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GSCats
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Basic sine-wave terrain generation

This commit is contained in:
blondie7575 2017-08-12 21:25:36 -07:00
parent e46d45272d
commit c412d4a021
4 changed files with 37 additions and 23 deletions
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BIN
gscats.2mg
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2
gscats.s
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@ -29,7 +29,7 @@ mainBank2:
ldx #$2222
jsr colorFill
; jsr generateTerrain
jsr generateTerrain
jsr compileTerrain
jsr clipTerrain

2
tables.s
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@ -30,7 +30,7 @@ sineTable:
.byte $26, $28, $2B, $2D, $2F, $32, $34, $37
.byte $39, $3C, $3F, $41, $44, $47, $4A, $4D
.byte $4F, $52, $55, $58, $5B, $5E, $61, $64
.byte $67, $6A, $6D, $70, $74, $77, $7A, $7D
.byte $67, $6A, $6D, $70, $74, $77, $7A, $7D, $80 ; One byte wrap for easier 16-byte sampling
vramRowEndsMinusOne:
.word $209f,$213f,$21df,$227f,$231f,$23bf,$245f,$24ff,$259f,$263f,$26df,$277f,$281f,$28bf,$295f,$29ff,$2a9f,$2b3f,$2bdf,$2c7f

56
terrain.s
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@ -232,31 +232,45 @@ compileTerrainOpcode:
;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;
; generateTerrain
;
; Trashes A and Y
; Trashes everything
;
generateTerrain:
ldy #0
ldx #0
lda #terrainData
sta SCRATCHL
generateTerrainLoop:
phy
tya ; Pull an interesting value out of the sine table
and #$00ff
tay
lda sineTable,y
and #$004f
ply
lda sineTable,x
lsr
lsr
lsr
lsr
lsr
lsr
lsr
lsr
lsr
lsr
clc
adc #30
sta (SCRATCHL),y
sec
lda #MAXTERRAINHEIGHT
sbc (SCRATCHL),y
sta (SCRATCHL),y
iny
iny
inx
inx
inx
txa
and #$00ff
tax
cpy #TERRAINWIDTH/2
bne generateTerrainLoop
@ -268,16 +282,16 @@ generateTerrainLoop:
; Terrain data, stored as height values 4 pixels wide
terrainData:
.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
; .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/2
.repeat TERRAINWIDTH/4 ; VISIBLETERRAINWIDTH
.word 0
.endrepeat