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Multiscatter GGX artefacts for rough glass
Confirmed, NormalPublic


System Information
Operating system: Windows-10-10.0.19041-SP0 64 Bits
Graphics card: GeForce RTX 2080/PCIe/SSE2 NVIDIA Corporation 4.5.0 NVIDIA 457.30

Blender Version
Broken: version: 2.93.0 Alpha, branch: master, commit date: 2021-01-29 16:35, hash: rBd0f59d38429d
Worked: (newest version of Blender that worked as expected)

It's been a long time this artefact hasn't been solved.
When you set a Glass BSDF or Principled BSDF distribution type to Multiscatter GGX, and roughness value higher than 0.2, you will get the artefact from almost every camera angle. It's easiest to see this glitch to observe the model in orthographic view.
And with roughness set to not 0, the whole reflection and refraction seems to have a anistropic-like affect.
This is a preview screenshot.

Here is a render result of 2000 samples without any noise reduction.

I have to use multiscatter ggx cause other distribution function just break energy preservation when shading forested glasses and make the glass itself dark.

test blend file here

Event Timeline

For comparison, this is the result with distribution function been set to GGX and other parameters remain the same.

baoyu (baoyu) updated the task description. (Show Details)Mon, Feb 1, 1:38 AM
Philipp Oeser (lichtwerk) changed the task status from Needs Triage to Confirmed.Tue, Feb 16, 5:23 PM

This looks indeed off.

Not familiar enough with that code to classify though, maybe @Lukas Stockner (lukasstockner97) would know?