Artifacts generated by Camera Motion Blur on particles

Development Rendering
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1

Hello, is there a way to mitigate/cancel the camera motion blur effects on particles without changing the Material Translucency Pass to After Motion Blur? Since a lot of our translucent materials are set to After DOF, using After Motion Blur would generate some sorting issues.

Setting the Motion Vector Setting to disable under the Sprite Renderer doesn’t seem to help too when rotating the camera around.

I have included a project example as well as a video and a screenshot showing the issue using the fountain emitter.

Thanks in advance for your help/input on this.

2

Steps to Reproduce

  1. Unzip ThirdPersonCamMotionBlurBug.zip which is the Unreal Project
  2. Open the project under unreal 5.6
  3. Select ThirdPersonCamMotionBlurBug as the project
  4. Open any map and do a PIE
  5. Rotate the camera around, you should see that the fountain emitters particles are generating artifact while rotating the camera
3

Hello [mention removed]​,

Thanks for the detailed report. I was able to reproduce the behavior you described in UE 5.6.

Could you try enabling the “Velocity from Depth Only” flag in the material? In my tests, this helped reduce the artiffcats without needing to change the Translucency Pass.

Let me know if that helps.

Best,

Francisco

4

Hello Francisco! Thanks for your suggestion. I gave it a try but unfortunately I don’t see any difference. I would also suspect this option to not be available in my material since we are reading depth via a Depth Fade.

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5

Hello [mention removed]​ ,

That’s unfortunate to hear, this suggestion did help on the repro project you shared. Given that, setting the Transparency Pass to “After Motion Blur” remains the most effective workaround I can suggest at the moment, although I understand it’s not ideal for your case.

I was also able to reproduce this behavior in a recent build from Main, and it doesn’t appear to be expected. I believe this may be an engine-side issue, so I’ll go ahead and register it internally as a potential bug for the rendering team to review.

I’ll keep you posted with an update soon.

Best,

Francisco

6

Thanks [mention removed]​ , this is much appreciated. For now we went ahead with the After Motion Blur which will create some sorting issues. On created, if you could share the link to the ticket (if it’s public) it would be very appreciated. Thanks!

7

Hello [mention removed]​,

Glad to help. I’ve made a JIRA report to be added to the Unreal issue tracker website. You will be able to track the resolution by checking this link: Unreal Engine Issues and Bug Tracker (UE\-306682)

Please note that Epic ultimately determines whether the issue will be made publicly accessible and the process may take a few days. The tracking link might not work immediately.

I’ll close the case now but feel free to reply if you have anything else to add.

Best,

Francisco