const pointer screen = $400
const byte row = 15

byte letter_index

void main () {
#if CBM_64_CRT
    vic_bg_color0 = blue
    vic_border = light_blue
    vic_cr1 = $9b
    vic_mem = $15
    vic_cr2 = $c8
#endif
    letter_index = 0
    disable_irq()
    init_screen()
    main_loop()
}
void init_screen() {
    byte i
    for i,0,paralleluntil,250 {
        screen[i+000] = logo[i-000]
        screen[i+250] = logo[i+250]
        screen[i+500] = logo[i+500]
        screen[i+750] = logo[i+750]
        c64_color_ram[i+000] = logo_colours[i+000]
        c64_color_ram[i+250] = logo_colours[i+250]
        c64_color_ram[i+500] = logo_colours[i+500]
        c64_color_ram[i+750] = logo_colours[i+750]
    }
}

void main_loop() {
    static byte scroll
    scroll = 7
    while true {
        while vic_raster != row * 8 - 1 + 50 {}
        stabilize(9)
        vic_38_columns()
        vic_set_scroll(scroll, 3)
        while vic_raster != row * 8 + 7 + 50 {}
        stabilize(22)
        vic_40_columns()
        vic_set_scroll(0,3)
        if scroll == 0 {
            scroll = 7
            hardscroll()
        } else {
            scroll -= 1
        }
    }
}


asm void stabilize(byte x){
    burn:
    DEX
    BNE burn
    RTS
}

void hardscroll() {
    byte i
    for i,0,until,39 {
        screen[40 * row + i] = screen[40 * row  + i + 1]
    }
    screen[40 * row + 39] = scroll_text[letter_index]
    letter_index += 1
    if letter_index == scroll_text.length {
        letter_index = 0
    }
}

const array scroll_text = [
    "this is a simple scroller demo written in millfork.  " scr,
    "as you can see, you don't need assembly to do simple effects.  " scr,
    "                    " scr
]

