(open) [HOU-3056] GPU strange artifacts in reflections

[gagui]

Hello.

I'm trying the GPU engine lately and I'm getting some strange artifacts in reflections.
Another thing I also notice is that reflections in the glass resolve much quicker in CPU than GPU mode. However GI resolves much quicker in GPU.

Both images were rendered in progressive mode (production render), 1 minute each.

My setup has a threadripper 2950x and a RTX 2080ti.
I'm on Houdinin 19.0.531 and Vray 21668 nighly on windows 11.

I've attached the scene for further exploration.

Thanks!

[hsz]

I can confirm the same bug on the GPU.
This is happening when the light cache is used (which is the recommended engine to use by chaos) if you changed to Brute force it doesn't happen. At least on my side.

Using the latest nightly

[gagui]

Yes, it seems something related to the light cache pass.

In other kind of tests I've done I can see that in CPU render the IPR doesn't match the production render and is waaaay slower to converge to a similar GI solution.
I will post my tests in another post.

[gagui]

What I think is happening here is that in IPR mode bruteforce is forced for GI even if Lightcache is selected so that's the reason for so huge difference in render time and not matching the production render.
In fact the IPR-Lightcahe render looks exactly like BruteForce render.

And in my tests this is happening in GPU and CPU.

Is this a known bug?

[Muhammed_Hamed]

Thanks for the report gagui
The issue is logged to our system, ID for the issue is Hou-3056 I will update you once this is fixed
For now a workaround is using 3000 LC Subdivs, it speeds up rendering a bit and reduces the artifacts.

What I think is happening here is that in IPR mode bruteforce is forced for GI even if Lightcache is selected so that's the reason for so huge difference in render time and not matching the production render.
In fact the IPR-Lightcahe render looks exactly like BruteForce render.

Correct!
IPR is forced to use BF/BF for now, in the next update it will use BF/LC for V-Ray GPU only. This is already working in 3Ds Max and should boost interactivity and IPR speed, and you will have a matching result to production rendering

Best,
Muhammed