RTX Color and Alpha Transparency issue

[Supremo]

I think I've seen someone post this issue a while ago, in the refraction "Affect channels" if Colour and Alpha is on, RTX renders everything behind it semi transparent, when you render with CPU it renders correctly.

I know the work around is to just use the CPU instead of GPU, but will this be fixed for the official VRay 5 for Maya release?

[hermit.crab]

Could you send the scene to support@chaosgroup.com so we can take a look? Mention this thread in the e-mail along with your V-Ray and host platform versions and a V-Ray log from the rendering.

[Supremo]

I've just sent it now, hopefully this bug can get fixed.

[seandunderdale]

Ive had this issue on a job Ive just completed. One thing we did was break out the glass shader into a blend setup like a carpaint. A vray material set to do refraction as the base, and a reflect only material in slot 1, with a fresnel to control the reflect amount. This way we found it behaved better. We ended up rendering with windows off anyway so we had full interior control and just adding the glass back on. But we did have the same render "bug" as you to start with.

It was only my second job using GPU so I didnt know if it was something Id done, and I didnt have time to look into why it was happening,

[hermit.crab]

Thanks for the report. It seems the fog color is causing the bad alpha when used with refractions affecting all channels in V-Ray GPU. I've logged the issue (internal bug-tracker id: VGPU-5019) for developer analysis. No easy workaround I'm afraid, you may need to render a second time with CPU to get the desired alpha (with a render mask for example).

[Supremo]

Ive had this issue on a job Ive just completed. One thing we did was break out the glass shader into a blend setup like a carpaint. A vray material set to do refraction as the base, and a reflect only material in slot 1, with a fresnel to control the reflect amount. This way we found it behaved better. We ended up rendering with windows off anyway so we had full interior control and just adding the glass back on. But we did have the same render "bug" as you to start with.

It was only my second job using GPU so I didnt know if it was something Id done, and I didnt have time to look into why it was happening,

Rendering with the windows off is what I would have just ended up doing too, easier just to do that.

[Supremo]

Thanks for the report. It seems the fog color is causing the bad alpha when used with refractions affecting all channels in V-Ray GPU. I've logged the issue (internal bug-tracker id: VGPU-5019) for developer analysis. No easy workaround I'm afraid, you may need to render a second time with CPU to get the desired alpha (with a render mask for example).

Thanks for figuring out what was causing it. Hopefully the bug can get fixed soon.

[seandunderdale]

This isnt just a fog colour issue. I get this no matter what I render. Any glass over a car interior destroys the alpha channel. I stopped using fog colour on GPIU because I heard it was broken but this is just using standard glass, no fog colour value. (its white) Im also not using "all channels" but only "colour+alpha". This is a huge deal as it basically means I cant render a full beauty on GPU. I really dont like workarounds that relies on a retoucher to have to rebuild layered glass in Photoshop as it rarely ends up looking correct.

Im on Vray Next 4.3 and Maya 2018

[goyko]

We are aware of an issue with alpha and refractive objects like glass. The issue is more evident with more refractive objects behind each other like in your car. It is not a straightforward fix and we are working on it. Also, please test with CUDA and see if the alpha is wrong there too.

[tim_pattinson]

Hi Team, just wanted to check in and see if there was any updates with this?
I too am struggling with Car renders that need to be a transparent format.

[hermit.crab]

Not yet started working on this, however, it is on our to-do lists.

[Muhammed_Hamed]

This is one is quite important, same for material wrapper Alpha. For product rendering and matching a backplate
The workflow now requires rendering multiple beauty passes to work around these 2 limitations..

It would be nice to have everything in a single beauty pass, should be the ultimate goal

[tim_pattinson]

Hey Muhammed,

Would you be able to share how you do your workflow to get around these issues?

[sam_wickert]

Any update here? Working on a huge project with vehicles and would love to have this corrected for that!

[piotrus3333]

nothing better than BlendMtl mentioned by seandunderdale above as far as I know. I've tried blends with a few VRayPluginMtls but no luck so far.