Artefacts with volume motion blur #97650

New Issue

Steffen Dünner · 2022-04-27T12:07:46+02:00

Steffen Dünner commented

2022-04-27 12:07:46 +02:00

System Information
Operating system: Linux-5.15.0-25-generic-x86_64-with-glibc2.31 64 Bits
Graphics card: NVIDIA GeForce RTX 2070 Super/PCIe/SSE2 NVIDIA Corporation 4.5.0 NVIDIA 510.47.03

Blender Version
Broken: version: 3.2.0 Alpha, branch: master, commit date: 2022-04-27 08:22, hash: 68ca12a7fc
Worked: (newest version of Blender that worked as expected)

Short description of error
When rendering VDBs with motion blur, I get a lot of artefacts in the shadows (?), especially when rendering with the GPU.
These artefacts look the same on Windows and Linux with different nVidia cards (RTX 2070 and GTX 1080ti).
Here's an example MP4 of how they look in an animation (watch the dark splotches on the floor plane):

VB_GPU_MB.mp4

Exact steps for others to reproduce the error

Unpack and open the attached blend file
Volume_MB_Bug_v01.zip
Press F12 to render, by default it should use GPU + motion blur:
Switch off motion blur:
Switch to CPU and turn motion blur back on:
And finally CPU without motion blur:

**System Information** Operating system: Linux-5.15.0-25-generic-x86_64-with-glibc2.31 64 Bits Graphics card: NVIDIA GeForce RTX 2070 Super/PCIe/SSE2 NVIDIA Corporation 4.5.0 NVIDIA 510.47.03 **Blender Version** Broken: version: 3.2.0 Alpha, branch: master, commit date: 2022-04-27 08:22, hash: `68ca12a7fc` Worked: (newest version of Blender that worked as expected) **Short description of error** When rendering VDBs with motion blur, I get a lot of artefacts in the shadows (?), especially when rendering with the GPU. These artefacts look the same on Windows and Linux with different nVidia cards (RTX 2070 and GTX 1080ti). Here's an example MP4 of how they look in an animation (watch the dark splotches on the floor plane): [VB_GPU_MB.mp4](https://archive.blender.org/developer/F13031826/VB_GPU_MB.mp4) **Exact steps for others to reproduce the error** - Unpack and open the attached blend file [Volume_MB_Bug_v01.zip](https://archive.blender.org/developer/F13031818/Volume_MB_Bug_v01.zip) - Press F12 to render, by default it should use GPU + motion blur: ![VB_GPU_MB.png](https://archive.blender.org/developer/F13031831/VB_GPU_MB.png) - Switch off motion blur: ![VB_GPU_noMB.png](https://archive.blender.org/developer/F13031833/VB_GPU_noMB.png) - Switch to CPU and turn motion blur back on: ![VB_CPU_MB.png](https://archive.blender.org/developer/F13031836/VB_CPU_MB.png) - And finally CPU without motion blur: ![VB_CPU_noMB.png](https://archive.blender.org/developer/F13031838/VB_CPU_noMB.png)

Steffen Dünner commented

2022-04-27 12:07:46 +02:00

Added subscriber: @SteffenD

blender-admin commented

2022-04-27 12:07:46 +02:00

#97815 was marked as duplicate of this issue

Steffen Dünner commented

2022-04-27 12:38:55 +02:00

Quick addition: After some experimentation I found that I can get rid of the artefacts by upping the "Transparent Max Bounces" value to something like 16 instead of 8:

I can totally live with that but I still don't get what volumes, transparency and motion blur have to do with each other...

Quick addition: After some experimentation I found that I can get rid of the artefacts by upping the "Transparent Max Bounces" value to something like 16 instead of 8: ![image.png](https://archive.blender.org/developer/F13031874/image.png) I can totally live with that but I still don't get what volumes, transparency and motion blur have to do with each other...

Kévin Dietrich commented

2022-04-27 14:52:09 +02:00

Added subscriber: @kevindietrich

Kévin Dietrich commented

2022-04-27 14:52:09 +02:00

Changed status from 'Needs Triage' to: 'Confirmed'

Kévin Dietrich commented

2022-04-27 14:52:09 +02:00

Volumes are rendered using a bounding mesh (that you can visualize by plugging a diffuse shader in the material output node), intersecting the mesh but not intersecting volume data counts as a transparency bounce. It could be that the extra volume mesh padding added for motion blur is making rays pass through more geometry, thus increasing the max transparent bounces fixes the artefacts.

Steffen Dünner commented

2022-04-27 18:38:20 +02:00

@kevindietrich Thanks for confirming this. The extra padding because of the motion blur sounds very plausible.
As I said, I can live with upping the ray bounces for transparency if this fixes the issue.

@kevindietrich Thanks for confirming this. The extra padding because of the motion blur sounds very plausible. As I said, I can live with upping the ray bounces for transparency if this fixes the issue.

Kévin Dietrich commented

2022-05-04 20:58:52 +02:00

Added subscriber: @Mimouni-Zied

Philipp Oeser removed the

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Artefacts with volume motion blur #97650