Motion blur acting up. #46404

New Issue

Braeden · 2015-10-07T10:05:12+02:00

Braeden commented

2015-10-07 10:05:12 +02:00

System Information
Windows8 x64 and Dual GTX 670s (but the problem still exists on CPU rendering - i7-3930k)

Blender Version
Broken: (example: 2.76 RC3 fb78f6d
Worked: Not sure, using most recent version of Blender RC3

Strange artifacts/displaced vertices in mesh when motion blur is enabled (images attached). The clean one is without MB.

I have animated a paper airplane being folded (armatures and shape keys), it randomly seems to happen in random spots. Only happens with motion blur enabled.

**System Information** Windows8 x64 and Dual GTX 670s (but the problem still exists on CPU rendering - i7-3930k) **Blender Version** Broken: (example: 2.76 RC3 fb78f6d Worked: Not sure, using most recent version of Blender RC3 Strange artifacts/displaced vertices in mesh when motion blur is enabled (images attached). The clean one is without MB. ![2015-10-07 03_57_17-.png](https://archive.blender.org/developer/F243050/2015-10-07_03_57_17-.png) ![2015-10-07 03_56_44-.png](https://archive.blender.org/developer/F243051/2015-10-07_03_56_44-.png) I have animated a paper airplane being folded (armatures and shape keys), it randomly seems to happen in random spots. Only happens with motion blur enabled.

Braeden commented

2015-10-07 10:05:12 +02:00

Changed status to: 'Open'

Braeden commented

2015-10-07 10:05:12 +02:00

Added subscriber: @BraedenLaverty

Braeden commented

2015-10-07 10:42:56 +02:00

I am using a mirror modifier and I found that by disabling the "merge" checkbox, this problem doesn't happen anymore... odd either way. Luckily I didnt need to use the merge setting for this, but hopefully this can be sorted out some how.

Sergey Sharybin commented

2015-10-08 07:50:45 +02:00

Added subscriber: @Sergey

Sergey Sharybin commented

2015-10-08 07:50:45 +02:00

It's really hard to tell what's going on there without having .blend file which demonstrates the issue.

Current guess is that with merge option either topology of the mesh change s cross the frames or order of output is not determenistic in certain cicrumstances which will surely confuse deformation motion blur.

In order to give any more definitive answer here we need .blend file.

It's really hard to tell what's going on there without having .blend file which demonstrates the issue. Current guess is that with merge option either topology of the mesh change s cross the frames or order of output is not determenistic in certain cicrumstances which will surely confuse deformation motion blur. In order to give any more definitive answer here we need .blend file.

Braeden commented

2015-10-09 04:33:11 +02:00

Attached is the blend file. Frame 14 seems to be the only one that this happens to. To be fair to blender, the mesh is not great, I was just doing a test for something and wasn't super careful with it... but it just seemed odd that it would suddenly just do that during motion blur, seems like a bug.

paper_test.blend

Hope this helps. Let me know if I can do anything else.

Thanks!

Attached is the blend file. Frame 14 seems to be the only one that this happens to. To be fair to blender, the mesh is not great, I was just doing a test for something and wasn't super careful with it... but it just seemed odd that it would suddenly just do that during motion blur, seems like a bug. [paper_test.blend](https://archive.blender.org/developer/F243578/paper_test.blend) Hope this helps. Let me know if I can do anything else. Thanks!

Brecht Van Lommel commented

2015-10-11 21:00:53 +02:00

Added subscriber: @brecht

Brecht Van Lommel commented

2015-10-11 21:00:53 +02:00

The problem is indeed that the topology changes during motion blur, which is not supported. Cycles only checks that the number of vertices is the same, so it doesn't detect that the topology changes. But if it would have detected that you'd still have the problem that motion blur is disabled for this frame.

Perhaps the Mirror modifier could use undeformed coordinates to determine which vertices to merge, so that the topology stays the same. But this is a bit of an unusual setup in that typically the mirror modifier comes before the armature modifier, so that both sides can be animated independently.

The problem is indeed that the topology changes during motion blur, which is not supported. Cycles only checks that the number of vertices is the same, so it doesn't detect that the topology changes. But if it would have detected that you'd still have the problem that motion blur is disabled for this frame. Perhaps the Mirror modifier could use undeformed coordinates to determine which vertices to merge, so that the topology stays the same. But this is a bit of an unusual setup in that typically the mirror modifier comes before the armature modifier, so that both sides can be animated independently.

Braeden commented

2015-10-13 15:04:03 +02:00

Makes sense, as I mentioned, this was created in a hurry just for reference. I created a second version with cleaner topology and I used the same modifiers in the same order in the stack and it worked fine. As I am not a developer, I had no clue how the motion blur is calculated, knowing now that verts are checked, it makes complete sense that there was an error. Thanks for the reply, it is much appreciated. Oh, and thanks for all the awesomeness you have brought to Blender.

Bastien Montagne commented

2015-10-21 08:23:21 +02:00

Added subscriber: @mont29

Bastien Montagne commented

2015-10-21 08:23:21 +02:00

Changed status from 'Open' to: 'Archived'

Bastien Montagne closed this issue

2015-10-21 08:23:21 +02:00

Bastien Montagne self-assigned this 2015-10-21 08:23:21 +02:00

Bastien Montagne commented

2015-10-21 08:23:21 +02:00

So, not a bug in the end, we can close it. ;)

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Motion blur acting up. #46404