SIGGRAPH 2011 PixelJunk Shooter 2 notes

8/13/2019 SIGGRAPH 2011 PixelJunk Shooter 2 notes

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PixelJunk Shooter 2Fluid dynamics and lighting implementation

Jaymin Kessler

Q-Games Technology Team

twitter: @okonomiyonda



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PixelJunk Shooter 2Fluid dynamics



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!Environmental puzzle-based shooter

!Puzzles based on interactions between solids, liquidgasses, and magnetics

!

Water cools magma to form rock, magma melts icrock, magma ignites gas, lasers melt rock into magmice into water, magnetics + water forms a poison g

!All Organically arising from physics, nothing is scripte

Shooter 2 for the uninitiated



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!

Good points!4th order accurate

!Greater stability than Euler

!Time-reversibility

!

Bad points!Bad handling of variable time steps

!Needs 2 steps to start, and initial conditions are cru

!Time-corrected verlet helps

Verlet integration



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!Flow is supposed to be incompressible

!Give particles an adjustable radius bias and arepulsive force

!Based on the max ingression of surroundingparticles

!

Lerp from current bias to desired bias!Bias contraction is 4x faster than expansion

Fix for flow compression



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!Different masses

!Some have rigid bodies and some dont!For different combinations of particle types (magma water, magma + rock, etc)

!Different force of repulsion values

!Different force of repulsion values

!Different chemical reactions simulated

!Different heat propagation

Particle type differences



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!Each particle carries thermal data

!When particles collide, heat is propagated!Warmer to cooler

!Same algorithm used for intra-particle repulsive fo

!Particle types have different thermal transfer value

Heat propagation



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!

Collision detection, repulsive force calculation!Force unification across grid cells

!For particles on the border of 2 or more cells

!Verlet update

!

Also events, such as sudden change in fluid direction!Particle deletion (one SPU used)

!Grid calculation for next frame

!O(n2/k) for k!1232 cells (44x28) is better than O(n

Fluid particle processing stages



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!Characters, missiles, and other in-game objects aresurrounded by special particles called interactors

!Uses the existing particle system!Any collision can be simply detected and tracked

Collision (via interactor particles)



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Collision (interactor particles)



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!

Uses signed distance fields!256x256 Chamfer distance with a 3x3window was !0.5ms on a single SPU

!Two distance fields: static for walls, dynamicfor destructibles, results merged into final

distance field!One lookup gets the distance and directionto closest object

!Also reused for SPU lighting

Collision (via distance field)



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Collision (distance field)



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PixelJunk Shooter 2Fluid rendering



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Fluid rendering

Grouped particles must be rendered as a smooth

flowing fluidExisting example: marching squares

Currently patented?

Just not by us



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Fluid rendering

Render particles to a low-res offscreen buf with a

luminance textureBlur the offscreen buffer

Scale up with bilinear filter and use the resultingbrightness to color the liquid



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Water surface

Use a smooth step function when rendering water to

an offscreen bufferTwo thresholds used for water surface and for tinting



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Cohesiveness

Particles move too far apart from each other in free

falling liquid Liquid loses cohesiveness Opposite problem as compression

Fixed by not fully clearing the buffer

Image lag effect maintains cohesiveness



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Cohesiveness (in motion)



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Cohesiveness (in motion)



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Refraction

From water and heat rising off magma

Ping-pong between offscreen buffersDegree and direction depends on particles fixed UV(RG value mentioned on the movement slide)



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PixelJunk Shooter 2SPU lighting



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SPU lighting

Four light types

Spot light (ship light suit)

Point light (enemy projectiles, light balls) Wall light (also called blacklight) Ice light (different light system)

Can handle 40~60 lights depending on particle load Reuses same distance field used for fluid particle col



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SPU lighting

Stage 1: Get ray length

Gets the point on a ray where it hits its first occlud

Stage 2: Rasterize Write ray pixels out to texture (slowest pass)

Stage 3: Merge with other lights

Blend can be add, sub, min, max, avg, and others

For first pass, offline-generated offset table maximizecoverage and minimizes redundant loads of source d



