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;;; Subroutine: render
;;; Convert 1px per byte array at pixarray to packed 8px/byte at screen.
; pixarray is 170x170. screen is 256x170 (TODO: fix display list).
; each screen line is: 43 blank px, 170 graphics px, 43 blank.
screenbyte = FR0
colcount = FR0+1
render:
lda #<screen
sta screenptr
lda #>screen
sta screenptr+1
lda #<pixarray
sta pixptr
lda #>pixarray
sta pixptr+1
ldx #0
rline:
lda #0
sta colcount
sta screenbyte
; ; clear 40px on left
; ldy #4
;lclr:
; sta (screenptr),y
; dey
; bpl lclr
;
; ; clear 40px on right
; ldy #$1b
;rclr:
; sta (screenptr),y
; iny
; cpy #$20
; bne rclr
; clear whole line. this is why pixarray is offset from screen by
; one screen line.
ldy #$1f
rclr:
sta (screenptr),y
dey
bpl rclr
; first pixels start at column 40, plus...
lda #5
sta screenbyte
lda #$10 ; ...mask starts out 0001000, 3 more blank px on left
sta pixmask
rpix:
ldy colcount ; ranges 0 to 169
lda (pixptr),y
beq notset ; 0 = not set, non-zero = set
; if we found a set pixel, set it in the bitmap
ldy screenbyte
lda (screenptr),y
ora pixmask
sta (screenptr),y
notset:
; pixmask >>= 1; if(pixmask == 0) { pixmask = 0x80; screenbyte++; }
lsr pixmask
bne pmok
;ror pixmask
lda #$80
sta pixmask
inc screenbyte
pmok:
inc colcount
lda colcount
cmp #$aa
bne rpix
; pixptr += 0xaa;
clc
adc pixptr
sta pixptr
lda pixptr+1
adc #0
sta pixptr+1
; screenptr += 0x20;
clc
lda screenptr
adc #$20
sta screenptr
lda screenptr+1
adc #0
sta screenptr+1
inx
cpx #$aa ; hit last line yet?
bne rline ; if not, go render next line.
rts
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