type of IRQ cli sei

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cli sei First delete the injection

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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

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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

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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)

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.macro request_raster_irq(line_number, handler) { } How to Choose Raster Line

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.macro request_raster_irq(line_number, handler) { } lda #handler sta irq_vector + 1 Inject the adress of the handler

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.macro request_raster_irq(line_number, handler) { } lda #handler sta irq_vector + 1 lda #line_number sta vic2_rasterline_register Choose Raster Line

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.macro request_raster_irq(line_number, handler) { } 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

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.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

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Raster IRQs need to be Acknowledged jmp irq_handler raster_bars_irq: :background(BLACK) :nops(230) :background(DARK_GRAY)

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raster_bars_irq: :background(BLACK) :nops(230) :background(DARK_GRAY) lda #%00000001 sta vic2_interrupt_status_register jmp irq_handler By touching special register

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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

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We need stabilization :exit_irq_handler() raster_bars_irq: :background(BLACK) :nops(230) :background(DARK_GRAY)

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But stabilization is… complicated :exit_irq_handler() raster_bars_irq: :background(BLACK) :nops(230) :background(DARK_GRAY)

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Let’s fake it ;) :exit_irq_handler() raster_bars_irq: :nops(14) :background(BLACK) :nops(230) :background(DARK_GRAY)

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We’ll hide jittering under the border ;) :exit_irq_handler() raster_bars_irq: :nops(14) :background(BLACK) :nops(230) :background(DARK_GRAY)

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Let’s make more bars! :exit_irq_handler() raster_bars_irq:

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: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!

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Meet Sprites Hardware-accelerated bitmaps

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// Enable all 8 sprites lda #%11111111 sta sprites.enable_bits Sprites on/off

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// 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

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.macro set_sprite_position_x(index, position_x) { } Sprite position

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.macro set_sprite_position_x(index, position_x) { } lda #position_x sta sprites.positions + index*2 + 0 Sprite position

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.macro set_sprite_position_x(index, position_x) { } .if (position_x > 255) { :set_bits(sprites.position_x_high_bits,1<

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Another “Shader”? raster_bars_irq: :exit_irq_handler() // ... :nops(14)

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sprite_row_irq1: :exit_irq_handler() // ... raster_bars_irq: :exit_irq_handler() // ... :nops(14) Another Interrupt

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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

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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

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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

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By the way

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WTH is Raster time?

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A simple way to measure the complexity of a routine Raster time

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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)

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Let’s display more sprites!

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Wait, what?

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More than 8?

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More than 8?

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Interrupt chain raster_bars_irq: :request_raster_irq( ) :exit_irq_handler() 60, sprite_row_irq1 sprite_row_irq1: // ... // ...

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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

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Let’s open the border!

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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()

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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()

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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

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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

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What’s the point? You can’t draw any characters in this area :(

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But you can draw a bar code ;) lda #%10110101 sta border_pattern

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And Sprites!

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Let’s play SID music

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What’s a SID file?

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It’s like an mp3 for C64…

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But the player is included!

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// Import music from a file .pc=$1000 music: .import binary "music.bin" Import SID file into the memory

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main: // initialize music jsr music // Import music from a file .pc=$1000 music: .import binary "music.bin" Initialize the player

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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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How did you like it?

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Want more?

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I can teach you to program Commodore 64 one bite at a time

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Short & Sweet Commodore 64 programming lessons

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Tons of Small Epiphanies

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Short Focused Deep

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BASIC to Assembly

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Difficult Concepts Explained

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Step By Step

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Modern Programming Techniques

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Useful For Games

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Useful For Demos

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1 episode • 5-10 minute video • 1 small epiphany • Full transcript • Source code • Exercises $3.99

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but…

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of short video lessons Huge library

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Videos 108

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Get everything • 108 videos • 235 exercises • 156 000 lines of code • Best price • less than $2 per episode $199

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