Streaks in metallic reflection from rectangle light

[KernitTheFont]

Hi all,
I've got an issue with a metallic bottle label that has streaks on it, seemingly caused by the front light:



Shader is full metallness with 0.7 glossiness
The file was a conversion from r25 to r2024 (although still Vray 6). I didn't know if that was an issue, so I tried the following:

• Copied everything into a new file.
• Recreated the light with the same parameters.
• Tried changing Light Evaluation Mode from Adaptive Lights to Full Evaluation.

EDIT: Weird! when the light is facing full forward at zero on the X, I get the streaks. If I move it 0.01mm on the X it disappears and I get a smooth reflection. (light has target, so it's rotating by 0.0232° too)


Really appreciate some guidance on what the hell is happening here.
Thanks in advance!
Tim

[fixeighted]

I still perceive lines, albeit very faint, in the second image. My guess would be that it's the mesh having long polygons that causes it, so subdividing would solve it.

[KernitTheFont]

The mesh is subdivided pretty well, so looks like something else

I've also tried removing the bump. It shows up more when I lower the glossiness:

[fixeighted]

Hmm...maybe some z-fighting with the underlying bottle mesh if the label has no thickness or is too close. Does it still happen with only the label visible?

[KernitTheFont]

There doesn't seem to be any z-fighting. I've tried rendering with the bottle and liquid turned off and I've also turned off the cloth object adding thickness.

[fixeighted]

Weird. The same occurs with new geometry, or using that shader on the bottle for example?
A process of elimination is all I can think to suggest, unless it's a bug of some sort.
I'm on Max, so can't test a setup unfortunately, though someone will turn up to do so I reckon

[KernitTheFont]

It's the light linking! I had the softbox linked to the label only. Cleared it out and no streaks. Guess it's a bug then.

[sirio76]

What projection are you using for the label? Is it UV or other mapping?

[zhanet.georgieva]

Hi KernitTheFont, could you please share the scene where the bug occurs?

[KernitTheFont]

Hi zhanet.georgieva, I'll Dm you a zip. The light in question is 'Softbox.F'.

Hey sirio76, It's UV mapped.

[zhanet.georgieva]

Hi KernitTheFont, I have managed to reproduce the lines and the issue is logged in our system [VC4D-2278].


As a workaround, you can render with V-Ray GPU.

[KernitTheFont]

Thanks for looking into this Zhanet, much appreciated. Additional note: it seems to only be a bucket rendering issue, as there's no problem with the progressive render.

[viktor_angelov]

Hello KernitTheFont I am happy to let you know that [VC4D-2278] has been resolved. You can find the fix in the latest Stable version here: https://nightlies.chaos.com/main#/vray6c4d/stable/6.2

Please, give it a try and let me know if it works with you.

[KernitTheFont]

Oh that's fantastic news! Thanks Viktor. Any idea when it will be rolled out to a main release? Our IT department would have a stroke if I asked them to install a nightly build!

[viktor_angelov]

We are unable to share such information. We will make sure to announce it everywhere once it happens, as well as on the Forum.