Principled hair BSDF shading incorrect when input is connected #93102

New Issue

Maurice Laveaux · 2021-11-15T19:58:37+01:00

Maurice Laveaux commented

2021-11-15 19:58:37 +01:00

System Information
Operating system: Windows-10-10.0.19043-SP0 64 Bits
Graphics card: NVIDIA GeForce GTX 1080/PCIe/SSE2 NVIDIA Corporation 4.5.0 NVIDIA 496.49

Blender Version
Broken: version: 3.0.0 Beta, branch: master, commit date: 2021-11-11 18:49, hash: bd734cc441 (and master 2021-11-15 hash: 7e82c840b7a43b0594ba274c745f3049e0148d12)
Worked: 2.93.5

Short description of error
For the principle hair BSDF there is a difference between filling in the "Melanin" input in the node itself and connecting this input to another node with the same value; see the screenshots below. This also happens for the "Melanin Redness" and "Coat" inputs. The issue is also present for CPU renders.

Exact steps for others to reproduce the error

Open the attached blend file; steps performed:
Add a particle hair system to the default cube.
Switch render engine to cycles with GPU.
Add a principle hair BSDF with melanin concentration.
Add a value node with value 0.8 and connect it to melanin input
Switch to the cycles preview.
Notice that some particles are blue, whereas with the value node disconnected all particles are dark brown as expected.

principled_hair_bsdf_issue.blend

Expected:

Problem:

**System Information** Operating system: Windows-10-10.0.19043-SP0 64 Bits Graphics card: NVIDIA GeForce GTX 1080/PCIe/SSE2 NVIDIA Corporation 4.5.0 NVIDIA 496.49 **Blender Version** Broken: version: 3.0.0 Beta, branch: master, commit date: 2021-11-11 18:49, hash: `bd734cc441` (and master 2021-11-15 hash: `7e82c840b7a43b0594ba274c745f3049e0148d12`) Worked: 2.93.5 **Short description of error** For the principle hair BSDF there is a difference between filling in the "Melanin" input in the node itself and connecting this input to another node with the same value; see the screenshots below. This also happens for the "Melanin Redness" and "Coat" inputs. The issue is also present for CPU renders. **Exact steps for others to reproduce the error** 1. Open the attached blend file; steps performed: 1. Add a particle hair system to the default cube. 2. Switch render engine to cycles with GPU. 3. Add a principle hair BSDF with melanin concentration. 4. Add a value node with value 0.8 and connect it to melanin input 2. Switch to the cycles preview. 3. Notice that some particles are blue, whereas with the value node disconnected all particles are dark brown as expected. [principled_hair_bsdf_issue.blend](https://archive.blender.org/developer/F11810564/principled_hair_bsdf_issue.blend) Expected: ![expected.png](https://archive.blender.org/developer/F11810601/expected.png) Problem: ![problem.png](https://archive.blender.org/developer/F11810599/problem.png)

Maurice Laveaux commented

2021-11-15 19:58:37 +01:00

Added subscriber: @mlaveaux

Maurice Laveaux changed title from ~~Principled hair BSFW shading incorrect when input are connected~~ to Principled hair BSDF shading incorrect when input are connected

2021-11-15 19:58:47 +01:00

Maurice Laveaux changed title from ~~Principled hair BSDF shading incorrect when input are connected~~ to Principled hair BSDF shading incorrect when input is connected

2021-11-15 19:58:56 +01:00

Pratik Borhade commented

2021-11-16 07:19:09 +01:00

Added subscriber: @PratikPB2123