mirror of
https://github.com/blondie7575/GSCats.git
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314 lines
5.5 KiB
ArmAsm
314 lines
5.5 KiB
ArmAsm
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; dirt
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;
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; Created by Quinn Dunki on 12/29/19
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;
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MAXPARTICLES = 64
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.macro PARTICLEPTR_XY
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txa ; Pointer to particle structure from index
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asl
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asl
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asl
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asl
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tay
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.endmacro
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;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;
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; createDirtExplosion
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;
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; Simulate a bunch of dirt flying everywhere
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;
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; PARAML0 = X pos of circle left edge
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; PARAML1 = Y pos of circle center
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; PARAML2 = Radius (16 bits)
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;
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; Trashes SCRATCHL,SCRATCHL2,CACHEDATA
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;
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createDirtExplosion:
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SAVE_AXY
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lda #1
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sta dirtExplosionActive
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lda #3 ; Radius hard-coded for now
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sta PARAML2
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asl
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sta CACHEDATA ; Cache diameter
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ldx #0
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ldy #0
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createDirtExplosionLoop:
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jsr createDirtExplosionColumn
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inc PARAML0
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inc PARAML0
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iny
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cpy CACHEDATA
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bne createDirtExplosionLoop
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RESTORE_AXY
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rts
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;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;
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; createDirtExplosionColumn
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;
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; Create one column of a starting dirt explosion circle
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; X = Particle index to start filling from
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; Y = Local X index of column
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; PARAML0 = X pos of column
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; PARAML1 = Y pos of circle center
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; PARAML2 = Radius (16 bits)
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;
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; X=> Last particle index we filled in +1
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; Trashse SCRATCHL,SCRATCHL2
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;
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createDirtExplosionColumn:
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SAVE_AY
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lda PARAML2
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pha
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stx SCRATCHL2 ; Cache particle index
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phy ; Look up circle table for our radius
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lda PARAML2
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asl
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tay
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lda circleTable,y
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sta SCRATCHL
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; Find starting Y from circle table
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pla
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asl
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tay
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lda (SCRATCHL),y
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tax ; Row counter
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pha
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eor #$ffff
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inc
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sta PARAML2 ; Row counter end
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pla
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clc
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adc PARAML1
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sta SCRATCHL ; Current Y position
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createDirtExplosionColumnLoop:
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phx ; Find pointer to next particle to fill out
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ldx SCRATCHL2
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PARTICLEPTR_XY
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plx
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; X position - Always the same
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lda PARAML0
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sta dirtParticles+DP_POSX,y
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asl ; Convert to 12.4
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asl
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asl
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asl
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sta dirtParticles+DP_PRECISEX,y
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; Y position - Iterates from computed cache
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lda SCRATCHL
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sta dirtParticles+DP_POSY,y
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asl ; Convert to 12.4
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asl
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asl
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asl
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sta dirtParticles+DP_PRECISEY,y
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; X velocity. Need half to be negative. I feel like there
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; should be a clever branchless way to do this, but I couldn't
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; come up with it.
