# Soft Particles Petter Börjesson, Mattias Thell. Particle Effects Smoke, fire, explosions, clouds, etc Camera-aligned 2D quads – Gives the illusion of.

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Soft Particles Petter Börjesson, Mattias Thell

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

Illusion breakers Intersection with world geometry

To the rescue! Soft Particles – Soften the edges Use depth information to blend the sprite with the background

Compare Z values Compare Sprite Z vs World Z Check distance and blend if needed

Blending Simple approach: D = saturate((Zscene – Zparticle) * scale) Can produce artifacts Better approach: D = 0.5 * saturate(2*X) Contrast Where X = 1 – input if input > 0.5 Input otherwise

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

2D Particles with depth Store extra depth values in sprite texture During comparison add extra depth

2D Particles with depth Billboards Billboards with depth

Volumetric Particles Enclose sprite in an imaginary sphere and trace rays through each pixel. Sprite Sphere Ray Camera

Volumetric Particles Find intersections with the sphere and step through. Sprite Sphere Ray Camera

Volumetric Particles Stop if we collide with the depth buffer. Do blending as before. Ray Camera Depth buffer

Volumetric Particles Billboards with depthVolumetric

Demo!

Performance FPS with GTX 260 – 1280x1024 SoftHard Mountain 215 215 Billboard 480 360 Tank demo: With depth 420 330 Volumetric 65 60

Questions?

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