Maniphest T96631

Principled GGX transmission handles fresnel incorrectly
Confirmed, NormalBUG
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Assigned To
None
Authored By
tempdevnova (tempdevnova)
Mar 19 2022, 4:52 PM
Tags
  • BF Blender
  • Render & Cycles
Subscribers
Anton Raves (Memento)
baoyu (baoyu)
Pratik Borhade (PratikPB2123)
tempdevnova (tempdevnova)

Description

System Information
Operating system: Windows-10-10.0.19043-SP0 64 Bits
Graphics card: GeForce GTX 1080/PCIe/SSE2 NVIDIA Corporation 4.5.0 NVIDIA 431.07

Blender Version
Broken: version: 3.0.0, branch: master, commit date: 2021-12-02 18:35, hash: rBf1cca3055776
Worked: (newest version of Blender that worked as expected)

Short description of error
When using the Principled GGX or Beckmnan transmission the fresnel effect does not decrease with increasing roughness as it should.

Exact steps for others to reproduce the error

Multitest3.blend1 MBDownload

In this test file only the specular reflection is visible. The gradient going into the roughness input goes from 0 at the top to 1 at the bottom. As can be seen there the fresnel effect does not otne down with increasing roughness.
Multiscatter GGX does not have this issue.

Edit: Both Beckman and GGX in the Glass BSDF have the same issue.

Apart from that I could not find a single source that documents how fresnel is calculated in the Principled BSDF. If you read this and know that please tell us the source.

Thank you and have a great day!

Related Objects

Event Timeline

tempdevnova (tempdevnova) created this task.Mar 19 2022, 4:52 PM
baoyu (baoyu) added a subscriber: baoyu (baoyu).Mar 20 2022, 3:02 AM

In your test file, I tried to switch the principled bsdf to a glass shader, then set it to MGGX. Just found another BUG.

tempdevnova (tempdevnova) added a comment.EditedMar 20 2022, 2:25 PM

@baoyu I already reported that one in T96602

tempdevnova (tempdevnova) updated the task description.Mar 20 2022, 2:26 PM
tempdevnova (tempdevnova) updated the task description.
Pratik Borhade (PratikPB2123) changed the task status from Needs Triage to Confirmed.Mar 21 2022, 5:51 AM
Pratik Borhade (PratikPB2123) added a project: Render & Cycles.
Pratik Borhade (PratikPB2123) added a subscriber: Pratik Borhade (PratikPB2123).
Anton Raves (Memento) added a subscriber: Anton Raves (Memento).Mar 21 2022, 7:31 AM
Brecht Van Lommel (brecht) changed the subtype of this task from "Report" to "Bug".Apr 28 2022, 5:48 PM
tempdevnova (tempdevnova) updated the task description.May 8 2022, 2:56 PM
tempdevnova (tempdevnova) mentioned this in T96606: Multiscatter GGX produces large difference in refraction brightness compared to GGX.May 8 2022, 3:16 PM