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Solve issue with importance sampling at Principle shader clearcoat calculation
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Authored by Pascal Schön (VanCantus) on Oct 20 2017, 11:20 AM.



The clearcoat component of the Principled BSDF is currently using GTR1 for the D term while using GGX for importance sampling. This causes the clearcoat highlight to be non-consistent for increasing clearcoat roughness values (see T53038).

With this patch, a switch from GTR1 to GGX is performed. This may produce some difference to the original Disney "principled" BRDF, but this should be negligibly small.

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Brecht Van Lommel (brecht) requested changes to this revision.Oct 20 2017, 2:07 PM

It's not quite correct yet, the G1o term is also used for the pdf, so with the modified alpha2 there's a mismatch with the actual sampling still.

This revision now requires changes to proceed.Oct 20 2017, 2:07 PM