The Persistence of Vision Raytracer (POV-Ray).

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Attached to Project: POV-Ray
Opened by Christoph Lipka - 2009-07-28
Last edited by William F Pokorny - 2017-01-19

FS#44 - Improve Normals Handling in Radiosity

Currently, radiosity does not make use of the fact that pertubed normals would theoretically just require a different weighting of already-sampled rays, leading to the following issues:

  • Honoring normal pertubations in radiosity leads to an increased number of samples, slowing down sample cache lookup.
  • The increased number of samples is generated from a proportionally higher number of sample rays, slowing down pretrace even further.
  • Low-amplitude pertubations tend to be smoothed out; “reviving” these is only possible by increasing the general sample density.
  • Handling of multi-layered textures with different normal pertubations is currently poorly implemented.

As a solution, I propose to store for each radiosity sample not only the resulting illumination for a perfectly unpertubed normal, but from the same set of sample rays also compute the illumination for an additional set of about a dozen standardized pertubed-normal directions, and interpolate among these when computing the radiosity-based illumination for a particular point that has a pertubed normal.

For backwards compatibility, this method of dealing with pertubed normals in radiosity might be activated by a different value for the “normal” statement in the radiosity block, say, “normal 2”.

Thorsten Fröhlich commented on Tuesday, 23 August 2011, 06:42 GMT

What is the status of this?

Christoph Lipka commented on Saturday, 03 December 2011, 03:08 GMT

Spherical harmonics might be the way to go; they might also allow radiosity to respect the brilliance parameter to some degree.

I don't intend to tackle this prior to 3.7.0 release proper though.

William F Pokorny commented on Thursday, 19 January 2017, 14:12 GMT

Now tracked on github as issue #188.


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