Soft Particles

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Soft Particles

• Petter Börjesson, Mattias Thell

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Particle Effects

• Smoke, fire, explosions, clouds, etc
• Camera-aligned 2D quads
• Gives the illusion of a 3D volume

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Illusion breakers

• Intersection with world geometry

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To the rescue!

• Soft Particles
• Soften the edges
• Use depth information to blend the sprite with
  the background

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Compare Z values

• Compare Sprite Z vs World Z
• Check distance and blendif needed

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Blending

• Simple approach D saturate((Zscene
  Zparticle) scale)
• Can produce artifacts
• Better approach D 0.5
  saturate(2X)Contrast

1 input if input gt 0.5
Where X
Input otherwise
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Depth Values

• How do we get depth information?
• Paper presents two ways
• Access depth buffer in pixel shader (DX 10)
• Use a render target to read depth information

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Read Z in pixel shader
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Render target
Render Target
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2D Particles with depth

• Store extra depth values in spritetexture
• During comparisonadd extra depth

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2D Particles with depth
Billboards
Billboards with depth
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Volumetric Particles

• Enclose sprite in an imaginary sphere and trace
  rays through each pixel.

Sphere
Ray
Sprite
Camera
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Volumetric Particles

• Find intersections with the sphere and step
  through.

Sphere
Ray
Sprite
Camera
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Volumetric Particles

• Stop if we collide with the depth buffer.
• Do blending as before.

Depth buffer
Ray
Camera
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Volumetric Particles
Billboards with depth
Volumetric
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Demo!
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Performance

• FPS with GTX 260 1280x1024

Soft
Hard
Mountain 215
215
Tank demo
Billboard 480
360
With depth 420
330
Volumetric 65
60
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Questions?