Regression: Cycles motion blur is causing geometry artifacts #112850

New Issue

Valentin Remy · 2023-09-25T14:24:57+02:00

Valentin Remy commented

2023-09-25 14:24:57 +02:00

System Information
Operating system: Windows 11 Pro
Graphics card: RTX 3090

Blender Version
Broken: Blender 4.0.0 Alpha (September 25)
Worked: Blender 3.4.1

Short description of error
Motion blur causes the geometry to appear stretched. It seems like individual vertices are getting distorted.

~~When applying a Butterworth filter on an armature, there are visual artefacts visible on the character's geometry.~~
It appears geometry is being stretched every few frames. !!Note that it only appears when Motion Blur is turned ON!!
~~I guess something is happening between frames, making the issue invisible if motion blur is off.~~

Exact steps for others to reproduce the error
~~Render frame 719 => Issue is visible on the character~~
~~Turn off the Butterworth Applied collection, turn on the "NO Butterworth" collection, render => no visible artefacts~~

Open butterworth_bug_simplified
make sure you are on f719
hit render
observe that the left character is distorted

Findings
It is animation related and has to do with the animation on clavicle_l
If the animation is modified slightly the glitch disappears
If you copy the rotation values of clavicle_l on f719 to the working armature, it will also start showing the glitch
Whatever glitch appears in the render is not visible in the viewport when scrubbing with subframes.
Only appears in Cycles, Eevee does not have that issue
Changing the skinning solver may fix the issue or introduce it

Redo these steps with Motion Blur turned off => no visible artefacts

Simplified File attached
I've also attached a test file saved in Blender 3.3 that I used for testing older versions (since opening the 4.0 file in 3.6 is not possible I exported the data as fbx). With that I found out that the bug was introduced between 3.4 and 3.5

Original File:
https://drive.google.com/file/d/1ygiIMm-8aVXWFf7R77m81qkWYCn7cEvl/view?usp=sharing

**System Information** Operating system: Windows 11 Pro Graphics card: RTX 3090 **Blender Version** Broken: Blender 4.0.0 Alpha (September 25) Worked: Blender 3.4.1 **Short description of error** Motion blur causes the geometry to appear stretched. It seems like individual vertices are getting distorted. ~~When applying a Butterworth filter on an armature, there are visual artefacts visible on the character's geometry.~~ ~~It appears geometry is being stretched every few frames. **!!Note that it only appears when Motion Blur is turned ON!!**~~ ~~I guess something is happening between frames, making the issue invisible if motion blur is off.~~ **Exact steps for others to reproduce the error** ~~Render frame 719 => Issue is visible on the character~~ ~~Turn off the Butterworth Applied collection, turn on the "NO Butterworth" collection, render => no visible artefacts~~ * Open `butterworth_bug_simplified` * make sure you are on f719 * hit render * observe that the left character is distorted ![image](/attachments/f98132d7-11ad-4b3b-ab18-1359a51e1490) **Findings** It is animation related and has to do with the animation on `clavicle_l` If the animation is modified slightly the glitch disappears If you copy the rotation values of `clavicle_l` on f719 to the working armature, it will also start showing the glitch Whatever glitch appears in the render is not visible in the viewport when scrubbing with subframes. Only appears in Cycles, Eevee does not have that issue Changing the skinning solver may fix the issue or introduce it Redo these steps with Motion Blur turned off => no visible artefacts **Simplified File attached** I've also attached a test file saved in Blender 3.3 that I used for testing older versions (since opening the 4.0 file in 3.6 is not possible I exported the data as fbx). With that I found out that the bug was introduced between 3.4 and 3.5 Original File: https://drive.google.com/file/d/1ygiIMm-8aVXWFf7R77m81qkWYCn7cEvl/view?usp=sharing

motion_blur_bug_3_3.blend

58 MiB

image.png

173 KiB

butterworth_bug_simplified.blend

53 MiB

Valentin Remy added the

labels 2023-09-25 14:24:58 +02:00

Valentin Remy commented

2023-09-25 14:32:26 +02:00

Here's an image of the issue:

Here's an image of the issue: ![image](/attachments/fa4ea07c-725b-4b2a-87d0-011db6a0049b)

image.png

106 KiB

Richard Antalik commented

2023-09-26 01:18:14 +02:00

@ChrisLend Can you debug this file, or do you request simplified version?

Richard Antalik added

and removed

labels 2023-09-26 01:18:37 +02:00

Christoph Lendenfeld self-assigned this 2023-09-26 09:26:05 +02:00

Christoph Lendenfeld commented

2023-09-26 11:18:06 +02:00

@Chpouky this doesn't seem to be caused by the butterworth filter. I applied the butterworth to the unfiltered armature and the artifacts don't show up.

disabling the base NLA layer in "Butterworth Applied" removes the issue, so it is somehow animation related
from the look of it I would expect it to be a skinning issue, since it seems like only individual verts are affected

@Chpouky this doesn't seem to be caused by the butterworth filter. I applied the butterworth to the unfiltered armature and the artifacts don't show up. disabling the base NLA layer in "Butterworth Applied" removes the issue, so it is somehow animation related from the look of it I would expect it to be a skinning issue, since it seems like only individual verts are affected

Christoph Lendenfeld added

Status

Needs Information from User

and removed

Status

Confirmed

labels 2023-09-26 11:18:22 +02:00

Valentin Remy commented

2023-09-26 11:21:53 +02:00

@ChrisLend the issue does not always appear at the same frame when you apply the filter, it depends on what settings you use.

For example, if you use 4Hz on Butterworth, see the issue at frame X, then try again with let's say 3Hz, the issue will appear at a different frame.

If you render an animation you will see it appear every now and then, just at different times.

