Differences CPU/GPU whats causing it?

[olika]

I tried to render a outdoor scene on Vray-RT GPU (quite a lot Forest Stuff, renders like a charm thats great!)
But when you then compare CPU and GPU Render, i recognize quite some differences.
As i`m pretty much a newbie in GPU, first question: is this normal behavior i have just to deal with?
Or should the result be quite the same?
Looking for your feedback about this, cause i don`t really have a clue why it happens.
The scene is (aside Forest Stuff) quite simple, there is a standard vray sun system as lighting, untuned.
Trees come from the lates Evermotion Collection 176, they seem to be pretty fine right of the box.

Hopefully when i post the renders underneath, it is working to scrub the both renders back and forth to see the differences.

What i realized is that:
- Trees come out a lot darker, could it be related to the 2-sided leave material?
- Asphalt texture looks totally diffferent, no clue why
- What i`m wondering is, it looks like shifted lighting at first but when you look closely to the untextured building at the top, you see it`s not changing at all?

Any tips? Thanks in advance

[savage309]

V-Ray GPU although sharing the same UI and mostly the same features with V-Ray is a different engine. Therefore, differences here and there are expected and there will be never 1:1 exact match between V-Ray and V-Ray GPU. This is way we strongly recommend to not switch between V-Ray and V-Ray GPU mid project - it will most likely have many differences.
This differences can sometimes be a bugs actually, but also can be rather normal.

We recently implemented a hybrid rendering for V-Ray GPU - meaning that you will be able to use the CPU just like a regular CUDA device. If you are using 3.5 nightlies, you can already use that - you have just to enable the C++/CPU device from the list of CUDA devices.

Best,
Blago.

[iancamarillo]

Hybrid rendering!? whoohooooo!!!!

[olika]

Hui! Thank you Blago for blazing fast replyl, even though, wait a second, wtf! your link tells me you had presentation yesterday bout also that topic, hihi nice thank you twice total respect for reply time! Would had loved to sit in audience...recorded?
And huh i wasn`t aware of that news you have! Looking forward can`t wait to try

[savage309]

Hui! Thank you Blago for blazing fast replyl, even though, wait a second, wtf! your link tells me you had presentation yesterday bout also that topic, hihi nice thank you twice total respect for reply time! Would had loved to sit in audience...recorded?
And huh i wasn`t aware of that news you have! Looking forward can`t wait to try

Yep. NVIDIA records and publlishes all talks some time after the event.
Also, everything that we showed during the talk, inclduing the hybrid rendering, is already avaiable in the 3.5+ nightlies, so you can try it if you use one.

Best,
Blago.

[Alex_M]

Most probably your vegetation has VrayMtl with translucency. Translucency in VrayMtl is currently unsupported by RT CUDA so your plants will render darker.

As for the asphalt, you might be using maps that are unsupported by RT CUDA. Check out this help page for supported maps, lights and other features. I always have it open on a tab in my browser when rendering with RT CUDA.

[olika]

Thanks Alex, great link wasn`t aware of it and you`re totally right for sure there is translucent and or 2-sided materials used.
I think the evermotion guys also change stuff from release to release to optimize further (cool!), but so some have 2-sided some others trails etc...