Principled shader Diffuse Indirect pass differs with Branched and Path Tracing modes #55252
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Reference: blender/blender#55252
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System Information
Windows 10 64bit AMD ryzen 7 1700 32GB DDR4, 2x GXT1070
Windows 10 64bit i7-5820k 2xGTX960
tested on a couple of different machines
Blender Version
Broken: 2.79b
f4dc9f9d68
(Official release version), buildbot latest 2.79b c72a204{F3504169}Worked: -
Short description of error
When using Principled shader Diffuse Indirect pass yields different results using Path Tracing or Branched Path Tracing.
When diffuse bounces are 0 Principled shader still appears in Diffuse Indirect pass with Path Tracing mode.
if pricipled shader roughness is at 0 both yield the same result
switching to cpu/gpu or experimental feature set doesn't affect it at all.
Exact steps for others to reproduce the error
Added subscriber: @SanteriHolm
Added subscribers: @brecht, @lichtwerk
Confirming, but not sure if this can be solved for the Principled BSDF (as it is kind of a mix between different BSDFs [and thus raytypes?]).
Described behavior is also true for a simple 50/50 mix between a standard diffuse and a standard glossy.
So in this situation glossy contributes... (if you set glossy bounces to zero then contribution in
Diffuse Indirect
pass also vanishes...)Still reading code here, and I am unsure why this is not the case for branched pathtracing, so for now (as I am hitting my timelimit), I would kindly ask @brecht to take over...
Added subscriber: @iss
Changed status from 'Confirmed' to: 'Needs User Info'
I see only very small differences when substracting PT image from BPT image.
Following image is difference multiplied by 10
Not sure if there is supposed to be no difference.
Changed status from 'Needs User Info' to: 'Resolved'
Ideally there is no difference, but there are some things like light clamping that do, and also float precision. I think the difference in this case is small enough not to be considered a bug. It was bigger when this was originally reported.