dos33fsprogs/demos/lovebyte2021/sier/sier_64.s
2021-03-14 20:49:24 -04:00

90 lines
1.1 KiB
ArmAsm

; fake sierpinski
; 64-byte Apple II demo
; with scrolling and colors
; by Vince `deater` Weaver, dSr, Lovebyte 2021
; just plot XX AND YY
; zero page
COLOR = $30
XX = $66
YY = $67
FRAME = $68
;X2 = $69
; soft-switches
FULLGR = $C052
; rom routines
PLOT = $F800 ;; PLOT AT Y,A
PLOT1 = $F80E ;; PLOT at (GBASL),Y (need MASK to be $0f or $f0)
SETCOL = $F864 ;; COLOR=A
SETGR = $FB40
;================================
; Clear screen and setup graphics
;================================
sier:
jsr SETGR ; set lo-res 40x40 mode
bit FULLGR ; make it 40x48
lda #0
sta FRAME
sier_loop:
inc FRAME
ldx #47 ; YY
sier_yloop:
lda #39
sta XX
tay
txa
jsr PLOT ; PLOT AT Y,A
; sets GBASL/GBASH and MASK
sier_xloop:
txa
clc
adc FRAME
and XX
bne black
lda FRAME ; color is based on frame
lsr
lsr
lsr
lsr
bne not_zero ; but no color 0 (would be all black)
lda #3 ; how about purple instead
not_zero:
.byte $2C ; bit trick
black:
lda #$00
jsr SETCOL ; set top/bottom nibble same color
ldy XX
txa
jsr PLOT1 ; PLOT AT (GBASL),Y
dec XX
bpl sier_xloop
dex
bpl sier_yloop
done:
bmi sier_loop