Multiscatter GGX is bugged #92520

New Issue

Alexander Fry · 2021-10-27T05:38:55+02:00

Alexander Fry commented

2021-10-27 05:38:55 +02:00

System Information
Operating system: Windows-10-10.0.19041-SP0 64 Bits
Graphics card: NVIDIA GeForce RTX 2070 SUPER/PCIe/SSE2 NVIDIA Corporation 4.5.0 NVIDIA 496.13

Blender Version
Broken: version: 2.93.5, branch: master, commit date: 2021-10-05 12:04, hash: a791bdabd0
Worked: (newest version of Blender that worked as expected)

Short description of error
On a glossy Multiscatter GGX material, highlight on reflection seem to look dark and kinda like a donut at around 0.02 roughness.
It also seems to change depending on focal length and only happens when using the environment to light the scene

rough 0.03 rough 0.02

Exact steps for others to reproduce the error

Add an HDRI to the scene
On an object (preferably flat) set a Glossy BRDF material with Multiscatter GGX
The HDRi used in the image is this one: https://polyhaven.com/a/autoshop_01
multiscatter_bug.blend

**System Information** Operating system: Windows-10-10.0.19041-SP0 64 Bits Graphics card: NVIDIA GeForce RTX 2070 SUPER/PCIe/SSE2 NVIDIA Corporation 4.5.0 NVIDIA 496.13 **Blender Version** Broken: version: 2.93.5, branch: master, commit date: 2021-10-05 12:04, hash: `a791bdabd0` Worked: (newest version of Blender that worked as expected) **Short description of error** On a glossy Multiscatter GGX material, highlight on reflection seem to look dark and kinda like a donut at around 0.02 roughness. It also seems to change depending on focal length and only happens when using the environment to light the scene > | rough 0.03 | rough 0.02 | > |---|---| > | ![r03.png](https://archive.blender.org/developer/F11538239/r03.png) | ![r02.png](https://archive.blender.org/developer/F11538242/r02.png) | **Exact steps for others to reproduce the error** - Add an HDRI to the scene - On an object (preferably flat) set a Glossy BRDF material with Multiscatter GGX The HDRi used in the image is this one: https://polyhaven.com/a/autoshop_01 [multiscatter_bug.blend](https://archive.blender.org/developer/F11551589/multiscatter_bug.blend)

Alexander Fry commented

2021-10-27 05:38:55 +02:00

Added subscriber: @DHX

Jesse Yurkovich commented

2021-10-27 08:45:36 +02:00

Added subscriber: @deadpin

Jesse Yurkovich commented

2021-10-27 08:45:36 +02:00

Changed status from 'Needs Triage' to: 'Needs Developer To Reproduce'

Jesse Yurkovich commented

2021-10-27 08:45:36 +02:00

I can confirm the issue as far back as 2.79 (with a similar, adjusted, roughness of 0.0004 since that was before we squared roughness inputs) so it's probably been there since Multiscatter GGX was introduced. That said, I'm not sure if it's the fault of the academic paper used for reference or the implementation hitting a numerical degenerate case. This happens for the general range of 0.018 through 0.03.

Will let the devs decide.

A decent HDRi to use is this one: https://polyhaven.com/a/autoshop_01

rough 0.03	rough 0.02

I can confirm the issue as far back as 2.79 (with a similar, adjusted, roughness of 0.0004 since that was before we squared roughness inputs) so it's probably been there since Multiscatter GGX was introduced. That said, I'm not sure if it's the fault of the academic paper used for reference or the implementation hitting a numerical degenerate case. This happens for the general range of 0.018 through 0.03. Will let the devs decide. A decent HDRi to use is this one: https://polyhaven.com/a/autoshop_01 | rough 0.03 | rough 0.02 | |---|---| | ![r03.png](https://archive.blender.org/developer/F11538239/r03.png) | ![r02.png](https://archive.blender.org/developer/F11538242/r02.png) |

Khana commented

2021-12-07 20:27:35 +01:00

Added subscriber: @khana

Khana commented

2021-12-07 20:27:35 +01:00

I have the same issue :
https://developer.blender.org/T82500
https://developer.blender.org/T88595

The whole rough range from 0 to 0.125 is wrong.

I have the same issue : https://developer.blender.org/T82500 https://developer.blender.org/T88595 The whole rough range from 0 to 0.125 is wrong.

Philipp Oeser removed the

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Multiscatter GGX is bugged #92520