The Close Objects Buffer: A Sharp Shadow Detection Technique for Radiosity Methods

A. C. Telea and C.W.A.M. van Overveld
Eindhoven University of Technology

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Abstract

Detecting sharp illumination variations such as shadow boundaries is an important problem for radiosity methods. Such illumination variations are captured using a nonuniform mesh that refines the areas exhibiting high illumination gradients. Nonuniform meshing techniques like discontinuity meshing often rely on shadow casting, and as a result their application is computationally expensive. This paper presents a sharp shadow detection technique for radiosity tools based on the progressive refinement method. The presented technique offers good results (especially for capturing sharp shadows cast by small “detail” objects), is very simple to implement, has negligible time and space requirements, and integrates well with other adaptive subdivision strategies in a radiosity tool based on progressive refinement.

Author Information

A. C. Telea, Eindhoven University of Technology, Dept of Math & CS, PO Box 5135600 MB Eindhoven, Netherlands alext@win.tue.nl

C.W.A.M. van Overveld, Eindhoven University of Technology, Dept of Math & CS, PO Box 5135600 MB Eindhoven, Netherlands wsinkvo@win.tue.nl

Images

Office room rendered with progressive refinement method, adaptive subdivision and close-objects buffer. Approx. 400 polygons, 3000 patches, 18000 subpatches. Rendering time: 2.5 minutes on a SGI INDY R4400, 300 refinement interations.

Same office room as above, view of the meshing created during the preogressive refinement process.

Another view of the office room.

Back view of the office (notice the shadow cast by the red beam on the right wall).

Hall with beams, rendered as a test for ray-tracing form factors. The image was rendered with 300 iterations.

Close view of a table lit by a desk lamp. There are two sheets of paper on the table casting a sharp shadow on it. The close objects buffer was used to accurately capture these shadows.

Discontinuity meshing generated by the close objects buffer for the scene depicted above. The subdivision proceeded along the papers' edges and the part of the table close to the light source. The mesh was constrained to be balanced.

BibTeX Entry

@article{TeleaVanOverveld97,
  author = "A. C. Telea and C.W.A.M. van Overveld",
  title = "The Close Objects Buffer: A Sharp Shadow Detection Technique for Radiosity Methods",
  journal = "journal of graphics tools",
  volume = "2",
  number = "2",
  pages = "1-8",
  year = "1997",
}