Principled shader Diffuse Indirect pass differs with Branched and Path Tracing modes #55252

Closed
opened 2018-05-29 17:52:15 +02:00 by Santeri Holm · 8 comments

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

  • 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
**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](https://archive.blender.org/developer/F3504169/principledShader_bugTest.blend)} 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
Author

Added subscriber: @SanteriHolm

Added subscriber: @SanteriHolm
Member

Added subscribers: @brecht, @lichtwerk

Added subscribers: @brecht, @lichtwerk
Brecht Van Lommel was assigned by Philipp Oeser 2018-05-30 13:38:44 +02:00
Member

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...

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...
Brecht Van Lommel was unassigned by Dalai Felinto 2019-12-23 16:36:11 +01:00

Added subscriber: @iss

Added subscriber: @iss

Changed status from 'Confirmed' to: 'Needs User Info'

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
diff.png

Not sure if there is supposed to be no difference.

I see only very small differences when substracting PT image from BPT image. Following image is difference multiplied by 10 ![diff.png](https://archive.blender.org/developer/F8333202/diff.png) Not sure if there is supposed to be no difference.

Changed status from 'Needs User Info' to: 'Resolved'

Changed status from 'Needs User Info' to: 'Resolved'
Brecht Van Lommel self-assigned this 2020-02-11 09:23:04 +01:00

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.

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.
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Reference: blender/blender#55252
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