mirror of
https://github.com/blondie7575/GSCats.git
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358 lines
5.3 KiB
ArmAsm
358 lines
5.3 KiB
ArmAsm
;
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; terrain
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;
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; Created by Quinn Dunki on 7/29/17
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;
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TERRAINWIDTH = 640 ; In pixels
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MAXTERRAINHEIGHT = 100 ; In pixels
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COMPILEDTERRAINROW = TERRAINWIDTH/4+3 ; In words, +2 to make room for clipping jump at end of row
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VISIBLETERRAINWIDTH = TERRAINWIDTH/4 ; In words- width minus jump return padding
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VISIBLETERRAINWINDOW = 80 ; In words
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;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;
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; renderTerrain
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;
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; No stack operations permitted here!
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;
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; Current implementation: X cycles per row
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; Trashes all registers
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;
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renderTerrain:
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FASTGRAPHICS
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ldy #MAXTERRAINHEIGHT
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lda #$9cff ; 4 Point stack to end of VRAM
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tcs ; 2
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sec
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lda #compiledTerrainEnd-VISIBLETERRAINWINDOW-3
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sbc mapScrollPos
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sta PARAML0
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renderTerrainLoop:
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lda #$0000 ; Background
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ldx #$1111 ; Foreground
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jmp (PARAML0)
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renderRowComplete:
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lda PARAML0
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sec
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sbc #COMPILEDTERRAINROW
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sta PARAML0
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dey
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bne renderTerrainLoop
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SLOWGRAPHICS
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rts
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;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;
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; craterTerrain
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;
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; PARAML0 = X pos of center in pixels from logical left terrain edge
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; PARAML1 = Y pos of center in pixels from bottom terrain edge
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; Y = Radius of circle, in pixels
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;
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; Trashes SCRATCHL
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craterTerrain:
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SAVE_AX
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lda #TERRAINWIDTH ; Convert X pos to terrain-right byte count
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sec
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sbc PARAML0
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sty SCRATCHL ; Center width
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sbc SCRATCHL
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and #$fffe ; Force even
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clc
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adc #terrainData
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sta PARAML0
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lda circleTable,y ; Look up circle data
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sta SCRATCHL
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tya ; Iterate over diameter
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asl
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tay
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craterTerrainLoop:
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dey
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dey
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bmi craterTerrainDone
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lda (SCRATCHL),y ; Fetch circle Y value
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clc
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adc PARAML1 ; Convert to terrain-space
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sta SCRATCHL2
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lda (PARAML0),y
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cmp SCRATCHL2
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bmi craterTerrainLoop
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lda SCRATCHL2 ; Circle value is lower, so use that
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sta (PARAML0),y
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bra craterTerrainLoop
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craterTerrainDone:
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lda #1
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sta terrainDirty
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RESTORE_AX
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rts
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;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;
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; clipTerrain
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;
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;
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clipTerrain:
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SAVE_AXY
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sec
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lda #COMPILEDTERRAINROW*MAXTERRAINHEIGHT-3
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sbc mapScrollPos
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tay
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ldx #MAXTERRAINHEIGHT
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clipTerrainLoop:
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clc ; Compute buffer to for saved data
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txa
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asl
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asl
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adc #clippedTerrainData-4
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sta PARAML0
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lda compiledTerrain,y
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sta (PARAML0) ; Preserve data we're overwriting
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inc PARAML0
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inc PARAML0
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and #$ff00
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ora #$004c ; jmp in low byte
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sta compiledTerrain,y
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iny
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lda compiledTerrain,y
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sta (PARAML0) ; Preserve data we're overwriting
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lda #renderRowComplete
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sta compiledTerrain,y
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tya
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sec
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sbc #COMPILEDTERRAINROW+1
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tay
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dex
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bne clipTerrainLoop
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RESTORE_AXY
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rts
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;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;
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; unclipTerrain
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;
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;
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unclipTerrain:
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SAVE_AXY
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sec
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lda #COMPILEDTERRAINROW*MAXTERRAINHEIGHT-3
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sbc mapScrollPos
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tay
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ldx #MAXTERRAINHEIGHT
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unclipTerrainLoop:
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clc ; Compute buffer that saved data is in
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txa
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asl
