Implement fix for scanline mode compensation in BG1

This commit is contained in:
Lucas Scharenbroich 2023-03-10 19:00:26 -06:00
parent 9021ee4506
commit 7dd690ac04

View File

@ -37,9 +37,9 @@ _ResetBG1YTable
:stride equ tmp1
cmp #1 ; scanline mode?
bne :default
lda #$A0
lda #0
sta :base
lda #324
lda #327
sta :stride
bra :begin
:default
@ -96,22 +96,25 @@ _CopyToBG1
:src_flags equ tmp9
:dstptr2 equ tmp10
; scanline mode is tricky -- there's not enough space to make two full copies of a 328x200 bitmap buffer, but we can
; *barely* fit a (164 + 163) x 200 buffer. And, since the zero offset could use either end, this covers all of the cases.
sta :srcptr
stx :srcptr+2
sty :dstptr+2 ; Everything goes into this bank
sty :dstptr2+2
lda #$00A0
lda #0 ; Start a byte 1 because odd offsets might go back 1 byte and don't want to wrap around
sta :dstptr
clc
adc #164 ; leave a 4-byte gap in the middle
adc #164 ; The first part is 1-byte short, the second part is a full 164 bytes
sta :dstptr2
; "Normal" BG1 mode as a stride of 164 bytes and mirrors the BG0 size (328 x 208)
; In "Scanline" mode, the BG1 is treated as a 320x200 bitfield with each horizontal line doubled
lda :src_width
min #160
min #164
sta :src_width
lda :src_height
@ -121,12 +124,22 @@ _CopyToBG1
stz :line_cnt
:rloop
ldy #0 ; move forward in the image data and image data
; Handle first word as a special case
lda [:srcptr],y
sta [:dstptr2],y ; copy directly into the 164-byte buffer
iny
xba
sep #$20
sta [:dstptr],y ; only copy the high byte because the previous line occupies the low byte
rep #$20
iny
:cloop
lda [:srcptr],y
sta [:dstptr],y
sta [:dstptr2],y
:skip
iny
iny
@ -135,7 +148,7 @@ _CopyToBG1
lda :dstptr
clc
adc #324
adc #327
sta :dstptr
adc #164
sta :dstptr2
@ -203,7 +216,8 @@ _ApplyScanlineBG1XPos
tcd
ldx #0
tya
; tya
lda #0
:loop
sta 00,x ; store the value
inc
@ -364,12 +378,25 @@ _ApplyScanlineBG1YPos
rts
:_ApplyConstBG1YPos
lda #164
sec
sbc :shift_value
lda #164
sec
sbc :shift_value
clc
adc BG1StartXMod164
cmp #164+1
bcc *+5
sbc #164
; sec
; sbc BG1StartXMod164
; bpl *+6
; clc
; adc #160
; adc #164
; cmp #164
; bcc *+3
; sbc #164
; clc
; adc :shift_value
sta :shift_value