@ChrisLend the issue does not always appear at the same frame when you apply the filter, it depends on what settings you use. For example, if you use 4Hz on Butterworth, see the issue at frame X, then try again with let's say 3Hz, the issue will appear at a different frame. If you render an animation you will see it appear every now and then, just at different times.

👍 1

Christoph Lendenfeld commented

2023-09-26 11:29:42 +02:00

it also depends on the shutter value. On frame 719 it disappears when the shutter is below 0.4 and higher than 0.8

Valentin Remy commented

2023-09-26 11:35:13 +02:00

Ah, nice catch ! So it seems stuff is happening in subframes ? I also just tried changing the Position in Motion Blur settings: "End of frame" seems to hide the problem. I checked a few other frames than 719 and I don't see it.

But it just hides the problem I guess, not sure what is happening under the hood.
My goal is to clean mocap data in Blender to use in Unreal Engine, but if vertices are jumping around in the background it could cause other problems.

Ah, nice catch ! So it seems stuff is happening in subframes ? I also just tried changing the Position in Motion Blur settings: "End of frame" seems to hide the problem. I checked a few other frames than 719 and I don't see it. But it just hides the problem I guess, not sure what is happening under the hood. My goal is to clean mocap data in Blender to use in Unreal Engine, but if vertices are jumping around in the background it could cause other problems.

Christoph Lendenfeld commented

2023-09-26 11:50:47 +02:00

I agree this needs a fix. It's just weird it only shows up in motion blur and not when scrubbing through subframes
Another thing I found: Disabling the animation of clavicle_l removes the glitch

I agree this needs a fix. It's just weird it only shows up in motion blur and not when scrubbing through subframes Another thing I found: Disabling the animation of `clavicle_l` removes the glitch

👍 1

Valentin Remy commented

2023-09-26 11:54:27 +02:00

Interesting !

Some info that might be useful: this is the UE4 Mannequin imported straight from Unreal (exported as FBX).
I also encountered this issue using the Newton character exported from a mocap session in Rokoko Studio.
Haven't tried any other character yet.

Interesting ! Some info that might be useful: this is the UE4 Mannequin imported straight from Unreal (exported as FBX). I also encountered this issue using the Newton character exported from a mocap session in Rokoko Studio. Haven't tried any other character yet.

Christoph Lendenfeld added

Status

Needs Info from Developers

and removed

Status

Needs Information from User

labels 2023-09-26 12:13:57 +02:00

Christoph Lendenfeld commented

2023-09-26 12:18:30 +02:00

@Chpouky I edited the description so everything is in one place and uploaded a cut down version of the file
have you experienced this bug with exported animation unreal as well? would be interesting to know because I can't reproduce it in EEVEE

@Chpouky I edited the description so everything is in one place and uploaded a cut down version of the file have you experienced this bug with exported animation unreal as well? would be interesting to know because I can't reproduce it in EEVEE

❤️ 1

Valentin Remy commented

2023-09-26 12:30:41 +02:00

I haven't tried importing the buggy one in Unreal yet, will do !

Nathan Vegdahl commented

2023-09-29 11:57:37 +02:00

I did a little experimentation as well with butterworth_bug_simplified.blend.

Something that wasn't immediately obvious to me is that the NLA setup isn't necessary at all to trigger the issue. On either character, you can just directly assign the following actions to make the issue show up and disappear:

root|clip|Base_Layer Retarget (does exhibit the issue)
root.002|clip|Base_Layer.001 Retarget (does not exhibit the issue)

Something else I noticed: if you change the armature modifier to use dual-quaternion skinning (the "Preserve Volume" option), the issue goes away for the left character (regardless of action), but is swapped for the right character: root|clip|Base_Layer Retarget does not exhibit the issue, but now root.002|clip|Base_Layer.001 Retarget does exhibit a similar issue (though the motion blur trails are different).

I did a little experimentation as well with `butterworth_bug_simplified.blend`. Something that wasn't immediately obvious to me is that the NLA setup isn't necessary at all to trigger the issue. On either character, you can just directly assign the following actions to make the issue show up and disappear: - `root|clip|Base_Layer Retarget` (does exhibit the issue) - `root.002|clip|Base_Layer.001 Retarget` (does *not* exhibit the issue) Something else I noticed: if you change the armature modifier to use dual-quaternion skinning (the "Preserve Volume" option), the issue goes away for the left character (regardless of action), but is *swapped* for the right character: `root|clip|Base_Layer Retarget` does *not* exhibit the issue, but now `root.002|clip|Base_Layer.001 Retarget` *does* exhibit a similar issue (though the motion blur trails are different).

Christoph Lendenfeld changed title from ~~Butterworth Filter is causing issues on geometry~~ to Regression: Cycles motion blur is causing geometry artifacts

2023-09-29 15:06:23 +02:00

Christoph Lendenfeld changed title from ~~Regression: Cycles motion blur is causing geometry artifacts~~ to Regression: Cycles motion blur is causing geometry artefacts

2023-09-29 15:09:36 +02:00

Christoph Lendenfeld changed title from ~~Regression: Cycles motion blur is causing geometry artefacts~~ to Regression: Cycles motion blur is causing geometry artifacts

2023-09-29 15:09:54 +02:00

Christoph Lendenfeld commented

2023-09-29 15:17:37 +02:00

I found out that it seems to be a regression that happened between 3.4 and 3.5
@brecht tagging you here to give your input on the cycles side

also since this turned out to be not about the butterworth filter, I've unassigned myself

I found out that it seems to be a regression that happened between 3.4 and 3.5 @brecht tagging you here to give your input on the cycles side also since this turned out to be not about the butterworth filter, I've unassigned myself

👍 1

Christoph Lendenfeld added

and removed

Needs Info from Developers

labels 2023-09-29 15:18:13 +02:00