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jsr random
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lda RANDOM
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bmi createDirtExplosionColumnLoopNegX
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and #$00ff
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bra createDirtExplosionColumnLoopNowY
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createDirtExplosionColumnLoopNegX:
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ora #$ff00
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createDirtExplosionColumnLoopNowY:
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sta dirtParticles+DP_VX,y
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; Y velocity
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jsr random
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lda RANDOM
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and #$00ff
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ora #$0100
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sta dirtParticles+DP_VY,y
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; Advance to next particle
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inc SCRATCHL2
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inc SCRATCHL
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inx
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cpx PARAML2
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bmi createDirtExplosionColumnLoop
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; Gather return values
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ldx SCRATCHL2
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pla
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sta PARAML2
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RESTORE_AY
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rts
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;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;
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; renderDirtExplosion
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;
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; Update and render the current dirt explosion
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;
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renderDirtExplosion:
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SAVE_AXY
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lda dirtExplosionActive
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beq renderDirtExplosionDone
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ldx #0
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stz dirtExplosionActive ; Assume we're done unless a particle says otherwise
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renderDirtExplosionLoop:
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PARTICLEPTR_XY
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jsr updateDirtParticle
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inx ; Advance array pointer to next particle
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cpx #MAXPARTICLES
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bne renderDirtExplosionLoop
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renderDirtExplosionDone:
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RESTORE_AXY
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rts
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;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;
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; updateDirtParticle
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;
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; Y = Offset to particle in array
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; Update and render the current dirt explosion
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;
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; Trashes SCRATCHL,PARAML0
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updateDirtParticle:
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SAVE_AXY
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lda dirtParticles+DP_POSX,y
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bpl updateDirtParticleContinue
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jmp updateDirtParticleDone ; Particle is dead
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updateDirtParticleContinue:
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; Erase old position
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lda #dirtParticles ; Calculate pointer to struct
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sta PARAML0
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clc
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tya
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adc PARAML0
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sta PARAML0
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jsr vramPtr
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lda #00
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sta SHADOWVRAMBANK,x
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; Integrate gravity over velocity
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lda dirtParticles+DP_VY,y
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clc
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adc #GRAVITY
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sta dirtParticles+DP_VY,y
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; Integrate X velocity over position
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lda dirtParticles+DP_VX,y
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; Convert 8.8 to 12.4
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cmp #$8000
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ror
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cmp #$8000
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ror
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cmp #$8000
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ror
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cmp #$8000
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ror
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clc
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adc dirtParticles+DP_PRECISEX,y
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sta dirtParticles+DP_PRECISEX,y
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; Convert to integer for rendering
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lsr
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lsr
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lsr
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lsr
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sta dirtParticles+DP_POSX,y
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; Integrate Y velocity over position
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lda dirtParticles+DP_VY,y
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; Convert 8.8 to 12.4
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cmp #$8000
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ror
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cmp #$8000
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ror
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cmp #$8000
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ror
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cmp #$8000
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ror
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clc
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adc dirtParticles+DP_PRECISEY,y
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sta dirtParticles+DP_PRECISEY,y
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; Convert to integer for rendering
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lsr
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lsr
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lsr
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lsr
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sta dirtParticles+DP_POSY,y
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; Check new position
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jsr vramPtr ; PARAML0 still holds struct pointer
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cpx #$ffff
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beq updateDirtParticleKill ; Offscreen, so we're done
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lda SHADOWVRAMBANK,x
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beq updateDirtParticleStillAlive ; All sky, so carry on
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; cmp #$11
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; bne updateDirtParticleKill ; Not dirt, so we're done
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lda dirtParticles+DP_VY,y
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bmi updateDirtParticleKill ; +Y velocity on dirt, so we're done
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updateDirtParticleStillAlive:
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; Draw new position
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lda #$11
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sta SHADOWVRAMBANK,x
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; Let everyone know we did work
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lda #1
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sta dirtExplosionActive
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updateDirtParticleDone:
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RESTORE_AXY
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updateDirtParticleDoneRTS:
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rts
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updateDirtParticleKill:
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lda #-1
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sta dirtParticles+DP_POSX,y
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bra updateDirtParticleDone
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dirtExplosionActive:
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.word 0
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dirtParticles:
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.repeat MAXPARTICLES
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.word -1 ; Pos X in pixels
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.word 100 ; Pos Y in pixels
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.word $a00 ; Pos X (12.4 fixed point)
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.word $640 ; Pos Y (12.4 fixed point)
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.word $ff00 ; Velocity X (8.8 fixed point)
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.word $100 ; Velocity Y (8.8 fixed point)
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.word 0,0 ; Pad to 16 bytes
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.endrepeat
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DP_POSX = 0 ; Byte offsets into dirtParticles data structure
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DP_POSY = 2
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DP_PRECISEX = 4
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DP_PRECISEY = 6
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DP_VX = 8
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DP_VY = 10
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