prog8/examples/c64/rasterbars.p8

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%import syslib
%import math
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main {
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sub start() {
c64.SCROLY &= %11101111 ; blank the screen
sys.set_rasterirq(&irq.irqhandler, 40) ; register exclusive raster irq handler
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repeat {
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; enjoy the moving bars :)
}
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}
}
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irq {
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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
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ubyte yanim = 0
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sub irqhandler() -> bool {
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if color!=len(colors) {
c64.EXTCOL = colors[color]
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c64.RASTER += barheight ; next raster Irq for next color
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color++
}
else {
c64.EXTCOL = 0
color = 0
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yanim += 2
c64.RASTER = math.sin8u(yanim)/2+30 ; new start of raster Irq
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}
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c64.SCROLY &= $7f ; set high bit of the raster pos to zero
return false
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}
}