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SPU lighting: stage 1

Ray length: 0



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Ray length: 16



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Ray length: 32



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Ray length: 41


l d t f k d t (i thi


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clgtbi $6, $35, 0

gbb $29, $6shli $6, $29, 16

clz $73, $6a $69, $73, $45

clgt $27, $49, $73selb $45, $69, $45, $40

or $40, $27, $40

0 0 42 0 1 1 1 1 1 1 1 1

real data fake data (in this exa


l d t fake data (in this exa


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clgtbi $6, $35, 0

gbb $29, $6shli $6, $29, 16

clz $73, $6a $69, $73, $45

clgt $27, $49, $73selb $45, $69, $45, $40

or $40, $27, $40

0 0 42 0 1 1 1 1 1 1 1 1

0 0 FF 0 FF FF FF FF FF FF FF FF





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clgtbi $6, $35, 0

gbb $29, $6shli $6, $29, 16

clz $73, $6a $69, $73, $45

clgt $27, $49, $73selb $45, $69, $45, $40

or $40, $27, $40

0 0 42 0 1 1 1 1 1 1 1 1


0000000000000000 0010111111111111





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clgtbi $6, $35, 0

gbb $29, $6shli $6, $29, 16

clz $73, $6a $69, $73, $45

clgt $27, $49, $73selb $45, $69, $45, $40

or $40, $27, $40

0 0 42 0 1 1 1 1 1 1 1 1


0000000000000000 0010111111111111


0010111111111111 0000000000000000



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SPU lighting stage 2: optimization16 bytes / 16 aligned



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safe angle range

"y > "xunsafe angle range

"x #"y



SPU li h i 2 i i i


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safe angle range


"x #"y




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SPU li hti t 2 ti i ti


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safe angle range


"x #"y

If two adjacent pixels ina ray can occur in the

same HW vector, wemust read, insert, write,read, insert, write...





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SPU lighting stage 2: optimization

8 6 7 x 8 6 x 5

values occur in

different quadwords




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8 6 7 x 8 6 x 5

non-mergingmasks

values occur in

different quadwords




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8 6 7 x 8 6 x 5

non-mergingmasks

8 6 7 x 8 6 x 5

values occur in

different quadwords




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8 6 7 x 8 6 x 5

non-mergingmasks

8 6 7 x 8 6 x 5

values occur in

different quadwords




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8 6 7 x 8 6 x 5

non-mergingmasks

8 6 7 x 8 6 x 5

values occur in

different quadwords




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8 6 7 x 8 6 x 5

non-mergingmasks

8 6 7 x 8 6 x 5

8 6 7 x 8 6

values occur in

same quadwor

values occur in

different quadwords




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8 6 7 x 8 6 x 5

non-mergingmasks

8 6 7 x 8 6 x 5

8 6 7 x 8 6

merging masks

values occur in

same quadwor

values occur in

different quadwords


SPU li htin sta e 2: optimi ation


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8 6 7 x 8 6 x 5

non-mergingmasks

8 6 7 x 8 6 x 5

8 6 7 x 8 6

merging masks

8 6 7 5 8 6

values occur in

same quadwor

values occur in

different quadwords



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8 6 7 x 8 6 x 5

non-mergingmasks

8 6 7 x 8 6 x 5

8 6 7 x 8 6

merging masks

8 6 7 5 8 6

values occur in

same quadwor

values occur in

different quadwords



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SPU Lighting: future improvement


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SPU Lighting: future improvement

Ray marching the distance field

Huge speedup in some cases

Integrating the SPA version

Gave about 15%~20% back

Write out linear, and swizzle later (on GPU?)

SPU outputs geometry info / vertex array for light, andGPU render it

Line info could also help with antialiasing

But the GPU is too busy


Frame overview


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Frame overview


Frame overview


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Frame overview

start dfstart light

start particle fx

start skinning


Frame overview


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Frame overview

start dfstart light

start particle fx

start skinning

wait

prevfluid

wait

distancefield


Frame overview


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Frame overview

start dfstart light

start particle fx

start skinning

wait

prevfluid

wait

distancefield

startfluid


Frame overview


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Frame overview

start dfstart light

start particle fx

start skinning

wait

prevfluid

wait

distancefield wait particle fx

wait skinningwait li ht

startfluid


Tuner capture


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Tuner capture


Tuner capture


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Tuner capture


Tuner capture


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Tuner capture


Tuner capture


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Tuner capture



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Tuner capture


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Tuner capture


Tuner capture


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Tuner capture



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Tuner capture


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Tuner capture



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Documents

SIGGRAPH 2011 PixelJunk Shooter 2 notes