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xmas2018: get colors right on scroll

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This commit is contained in:
Vince Weaver 2018-12-20 11:40:56 -05:00
parent 2426cae3c3
commit 816edd964a
1 changed files with 18 additions and 12 deletions
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30
xmas_2018/merry.s
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@ -312,7 +312,8 @@ scroll_done:
; increment and loop: 7 ; increment and loop: 7
; 5 return ; 5 return
; ;
; total = (93*40)+7=3727 ; original total = (93*40)+7=3727
;
hgr_scroll_line: hgr_scroll_line:
ldy #0 ; 2 ldy #0 ; 2
@ -328,7 +329,21 @@ hgr_scroll_line_loop:
dey ; restore Y ; 2 dey ; restore Y ; 2
;============ ;============
; 20 ; 20
get_offpage_byte:
cpy #39 ; 2
bne not_thirtynine ; 3
sty TEMPY ; 3
ldy #0 ; 2
lda (INL),Y ; 5
sta NEXT ; 3
ldy TEMPY ; 3
not_thirtynine:
;===================
; usually: 5
; if in bit 2 or 6 of horiz scroll, shift the color bit over
; makes some color flicker, is there a better way?
high_bit: high_bit:
lda COUNTL ; 3 lda COUNTL ; 3
cmp #2 ; 2 cmp #2 ; 2
@ -348,18 +363,8 @@ done_high_bit:
;=================== ;===================
; worst: 22 ; worst: 22
get_offpage_byte:
cpy #39 ; 2
bne not_thirtynine ; 3
sty TEMPY ; 3
ldy #0 ; 2
lda (INL),Y ; 5
sta NEXT ; 3
ldy TEMPY ; 3
;===================
; usually: 5
not_thirtynine: prepare_bits:
; get right byte, bottom 2 bits, shifted left to be in 6+5 ; get right byte, bottom 2 bits, shifted left to be in 6+5
lda NEXT ; 3 lda NEXT ; 3
and #$3 ; 2 and #$3 ; 2
@ -372,6 +377,7 @@ not_thirtynine:
;========== ;==========
; 18 ; 18
output_new:
; get current, mask off bottom 2 bits (no longer needed) ; get current, mask off bottom 2 bits (no longer needed)
; then OR in the saved high (color) bit as well as NEXT bits ; then OR in the saved high (color) bit as well as NEXT bits
lda CURRENT ; 3 lda CURRENT ; 3