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brush lag in texture painting
Open, Confirmed, MediumPublic


System Information
Operating system: Windows 10
Graphics card: GTX 1080Ti

Blender Version
2.80 0f5b53ba4dc

Short description of error
When painting textures in 3D viewport brush lags very much, so that it is not even possible to draw a circle. In Texture editor it works fine.

Exact steps for others to reproduce the error
The same issue with any mesh. Does not matter how many polygons. increased brush spacing also does not help.
Attaching short video with this issue.



Event Timeline

I also noticed, that if the brush size is much smaller, then the issue disappears, or even with larger brush the lag is not so bad. the worst lag is with medium size brush..

Sebastian Parborg (zeddb) triaged this task as Confirmed, Medium priority.Jan 4 2019, 2:02 PM

I get this as well. I wouldn't think that the projection calculation of the brush in 3D space onto a plane would be this slow.

I'm not seeing any poor performance, please attach a .blend file so we're sure to be testing the same setup?

It might also be a threading issue, try changing Render > Performance > Threads to 1 or other values to see if it makes a difference.

Projection painting code is very different than our 2D painting code, the bottleneck here may not be in the 3D viewport, so not necessarily an issue for @Clément Foucault (fclem).

For me it happens with any blend file (just tested again with latest builds). I have also tested it on few different PCs (one pc with amd ryzen 1700 CPU/GTX 1080Ti and another with amd ryzen 2700x/GTX 1080Ti)
Blender 2.79 has also the same issue for me.
Sorry, but I could not find (Render > Performance > Threads to 1) option.

@Sarunas Atkocaitis (Sarunas) you have to switch to cycles for that option to be visible.

Here is a simple test file:

@Brecht Van Lommel (brecht) ah, I see. I guess I was too hasty with the assign then. How should we assign this to (if any)?
If I set the threads to 1, the issue becomes even more apparent. If I try to draw in a circle, the 2D painting code is able to keep up quite well, but the 3D viewport seems to struggle quite a bit.
Do you know if we handle the poll rate of the mouse differently in the 2D viewport than in the 3D viewport?

@Sebastian Parborg (zeddb)
Thanks for adivice.
I have switched threads to 1 and it actually fixed the issue it draws without the lag, but if I put anything else then 1 to the thread count it starts lagging again.

@Sarunas Atkocaitis (Sarunas) interesting, I guess it might just be that I have a really crappy CPU (AMD bulldozer) that I get other results. (Or could also be different under Linux than in Windows)

I can confirm as well that setting rendering threads to 1 resolves the issue but setting rendering threads to anything above 1 causes problems.