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!
;
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; Current implementation: Unknown cycles per row
; Trashes all registers
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;
renderTerrain:
FASTGRAPHICS
lda #MAXTERRAINHEIGHT
sta SCRATCHL2 ; Row counter
lda #$9cff ; 4 Point stack to end of VRAM
tcs ; 2
sec
lda #compiledTerrainEnd-VISIBLETERRAINWINDOW-3
sbc mapScrollPos
sta PARAML0
renderTerrainLoop:
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; Note that DP register is normally $0000, so that is used as the BG/BG case
lda #$0011 ; BG/FG
ldx #$1111 ; FG/FG
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ldy #$1100 ; FG/BG
jmp (PARAML0)
renderRowComplete:
lda PARAML0
sec
sbc #COMPILEDTERRAINROW
sta PARAML0
dec SCRATCHL2
bne renderTerrainLoop
SLOWGRAPHICS
rts
;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;
; craterTerrain
;
; PARAML0 = X pos of center in pixels from logical left terrain edge
; PARAML1 = Y pos of center in pixels from bottom terrain edge
; Y = Radius of circle, in pixels
;
; Trashes SCRATCHL
craterTerrain:
SAVE_AX
lda #TERRAINWIDTH ; Convert X pos to terrain-right byte count
sec
sbc PARAML0
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sty SCRATCHL ; Center width in bytes
sbc SCRATCHL
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and #$fffe ; Force even
clc
adc #terrainData
sta PARAML0
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lda circleTable,y ; Look up circle data
sta SCRATCHL
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tya ; Iterate over diameter
asl
tay
craterTerrainLoop:
dey
dey
bmi craterTerrainDone
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tya
clc
adc PARAML0 ; Clip to terrain edges
cmp #terrainData
bmi craterTerrainDone
cmp #terrainDataEnd
bpl craterTerrainLoop
lda (SCRATCHL),y ; Fetch circle Y value
clc
adc PARAML1 ; Convert to terrain-space
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bmi craterTerrainZero
sta SCRATCHL2
lda (PARAML0),y
cmp SCRATCHL2
bmi craterTerrainLoop
lda SCRATCHL2 ; Circle value is lower, so use that
sta (PARAML0),y
bra craterTerrainLoop
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craterTerrainZero: ; Circle went negative so clip to 0
lda #0
sta (PARAML0),y
bra craterTerrainLoop
craterTerrainDone:
lda #1
sta terrainDirty
RESTORE_AX
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
;
; Note: DA = PHX = FG/FG
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; 48 = PHA = FG/BG
; 5A = PHY = BG/FG
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; 0B = PHD = BG/BG
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compileTerrainRow:
SAVE_AXY
ldy #0
ldx #0
compileTerrainColumnLoop:
stz compileTerrainOpcode
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; Check column 0
lda terrainData,x
cmp PARAML1
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bcc compileTerrainColumn0BG
beq compileTerrainColumn0BG
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; Column 0 is FG, so check column 1
inx
inx
lda terrainData,x
cmp PARAML1
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bcc compileTerrainColumn1BG
beq compileTerrainColumn1BG
; Columns 0 and 1 are FG/FG, so PHX
lda #$00da
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compileTerrainColumn2:
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sta compileTerrainOpcode ; Cache results so far
; Check column 2
inx
inx
lda terrainData,x
cmp PARAML1
bcc compileTerrainColumn2BG
beq compileTerrainColumn2BG
; Column 2 is FG, so check column 3
inx
inx
lda terrainData,x
cmp PARAML1
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bcc compileTerrainColumn3BG
beq compileTerrainColumn3BG
; Columns 2 and 3 are FG/FG, so PHX
lda compileTerrainOpcode
ora #$da00
compileTerrainColumnStore:
sta (PARAML0),y
inx
inx
iny
iny
cpy #VISIBLETERRAINWIDTH
bne compileTerrainColumnLoop
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RESTORE_AXY
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rts
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compileTerrainColumn0BG:
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; Column 0 is BG, so check column 1
inx
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inx
lda terrainData,x
cmp PARAML1
bcc compileTerrainColumn01BG
beq compileTerrainColumn01BG
; Columns 0 and 1 are BG/FG, so PHA
lda #$0048
bra compileTerrainColumn2
compileTerrainColumn01BG:
; Columns 0 and 1 are BG/BG, so PHD
lda #$000b
bra compileTerrainColumn2
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compileTerrainColumn1BG:
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; Columns 0 and 1 are FG/BG, so PHY
lda #$005a
bra compileTerrainColumn2
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compileTerrainColumn2BG:
; Column 2 is BG, so check column 3
inx
inx
lda terrainData,x
cmp PARAML1
bcc compileTerrainColumn23BG
beq compileTerrainColumn23BG
; Columns 2 and 3 are BG/FG, so PHA
lda compileTerrainOpcode
ora #$4800
bra compileTerrainColumnStore
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compileTerrainColumn23BG:
; Columns 2 and 3 are BG, so PHD
lda compileTerrainOpcode
ora #$0b00
bra compileTerrainColumnStore
compileTerrainColumn3BG:
; Columns 2 and 3 are FG/BG, so PHY
lda compileTerrainOpcode
ora #$5a00
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
clc
adc #30
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sta (SCRATCHL),y
iny
iny
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inx
inx
inx
inx
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txa
and #$03ff
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tax
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cpy #TERRAINWIDTH
bne generateTerrainLoop
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; lda #1 ; Debug values
; sta terrainData
; lda #2
; sta compiledTerrain-4
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rts
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; Terrain data, stored as height values 2 pixels wide (bytes)
terrainData:
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.repeat TERRAINWIDTH/2
.word 0
.endrepeat
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terrainDataEnd:
compiledTerrain:
.repeat COMPILEDTERRAINROW * MAXTERRAINHEIGHT
.byte 0
.endrepeat
compiledTerrainEnd:
clippedTerrainData:
.repeat MAXTERRAINHEIGHT
.byte 0,0,0,0 ; xx,jmp,addr
.endrepeat
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