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Crushed Velvet Eevee render problems in Cycles
Confirmed, LowPublicBUG


System Information
Operating system: Windows-10-10.0.18362-SP0 64 Bits
Graphics card: GeForce RTX 2070/PCIe/SSE2 NVIDIA Corporation 4.5.0 NVIDIA 445.75

Blender Version
Broken: version:

  • 2.93.0 Alpha, branch: master, commit date: 2021-01-24 23:16, hash: rBcf6d17a6aa42
  • 2.82 (sub 7), branch: master, commit date: 2020-03-12 05:06, hash: rB375c7dc4caf4

Worked: ?

Short description of error
The Crushed Velvet material from the Material Library does not render properly with Cycles when setting the device to GPU.

Exact steps for others to reproduce the error

  1. Load the simplified material attached below
  2. Set the render device to CPU and render. The output should be all black
  3. Set the render device to GPU and render.. Depending whether you have only GPU(s) activated in the preferences or also CPU(s) you should see one of the following. When only GPU(s) are enabled you should get a proper render. When CPU(s) are also enabled you should get dark render tiles that are rendered on the CPUs.

Original description:
I'm attaching the .blend file I used to test this issue. I'm not even sure this is a bug or simply me not being overly familiar with materials yet, but it feels like a bug. An dit may be a Blender bug and nothing to do with this add-on. Obviously, this material renders fine in Eevee, but it also renders fine in Cycles when using CPU to render, but has major artifacts when using GPU to render. I've attached a render to show what I'm getting in case you don't experience it.

The steps I took to get here are,

Basically, I have a default scene I use to do my modeling or as a start point. It's very basic. I was experiencing this issue in another project I was working on and noticed it went away when I changed the material on one object.

  • I loaded up my basic start file
  • selected the sphere
  • Scrolled down to the Material Library VX panel in the Material Properties tab
  • Loaded the Sample Library
  • Chose the Crushed Velvet Eevee material and clicked Apply to Selected

That's it. I had initially thought it was simply a problem rendering in Cycles but for my first render, I forgot to switch from CPU to GPU and noticed it rendered fine. So I did a few more tests and it renders fine with CPU every time, but not with GPU.

Event Timeline

The problem appears to be that transmission is non-zero, the IOR is zero and there is subsurface scattering. This results in a black output on CPU but not on GPU. Below is a simplified file with a simplified material where the settings of the Principled BSDF are at the default except for the Subsurface, IOR and Transmission.

This is an edge case as even with an IOR slightly above zero it renders properly on both.

Robert Guetzkow (rjg) changed the task status from Needs Triage to Confirmed.Jan 26 2021, 11:40 AM
Robert Guetzkow (rjg) triaged this task as Low priority.
Robert Guetzkow (rjg) updated the task description. (Show Details)
Robert Guetzkow (rjg) updated the task description. (Show Details)

My edit should perhaps be a new separate report as I've noticed that the original report had the problem in reverse, works fine on CPU but not with GPU.

Brecht Van Lommel (brecht) changed the subtype of this task from "Report" to "Bug".Jan 26 2021, 4:34 PM