GSCats/dirt.s

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;
; dirt
;
; Created by Quinn Dunki on 12/29/19
;
MAXPARTICLES = 64
.macro PARTICLEPTR_XY
txa ; Pointer to particle structure from index
asl
asl
asl
asl
tay
.endmacro
;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;
; createDirtExplosion
;
; Simulate a bunch of dirt flying everywhere
;
; PARAML0 = X pos of circle left edge
; PARAML1 = Y pos of circle center
; PARAML2 = Radius (16 bits)
;
; Trashes SCRATCHL,SCRATCHL2,CACHEDATA
;
createDirtExplosion:
SAVE_AXY
lda #1
sta dirtExplosionActive
lda #3 ; Radius hard-coded for now
sta PARAML2
asl
sta CACHEDATA ; Cache diameter
ldx #0
ldy #0
createDirtExplosionLoop:
jsr createDirtExplosionColumn
inc PARAML0
inc PARAML0
iny
cpy CACHEDATA
bne createDirtExplosionLoop
RESTORE_AXY
rts
;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;
; createDirtExplosionColumn
;
; Create one column of a starting dirt explosion circle
; X = Particle index to start filling from
; Y = Local X index of column
; PARAML0 = X pos of column
; PARAML1 = Y pos of circle center
; PARAML2 = Radius (16 bits)
;
; X=> Last particle index we filled in +1
; Trashse SCRATCHL,SCRATCHL2
;
createDirtExplosionColumn:
SAVE_AY
lda PARAML2
pha
stx SCRATCHL2 ; Cache particle index
phy ; Look up circle table for our radius
lda PARAML2
asl
tay
lda circleTable,y
sta SCRATCHL
; Find starting Y from circle table
pla
asl
tay
lda (SCRATCHL),y
tax ; Row counter
pha
eor #$ffff
inc
sta PARAML2 ; Row counter end
pla
clc
adc PARAML1
sta SCRATCHL ; Current Y position
createDirtExplosionColumnLoop:
phx ; Find pointer to next particle to fill out
ldx SCRATCHL2
PARTICLEPTR_XY
plx
; X position - Always the same
lda PARAML0
sta dirtParticles+DP_POSX,y
asl ; Convert to 12.4
asl
asl
asl
sta dirtParticles+DP_PRECISEX,y
; Y position - Iterates from computed cache
lda SCRATCHL
sta dirtParticles+DP_POSY,y
asl ; Convert to 12.4
asl
asl
asl
sta dirtParticles+DP_PRECISEY,y
; X velocity. Need half to be negative. I feel like there
; should be a clever branchless way to do this, but I couldn't
; come up with it.
jsr random
lda RANDOM
bmi createDirtExplosionColumnLoopNegX
and #$00ff
bra createDirtExplosionColumnLoopNowY
createDirtExplosionColumnLoopNegX:
ora #$ff00
createDirtExplosionColumnLoopNowY:
sta dirtParticles+DP_VX,y
; Y velocity
jsr random
lda RANDOM
and #$00ff
ora #$0100
sta dirtParticles+DP_VY,y
; Advance to next particle
inc SCRATCHL2
inc SCRATCHL
inx
cpx PARAML2
bmi createDirtExplosionColumnLoop
; Gather return values
ldx SCRATCHL2
pla
sta PARAML2
RESTORE_AY
rts
;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;
; renderDirtExplosion
;
; Update and render the current dirt explosion
;
renderDirtExplosion:
SAVE_AXY
lda dirtExplosionActive
beq renderDirtExplosionDone
ldx #0
stz dirtExplosionActive ; Assume we're done unless a particle says otherwise
renderDirtExplosionLoop:
PARTICLEPTR_XY
jsr updateDirtParticle
inx ; Advance array pointer to next particle
cpx #MAXPARTICLES
bne renderDirtExplosionLoop
renderDirtExplosionDone:
RESTORE_AXY
rts
;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;
; updateDirtParticle
;
; Y = Offset to particle in array
; Update and render the current dirt explosion
;
; Trashes SCRATCHL,PARAML0
updateDirtParticle:
SAVE_AXY
lda dirtParticles+DP_POSX,y
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bpl updateDirtParticleContinue
jmp updateDirtParticleDone ; Particle is dead
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updateDirtParticleContinue:
; Erase old position
lda #dirtParticles ; Calculate pointer to struct
sta PARAML0
clc
tya
adc PARAML0
sta PARAML0
jsr vramPtr
lda #00
sta SHADOWVRAMBANK,x
; Integrate gravity over velocity
lda dirtParticles+DP_VY,y
clc
adc #GRAVITY
sta dirtParticles+DP_VY,y
; Integrate X velocity over position
lda dirtParticles+DP_VX,y
; Convert 8.8 to 12.4
cmp #$8000
ror
cmp #$8000
ror
cmp #$8000
ror
cmp #$8000
ror
clc
adc dirtParticles+DP_PRECISEX,y
sta dirtParticles+DP_PRECISEX,y
; Convert to integer for rendering
lsr
lsr
lsr
lsr
sta dirtParticles+DP_POSX,y
; Integrate Y velocity over position
lda dirtParticles+DP_VY,y
; Convert 8.8 to 12.4
cmp #$8000
ror
cmp #$8000
ror
cmp #$8000
ror
cmp #$8000
ror
clc
adc dirtParticles+DP_PRECISEY,y
sta dirtParticles+DP_PRECISEY,y
; Convert to integer for rendering
lsr
lsr
lsr
lsr
sta dirtParticles+DP_POSY,y
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; Check new position
jsr vramPtr ; PARAML0 still holds struct pointer
cpx #$ffff
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beq updateDirtParticleKill ; Offscreen, so we're done
lda SHADOWVRAMBANK,x
beq updateDirtParticleStillAlive ; All sky, so carry on
; cmp #$11
; bne updateDirtParticleKill ; Not dirt, so we're done
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lda dirtParticles+DP_VY,y
bmi updateDirtParticleKill ; +Y velocity on dirt, so we're done
updateDirtParticleStillAlive:
; Draw new position
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lda #$33
sta SHADOWVRAMBANK,x
; Let everyone know we did work
lda #1
sta dirtExplosionActive
updateDirtParticleDone:
RESTORE_AXY
updateDirtParticleDoneRTS:
rts
updateDirtParticleKill:
lda #-1
sta dirtParticles+DP_POSX,y
bra updateDirtParticleDone
dirtExplosionActive:
.word 0
dirtParticles:
.repeat MAXPARTICLES
.word -1 ; Pos X in pixels
.word 100 ; Pos Y in pixels
.word $a00 ; Pos X (12.4 fixed point)
.word $640 ; Pos Y (12.4 fixed point)
.word $ff00 ; Velocity X (8.8 fixed point)
.word $100 ; Velocity Y (8.8 fixed point)
.word 0,0 ; Pad to 16 bytes
.endrepeat
DP_POSX = 0 ; Byte offsets into dirtParticles data structure
DP_POSY = 2
DP_PRECISEX = 4
DP_PRECISEY = 6
DP_VX = 8
DP_VY = 10