dos33fsprogs/demos/trogdor/vertical_scroll.s
Vince Weaver 626121ef29 trogdor: scroll in cottage
also move things around as we hit the 16k limit
2024-01-25 00:19:13 -05:00

92 lines
1.4 KiB
ArmAsm

;=======================================
; hgr_vertical scroll
;=======================================
; scrolls from $6000 to page1
; jumps increments of 8 for speed
;=======================================
; offset line in $6000 to copy in from in COUNT
hgr_vertical_scroll_left:
lda #0
beq hgr_vertical_scroll_common
hgr_vertical_scroll_right:
lda #20
hgr_vertical_scroll_common:
sta vscroll_offset_smc+1
hgr_vertical_scroll:
ldx #0 ; start at top
outer_vscroll_loop:
lda hposn_low,X ; get page1 address
sta OUTL ; set as output
lda hposn_high,X
sta OUTH
txa ; get address of X+8
clc ; and set as input
adc #8
tay
lda hposn_low,y
sta INL
lda hposn_high,Y
sta INH
ldy #29 ; only scroll from 9..29
inner_vscroll_loop:
lda (INL),Y
sta (OUTL),Y
dey
cpy #9
bpl inner_vscroll_loop
inx
cpx #184
bne outer_vscroll_loop
;================================
; copy in off screen
; for now from 0..19
hgr_vertical_scroll2:
ldx #184 ; start 8 from bottom
outer_vscroll_loop2:
lda hposn_low,X
clc
adc #10 ; copy to middle of screen
sta OUTL
lda hposn_high,X
sta OUTH
ldy COUNT
lda hposn_low,Y
clc
vscroll_offset_smc:
adc #$0
sta INL
lda hposn_high,Y
clc
adc #$40 ; load from $6000
sta INH
ldy #19
inner_vscroll_loop2:
lda (INL),Y
sta (OUTL),Y
dey
bpl inner_vscroll_loop2
inc COUNT
inx
cpx #192
bne outer_vscroll_loop2
rts