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Indirect illumination of SSS component

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Hi - when using the mantraSurface shader, or building a surface from physicalSSS or surfacemodel, I find that the SSS shading does not receive indirect illumination.


Have a look at the attached image. Bounce light from the card is visible on the underside of the sphere when shaded with simple diffuse, but neither the single scatter or multi scatter pick up those contributions.


Is there anything that can be done to include indirect paths in SSS calculations. Or is that an RFE?






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I think you need to have Diffuse Enabled for SSS to work. You get the same result of black if you enable Diffuse and then set the diffuse color to black. I think that is what you are experiencing. When Diffuse is disabled you are effectively multiplying against black which is zero, thus zero contribution. I am no shader expert perhaps others will chime in.

Edited by Atom
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sss uses illuminance loops to compute lighting directly rather than utilizing the path tracer or anything more complex.  as a result, you won't get any bounced light or anything along those lines.  an area light should theoretically work, but then you'd have additional contributions on your diffuse.


sss is kind of outside the path tracer bsdf model as it's currently set up.  maybe they'll unify it at some point.

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