131 lines
1.8 KiB
ArmAsm
131 lines
1.8 KiB
ArmAsm
;=========================================================
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; gr_twoscreen_scroll, 40x48 version
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;=========================================================
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; offset is in BG_SCROLL, must be multiple of 2
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;
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; two screens, top is at $1000, bottom at $BC00
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; copy lines Y-48 from $1000 to $c00
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; copy lines 0 - (48-y) from $BC00 to $c00
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gr_twoscreen_scroll:
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lda #0
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sta TEMPY ; dest
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ldy BG_SCROLL
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cpy #48
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beq gr_twoscreen_bottom ; no top to draw
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gr_twoscreen_top:
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; calculate source
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lda gr_offsets+1,Y
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clc
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adc #($10-4)
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sta gr_twoscreen_smc_src+2
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lda gr_offsets,Y
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sta gr_twoscreen_smc_src+1
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tya
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pha
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; calculate destination
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lda TEMPY
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tay
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lda gr_offsets+1,Y
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clc
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adc #($c-4)
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sta gr_twoscreen_smc_dst+2
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lda gr_offsets,Y
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sta gr_twoscreen_smc_dst+1
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ldx #0
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gr_twoscreen_line_loop:
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gr_twoscreen_smc_src:
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lda $1000,X
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gr_twoscreen_smc_dst:
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sta $c00,X
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inx
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cpx #40
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bne gr_twoscreen_line_loop
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inc TEMPY
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inc TEMPY
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pla
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tay
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iny
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iny
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cpy #48
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bne gr_twoscreen_top
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;===============================
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; now copy the bottom from $BC00
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lda BG_SCROLL
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beq done_twoscreen_bottom ; if 0, no bottom
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gr_twoscreen_bottom:
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ldy #0
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gr_twoscreen_bottom_loop:
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; calculate source
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lda gr_offsets+1,Y
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clc
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adc #($bc-4)
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sta gr_twoscreen_bottom_smc_src+2
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lda gr_offsets,Y
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sta gr_twoscreen_bottom_smc_src+1
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tya
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pha
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; calculate destination
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lda TEMPY
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tay
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lda gr_offsets+1,Y
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clc
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adc #($c-4)
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sta gr_twoscreen_bottom_smc_dst+2
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lda gr_offsets,Y
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sta gr_twoscreen_bottom_smc_dst+1
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ldx #0
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gr_twoscreen_bottom_line_loop:
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gr_twoscreen_bottom_smc_src:
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lda $BC00,X
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gr_twoscreen_bottom_smc_dst:
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sta $c00,X
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inx
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cpx #40
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bne gr_twoscreen_bottom_line_loop
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inc TEMPY
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inc TEMPY
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pla
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tay
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iny
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iny
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cpy BG_SCROLL
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bne gr_twoscreen_bottom_loop
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done_twoscreen_bottom:
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rts ; 6
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