Darker reflections compared to CPU

[Alex_M]

THANK YOU! I'm not going insane after all! Is there anything we can do about this problem until a fix is available? Any workaround? I've already converted my project to CPU and managed to deliver it (thank god!), but it would be good to know if I can still use and rely on Vray GPU for future projects without it breaking like this if a workaround is available.

[piotrus3333]

wow. among all the easy and straightforward ways to break vray gpu you’ve just found the most elaborate one I know.. hats off, sir.

[Alex_M]

Hi

After testing it was confirmed in a simple scene that

If we have instanced VRay IES Lights
and we have a Physical Camera Exposure Control
and we have an additional VRayLight with include/exclude list set to include
and we have a refractive object with a VRayLight inside it and refraction glossiness lower than 1

the refraction of the refractive object does not render correctly in V-Ray GPU




In the video above I am switching on and off the single VRayLight that has include/exclude list but does not contribute to the lighting.

I logged this under VMAX-12222 for developer review.

Hi vladimir_krastev ,

Unfortunately, I'm still encountering this bug in another scene. I was very careful not to use any IES lights, include/exclude lists in the lights, and any Exposure controls, as suggested by you in the list above. For the bulb I'm also using an extremely simple refractive VrayMtl material (no 2-sided materials). So a very very simple lighting and material setup. Yet, the bug still happens. Please see the screenshots below. Now I'll have to yet again waste time converting my scene to the CPU engine mid project. I'm very disappointed and frustrated.

I'm frankly afraid to continue using the GPU engine for any remotely serious work from now on and I'll probably be doing all of my future project on CPU instead. Even though GPU is faster in a lot of cases, I'm finding myself actually losing time and money with the GPU engine because I'm constantly fighting bugs like this one and other strange behaviors. I can't be the only person using GPU for production work, can I? I'm dumbfounded that no one else has noticed this bug before.

[piotrus3333]

Hi vladimir_krastev ,

waste time converting my scene to the CPU engine mid project. I'm very disappointed and frustrated.

what do you mean by that? what do you change going from gpu to cpu?

[fixeighted]

If I try a similar setup (assuming absolute simplicity) then the results are practically identical, so possibly something else is causing this.
Post the lamp/light and maybe we can discover the culprit.

Alternatively, yes CPU will just do what you need without having to convert anything. It's really only the other way around that it can be
a little tiresome

[Alex_M]

what do you mean by that? what do you change going from gpu to cpu?

You don't need to change much, if anything, if a scene is simple. But with complex scenes (interiors, exteriors), there often are a lot of things that need to be readjusted to make them render the same. Bump map and normal map strength values are very different between CPU and GPU. The bump and normal textures themselves also often need to be different too, because CPU requires much sharper textures. Alternatively, you can use the same bump and normal textures but you'll need to set their Blur amount to 0.1 - 0.01 in order for them to appear the same as GPU. The latter is not a good solution though since low texture Blur amounts leads to longer render times. There can also be differences in light intensities with dome lights with HDRI textures. VrayBlendMtl doesn't work the same. 2-sided and SSS materials will also render a bit different. Etc. etc.

I've just realized the images above are not very clear. Here are a couple of new ones that shows things better. BTW, I haven't changed the lights' colors and intensities, nor the bulb material settings.

If I try a similar setup (assuming absolute simplicity) then the results are practically identical, so possibly something else is causing this.
Post the lamp/light and maybe we can discover the culprit.

Alternatively, yes CPU will just do what you need without having to convert anything. It's really only the other way around that it can be
a little tiresome

Yes, very simple scenes won't show much difference between CPU and GPU, if any. It's more complex scenes when things start to fall apart. What do you mean by "Post the lamp/light" ?

[fixeighted]

I meant upload the lamp mode and light only, so that will keep whatever render setting are in the main file, so it's easier to spot anything odd in settings e.g.

It's hard to believe that simply the scene having other objects in it would cause this, however you could very simply test that theory if you delete everything
other than that lamp and see if it renders as expected

[Alex_M]

Yes, as I already mentioned on the previous page, turning off or deleting all other lights except for the one in the table lamp fixes the issue with the refractive materials. So not much sense in uploading just the lamp model and its light - this will render fine in such simple scenario. Of course, deleting all lights except the table lamp light is not a realistic solution to the problem for me since I need to have proper lighting in the interior.

Below are a couple of new screenshots that show what happens when I delete all lights except the one in the table lamp. The glass bulb renders properly with GPU in this case. Interestingly, now I see another problem with GPU happening. The light's color is way off and some purple noise appears when I use Light Mix. Both images below have Light Mix turned on and the only thing changed there is the light's color from 6500K to 4000K, so nothing elaborate or unusual in terms of settings.

[fixeighted]

Are these IPR screenshots?
I know that GPU doesn't update properly when changing settings, so can give weird results, needing a a restart after changes.
In any case, support has your file, so maybe they can discern what is happening, as
I built a scene with a bunch of lights to sort of mimic yours but I can't get it to misbehave as yours is...

[Alex_M]

Both are IPR, but I have not changed any settings after starting IPR. BTW, for me it's the other way around - GPU IPR updates a lot more changes than CPU IPR does which is a bit strange. One would expect it to be the other way around given that the CPU engine is more feature rich and is given more attention to. Sometimes I miss this flexibility when using CPU rendering and I find myself restarting its IPR more frequently for changes to take effect.

[piotrus3333]

Alex_M regarding texture filtering I think the best match on cpu would be to turn it off completely.

[Alex_M]

Hi,

Any updates on this issue? Do you think this can be fixed for the release of Vray 6? I would love to use Vray GPU, but unfortunately can't because of this bug.

[Muhammed_Hamed]

Hey Alex, we did give this priority in our planning. I will make sure this gets addressed ASAP

Best,
Muhammed

[Alex_M]

Awesome. Thank you! I can't wait to start using Vray GPU once this is fixed.

[Alex_M]

Hi, Muhammed_Hamed . I was wondering if this is still being looked into. Do you think a fix can be implemented in the new updates or is it a more complex issue?