GPU/CUDA - some wishes for supported features

[Tete]

Hello,

I'm playing a bit with V-Ray CUDA, trying to see if we'll use it for our current project and here is a list of some features that I would love to see supported :
- bucket rendering
- irradiance map (I know I can load a file but it would be great to have the other modes like single frame)
- matteshadow render layer

Can I ask, are those features planned to be included?
I think both bucket rendering and irradiance map calculations could speed rendering a lot, but maybe I'm wrong.

Thanks for your time.

Windows 10, Maya 2016, V-Ray 3.52.03

[savage309]

Bucket rendering is something that we intend to look at, at some point. Not sure when.
We can make irradiance map work not only from file, but usually we tend to move more to BF/LC computation, since it often gives better results. I really would like for us to not invest into it much.
I haven't looked into the matte shadow render element yet, so I can't say much there.

Thanks a lot for the feedback!

Best,
Blago.

[Tete]

Great, thanks for your quick answer, I understand about BF/LC.
I also asked because I've used redshift before with bucket/irradiance and it was faster than progressive/BF, and wished to have them available in V-Ray too.
It would be great to have the matte shadow RE since I use it a lot in compositing as a mask to change the colors of the shadows or grade them.

By the way it seems that there's a bug with the No Decay settings in the V-Ray Rect lights with CUDA, unchecking doesn't affect the render. It always renders with a decay. Is this supposed to work?
( tested on both computers - Windows 10, Maya 2016, V-Ray 3.52.03 )

Thanks

[savage309]

I think V-Ray GPU might be the only GPU raytracer that supported adaptive image sampling with progressive mode (it is trickier than in bucket mode), so this might be the case your rendering in bucket mode were faster. But also, for some setups bucket modes might actually help, so we plan to look at that.

As for irradiance map - it is a very old algorithm, and although it might be very fast in some cases, it has many defficencies - like the result might be not as good, it causes problems in animations, it is leaks prone, takes a lot of memory, is not very GPU friendly, etc. I don't think that investing in it is worth it. The adpative lights algorithm (video is for max, but it works just as well in Maya) that we developed for efficiently lighting calculation on the GPU is however both unbiased in its nature and can give even bigger performance gains.

No decay should be supported for Rect Lights. Are you testing with such?

Best,
Blago.

[Tete]

Thanks for your reply, it makes sense.
I knew about adaptive lights and this is great but as my scenes usually have very few lights I don't find the need to use it.

Yes, I'm confirming that No decay is not working for me with Rect Light, both in IPR and Production mode (attached is a very basic scene if that helps - just rename the .txt with .ma, for a reason I can't upload .ma files).
As a side note, if I set the secondary bounce engine to light cache it seems that the light cache calculation only is working with the no decay.

Best

[savage309]

Thanks for the report, will check that asap!

Best,
Blago.

p.s. Adaptive Lights may speed up a lot scenes with as little as one light as well - they are general purpose algorithm for efficient lighting.

[Tete]

Just wanted to know if you had any time to try to reproduce the issue with the no decay? Just so I know if the problem is on my side or not.
Thanks

p.s : Oh great, thanks for the tips, I will try Adaptive Lights then.

[savage309]

Just wanted to know if you had any time to try to reproduce the issue with the no decay? Just so I know if the problem is on my side or not.
Thanks

p.s : Oh great, thanks for the tips, I will try Adaptive Lights then.

Sorry, I thought I had replied, but apperantly I haven't!

We reproduced it, but it turns out that the no-decay option will be deprecated all together from some of the next V-Ray versions.

Best,
Blago.

[Tete]

No problem, thanks for the info.

Does that mean that we won't be able to use no decay lights in the future? I'm asking because I use it quite a lot, especially for outdoor shots.
But maybe there will be a new system with more decay options? In that case that would be great, because having only the inverse square decay is realistic but not really artistic friendly in every case imho.

As a side note, what I also like with the no decay light is that when positionning a light I can adjust its position while keeping the same lighting intensity, with decay light when I move it I have to adjust the intensity to get the same lighting intensity (if I move it closer or further).

Thanks

[vlado]

Most render engines today do not support unrealistic decay (f.e. Arnold 5 supports only inverse square decay; I don't think RenderMan RIS ever supported other modes); it makes impossible certain optimizations that depend on physically plausible light behavior.

Things like light directionality should give you enough options to control lighting.

Keeping the light intensity constant for a given point can be achieved in other ways (f.e. we could follow the light target and make sure that the intensity there is locked to a desired value).

Best regards,
Vlado

[Tete]

Thanks for your reply and explanations, I understand.
Keeping the light intensity constant to the light target could be useful.

In Arnold (and I think Renderman too) there are light filters (far/near etc.) which can be helpful to achieve certain results. Maybe that would be nice to have something like that instead.

Best,