dos33fsprogs/ootw/gr_make_quake.s

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;=========================================================
; gr_make_quake
;=========================================================
; Take image in $c00
; Copy to $BC00
; Actually copy lines 2..41 to 0..39
gr_make_quake:
ldx #0
make_quake_loop:
lda gr_offsets,x
sta OUTL
lda gr_offsets+1,x
clc
adc #$B8
sta OUTH
inx
inx
lda gr_offsets,x
sta INL
lda gr_offsets+1,x
clc
adc #$8
sta INH
ldy #39
quake_inner:
lda (INL),Y
sta (OUTL),Y
dey
bpl quake_inner
cpx #40
bne make_quake_loop
; write zeros to the rest
quake_clear_bottom:
lda gr_offsets,x
sta OUTL
lda gr_offsets+1,x
clc
adc #$B8
sta OUTH
inx
inx
ldy #39
lda #0
quake_clear_inner:
sta (OUTL),Y
dey
bpl quake_clear_inner
cpx #48
bne quake_clear_bottom
; clear the extra two lines from the original
quake_clear_extra:
ldx #40
lda gr_offsets,x
sta OUTL
lda gr_offsets+1,x
clc
adc #$8
sta OUTH
ldy #39
lda #0
quake_clear_extra_inner:
sta (OUTL),Y
dey
bpl quake_clear_extra_inner
rts ; 6