GSCats/terrain.s

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;
; terrain
;
; Created by Quinn Dunki on 7/29/17
;
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TERRAINWIDTH = 640 ; In pixels
MAXTERRAINHEIGHT = 100 ; In pixels
COMPILEDTERRAINROW = TERRAINWIDTH/4+3 ; In words, +2 to make room for clipping jump at end of row
VISIBLETERRAINWIDTH = TERRAINWIDTH/4 ; In words- width minus jump return padding
VISIBLETERRAINWINDOW = 80 ; In words
;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;
; renderTerrain
;
; No stack operations permitted here!
;
; Current implementation: X cycles per row
; Trashes all registers
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;
renderTerrain:
FASTGRAPHICS
ldy #MAXTERRAINHEIGHT
lda #$9cff ; 4 Point stack to end of VRAM
tcs ; 2
sec
lda #compiledTerrainEnd-VISIBLETERRAINWINDOW-3
sbc mapScrollPos
sta PARAML0
renderTerrainLoop:
lda #$0000 ; Background
ldx #$1111 ; Foreground
jmp (PARAML0)
renderRowComplete:
lda PARAML0
sec
sbc #COMPILEDTERRAINROW
sta PARAML0
dey
bne renderTerrainLoop
SLOWGRAPHICS
rts
;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;
; clipTerrain
;
;
clipTerrain:
SAVE_AXY
sec
lda #COMPILEDTERRAINROW*MAXTERRAINHEIGHT-3
sbc mapScrollPos
tay
ldx #MAXTERRAINHEIGHT
clipTerrainLoop:
clc ; Compute buffer to for saved data
txa
asl
asl
adc #clippedTerrainData-4
sta PARAML0
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lda compiledTerrain,y
sta (PARAML0) ; Preserve data we're overwriting
inc PARAML0
inc PARAML0
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and #$ff00
ora #$004c ; jmp in low byte
sta compiledTerrain,y
iny
lda compiledTerrain,y
sta (PARAML0) ; Preserve data we're overwriting
lda #renderRowComplete
sta compiledTerrain,y
tya
sec
sbc #COMPILEDTERRAINROW+1
tay
dex
bne clipTerrainLoop
RESTORE_AXY
rts
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;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;
; unclipTerrain
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;
;
unclipTerrain:
SAVE_AXY
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sec
lda #COMPILEDTERRAINROW*MAXTERRAINHEIGHT-3
sbc mapScrollPos
tay
ldx #MAXTERRAINHEIGHT
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unclipTerrainLoop:
clc ; Compute buffer that saved data is in
txa
asl
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asl
adc #clippedTerrainData-4
sta PARAML0
lda (PARAML0)
sta compiledTerrain,y
inc PARAML0
inc PARAML0
iny
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lda (PARAML0)
sta compiledTerrain,y
tya
sec
sbc #COMPILEDTERRAINROW+1
tay
dex
bne unclipTerrainLoop
RESTORE_AXY
rts
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;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;
; compileTerrain
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;
;
;
compileTerrain:
SAVE_AY
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ldy #MAXTERRAINHEIGHT-1
lda #compiledTerrain
sta PARAML0
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compileTerrainLoop:
sty PARAML1
jsr compileTerrainRow
dey
bmi compileTerrainDone
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clc
lda #COMPILEDTERRAINROW
adc PARAML0
sta PARAML0
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bra compileTerrainLoop
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compileTerrainDone:
RESTORE_AY
rts
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;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;
; compileTerrainRow
;
; PARAML0 = Start of compiled row data
; PARAML1 = Row index
;
compileTerrainRow:
SAVE_AXY
ldy #0
ldx #0
compileTerrainColumnLoop:
stz compileTerrainOpcode
; Right half
lda terrainData,x
cmp PARAML1
bcc compileTerrainColumnBGRight
beq compileTerrainColumnBGRight
lda #$00da
compileTerrainColumnLeft:
sta compileTerrainOpcode
inx
inx
lda terrainData,x
cmp PARAML1
bcc compileTerrainColumnBGLeft
beq compileTerrainColumnBGLeft
lda compileTerrainOpcode
ora #$da00
compileTerrainColumnStore:
sta (PARAML0),y
inx
inx
iny
iny
cpy #VISIBLETERRAINWIDTH
bne compileTerrainColumnLoop
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RESTORE_AXY
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rts
compileTerrainColumnBGRight:
lda #$0048
bra compileTerrainColumnLeft
compileTerrainColumnBGLeft:
lda compileTerrainOpcode
ora #$4800
bra compileTerrainColumnStore
compileTerrainOpcode:
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.word 0
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;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;
; generateTerrain
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;
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; Trashes everything
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;
generateTerrain:
ldy #0
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ldx #0
lda #terrainData
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sta SCRATCHL
generateTerrainLoop:
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lda sineTable,x
lsr
lsr
lsr
lsr
lsr
lsr
lsr
lsr
lsr
lsr
clc
adc #30
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sta (SCRATCHL),y
iny
iny
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inx
inx
inx
txa
and #$00ff
tax
cpy #TERRAINWIDTH/2
bne generateTerrainLoop
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rts
; Terrain data, stored as height values 4 pixels wide
terrainData:
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; .word 0,1,2,3,4,5,6,7,8,9,10,11,12,13,14,15,16,17,18,19
; .word 20,21,22,23,24,25,26,27,28,29,30,31,32,33,34,35,36,37,38,39
; .word 40,39,38,37,36,35,34,33,32,31,30,29,28,27,26,25,24,23,22,21
; .word 20,19,18,17,16,15,14,13,12,11,10,9,8,7,6,5,4,3,2,80
; .word 1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1
; .word 1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1
; .word 1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1
; .word 1,1,1,1,1,1,1,1,1,1,1,1,1,1,0,1,0,0,0,80
.repeat TERRAINWIDTH/4 ; VISIBLETERRAINWIDTH
.word 0
.endrepeat
compiledTerrain:
.repeat COMPILEDTERRAINROW * MAXTERRAINHEIGHT
.byte 0
.endrepeat
compiledTerrainEnd:
clippedTerrainData:
.repeat MAXTERRAINHEIGHT
.byte 0,0,0,0 ; xx,jmp,addr
.endrepeat
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