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View Full Version : Photon killing

CurtJ
03-11-2009, 09:12 AM
What's the best way to have a material kill any photons that strike it's surface(s)?

I thought using a simple surface shader with out col set to zero would work but I get the same effect as firing photons into space. i.e. MR takes a long time to compute it, even if it's set to just 100 photons and I get 'errors' in the output window:

RCGI 0.4 warn 362004: no photons stored after emitting 10000 photons from light "spotLightShape1" (tag f88)
RCGI 0.4 error 361053: no photons stored after emitting 1000000 photons from light "spotLightShape1" (tag f88): canceling emission job

I get the same result using other materials too.

I want a texture on a surface that reflects a certain shape of (caustic) photons, but kills photons where it's non-reflective.
CurtJ
03-11-2009, 07:09 PM
Ah - seems photons don't work in the way I though they did.

If all caustic photons strike a (photonic) non-reflective surface, or if they are all reflected toward infinity then the above error is returned. But if there is even one tiny area that they can work with (i.e. not reflected to infinity, or strike a reflective area) then whatever the photon emitter's photon count is set to will generate that many photons for that area.

To put it simply, no photons are ever 'killed' - it seems that they are just disregarded, the emission count is not affected, and another photon is emitted.

Similar results for GI photons, based on diffuse rather than reflection.

I noticed that the photons on the map viz are sometimes two colours. What does this represent?