Weird rendering of points with velocity attribute #103918
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Reference: blender/blender#103918
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System Information
Operating system: Linux-5.15.0-58-generic-x86_64-with-glibc2.35 64 Bits
Graphics card: NVIDIA GeForce RTX 2070 Super/PCIe/SSE2 NVIDIA Corporation 4.5.0 NVIDIA 525.60.13
Blender Version
Broken: version: 3.5.0 Alpha, branch: master, commit date: 2023-01-16 11:41, hash:
154d3e95f8also broken: 3.4.1, 3.3.2
Worked: Never?
Short description of error
Shading of points is totally broken in Cycles when using a "velocity" attribute. I noticed this during a project that needs motion blur on point clouds.
At first I thought it was something broken with the incoming Alembics (I use 2 to work around the current shortcomings of importing attributes on Alembic point clouds following this tutorial by Entagma ).
But when I started to boil down my scene to create an "as simple as possible repro scene" I noticed that something is seriously broken, at least with points, Geometry Nodes and motion blur in Cycles.
I'm currently trying to work around by using instanced spheres instead of points but first results don't look too good either.
The error itself is that as soon as there's a "velocity" attribute on points and I use Motion Blur during rendering, the shading completely breaks. Even if the velocity vectors are at 0, 0, 0.
This is a render of the attached blend file without motion blur:
And this with motion blur on:
Notice the "velocity" attribute which is basically set to no motion whatsoever:
The render doesn't become better if I e.g. set it to any other values.
Exact steps for others to reproduce the error
Point_MB_v01.blend
It's just some points distributed on a grid
Added subscriber: @SteffenD
Added subscriber: @mod_moder
I can confirm behavior. But the velocity attribute must be used for blurring. And it's coming through. Just not sure what it should look like for velocity close to 0...
Thanks for confirming. A velocity vector of length 0 should result in no blurring at all. If you e.g. in my blend file manually set the velocity vectors to 0, 0, 10 (which should result in vertical motion blur), it looks like this
So there is a vertical blur but the spherical shape of the points is totally gone. In my renderings above you can also see that the size of the points gets visually smaller, even if there should be no blur.
Changed status from 'Needs Triage' to: 'Needs Developer To Reproduce'
Added subscriber: @HooglyBoogly
Based on the description I don't think this is related to geometry nodes directly. Thanks for the report.
Added subscriber: @EAW
I did test this in 3.4.1 and current master, and would like to note that with CPU rendering the issue doesn't occur.
(My GPU is too old to be used with Cycles.)
@SteffenD and @mod_moder, can either of you please re-test using CPU rendering to see if this is GPU only?
3.5 with Motion Blur
3.4.1 with Motion Blur and 10.0 velocity in Z.
Changed status from 'Needs Developer To Reproduce' to: 'Confirmed'
Thx @EAW ! Now i see that this bug only for GPU render
Indeed, CPU rendering looks fine. Optix and CUDA are broken.
Thank you for testing. ☺️
This bug bit me again today. I had already forgotten about it, but it's annoying as hell.
Same problem here.
CPU Only:
GPU Only:
CPU + GPU (Mixes the results of both):
CPU+GPU Detail:
And I agree, this is dangerous for production and it's very annoying.
I don't see this bug assigned to anyone, so I'll mention @brecht because I think it's mainly related to Cycles and the Point Cloud implementation :)
Brecht Van Lommel referenced this issue2023-07-07 20:19:07 +02:00