%import syslib
%import math

main {

    sub start() {
        c64.SCROLY &= %11101111                    ; blank the screen
        c64.set_rasterirq(&irq.irqhandler, 40, false)     ; register exclusive raster irq handler

        repeat {
            ; enjoy the moving bars :)
        }

    }
}


irq {

    const ubyte barheight = 3       ; should be big enough to re-trigger the Raster irq properly.
    ubyte[] colors = [6,2,4,5,15,7,1,13,3,12,8,11,9]
    ubyte color = 0
    ubyte yanim = 0

    sub irqhandler() {
        if color!=len(colors) {
            c64.EXTCOL = colors[color]
            c64.RASTER += barheight         ; next raster Irq for next color
            color++
        }
        else {
            c64.EXTCOL = 0
            color = 0
            yanim += 2
            c64.RASTER = math.sin8u(yanim)/2+30  ; new start of raster Irq
        }
        c64.SCROLY &= $7f    ; set high bit of the raster pos to zero
    }
}