dos33fsprogs/megademo/gr_scroll.s

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2018-10-03 03:13:17 +00:00
;.ifndef scroll_row1
;scroll_row1 EQU $8A00
;scroll_row2 EQU $8B00
;scroll_row3 EQU $8C00
;scroll_row4 EQU $8D00
;.endif
SCROLL_LENGTH = $61
;OFFSET = $62
;========================
; scroll some text
;========================
; RLE compressed data in INL/INH
; CV is Y position to display at
gr_scroll:
lda #0
sta OFFSET
;=======================
; decompress scroll text
;=======================
jsr decompress_scroll
scroll_loop:
ldx #0
ldy CV
lsr
lda gr_offsets,Y ; get position
sta sm1+1
lda gr_offsets+2,Y ; get position
sta sm2+1
lda gr_offsets+4,Y ; get position
sta sm3+1
lda gr_offsets+6,Y ; get position
sta sm4+1
iny
clc
lda gr_offsets,Y ; get position
adc DRAW_PAGE
sta sm1+2
lda gr_offsets+2,Y ; get position
adc DRAW_PAGE
sta sm2+2
lda gr_offsets+4,Y ; get position
adc DRAW_PAGE
sta sm3+2
lda gr_offsets+6,Y ; get position
adc DRAW_PAGE
sta sm4+2
ldy OFFSET
draw_loop:
lda scroll_row1,Y
sm1:
sta $400,X
lda scroll_row2,Y
sm2:
sta $480,X
lda scroll_row3,Y
sm3:
sta $500,X
lda scroll_row4,Y
sm4:
sta $580,X
iny
inx
cpx #40
bne draw_loop
;==================
; flip pages
;==================
jsr page_flip ; 6
;==================
; delay
;==================
lda #125
jsr WAIT
;==================
; loop forever
;==================
clc
lda OFFSET
adc #40
cmp SCROLL_LENGTH
beq done_scrolling
inc OFFSET
jmp scroll_loop ; 3
done_scrolling:
rts
;=======================
; decompress scroll
;=======================
decompress_scroll:
ldy #0
jsr scroll_load_and_increment
sta SCROLL_LENGTH
lda #<scroll_row1
sta OUTL
lda #>scroll_row1
sta OUTH
decompress_scroll_loop:
jsr scroll_load_and_increment ; load compressed value
cmp #$A1 ; EOF marker
beq done_decompress_scroll ; if EOF, exit
pha ; save
and #$f0 ; mask
cmp #$a0 ; see if special AX
beq decompress_scroll_special
pla ; note, PLA sets flags!
ldx #$1 ; only want to print 1
bne decompress_scroll_run
decompress_scroll_special:
pla
and #$0f ; check if was A0
bne decompress_scroll_color ; if A0 need to read run, color
decompress_scroll_large:
jsr scroll_load_and_increment ; get run length
decompress_scroll_color:
tax ; put runlen into X
jsr scroll_load_and_increment ; get color
decompress_scroll_run:
sta (OUTL),Y
pha
clc ; increment 16-bit pointer
lda OUTL
adc #$1
sta OUTL
lda OUTH
adc #$0
sta OUTH
pla
dex ; repeat for X times
bne decompress_scroll_run
beq decompress_scroll_loop ; get next run
done_decompress_scroll:
rts
scroll_load_and_increment:
lda (INL),Y ; load and increment 16-bit pointer
pha
clc
lda INL
adc #$1
sta INL
lda INH
adc #$0
sta INH
pla
rts