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132 lines
2.0 KiB
ArmAsm
132 lines
2.0 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 = 128 ; In pixels
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;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;
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; renderTerrainColumn
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;
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; This is not fast- probably only useful for debugging
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;
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; Y = Index into height data
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; PARAM24 = 24-bit pointer to bottom of column in VRAM
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;
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; Trashes A and X
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renderTerrainColumn:
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phy
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BITS8
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lda PARAM24+2
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sta renderTerrainColumnSMC+3
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BITS16
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ply
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lda PARAM24
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sta renderTerrainColumnSMC+1
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pha ; Cache 16-bit VRAM pointer on the stack
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lda terrainData,y ; Cache terrain height on the stack
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and #$00ff
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sta renderTerrainColumnHeight
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ldx #0
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renderTerrainColumnLoop:
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inx
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cpx #MAXTERRAINHEIGHT
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beq renderTerrainColumnDone
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cpx renderTerrainColumnHeight
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bpl renderTerrainColumnBlack
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lda #$1111
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bra renderTerrainColumnSMC
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renderTerrainColumnBlack:
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lda #$0000
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renderTerrainColumnSMC:
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sta $e19c60
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pla
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sec
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sbc #160
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sta renderTerrainColumnSMC+1
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pha
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bra renderTerrainColumnLoop
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renderTerrainColumnDone:
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pla
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rts
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renderTerrainColumnHeight:
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.word 0
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;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;
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; renderTerrainColumns
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;
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; This is not fast- probably only useful for debugging
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;
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; Y = Start column
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;
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; Trashes all registers
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;
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renderTerrainColumns:
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LOADPARAM24 $e1e1,$9c60
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tya
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clc
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adc #80
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sta SCRATCHL
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renderTerrainColumnsLoop:
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jsr renderTerrainColumn
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iny
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cpy SCRATCHL
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beq renderTerrainColumnsDone
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inc PARAM24
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inc PARAM24
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bra renderTerrainColumnsLoop
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renderTerrainColumnsDone:
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rts
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;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;
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; generateTerrain
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;
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; Trashes A and Y
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;
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generateTerrain:
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ldy #0
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lda #terrainData
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sta SCRATCHL
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generateTerrainLoop:
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phy
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tya ; Pull an interesting value out of the sine table
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and #$00ff
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tay
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lda sineTable,y
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and #$7f7f
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ply
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sta (SCRATCHL),y
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iny
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cpy #TERRAINWIDTH/4
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bne generateTerrainLoop
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rts
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; Terrain data, stored as height values 4 pixels wide
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terrainData:
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.repeat TERRAINWIDTH/2
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.byte 0
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.endrepeat
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