Caustics by photons in Cycles?

[Nubnubbud]

@EusebioPtolomeu

I don’t know how accurate it would get, but I was reading about an idea to get cycles or any path tracing to calculate places where caustics should appear: you basically put a camera at the location of the light source, points toward a glass material and checks what portions of the plane behind it the camera rays reach thanks to refraction from the glass material, and try to take account of all these portions. Than you could try to “bake” some sorte of caustic map for the plane (since, if rays emitted from the camera were able to hit those points, so it would be rays emitted by any light at the same location as the camera). Perharps a black and white texture you can use as factor for a mix node between the normal surface shader and an emission shader (where the caustics are located). I don’t know how hard is, or how efficient this method is compared with other methods to solve caustics, however. Is it possible to create an output in the LightPath node that gives only the points of a given object that are intersected by camera rays (that is, points that would be seen by the camera). This way it’s easy to take into account even factors like roughness and normal maps at the glass material

This would not work that great with area lights (and you would have to do this for every light source in your scene), but perharps it would be good enough to fake it? As I said, I don’t know how good the results would turn out to be, I just think this could be a way for cycles to clculate caustics whithout major changes in it’s engine

here’s the issue, though… does this method follow conservation of energy? that’s really important when considering it as a cycles feature.in any case, There’s actually some ongoing (maybe slow right now) work on adaptive rendering, where the program finds noisy areas to keep rendering longer. caustics are smooth and continuous, so it should work better for them than something like trees in the distance. I also agree with Brecht on the “caustic shadow” pass, though it really does feel like we’re missing some elegant solution for it.