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V-Ray supports the rendering of caustics effects by using one of the following techniques: photon mapping or progressive.

The new Progressive caustics solver uses advanced sampling techniques, and is able to trace as many photons as required without suffering the memory constraints of traditional Photon Mapping techniques.

It is loosely based on two papers: one on Progressive Photon Mapping from Knaus and Zwicker, and another on Metropolis-guided caustics tracing from Šik and Krivánek.

The other method, Photon Mapping, is a two-pass technique.
The first pass consists of shooting light particles (photons) from the light sources in the scene, tracing them as they bounce around the scene, and recording the places where the photons hit the object surfaces.
The second pass is the final rendering, which is when the caustics are calculated by using density estimation techniques on the photon hits stored during the first pass.

 

UI Path: ||Render Setup window|| > GI tab > Caustics rollout

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Progressive Caustics Advantages

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  • they require nearly no setup;

  • each cast photon is more useful than those in traditional Photon Mapping;
  • the number of photons castable is only limited by time, not memory;
  • they can resolve tiny caustic details, compared to the scene size;
  • they can resolve caustic details also when a camera is very zoomed in on them;
  • statistics about the photon tracing can be found in the VFB2 stats panel;

 

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