Extended light maps store pre-computed illumination in light maps to improve rendering efficiency. The light map contains two channels - a light channel that stores values like diffuse lighting, and a shadow channel that stores depth values to determine lit pixels. This approach better utilizes hardware and reduces rendering passes. It allows effects like bump mapping and reflections to be pre-computed and applied during rendering. However, the light channel can only affect lit pixels, and high-resolution textures are needed for accurate shadows. Future work includes improving shadow quality and adding more applications of the light channel.

1. Extended Light Maps Stefan Brabec and Hans-Peter Seidel Max-Planck-Institut für Informatik Saarbrücken, Germany {brabec|hpseidel}@mpi-sb.mpg.de

2. Overview Motivation Extended Light Maps Shadow Channel Light Channel Example Applications Conclusion & Future Work

3. Motivation Our Shadow Mapping Approach [Brabec/Heidrich `00] Render scene as seen by light source Encode depth values in alpha channel Project this texture into the final scene Subtract depth values to determine lit pixels

4. Motivation Generation of shadow map is expensive Whole scene must be rendered ! Idea: Do some additional calculations during generation phase (pre-computation) Utilize special hardware features, e.g. on GeForce Pre-compute light-relative ‘static’ things (e.g. diffuse illumination) Use as much hardware resources as available !

5. Extended Light Maps Light Maps store pre-computed illumination Extended Light Map Light Channel (RGB) Normal light map Shadow Channel (Alpha) Alpha-encoded depth values

6. Shadow Channel Distance to light source in alpha channel: Use 1D ramp texture and automatic texture coordinate generation Use fog factor as linear distance function

7. Light Channel Use RGB channel for arbitrary calculations e.g. OpenGL lighting Object textures Realistic spotlights Special effects Reflection mapping Bump mapping

8. Example Applications Illuminating a scene with two extended light maps

9. Example Applications Render scene as seen by light source #1 Apply object textures and OpenGL lighting Use fog computation for linear z-distance function Light Channel Shadow Channel

10. Example Applications Same for light source #2: Light Channel Shadow Channel

11. Example Applications Problem: Lighting needs to be calculated in camera space Solution: Diffuse and ambient lighting is already correct (does not depend on camera position) Specular part needs special treatment Additional helper light source at camera position Attenuation and spotlight effect Simulate using texture mapping (better since texture maps are applied per pixel)

12. Example Applications Advantages: Faster: pre-computed illumination Disadvantages: Light channel will only be applied to lit pixels Final step(s): render from camera position Apply light channel value if pixel passes shadow test

13. Example Applications Pre-computed reflection mapping

14. Example Applications First pass: Use color channel for environment cube map Use alpha channel for z-distance

15. Example Applications How to perform cube mapping in light source space ? Need correct reflection vector Calculate in camera space: Viewing Matrix Projection Matrix

16. Example Applications Two final passes Render normal scene (textures & lighting) Apply extended light map (shadows & reflections)

17. Conclusion Combined light and shadow mapping Benefits Better use of available hardware resources Reduced number of rendering passes Problems Light channel can only be applied to lit pixels High resolution textures needed for accurate shadows

18. Future Work Improve quality of shadows Filtering Precision (currently 8 bits only) More light channel applications Bump mapping Sophisticated lighting models

19. Thank you ! Visit us at http://www.mpi-sb.mpg.de AG4 Computer Graphics Group