2012-04-18, 02:40 PM
Code:
SUB plotPoint (x as uByte, y as uByte)
ASM
ld d,a ;'X
ld a, 191
sub (IX+7) ;' y
jr c, plotPoint_end
ld l,a
ld h,ScreenTables/256
ld a,(HL)
inc h
ld l,(HL)
ld h,a
; now we're on the right row on screen.
ld a,d
RRCA ; divide column by 8 for bytes.
RRCA
RRCA
AND 31
add a,l
ld l,a
ld a, d
and 7
ld b, a
inc b
ld a, 1
plotPoint_loop:
rrca
djnz plotPoint_loop
ld b, a
ld a, (hl)
or b
ld (hl), a
plotPoint_end:
END ASM
END SUBUsing screen address tables shaves this down to 6.42 seconds for 50,000 points plotted. That's not too bad, all told.
(screentables.asm is available elsewhere in the forum, I promise!)
Considering that quite a few routines can use the screen lookup tables, 512 bytes of screen tables isn't crazy for a solid speedup (and of course, if you are using a shadow screen, then you could either rewrite a bit, or make screen tables that point to your shadow screen memory).
Not sure requiring rotate tables, which is much bigger, is a win, here for one loop removal.