RT Render with GTX980Ti doesnt match with normal CPU Render

[Komposer]

Hi guys,
I hope You can help me to fix this problem here.
You can see on the two renderings, that the normal render looks OK so far...
...but with the same settings, RT render per Cuda has totaly overbright refs and hightlights on the carpaint- and windowGlas-shader.
I´m not able to find the reason for that.

And now I´m realy scary, if there is´nt any hope here.
Because the card and the new powersupply costs some money...
...and if there is no way to work with that nice and fast tools, it would be catastrophic for me...

So I hope there are some mistakes I make here...
...perhaps I need a special driver?
...or some setups or tricks?

Hopefully for help,
Jörg

[savage309]

It will be best if you can share the scene. We will examine it and see what is going on.

[Komposer]

Hi,
here is the link to the scene.
https://www.hidrive.strato.com/lnk/gDhUxT4D
(Maya2015, Vray 3.1, Win7)
I did some optimize steps for simplify the scene. No textures are needed.
I made in hypershade one bin, named "shaders" with the two shaders where it happens most.

I made some tests here and found following things:
1. when I reduce BaseReflection on the CarPaint to "0", the looks become much more like the normal rendering.
2. when I switch off the Vray renderAttribute "Render as subdivision surface" the wrong overbright is gone.
(this may have to do with the meshmodel - it´s a very simple construction)
3. please take a look on the overall light brightness - I mean that it´s brighter than in normal render.

Hopefully for hints and thanks for help,
Jörg

[Komposer]

Hi, here is the next scene, with a "GPU difference problem". (same system and versions)
(with two textures included-one HDRI - one refMap)
https://www.hidrive.strato.com/lnk/JCh0x1TE
Please render it per CPU and then per GPU.
The GPU result looks much rougher and darker in ref.
Please click on and off, inside the VrayPluginNodeTex "colorCorrect" Pre-process On, while rendering per GPU.
For GPU render it doesn´t make any difference. So I think, that it´s a bug here!?
When I use "RemapColor" from Maya instead, there is no diff between CPU and GPU.

And a second question: Vray round edges are not rendered in GPU - is this normal in this moment and comes later?

Thanks for help,
Jörg

[savage309]

Okay, after a quick investigation with help of my colleagues - Alexander and Tashko, here is what we got.
1. The render of the car is wrong, because of a bug in the RT GPU displacement code, that was messing up the normals of the geometry in case of there is negative scale in the node transformation. There is a couple of ways for you to fix this. You can just wait (a couple of days maybe) until our fix hit the nightlies and just download new V-Ray (we can notify you when it is there, if you want). If you are in a hurry however, I think you can just export to .obj and import again ... it is a workaround that will remove the negative scale (I haven't test that workaround myself). But I will suggest just to wait a few days until it is fixed.
2. There a few color correction nodes in Max, Maya, etc, and RT GPU supports most of them. "ColorCorrect" node however is not supported - RT GPU will only apply the gamma from it. We support RemapColor (which can be used as color correction) and a node named "ColorCorrection" (you can create it from Create/V-Ray/Create from V-Ray Plugin). The support for the ColorCorrect is in our todo list.
Round Edges is not supported too. Efficient GPU implementation is patented. Fortunately, we managed to license those patens and round edges will come for the GPU at some point, too.
p.s. this might be helpful http://docs.chaosgroup.com/display/V...orted+Features

[Komposer]

Thanks for Your tests and explanations!
1. With the car I´m not in hurry and can live with the situation.
2. Yes please inform me for the fixed build, that would be great - but only for Maya 3.1, if You mean the same?!
(but I´ve no login for the nightlys, would be fine to get it than...)
3. Thanks for the link to supported features - I stepped to MAYA RT
This is good to know!

Cheers, Jörg

[tashko.zashev]

Hi,

We will inform you as soon as we have a fix for this issue.
Meanwhile please send us an email to support@chaosgroup.com to check your account permission and extend it if needed (nightly access). So you would be able to get the fix shortly.

Thank you.

[tashko.zashev]

Hi Jörg,

The issue with the mesh normals and scene negative scale is now fixed in the latest Stable nightly build and the render should of the glass windows should be the same on both render engines.
There is still a small render difference in the car body shading, the main reason for this is due to the lack of support for Ignore light normals in the GPU. This option is deprecated and most probably will be removed in future releases. And the second is caused by the material (probably a parameter), but unfortunately we have to perform a few more tests in order to find it out.

[ivaylo.ivanov]

This is build number 26295 in the stable 3.1 nightlies.

[Komposer]

hi, thanks for the infos!
Now I´m using build 26295 and will never use vray colorCorrect again
But after some days working with it, there are a few things, that will not work correctly here with RT GPU:
1. Bumpmap per (Maya) fractal and noise and also per (Vray) Cellular - nothing with GPU (bump per texture works perfect!)
2. Vray RectLight with activated "directional", results in totally diff results between RT and normal render
3. When I assign two diff materials on a cube (per face select) and switch on "round edges" (which I´ll use in softrender), the cube get totaly black!
...when I deactivate temporarely the "round edges" the mats comes back!
If these are bugs, it would be great when it will "repaired" in future.
Cheers, Jörg

[savage309]

Thanks for your feedback !
Procedural maps are not supported in the bump map yet, the same goes for the directional attribute of the Rect Lights and for round edges.
The next SP will have round edges for sure, we are also working on light directionality and procedural maps for bump support.
So these are known limitations, however we probably have to find a better way letting you know what is V-Ray CPU only.