const array logo = [
             32,32,32,32,32,32,32,32,32,32,32,32,32,32,32,32,32,32,32,32,32,32,32,32,32,32,32,32,32,32,32,32,32,32,32,32,32,32,32,32,
             32,32,32,32,32,32,32,32,32,32,32,32,32,32,32,32,32,32,32,32,32,32,32,32,32,32,32,32,32,32,32,32,32,32,32,32,32,32,32,32,
             32,32,32,32,32,32,32,32,32,32,32,32,32,32,32,32,32,32,32,32,32,32,32,32,32,32,32,32,32,32,32,32,32,32,32,32,32,32,32,32,
             32,32,32,32,32,32,32,32,32,32,32,32,32,32,32,32,32,32,32,32,32,32,32,32,32,32,32,32,32,32,32,32,32,32,32,32,32,32,32,32,
             32,32,32,32,32,32,32,32,32,32,32,32,32,32,32,32,32,32,32,32,32,32,32,32,32,32,32,32,32,32,32,32,32,32,32,32,32,32,32,32,
             82,70,64,68,69,68,64,70,82,70,64,68,69,68,64,70,82,70,64,68,69,68,64,70,82,70,64,68,69,68,64,70,82,70,64,68,69,68,64,70,
             32,32,32,32,32,108,123,32,32,32,32,32,32,32,32,32,32,32,32,32,32,32,32,32,32,32,32,32,32,32,32,32,32,32,32,32,32,32,32,32,
             32,32,32,32,108,224,224,123,32,32,32,32,32,32,32,32,32,32,32,32,32,32,32,32,32,32,32,32,32,32,32,32,32,32,32,32,32,32,32,32,
             32,32,32,32,32,225,97,32,32,32,32,32,32,32,32,32,32,32,32,32,32,32,32,32,32,32,32,32,32,32,32,32,32,32,32,32,32,32,32,32,
             32,32,32,32,32,225,97,32,32,32,32,32,32,32,32,32,32,32,32,32,32,32,32,32,32,32,32,32,32,32,32,32,32,32,32,32,32,32,32,32,
             32,108,32,32,32,225,97,32,225,252,108,224,32,251,236,32,225,97,32,32,225,97,32,32,225,236,226,126,108,236,251,123,225,236,251,123,225,97,254,126,
             108,224,98,98,98,254,97,32,225,236,236,224,32,225,97,32,225,97,32,32,225,97,32,32,225,252,123,32,225,97,225,97,225,252,254,126,225,224,126,32,
             124,224,226,226,226,226,126,32,225,97,32,224,32,225,97,32,225,97,32,32,225,97,32,32,225,97,32,32,225,97,225,97,225,236,252,32,225,236,252,32,
             32,124,32,32,32,32,32,32,124,126,32,226,32,226,226,32,124,226,226,126,124,226,226,126,124,126,32,32,32,226,226,32,124,126,124,126,124,126,124,126,
             32,32,32,32,32,32,32,32,32,32,32,32,32,32,32,32,32,32,32,32,32,32,32,32,32,32,32,32,32,32,32,32,32,32,32,32,32,32,32,32,
             32,32,32,32,32,32,32,32,32,32,32,32,32,32,32,32,32,32,32,32,32,32,32,32,32,32,32,32,32,32,32,32,32,32,32,32,32,32,32,32,
             32,32,32,32,32,32,32,32,32,32,32,32,32,32,32,32,32,32,32,32,32,32,32,32,32,32,32,32,32,32,32,32,32,32,32,32,32,32,32,32,
             82,70,64,68,69,68,64,70,82,70,64,68,69,68,64,70,82,70,64,68,69,68,64,70,82,70,64,68,69,68,64,70,82,70,64,68,69,68,64,70,
             32,32,32,32,32,32,32,32,32,32,32,32,32,32,32,32,32,32,32,32,32,32,32,32,32,32,32,32,32,32,32,32,32,32,32,32,32,32,32,32,
             32,32,32,32,32,32,32,32,32,32,32,32,32,32,32,32,32,32,32,32,32,32,32,32,32,32,32,32,32,32,32,32,32,32,32,32,32,32,32,32,
             32,32,32,32,32,32,32,32,32,32,32,32,32,32,32,32,32,32,32,32,32,32,32,32,32,32,32,32,32,32,32,32,32,32,32,32,32,32,32,32,
             32,32,32,32,32,32,32,32,32,32,32,32,32,32,32,32,32,32,32,32,32,32,32,32,32,32,32,32,32,32,32,32,32,32,32,32,32,32,32,32,
             32,32,32,32,32,32,32,32,32,32,32,32,32,32,32,32,32,32,32,32,32,32,32,32,32,32,32,32,32,32,32,32,32,32,32,32,32,32,32,32,
             32,32,32,32,32,32,32,32,32,32,32,32,32,32,32,32,32,32,32,32,32,32,32,32,32,32,32,32,32,32,32,32,32,32,32,32,32,32,32,32,
             32,32,32,32,32,32,32,32,32,32,32,32,32,32,32,32,32,32,32,32,32,32,32,32,32,32,32,32,32,32,32,32,32,32,32,32,32,32,32,32
]

