Geometry nodes: Instances Incorrectly Rendered with Motion Blur when deleting Instances. #101152

New Issue

Riccardo Bancone · 2022-09-17T17:53:53+02:00

Riccardo Bancone commented

2022-09-17 17:53:53 +02:00

System Information
Operating system: Windows-10-10.0.22000-SP0 64 Bits
Graphics card: NVIDIA GeForce RTX 3080 Ti Laptop GPU/PCIe/SSE2 NVIDIA Corporation 4.5.0 NVIDIA 512.96

Blender Version
Broken: version: 3.3.0, branch: master, commit date: 2022-09-06 15:39, hash: 0759f671ce
Worked: None that I'm aware of. 3.4 alpha shows the same behavior

Short description of error
Motion Blur artifacts appear when deleting instances in both EEVEE and cycles

I suspect that deleting the instances causes indices shifts that tricks motion blur code to "think" that a particular instance moved. Motion blur from the old position to the new is rendered. But actually the instance didn't move, It's only the index that has changed.
This is pure speculation based on my intuition, I don't know how motion blur is actually implemented, so I may be wrong about the cause.
Realizing instances seems to "fix" the problem.

I Experienced the same glitch in a production file using the "scale elements" node, scaling some elements from zero to one and others viceversa, but currently I can't replicate the error. Real geometry, no instances this time. I had to scale from a very small scale instead of zero to work around it.

Exact steps for others to reproduce the error

Render frame 10 of the attached file and the motion blur glitch will appear on the instanced geometry, but not on the realized instances. It's also present in other frames, but not all.

geometry_nodes_motion_blur_bug_v01.blend

**System Information** Operating system: Windows-10-10.0.22000-SP0 64 Bits Graphics card: NVIDIA GeForce RTX 3080 Ti Laptop GPU/PCIe/SSE2 NVIDIA Corporation 4.5.0 NVIDIA 512.96 **Blender Version** Broken: version: 3.3.0, branch: master, commit date: 2022-09-06 15:39, hash: `0759f671ce` Worked: None that I'm aware of. 3.4 alpha shows the same behavior **Short description of error** Motion Blur artifacts appear when deleting instances in both EEVEE and cycles ![image.png](https://archive.blender.org/developer/F13504270/image.png) ![image.png](https://archive.blender.org/developer/F13504319/image.png) I suspect that deleting the instances causes indices shifts that tricks motion blur code to "think" that a particular instance moved. Motion blur from the old position to the new is rendered. But actually the instance didn't move, It's only the index that has changed. This is pure speculation based on my intuition, I don't know how motion blur is actually implemented, so I may be wrong about the cause. Realizing instances seems to "fix" the problem. I Experienced the same glitch in a production file using the "scale elements" node, scaling some elements from zero to one and others viceversa, but currently I can't replicate the error. Real geometry, no instances this time. I had to scale from a very small scale instead of zero to work around it. **Exact steps for others to reproduce the error** Render frame 10 of the attached file and the motion blur glitch will appear on the instanced geometry, but not on the realized instances. It's also present in other frames, but not all. [geometry_nodes_motion_blur_bug_v01.blend](https://archive.blender.org/developer/F13504297/geometry_nodes_motion_blur_bug_v01.blend)

Riccardo Bancone commented

2022-09-17 17:53:53 +02:00

Added subscriber: @RiccardoBancone

Riccardo Bancone changed title from ~~Cycles Incorrectly Rendered in Geometry Nodes when deleting Instances.~~ to Cycles Incorrectly Rendered Motion Blur in Geometry Nodes when deleting Instances.

2022-09-17 17:54:20 +02:00

Iliya Katushenock commented

2022-09-17 21:30:00 +02:00

Added subscriber: @mod_moder

Iliya Katushenock commented

2022-09-17 21:30:00 +02:00

Changed status from 'Needs Triage' to: 'Needs Developer To Reproduce'

Iliya Katushenock commented

2022-09-17 21:30:00 +02:00

It clearly doesn't look like it should. But there is a small chance that it was intended, just in case, I'll ask

geometry_nodes_motion_blur_bug_v01.blend
@HooglyBoogly

It clearly doesn't look like it should. But there is a small chance that it was intended, just in case, I'll ask ![image.png](https://archive.blender.org/developer/F13504697/image.png) [geometry_nodes_motion_blur_bug_v01.blend](https://archive.blender.org/developer/F13504699/geometry_nodes_motion_blur_bug_v01.blend) @HooglyBoogly

Iliya Katushenock commented

2022-09-17 21:31:05 +02:00

Added subscriber: @HooglyBoogly

Pratik Borhade changed title from ~~Cycles Incorrectly Rendered Motion Blur in Geometry Nodes when deleting Instances.~~ to Geometry nodes: Instances Incorrectly Rendered with Motion Blur when deleting Instances.

2022-10-13 06:44:28 +02:00

Jacques Lucke commented

2022-10-20 15:47:37 +02:00

Added subscriber: @JacquesLucke

Jacques Lucke commented

2022-10-20 15:47:37 +02:00

Changed status from 'Needs Developer To Reproduce' to: 'Archived'

Jacques Lucke closed this issue

2022-10-20 15:47:37 +02:00

Jacques Lucke commented

2022-10-20 15:47:38 +02:00

The id attribute is used to map instances between different frames for motion blur. If the attribute does not exist, the index will be used instead. The solution here is to set the ids before starting to delete instances. Just adding a Set ID node before Delete Geometry fixes it.

The `id` attribute is used to map instances between different frames for motion blur. If the attribute does not exist, the index will be used instead. The solution here is to set the ids before starting to delete instances. Just adding a `Set ID` node before `Delete Geometry` fixes it.

Dave Whitney referenced this issue

2023-12-07 19:28:58 +01:00

Animating The 'end' factor in a Trim Curve node messes up motion blur #115910

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Geometry nodes: Instances Incorrectly Rendered with Motion Blur when deleting Instances. #101152