Wrong motion blur with RBDs (wrong subframe interpolation?) #93520

New Issue

Steffen Dünner · 2021-11-30T18:25:52+01:00

Steffen Dünner commented

2021-11-30 18:25:52 +01:00

System Information
Operating system: Linux-5.11.0-41-generic-x86_64-with-glibc2.31 64 Bits
Graphics card: NVIDIA GeForce RTX 2070 Super/PCIe/SSE2 NVIDIA Corporation 4.5.0 NVIDIA 495.29.05

Blender Version
Broken: version: 3.1.0 Alpha, branch: master, commit date: 2021-11-30 16:37, hash: 88b37b639e
Worked: (newest version of Blender that worked as expected)

Short description of error
I noticed that (even cached) RBD objects show wrong motion blur in a scene with a camera moving along with them.
I attached a simple scene with 3 falling cubes, from left to right:
Cube 1 is a cached RBD simulation, cube 2 is a cube thats transformation is constrained to cube 1 and cube 3 is a cube that was originally constrained to cube 1 as well but then has been baked to keyframes.
These 3 cubes are being shot from a camera that's falling at a similar speed as themselves and therefore there should be almost no motion blur on the cubes while falling.

Exact steps for others to reproduce the error

Open the attached blend file:
RBD_Jitter_v03.blend
Go to a frame where the 3 falling cubes have roughly the same downward speed as the camera (e.g. frame 16)
It looks like this:
Only the rightmost cube shows the correct (i.e. nearly no) motion blur. The two cubes on the left are blurred like they were not falling and only the camera motion blur was applied.

Here's a quickly rendered animation of it:
RBD_Jitter.0001-0140.mp4

**System Information** Operating system: Linux-5.11.0-41-generic-x86_64-with-glibc2.31 64 Bits Graphics card: NVIDIA GeForce RTX 2070 Super/PCIe/SSE2 NVIDIA Corporation 4.5.0 NVIDIA 495.29.05 **Blender Version** Broken: version: 3.1.0 Alpha, branch: master, commit date: 2021-11-30 16:37, hash: `88b37b639e` Worked: (newest version of Blender that worked as expected) **Short description of error** I noticed that (even cached) RBD objects show wrong motion blur in a scene with a camera moving along with them. I attached a simple scene with 3 falling cubes, from left to right: Cube 1 is a cached RBD simulation, cube 2 is a cube thats transformation is constrained to cube 1 and cube 3 is a cube that was originally constrained to cube 1 as well but then has been baked to keyframes. These 3 cubes are being shot from a camera that's falling at a similar speed as themselves and therefore there should be almost no motion blur on the cubes while falling. **Exact steps for others to reproduce the error** - Open the attached blend file: [RBD_Jitter_v03.blend](https://archive.blender.org/developer/F12669533/RBD_Jitter_v03.blend) - Go to a frame where the 3 falling cubes have roughly the same downward speed as the camera (e.g. frame 16) - It looks like this: ![RBD_Jitter_v03.png](https://archive.blender.org/developer/F12669535/RBD_Jitter_v03.png) - Only the rightmost cube shows the correct (i.e. nearly no) motion blur. The two cubes on the left are blurred like they were not falling and only the camera motion blur was applied. Here's a quickly rendered animation of it: [RBD_Jitter.0001-0140.mp4](https://archive.blender.org/developer/F12669549/RBD_Jitter.0001-0140.mp4)

Steffen Dünner commented

2021-11-30 18:25:52 +01:00

Added subscriber: @SteffenD

Steffen Dünner commented

2021-12-01 12:55:54 +01:00

Small addition. Here's a viewport render (with subsamples) of the 3 cubes above. You can clearly see that only the rightmost cube falls smoothly. The two on the left (RBD cache and constrained) always accelerate / decelerate during a frame.
RBD_Jitter.0001-0180.mp4

Small addition. Here's a viewport render (with subsamples) of the 3 cubes above. You can clearly see that only the rightmost cube falls smoothly. The two on the left (RBD cache and constrained) always accelerate / decelerate during a frame. [RBD_Jitter.0001-0180.mp4](https://archive.blender.org/developer/F12672690/RBD_Jitter.0001-0180.mp4)

Philipp Oeser commented

2022-01-20 08:50:03 +01:00

Added subscriber: @lichtwerk

Philipp Oeser commented

2022-01-20 08:50:03 +01:00

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

Philipp Oeser commented

2022-01-20 08:50:03 +01:00

Can confirm, thx investigating.
Can also imagine that the (supposedly wrong?) subframe interpolation results in the misbehavior.

Can confirm, thx investigating. Can also imagine that the (supposedly wrong?) subframe interpolation results in the misbehavior.

Philipp Oeser changed title from ~~Wrong motion blur with RBDs~~ to Wrong motion blur with RBDs (wrong subframe interpolation?)

2022-01-20 08:50:18 +01:00

Brecht Van Lommel commented

2022-01-20 20:09:53 +01:00

Added subscriber: @brecht

Brecht Van Lommel commented

2022-01-20 20:09:53 +01:00

With bpy.context.scene.show_subframe = True we can see the same non-smooth motion in the viewport, so the problem is in the rigid body implementation.

With `bpy.context.scene.show_subframe = True` we can see the same non-smooth motion in the viewport, so the problem is in the rigid body implementation.

blender-admin commented

2022-01-20 20:28:56 +01:00

This issue was referenced by e1ae95f6b2

This issue was referenced by e1ae95f6b2a3106c008e94b11cda9ba3e6d59ae3

Brecht Van Lommel commented

2022-01-20 20:41:34 +01:00

Changed status from 'Confirmed' to: 'Resolved'

Brecht Van Lommel closed this issue

2022-01-20 20:41:34 +01:00

Brecht Van Lommel self-assigned this 2022-01-20 20:41:34 +01:00

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Wrong motion blur with RBDs (wrong subframe interpolation?) #93520