1. VLF Rendering & Implementation Details Virtual Light Field Group vlfproject@cs.ucl.ac.uk University College London GR/R13685/01 Research funded by: Jesper Mortensen j.mortensen@cs.ucl.ac.uk

2. VLF Project Overview Rendering from the VLF Implementation details Walkthrough results Limitations Future work Questions

3. VLF Project Rendering: VLF The VLF can be used to render any ray Determine intersected polygons with false colour rendering Lookup hemisphere triangle in which direction falls, with barycentric coordinates In each direction lookup the TRM for the intersected polygon Interpolate radiance in TRM from 8-neighbourhood Apply barycentric weights to interpolate the 3 radiances

4. VLF Project Rendering: VLF However, due to limited resolution blurring may occur Especially for specular surfaces Expensive: - 3 dirs * 9 TRM cells * rays Example has 2K directions, 128x128 resolution

5. VLF Project Rendering: Diffuse textures The VLF also stores diffuse maps for any diffuse surface These can be efficiently rendered using D3D/OpenGL Limiting blurring to non-diffuse surfaces

6. VLF Project Rendering: Backwards ray tracing Backwards ray tracing can be used for specular parts Can reconstruct specularly reflected geometry well Bounces until diffuse surface hit Can be slow if a large part of the scene is specular

7. VLF Project Rendering: Progressive method Hybrid method Uses OpenGL texturing for diffuse surfaces Uses direct VLF lookup for specular surfaces during motion If viewpoint is stationary renders specular reflection using backwards ray tracing

8. VLF Project Implementation: Language Class based C++ Heavy use of class templates - flexibility - efficiency, can tailor implementation - con: must recompile

9. VLF Project Implementation: Platform PC based Windows 2000/XP Visual Studio.NET

10. VLF Project Implementation: Graphics API Graphics API: OpenGL Standard pbuffers Used for ‘false colour’ rendering [visibility] - exchange buffers - rendering phase Main issue is slow framebuffer readback

11. VLF Project Implementation: Libraries Hierarchical scene graph library - facesets, spheres, blobs etc. Graphics library - matrices, vectors, materials, cameras etc. VLF library - tiles, radiance maps, diffuse maps etc.

12. VLF Project Implementation: Dependencies Glut - http://www.opengl.org/developers/documentation/glut/ Zlib - http://www.gzip.org/zlib/ Jpeglib - http://www.ijg.org/

13. VLF Project Implementation: GI framework General framework for Global Illumination Supports many approximations…

14. VLF Project Implementation: OpenGL real-time OpenGL rendering for real-time local illumination

15. VLF Project Implementation: Radiosity Progressive radiosity - Cohen et.al 1988

16. VLF Project Implementation: Classic ray tracing Whitted ray tracing - Turner Whitted 1980

17. VLF Project Implementation: Distributed ray tracing Distributed ray tracing - Robert L. Cook et. al. 1984

18. VLF Project Implementation: Path tracing Coming soon … Monte Carlo path tracing - James T. Kajiya 1986

19. VLF Project Implementation: VLFs And of course – Virtual Light Fields… Diffuse Specular Caustics

20. VLF Project Implementation: VLF applications There are three main applications currently: VLF analyser - visualises elements of the VLF, PSFs, tiles, maps, visibility etc. good debugging tool VLF propagator - solves GI for a VLF, outputs binary VLF files, can reload and continue from a binary file VLF walkthrough - loads a binary VLF file and renders it in real-time

21. VLF Project Implementation: HDR viewer GI results are natively HDR but display devices are inherently LDR [24 bit RGB]! We have our own file format - similar to Wards radiance format 32 bit floats RGB interleaved - optionally zip compressed … and an associated viewer

22. VLF Project Implementation: HDR viewer (contd.) Uses simple linear scaling approaches Or tone mapping a la Reinhard et. al. 2002

23. VLF Project Walkthrough results The following shows results from walkthroughs of VLFs The illustrate real-time performance for scenes with global illumination effects They were all rendered on a dual 2.8 GHZ Pentium 4 Xeon with 3GB RAM, and a NVIDIA GeForce FX5800

24. VLF Project Walkthrough results: Cornell scene This illustrates diffuse GI effects such as colour bleeding and soft shadows The VLF uses 2K directions and 8x8 tiles each having 16x16 cells The progressive method is used for rendering

25. VLF Project Walkthrough results: Cornell scene SHOW CORNELL VIDEO

26. VLF Project Walkthrough results: Office scene This illustrates GI effects such as specular reflections, soft shadows and colour bleeding The VLF uses 2K directions and 8x8 tiles each having 16x16 cells Memory usage is 980MB, propagation time was 36 hrs. The progressive method and CRT method used for rendering

27. VLF Project Walkthrough results: Office scene SHOW PROGRESSIVE OFFICE VIDEO SHOW CRT OFFICE VIDEO

28. VLF Project Walkthrough results: GI benchmark Global illumination test scene from Smits & Jensens repository: - http://www.cs.utah.edu/~bes/papers/scenes/http://www.cs.utah.edu/~bes/papers/scenes/ Illustrates several interesting light paths: LDE, LDSE, LDSDE (of which the last is a caustic) The VLF uses 2K directions and 8x8 tiles each having 16x16 cells Propagation time was 33 hrs. The progressive method used for rendering

29. VLF Project Walkthrough results: GI benchmark SHOW GI BENCHMARK VIDEO

30. VLF Project Limitations Limited to planar geometry Support for basic materials No participating media Closed polyhedra

31. VLF Project Whats next? Investigate alternative rendering methods - Lens approach Optimise, graphics hardware

32. VLF Project Questions ?