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Persistent data, motion blur, and geometry displacement results in glitchy meshes during rendering
Closed, ResolvedPublicBUG

Description

System Information:
Operating system: Windows-10-10.0.19041-SP0 64 Bits
Graphics card: GeForce GTX 1070 Ti/PCIe/SSE2 NVIDIA Corporation 4.5.0 NVIDIA 461.92

Blender Version:
Broken: version: 2.93.1, branch: master, commit date: 2021-06-22 05:57, hash: rB1b8d33b18c2f
Worked: N/A

Short description of error:
I don't know if this is a bug or a limitation, when rendering with Cycles with Persistent Data and Motion Blur are enabled and there is an object with Displacement, the mesh will start to glitch. I tried also with a fixed camera and the result is the same.

Persistent Data offPersistent Data on

Exact steps for others to reproduce the error:
open the attached .blend file and render the animation

or

  1. Create a new file.
  2. Change the render engine to Cycles and enable Motion Blur and the Persistent Data option.
  3. Create an object and give it a material, making sure you change the Displacement method for this material to Displacement Only
  4. In that material, attach something to the Displacement output of the node tree. A noise texture works.
  5. Ensure the object with the material created in the precious steps has enough geometry for the displacement to be noticeable.
  6. Render an animation with this setup and observe the mesh changing as the animation progresses, this should not be happened.

Event Timeline

Alaska (Alaska) changed the task status from Needs Triage to Confirmed.Fri, Jul 9, 12:58 AM
Alaska (Alaska) added a subscriber: Alaska (Alaska).

I can confirm this issue, information can be found below:

I believe I saw a report similar to this one but I can't find it at the moment.

System Information
Operating system: Linux-5.10.0-7-amd64-x86_64-with-glibc2.31 64 Bits
Graphics card: NVIDIA GeForce RTX 3070/PCIe/SSE2 NVIDIA Corporation 4.5.0 NVIDIA 465.31

Blender Version
Broken: version: 3.0.0 Alpha, branch: master, commit date: 2021-07-08 17:54, hash: rBaf8fb707dab1

I believe I saw a report similar to this one but I can't find it at the moment.

May be T89396: Environment Pass does not work with "Persistent Data" turned on ?

I've looked into the issue further and found that this issue only occurs when persistent data, motion blur, and shader displacement is enabled.

I will update the report to reflect these conditions.

Alaska (Alaska) renamed this task from mesh glitch when Adaptive Subdivision and Persistent Data are enabled to Persistent data, motion blur, and geometry displacement results in glitchy meshes during rendering.Fri, Jul 9, 8:36 AM
Alaska (Alaska) updated the task description. (Show Details)

I've looked into the issue further and found that this issue only occurs when persistent data, motion blur, and shader displacement is enabled.

I will update the report to reflect these conditions.

thank you so much! I don't need motion blur in my project and this is a great workaround, now wait for a fix 😬

Alaska (Alaska) changed the subtype of this task from "Report" to "Bug".Sat, Jul 10, 3:25 AM

CC @Brecht Van Lommel (brecht) as this seems to be a area you have knowledge in.

Also when you render with a given sample rate and you turn afterwords Persistant Data on and change the samples. It will render still the old setting for Samples.

Also when you render with a given sample rate and you turn afterwords Persistant Data on and change the samples. It will render still the old setting for Samples.

For separate bugs, please make a separate report