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Principled shader Diffuse Indirect pass differs with Branched and Path Tracing modes
Open, Confirmed, MediumPublic

Description

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 f4dc9f9d68b (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

-make a simple scene with objects using principled shader (default settings)
-drop diffuse bounces to 0
-enable diffuse indirect pass
-render image with both Branched Path Tracing and Path Tracing modes
-compare

Details

Type
Bug

Event Timeline

Philipp Oeser (lichtwerk) triaged this task as Confirmed, Medium priority.

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 Van Lommel (brecht) to take over...