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Extended Light Maps
Extended Light Maps
Extended Light Maps
Extended Light Maps
Extended Light Maps
Extended Light Maps
Extended Light Maps
Extended Light Maps
Extended Light Maps
Extended Light Maps
Extended Light Maps
Extended Light Maps
Extended Light Maps
Extended Light Maps
Extended Light Maps
Extended Light Maps
Extended Light Maps
Extended Light Maps
Extended Light Maps
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Extended Light Maps


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Talk given at GameOn 2000, London

Talk given at GameOn 2000, London

Published in: Technology, Art & Photos
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  • 1. Extended Light Maps Stefan Brabec and Hans-Peter Seidel Max-Planck-Institut für Informatik Saarbrücken, Germany {brabec|hpseidel}
  • 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 AG4 Computer Graphics Group