Motion Vectors NOT working in HDRP Unity 2020.2 or HDRP V 8.3.1 and above

Unity Engine
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1

NO motion vectors in HDRP V 8.3.1 and above

DecodeMotionVector(LOAD_TEXTURE2D_X(_CameraMotionVectorsTexture, UV), MotionVector);

Gives nothing, what has changed?

It is working perfectly fine in Unity 2019 , 2020.1 but nothing in Unity 2020.2

1 Like
2

WHAT THE F happened to the MOTION VECTORS UNITY!! in 2020.2 This is so frustrating. They are a MUST HAVE, did someone just ’ accidently ’ disabled it, Please at least have the curtesy to get back! We have sent numerous emails to support with no feed back, ZERO, asking in the forums, ZERO, looking at the documentation, ZERO, looking at the latest RP source code for a hint, ZERO!

I hate to say it but PLEASE learn something from Unreal Engine, they do NOT make MAJOR and significant breaking changes that often, Unity seems like they can do what ever they like with complete disregard to developers.

3

Have you sent a bug report? Movecs do work on stock HDRP so it’s unlikely that it’s fully broken.

4

Thanks for your reply! really appreciate it and we figured out why motion vectors were not working. Due to lack of updated documentation It took us more than two weeks to solve ‘well’ find a workaround for this issue and now they are working perfectly and we can finaly submit the latest upgrade for CTAA which will work in all version of Unity upto the latest one.

As of HDRP 10.2 Unity introduced the experimental Render Graph system and it is ON by default in any Unity version using 10.2 and above. When it is enabled, motion vector Data is un-accessable via the standard Postprocessing pipeline method. We first seen it on in the render debug viewer (it is on by default and when it is unchecked the next time pressing play it defaults back to enabled! ) and we didn’t realise there is an option to turn it off in the HDRP default settings right at the top! as soon as we disable it, bang, motion vectors working again. This setting is not available in Unity version prior to 10.2 in the Default HDRP settings.

1 Like
5

You will probably need a fix for this in the render graph version of the system because as far as I recall, the non-rendergraph way of HDRP working was removed in HDRP 11. Probably a good idea to check HDRP 11 and 12 to see if they solved that issue already.

6

By the way, there are several references to motion vectors in the 8.x->10.x upgrade guide, but I cannot say whether they are relevant to you.

https://docs.unity3d.com/Packages/com.unity.render-pipelines.high-definition@10.4/manual/Upgrading-from-2020.1-to-2020.2.html

eg:

7

Now that we know what is going on it’s relatively easy , we will be doing a render graph version when hdrp 11 or 12 is final, no problem.

Yes we know about this however it’s irrevelent for our requirement. For others which this maybe relevant, the movecs are clamped for motion blur PP so keep an eye out for this and apparently this will be an option in the upcoming versions.

Thank you again for your help!