Question about Mantra Surface Shader.

[~nature~]

Dear all,

I was trying to understand the mantra surface shader under the hood, I noticed the SSS bsdf component is added to other bsdf components(diffuse, reflection, refraction) before computing the energy conserve scaling factor, however after that, SSS component is exclued when actually multiplying the scaling factor with the sum of the bsdf.

anybody knows why ?

Cheers. ^-^

Edited September 28, 2011 by ~nature~

[eetu]

I was trying to understand the mantra surface shader under the hood, I noticed the SSS bsdf component is added to other bsdf components(diffuse, reflection, refraction) before computing the energy conserve scaling factor, however after that, SSS component is exclued when actually multiplying the scaling factor with the sum of the bsdf.

anybody knows why ?

Uhh, that is quite a knot to unravel in there

Seems like the properly calculated SSS is added in as a straight color in the "emission" part of the vopnet (above your screenshot).

For the energy conservation calculations a fake albedo is calculated with a pbr diffuse node, with the subsurf intensity as a diffuse multiplier. I guess the idea is that the energy conservation is calculated at the "point of entry" into the shading point, and that behaves like a diffuse distribution.

The subsurface light exiting a surface somewhere else should not change the conservation of incoming energy, as it is "extra energy" from the point of view of the exit shading point. Similarly, the point where the energy goes into the subsurface layers, the conservation of energy should take into account all that energy - even though it doesn't add up the color value of that point.

Apologies if this sounds obfuscated

eetu.

[~nature~]

Uhh, that is quite a knot to unravel in there

Seems like the properly calculated SSS is added in as a straight color in the "emission" part of the vopnet (above your screenshot).

For the energy conservation calculations a fake albedo is calculated with a pbr diffuse node, with the subsurf intensity as a diffuse multiplier. I guess the idea is that the energy conservation is calculated at the "point of entry" into the shading point, and that behaves like a diffuse distribution.

The subsurface light exiting a surface somewhere else should not change the conservation of incoming energy, as it is "extra energy" from the point of view of the exit shading point. Similarly, the point where the energy goes into the subsurface layers, the conservation of energy should take into account all that energy - even though it doesn't add up the color value of that point.

Apologies if this sounds obfuscated

eetu.

Thanks for your explanation^^ I think I understand it a bit now, reeaally appreciate your help.

Best regards.

Edited September 28, 2011 by ~nature~