prog8/examples/plasma.p8

%target c64
%import syslib
%import textio

;  converted from plasma test program for cc65.
;  which is (w)2001 by groepaz/hitmen
;
;  Cleanup and porting to C by Ullrich von Bassewitz.
;  Converted to prog8 by Irmen de Jong.


main {
    const uword SCREEN1 = $E000
    const uword SCREEN2 = $E400
    const uword CHARSET = $E800

    const ubyte PAGE1 = ((SCREEN1 >> 6) & $F0) | ((CHARSET >> 10) & $0E)
    const ubyte PAGE2 = ((SCREEN2 >> 6) & $F0) | ((CHARSET >> 10) & $0E)

    sub start() {
        txt.color(1)
        txt.print("creating charset...\n")
        makechar()

        ubyte block = c64.CIA2PRA
        ; ubyte v = c64.VMCSB
        c64.CIA2PRA = (block & $FC) | (lsb(SCREEN1 >> 14) ^ $03)

        repeat {
            doplasma(SCREEN1)
            c64.VMCSB = PAGE1
            doplasma(SCREEN2)
            c64.VMCSB = PAGE2
        }

        ; restore screen (if you want)
        ;c64.VMCSB = v
        ;c64.CIA2PRA = block
        ;txt.print("done!\n")
    }

    ; several variables outside of doplasma to make them retain their value
    ubyte c1A
    ubyte c1B
    ubyte c2A
    ubyte c2B

    sub doplasma(uword screen) {
        ubyte[40] xbuf
        ubyte[25] ybuf
        ubyte c1a = c1A
        ubyte c1b = c1B
        ubyte c2a = c2A
        ubyte c2b = c2B
        ubyte @zp x
        ubyte @zp y

        for y in 24 downto 0 {
            ybuf[y] = sin8u(c1a) + sin8u(c1b)
            c1a += 4
            c1b += 9
        }
        c1A += 3
        c1B -= 5
        for x in 39 downto 0 {
            xbuf[x] = sin8u(c2a) + sin8u(c2b)
            c2a += 3
            c2b += 7
        }
        c2A += 2
        c2B -= 3

        for y in 24 downto 0 {
            for x in 39 downto 0 {
                ; using a temp var here to enable expression optimization that can't be done on a 'problematic' ROM/RAM memory location
                ubyte cc = xbuf[x] + ybuf[y]
                @(screen) = cc
; this is the fastest way to do this inner part:
;                %asm {{
;                     ldy  i
;                     lda  xbuf,y
;                     ldy  ii
;                     clc
;                     adc  ybuf,y
;                     ldy  #0
;                     sta  (screen),y
;                 }}
                screen++
             }
        }
    }

    sub makechar() {
        ubyte[8] bittab = [ $01, $02, $04, $08, $10, $20, $40, $80 ]
        ubyte c
        for c in 0 to 255 {
            ubyte @zp s = sin8u(c)
            ubyte i
            for i in 0 to 7 {
                ubyte b=0
                ubyte @zp ii
                for ii in 0 to 7 {
                    ; use 16 bit rng for a bit more randomness instead of the 8-bit rng
                    if lsb(rndw()) > s {
                        b |= bittab[ii]
                    }
                }
                @(CHARSET + i + c*$0008) = b
            }
        }
    }
}