RT CUDA vs RT CPU - strange problem - help needed

[jironomo]

HI Guys,

I am getting a strange result when using VrayRT Cuda vs VrayRT CPU - basically the glass in the image below is different for each. As you can see the glass on the right (rendered with RT cpu) looks how it should look. And the left is rendered with RT cuda and seems to be less transparent and darker.

The glass is a very basic vray material - no maps or anything. And the exact same render settings etc are used to render both versions.

Whats going on? Any ideas why RT cuda is rendering this basic glass material so differently?

[svetlozar.draganov]

Would it be possible to attach that scene for investigation?
We won't need the complete scene, if you could simplify it by removing unrelated to the issue objects it would be even better.

Looking forward to hearing from you.

[savage309]

Whats going on? Any ideas why RT cuda is rendering this basic glass material so differently?

[ATTACH=CONFIG]36472[/ATTACH]

This looks strange indeed, so having the scene here will be very helpful. Keep in mind though that V-Ray GPU is completely different code written to be efficient on GPU architecture and it will never match the CPU render 1:1 (this is not the goal as well). With that being said, there is "trace depth" and "gi depth" settings in the V-Ray RT Settings - you can try bumping those a bit.

Best,
Blago.

[jironomo]

HI Guys, I tested all the trace depth values (increased them in both the material and the RT settings) and this doesn't change anything. I think it is somehow related to the dome light/hdri that I used to light the scene. There were no other lights in the scene, so the dome was lighting everything.

I deleted the dome and used a vray sun/sky to light the scene and the problem was fixed. I then tried a different dome/hdri combination and the problem came back. I then tried one more dome/hdri combo and the problem was still there.

I then setup a basic scene with just a plane and some glasses (all with different glass materials on them) and tested both cpu and cuda with dome/hdri and vray sun/sky and everything behaved as it should.

So my guess would be there is some weird bug in that first scene. I would send it through but the zipped file size is larger than is allowed (9mb).

Anyway, doesn't seem to be a bug in vray... maybe just in 1 isolated scene. So... please carry on with your business.

[svetlozar.draganov]

It could be a bug in V-Ray and we would like to investigate the scene.
Please send the scene to support@chaosgroup.com and include a link to this thread for reference.
For larger files please contact us at the same email address and request access to the FTP server.

Thank you very much in advance.