55 lines
1.0 KiB
ArmAsm
55 lines
1.0 KiB
ArmAsm
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;=========================================
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; vlin
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;=========================================
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; X, V2 at Y
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vlin:
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sty TEMPY ; save Y (x location)
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vlin_loop:
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txa ; a=x (get first y)
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and #$fe ; Clear bottom bit
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tay ;
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lda gr_offsets,Y ; lookup low-res memory address low
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sta GBASL ; put it into our indirect pointer
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iny
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lda gr_offsets,Y ; lookup low-res memory address high
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clc
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adc DRAW_PAGE ; add in draw page offset
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sta GBASH ; put into top of indirect
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ldy TEMPY ; load back in y (x offset)
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txa ; load back in x (current y)
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lsr ; check the low bit
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bcc vlin_low ; if not set, skip to low
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vlin_high:
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lda #$F0 ; setup masks
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sta MASK
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lda #$0f
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bcs vlin_too_slow
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vlin_low: ; setup masks
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lda #$0f
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sta MASK
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lda #$f0
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vlin_too_slow:
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and (GBASL),Y ; mask current byte
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sta (GBASL),Y ; and store back
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lda MASK ; mask the color
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and COLOR
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ora (GBASL),Y ; or into the right place
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sta (GBASL),Y ; store it
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inx ; increment X (current y)
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cpx V2 ; compare to the limit
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bcc vlin_loop ; if <= then loop
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rts ; return
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