Cycles Alembic Motion Blur Problem #80076

New Issue

Steffen Dünner · 2020-08-24T13:15:46+02:00

Steffen Dünner commented

2020-08-24 13:15:46 +02:00

System Information
Operating system: Linux-5.4.0-42-generic-x86_64-with-debian-bullseye-sid 64 Bits
Graphics card: GeForce GTX 1080 Ti/PCIe/SSE2 NVIDIA Corporation 4.5.0 NVIDIA 450.51.06

Blender Version
Broken: version: 2.91.0 Alpha, branch: master, commit date: 2020-08-24 10:28, hash: cb8da6efce

Short description of error
Motion blur looks totally wrong when rendered with Cycles, when adding a subdivision modifier after the MeshSequenceCache modifier that loads an Alembic:

Eevee renders the motion blur fine:

If you delete the subdivision modifier Cycles also renders correct motion blur.

Exact steps for others to reproduce the error

Load the attached blend file (don't forget to put the Alembic abc file next to it):
MB_Problem_v02.blend
MB_Problem_v02.abc
Press F12 to render with Eevee. All is fine.
Switch render engine to Cycles.
Render again -> result is wrong, no matter if using GPU or CPU.
Remove the subdivision modifer.
Render again -> result is correct.

**System Information** Operating system: Linux-5.4.0-42-generic-x86_64-with-debian-bullseye-sid 64 Bits Graphics card: GeForce GTX 1080 Ti/PCIe/SSE2 NVIDIA Corporation 4.5.0 NVIDIA 450.51.06 **Blender Version** Broken: version: 2.91.0 Alpha, branch: master, commit date: 2020-08-24 10:28, hash: `cb8da6efce` **Short description of error** Motion blur looks totally wrong when rendered with Cycles, when adding a subdivision modifier after the MeshSequenceCache modifier that loads an Alembic: ![MB_Problem_Cycles.jpg](https://archive.blender.org/developer/F8808122/MB_Problem_Cycles.jpg) Eevee renders the motion blur fine: ![MB_Problem_Eevee.jpg](https://archive.blender.org/developer/F8808124/MB_Problem_Eevee.jpg) If you delete the subdivision modifier Cycles also renders correct motion blur. **Exact steps for others to reproduce the error** - Load the attached blend file (don't forget to put the Alembic abc file next to it): [MB_Problem_v02.blend](https://archive.blender.org/developer/F8808128/MB_Problem_v02.blend) [MB_Problem_v02.abc](https://archive.blender.org/developer/F8808130/MB_Problem_v02.abc) - Press F12 to render with Eevee. All is fine. - Switch render engine to Cycles. - Render again -> result is wrong, no matter if using GPU or CPU. - Remove the subdivision modifer. - Render again -> result is correct.

Steffen Dünner commented

2020-08-24 13:15:46 +02:00

Added subscriber: @SteffenD

blender-admin commented

2020-08-24 16:53:14 +02:00

This issue was referenced by 5303509354

This issue was referenced by 530350935472970dccc211b0e728e2db4fd1d8ef

Kévin Dietrich commented

2020-08-24 19:39:29 +02:00

Added subscriber: @kevindietrich

Kévin Dietrich commented

2020-08-24 19:39:29 +02:00

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

Kévin Dietrich closed this issue

2020-08-24 19:39:29 +02:00

Kévin Dietrich self-assigned this 2020-08-24 19:39:29 +02:00

Kévin Dietrich commented

2020-08-24 19:39:29 +02:00

Committed fix 5303509354, but this did not get closed automatically for some reason.

Also note that if you have a modifier after the MeshSequenceCache, the custom velocities from the Alembic cache will not be read, and Cycles will default to generating motion blur data based on the vertices of the previous and the next frame, if and only if the vertex count does not change between frames.

Committed fix 5303509354, but this did not get closed automatically for some reason. Also note that if you have a modifier after the MeshSequenceCache, the custom velocities from the Alembic cache will not be read, and Cycles will default to generating motion blur data based on the vertices of the previous and the next frame, if and only if the vertex count does not change between frames.

Steffen Dünner commented

2020-08-24 22:28:30 +02:00

This comment was removed by @SteffenD

*This comment was removed by @SteffenD*

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Cycles Alembic Motion Blur Problem #80076