dos33fsprogs/demos/trogdor/horiz_scroll_double.s
2024-01-20 23:10:30 -05:00

120 lines
1.7 KiB
ArmAsm

;======================================
; do very simple horizontal scroll
;======================================
; skips by 4 because we need fairly high FPS
; originally ~12 seconds to scroll 80 (twice)
; also assumes every-other line the same
; screens to pan in $2000/$4000 to left
horiz_pan_skip:
pan_loop:
; how many times to scroll
lda #0
sta COUNT
pan_outer_outer_loop:
ldx #191
pan_outer_loop:
txa
pha
; self-modify the PAGE1 high input addresses
lda hposn_high,X
sta pil_in_smc1+2 ; input source
sta pil_out_smc1+2 ; output odd
sta pil_out_smc4+2
;self modify the PAGE2 high input addresses
eor #$60
sta pil_in_page2_smc1+2
; self modify the PAGE1 LOW addresses
lda hposn_low,X
sta pil_out_smc1+1 ; output odd
sta pil_out_smc4+1 ; output odd
; self modify the PAGE1 LOW input addresses
sta pil_in_smc1+1 ; input is regular+1
inc pil_in_smc1+1
; offset in PAGE2 to get input from
clc
adc COUNT
sta pil_in_page2_smc1+1
inx
lda hposn_high,X
sta pil_out_smc2+2 ; output even high
sta pil_out_smc5+2
lda hposn_low,X ; output even low
sta pil_out_smc2+1
sta pil_out_smc5+1
;=========================
; inner loop, from 0-39
ldy #0
pan_inner_loop:
; load in+1, store to in
; if completely unrolled, would save 1 cycle for store and
; 5 for the branch/loop
; 192*6=not a lot
pil_in_smc1:
lda $2000+1,Y ; 4
pil_out_smc1:
sta $2000,Y ; 5
pil_out_smc2:
sta $2000,Y ; 5
iny ; 2
cpy #39 ; 2
bne pan_inner_loop ; 2/3
; for right edge, scroll in from PAGE2
pil_in_page2_smc1:
lda $4000
pil_out_smc4:
sta $2000,Y
pil_out_smc5:
sta $2000,Y
pla
tax
dex
dex
cpx #$ff
bne pan_outer_loop
inc COUNT
lda COUNT
cmp #39
bne pan_outer_outer_loop
rts