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asl
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adc #clippedTerrainData-4
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sta PARAML0
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lda (PARAML0)
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sta compiledTerrain,y
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inc PARAML0
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inc PARAML0
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iny
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lda (PARAML0)
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sta compiledTerrain,y
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tya
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sec
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sbc #COMPILEDTERRAINROW+1
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tay
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dex
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bne unclipTerrainLoop
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RESTORE_AXY
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rts
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;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;
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; compileTerrain
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;
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;
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;
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compileTerrain:
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SAVE_AY
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ldy #MAXTERRAINHEIGHT-1
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lda #compiledTerrain
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sta PARAML0
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compileTerrainLoop:
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sty PARAML1
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jsr compileTerrainRow
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dey
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bmi compileTerrainDone
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clc
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lda #COMPILEDTERRAINROW
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adc PARAML0
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sta PARAML0
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bra compileTerrainLoop
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compileTerrainDone:
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RESTORE_AY
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rts
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;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;
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; compileTerrainRow
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;
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; PARAML0 = Start of compiled row data
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; PARAML1 = Row index
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;
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; Note: DA = PHX = BGBG
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; 48 = PHA = FGFG
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; 5A = PHY =
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; 0B = PHD =
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compileTerrainRow:
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SAVE_AXY
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ldy #0
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ldx #0
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compileTerrainColumnLoop:
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stz compileTerrainOpcode
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; Right half
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lda terrainData,x
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cmp PARAML1
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bcc compileTerrainColumnBGRight
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beq compileTerrainColumnBGRight
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lda #$00da
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compileTerrainColumnLeft:
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sta compileTerrainOpcode
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inx
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inx
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inx ; Double-up for now
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inx
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lda terrainData,x
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cmp PARAML1
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bcc compileTerrainColumnBGLeft
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beq compileTerrainColumnBGLeft
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lda compileTerrainOpcode
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ora #$da00
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compileTerrainColumnStore:
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sta (PARAML0),y
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inx
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inx
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inx ; Double-up for now
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inx
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iny
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iny
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cpy #VISIBLETERRAINWIDTH
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bne compileTerrainColumnLoop
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RESTORE_AXY
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rts
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compileTerrainColumnBGRight:
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lda #$0048
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bra compileTerrainColumnLeft
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compileTerrainColumnBGLeft:
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lda compileTerrainOpcode
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ora #$4800
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bra compileTerrainColumnStore
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compileTerrainOpcode:
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.word 0
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;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;
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; generateTerrain
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;
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; Trashes everything
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;
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generateTerrain:
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ldy #0
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ldx #0
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lda #terrainData
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sta SCRATCHL
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generateTerrainLoop:
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lda sineTable,x
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lsr
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lsr
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clc
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adc #30
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sta (SCRATCHL),y
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iny
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iny
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sta (SCRATCHL),y ; Double-up for now
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iny
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iny
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inx
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inx
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inx
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inx
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inx
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inx
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txa
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and #$03ff
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tax
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cpy #TERRAINWIDTH
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bne generateTerrainLoop
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lda #1
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sta terrainData
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rts
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; Terrain data, stored as height values 2 pixels wide (bytes)
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terrainData:
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.repeat TERRAINWIDTH/2
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.word 0
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.endrepeat
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compiledTerrain:
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.repeat COMPILEDTERRAINROW * MAXTERRAINHEIGHT
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.byte 0
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.endrepeat
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compiledTerrainEnd:
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clippedTerrainData:
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.repeat MAXTERRAINHEIGHT
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.byte 0,0,0,0 ; xx,jmp,addr
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.endrepeat
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