prog8/examples/c64/charset.p8

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%import syslib
%import textio
%zeropage basicsafe
%option no_sysinit
; Create a custom character set on the C64.
main {
sub start() {
txt.color(1)
txt.print("creating charset...\n")
charset.make_custom_charset()
; activate the new charset in RAM
ubyte block = c64.CIA2PRA
const ubyte PAGE1 = ((cbm.Screen >> 6) & $F0) | ((charset.CHARSET >> 10) & $0E)
c64.CIA2PRA = (block & $FC) | (lsb(cbm.Screen >> 14) ^ $03)
c64.VMCSB = PAGE1
txt.print("\n @ @ @ @\n")
}
}
charset {
const uword CHARSET = $2000
sub copy_rom_charset() {
; copies the charset from ROM to RAM so we can modify it
sys.set_irqd()
ubyte bank = @($0001)
@($0001) = bank & %11111011 ; enable CHAREN, so the character rom accessible at $d000
sys.memcopy($d000, CHARSET, 256*8*2) ; copy the charset to RAM
@($0001) = bank ; reset previous memory banking
sys.clear_irqd()
}
sub make_custom_charset() {
copy_rom_charset()
; make all characters italic
ubyte c
for c in 0 to 255 {
uword ptr = CHARSET + c*$0008
@(ptr) >>= 2
@(ptr+1) >>= 2
@(ptr+2) >>= 1
@(ptr+3) >>= 1
;@(ptr+4) >>= 0
;@(ptr+5) >>= 0
@(ptr+6) <<= 1
@(ptr+7) <<= 1
ptr = CHARSET + 256*8 + c*$0008
@(ptr) >>= 2
@(ptr+1) >>= 2
@(ptr+2) >>= 1
@(ptr+3) >>= 1
;@(ptr+4) >>= 0
;@(ptr+5) >>= 0
@(ptr+6) <<= 1
@(ptr+7) <<= 1
}
; add a smiley over the '@'
ubyte[] smiley = [
%00111100,
%01000010,
%10100101,
%10000001,
%10100101,
%10011001,
%01000010,
%00111100
]
sys.memcopy(smiley, CHARSET, len(smiley))
}
}