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85 lines
1.7 KiB
ArmAsm
85 lines
1.7 KiB
ArmAsm
include "includes.i"
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xdef InitialiseBackground
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xdef RenderNextBackgroundFrame
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xdef backgroundScrollX
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xdef backgroundOnscreen
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xdef backgroundOffscreen
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InitialiseBackground:
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move.l #0,backgroundScrollX
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move.l backgroundOffscreen,a0
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move.l #0,d0
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move.l #256+10,d1
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move.l #0,d2
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jsr BlitFillColor
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jsr WaitVerticalBlank
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jsr SwitchBuffers
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move.l backgroundOffscreen,a0
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move.l #0,d0
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move.l #256+10,d1
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move.l #0,d2
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jsr BlitFillColor
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rts
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RenderBackgroundTile:
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;; a2 - map
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move.l backgroundScrollX,d0
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lsr.w #BACKGROUND_SCROLL_SHIFT_CONVERT,d0 ; convert to pixels
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lsr.w #3,d0 ; bytes to scroll
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move.l backgroundOffscreen,a0
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add.l d0,a0
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lea backgroundTilemap,a1
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add.l #BITPLANE_WIDTH_BYTES-2,a0 ; dest
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add.w (a2),a1 ; source tile
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move.l backgroundScrollX,d2
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lsr.b #BACKGROUND_SCROLL_SHIFT_CONVERT,d2 ; convert to pixels
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andi.w #$f,d2 ; find the shift component
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jsr BlitBackgroundTile
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cmp.l #backgroundBitplanes1,backgroundOffscreen
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bne .offsetSub
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add.l #backgroundBitplanes2-backgroundBitplanes1,a0
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bra .doBlit
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.offsetSub:
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sub.l #backgroundBitplanes2-backgroundBitplanes1,a0
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.doBlit:
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jsr BlitBackgroundTile
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rts
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RenderNextBackgroundFrame:
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lea backgroundMap,a2
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move.l backgroundScrollX,d0
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lsr.l #BACKGROUND_SCROLL_TILE_INDEX_CONVERT,d0
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and.b #$fe,d0
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add.l d0,a2
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cmp.w #$FFFF,20(a2)
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bne .skip
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move.l #0,backgroundScrollX
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.skip:
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bsr RenderBackgroundTile
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rts
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backgroundScrollX:
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dc.l 0
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backgroundTilemap:
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incbin "out/background.bin"
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backgroundMap:
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include "out/background-map.s"
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dc.w $FFFF
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backgroundOnscreen:
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dc.l backgroundBitplanes1
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backgroundOffscreen:
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dc.l backgroundBitplanes2
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section .bss
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backgroundBitplanes1:
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ds.b IMAGESIZE
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ds.b LINESIZE*10
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backgroundBitplanes2:
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ds.b IMAGESIZE
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ds.b LINESIZE*10
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