const array logo_colours = [
14,14,14,14,14,14,14,14,14,14,14,14,14,14,14,14,14,14,14,14,14,14,14,14,14,14,14,14,14,14,14,14,14,14,14,14,14,14,14,14,
14,14,14,14,14,14,14,14,14,14,14,14,14,14,14,14,14,14,14,14,14,14,14,14,14,14,14,14,14,14,14,14,14,14,14,14,14,14,14,14,
14,14,14,14,14,14,14,14,14,14,14,14,14,14,14,14,14,14,14,14,14,14,14,14,14,14,14,14,14,14,14,14,14,14,14,14,14,14,14,14,
14,14,14,14,14,14,14,14,14,14,14,14,14,14,14,14,14,14,14,14,14,14,14,14,14,14,14,14,14,14,14,14,14,14,14,14,14,14,14,14,
14,14,14,14,14,14,14,14,14,14,14,14,14,14,14,14,14,14,14,14,14,14,14,14,14,14,14,14,14,14,14,14,14,14,14,14,14,14,14,14,
7,7,7,7,7,7,7,7,7,7,7,7,7,7,7,7,7,7,7,7,7,7,7,7,7,7,7,7,7,7,7,7,7,7,7,7,7,7,7,7,
14,14,14,14,14,5,5,14,14,14,14,14,14,14,14,14,14,14,14,14,14,14,14,14,14,14,14,14,14,14,14,14,14,14,14,14,14,14,14,14,
14,14,14,14,5,5,5,5,14,14,14,14,14,14,14,14,14,14,14,14,14,14,14,14,14,14,14,14,14,14,14,14,14,14,14,14,14,14,14,14,
14,14,14,14,14,5,5,5,14,14,14,0,14,14,14,14,14,14,14,14,14,14,14,14,14,14,14,14,14,14,14,14,14,14,14,14,14,14,14,14,
14,14,14,14,14,5,5,14,0,14,0,0,14,0,14,0,0,0,14,0,0,14,14,14,14,14,14,14,14,14,14,14,14,14,14,14,14,14,14,14,
14,5,14,14,14,5,5,14,0,0,0,0,14,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,
5,5,5,5,5,5,5,14,0,0,0,0,14,0,0,14,0,0,14,14,0,0,14,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,14,
5,5,5,5,5,5,5,14,0,0,0,0,14,0,0,14,0,0,0,0,0,0,14,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,
14,5,5,14,14,14,14,14,0,0,14,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,
14,14,14,14,14,14,14,14,14,14,14,14,14,14,14,14,14,14,14,14,14,14,14,14,14,14,14,14,14,14,0,14,14,14,0,0,0,14,14,14,
14,14,14,14,14,14,14,14,14,14,14,14,14,14,14,14,14,14,14,14,14,14,14,14,14,14,14,14,14,14,14,14,14,14,14,14,14,14,14,14,
14,14,14,14,14,14,14,14,14,14,14,14,14,14,14,14,14,14,14,14,14,14,14,14,14,14,14,14,14,14,14,14,14,14,14,14,14,14,14,14,
7,7,7,7,7,7,7,7,7,7,7,7,7,7,7,7,7,7,7,7,7,7,7,7,7,7,7,7,7,7,7,7,7,7,7,7,7,7,7,7,
14,14,14,14,14,14,14,14,14,14,14,14,14,14,14,14,14,14,14,14,14,14,14,14,14,14,14,14,14,14,14,14,14,14,14,14,14,14,14,14,
14,14,14,14,14,14,14,14,14,14,14,14,14,14,14,14,14,14,14,14,14,14,14,14,14,14,14,14,14,14,14,14,14,14,14,14,14,14,14,14,
14,14,14,14,14,14,14,14,14,14,14,14,14,14,14,14,14,14,14,14,14,14,14,14,14,14,14,14,14,14,14,14,14,14,14,14,14,14,14,14,
14,14,14,14,14,14,14,14,14,14,14,14,14,14,14,14,14,14,14,14,14,14,14,14,14,14,14,14,14,14,14,14,14,14,14,14,14,14,14,14,
14,14,14,14,14,14,14,14,14,14,14,14,14,14,14,14,14,14,14,14,14,14,14,14,14,14,14,14,14,14,14,14,14,14,14,14,14,14,14,14,
14,14,14,14,14,14,14,14,14,14,14,14,14,14,14,14,14,14,14,14,14,14,14,14,14,14,14,14,14,14,14,14,14,14,14,14,14,14,14,14,
14,14,14,14,14,14,14,14,14,14,14,14,14,14,14,14,14,14,14,14,14,14,14,14,14,14,14,14,14,14,14,14,14,14,14,14,14,14,14,14
]