Soft Particles

1. Soft Particles Petter Börjesson, Mattias Thell

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

3. Illusion breakers • Intersection with world geometry

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

5. Compare Z values • Compare Sprite Z vs World Z • Check distance and blendif needed

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

7. DepthValues • 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

8. Read Z in pixel shader Pass 1 Pass 2 VertexShader VertexShader Geo. Shader Geo. Shader creates sprites Scene Z Pixel Shader Sprite Z Pixel Shader Color Buffer DepthBuffer Color Buffer

9. Rendertarget Pass 1 Pass 2 VertexShader VertexShader Geo. Shader Geo. Shader creates sprites Scene Z Pixel Shader Sprite Z Pixel Shader Render Target Color Buffer DepthBuffer Color Buffer

10. 2D Particles with depth • Store extra depth values in spritetexture • During comparisonadd extra depth

11. 2D Particles with depth Billboards Billboards with depth

12. VolumetricParticles • Enclose sprite in an imaginary sphere and trace rays through each pixel. Sphere Ray Sprite Camera

13. VolumetricParticles • Find intersections with the sphere and step through. Sphere Ray Sprite Camera

14. VolumetricParticles • Stop if we collide with the depth buffer. • Do blending as before. Depth buffer Ray Camera

15. VolumetricParticles Billboards with depth Volumetric

16. Demo!

17. Performance • FPS with GTX 260 – 1280x1024 Hard Soft Mountain 215 215 Tank demo: Billboard 480 360 With depth 420 330 Volumetric 65 60

18. Questions?