Reflect on back side strange behaviour (Vray Next update 3.2)

[justini]

"Reflect on back side" seems to do very weird things as soon as reflective glossiness value changes to anything other than 1.

Here are 3 renders displaying the effects on glass with:

1) Reflect on Back Side OFF
2) Reflect on Back Side ON, Reflect Glossiness 1.0
3) Reflect on Back Side ON, Reflect Glossiness 0.999

[justini]

no explanation for this??

[hermit.crab]

Could you send the scene to support@chaosgroup.com along with your V-Ray and 3ds max versions so we can take a look? Mention this thread in the e-mail as well.

[justini]

Sent.

Just noticed that this only happens when Phong BRDF is selected.

[fixeighted]

Coincidentally I noticed a similar issue yesterday.
This piece of glass has a turbosmooth and bend applied. With glossiness at 1 there is no issue. In the other bad images one is with .99 glossiness and the other is the same but with the bend and smooth mods turned off, which makes it even worse.
Justini, weirdly I get the exact opposite findings - all BUT Phong show these artifacts.
This is with (today) Max 2021 and 5 beta, though it happens with Next lates and Max 2020 the same.

[hermit.crab]

fixeighted Could you attach the scene here (or send it to support@chaosgroup.com)?

[fixeighted]

Sure - very simplified part here. Even just tried the second uncollapsed box as you see it, to eliminate the smooth or other poly stuff. It's Ok flat - turn on the bend and it's screwed
https://www.dropbox.com/s/3pzqdi3hhf...x?dl=0It's

[hermit.crab]

fixeighted Thank you for the provided scene. It seems like a newly introduced issue. I've logged it (internal bug-tracker id: VMAX-9978 ) for developer analysis. Using the Phong BRDF mode indeed resolves it and may be used as a workaround.

justini Could you share your ticket number? I can't seem to find your scene.

[fixeighted]

Thanks for the response.
Actually it's not new - I had to rework a year old project and yesterday noticed the exact same thing, again on curved/shelled objects. I remember at the time wondering what was happening but was in a rush and it was not so obvious in that situation. EDIT: Ignore that - I can't find the original images to support that statement, so cannot be sure
Anyway, we know about it now and Phong works

[justini]

justini Could you share your ticket number? I can't seem to find your scene.[/QUOTE]

not sure where to find a ticket number. You can download the scene here though:
https://drive.google.com/file/d/1gN9...ew?usp=sharing

[hermit.crab]

justini Thank you for the provided scene. It seems to be the same issue as mentioned above, manifested differently though the Phong BRDF model. In your case, using other than Phong models seem to suffice as a workaround.

[fixeighted]

I just came up against this again and thought I'd see if it was progressing.
The problem is that you advised using phong as a workaround, however phong causes the weird double, or offset reflection, plus facetting behaviour. So neither are working as intended unfortunately
- gives us a choice of weird stuff with microfacet and even weirder stuff with phong.
I'll keep an eye out for an update and hold off on this project until there's a fix.
Fingers crossed for 'soon'