dos33fsprogs/demos/another_myst/gr_unrle.s

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2020-06-20 18:48:19 +00:00
;=================
; load RLE image
;=================
; Output is A:00 (assume page aligned)
; Input is in GBASH/GBASL
; format: first byte=xsize
; A0,X,Y means run of X bytes of Y color
; A1 means end of file
; A2-AF,X means run of low nibble, X color
; if high nibble not A: just display color
; CV = current Y
; CH = max xsize (usually 40)
; TEMP = page
; TEMPY= current X
load_rle_gr:
sec
sbc #4 ; adjust page to write to
; to match gr_offsets
sta TEMP
ldy #$0 ; init Y to 0
sty CV
jsr load_and_increment ; load xsize
sta CH
jsr unrle_new_y
rle_loop:
jsr load_and_increment
tax
cmp #$A1 ; if 0xa1
beq rle_done ; we are done
and #$f0 ; mask
cmp #$a0 ; see if special AX
beq decompress_special
; not special, just color
txa ; put color back in A
ldx #$1 ; only want to print 1
bne decompress_run
decompress_special:
txa ; put read value back in A
and #$0f ; check if was A0
bne decompress_color ; if A0 need to read run, color
decompress_large:
jsr load_and_increment ; run length now in A
decompress_color:
tax ; put runlen into X
jsr load_and_increment ; get color into A
decompress_run:
rle_run_loop:
sta (BASL),y ; write out the value
inc BASL
dec TEMPY
bne rle_not_eol ; if less then keep going
; if here, we are > max_X
inc CV
inc CV
pha
jsr unrle_new_y
pla
rle_not_eol:
dex
bne rle_run_loop ; if not zero, keep looping
beq rle_loop ; and branch always
rle_done:
lda #$15 ; move the cursor somewhere sane
sta CV
rts
load_and_increment:
lda (GBASL),Y
inc GBASL
bne lai_no_oflo
inc GBASH
lai_no_oflo:
rts
unrle_new_y:
ldy CV
lda gr_offsets,Y
sta BASL
lda gr_offsets+1,Y
clc
adc TEMP ; adjust for page
sta BASH
lda CH
sta TEMPY
ldy #0
rts