1. Realishtime Radiosity And Next Shooter Selection Jeff Pool COMP 870 Final December 4, 2008 UNC Dept. of Computer Science

2. Approaches to Radiosity CPU matrix solving GPU gathering GPU scattering GPU scatter/gathering Hemicubes Hemispheres

3. I tried: GPU gathering Hemicubes – 5 renders per subelement – No form factor calculations, though FBOs Hemispheres Scatter/Gather

4. Approach 1 - Hemicubes Gathering – 50x50 elements Hemicubes – 5 renders per element CPU processing – Bandwidth issues  ~24 hours

5. Approach 2 – Hemicubes w/ FBO Gathering Hemicubes FBO – No sending data back and forth ~5 minutes 

6. Approach 3 – Coombe, et al. Scatter/Gather Hemispheres FBO  ~1/2 second

7. Key Points ID Buffer Hemispheres Progressive refinement – Next shooter selection – (fp MipMap generation) Texture packing for residual/full textures – (HW now has MRT)

8. ID Buffer Elements rendered with ID colors for visibility (hard part of form factors) Correlated to hemisphere rendered by shooter

9. Hemispheres Only one pass, not 5 Can be some distortion, so target framebuffer must be large for accurate visibility

10. ID texture size

11. Shooting Pass Scene rendered into hemisphere by shooter Each element is rendered as a quad Per fragment: – Form factor computation – Visibility = Idcolor==hemisphere(projectedPos) – Energy = FF * Reflectance * Visibility

12. Updating the elements Easy: Blend 1 + 1 (src + dst) = additive rendering Render to multiple targets – residual AND full Shooter’s residual framebuffer is simply cleared

13. Next Shooter Selection Trivial to select element with most energy left – Multiply lowest mipmap level by area HOWEVER, two things to consider – Visual impact of color bleeding – Frame-frame coherence

14. Problem #1 Importance of color over brightness 6 shots over 64x64 (~0.3 seconds)

15. Problem #2 Note the flickering as the light source descends, which can be pretty distracting

16. Problem #2 (2)

17. Different Preference Measures Sum of components Max of components Variance (+mean) Luminance

18. SO: Radiosity at realtime framerates (1-10 fps) Quality tradeoffs for speed: – Size of hemisphere texture – Subdivision size – Aggregate shooting Preferential next shooter selection – Brightness – Color – Coherence