VrayMtl Reflection Problem

[CrispyDuck]

Hi,

I'm using large (6K png) file textures on a flat plane, and finding some glitches with reflections from a spotlight. I'm pretty sure that I should be getting a smooth highlight here, but the light seems to be interacting with the file textures in an unexpected way.
I've been substituting textures, experimenting with color space and file type, but I think the problem seems to be to do with the GGX glossy fresnel and the light cutoff settings, but would appreciate if anyone had any better ideas.

Thanks.

[seandunderdale]

Have you got "use roughness" in the relfections enabled?

[CrispyDuck]

Thanks for the suggestion, but nope, not using roughness, and it's definitely something to do with the light cutoff threshold. Reducing it to 0 eliminates my problem, but I'm not sure why I'm seeing the problem in the first place - is it something to do with world scale units? Number of lights in scene? Light intensity? Glossy surfaces? I've never had to reduce this setting to 0 before, and it's clearly going to have an effect on my render times, so it would be good to know from the Vray team what the associated factors for this problem are.

[damaggio]

Please provide more details and scene file, we need more information here to troubleshoot the issue.

[CrispyDuck]

Hi,

So I've included a simple scene file in the link below. The problem I'm having is that with the default light cutoff values of 0.001 I'm seeing the reflection of those lights literally 'cut off' in a very simple scene.
The problems seems to get worse/more unpredictable when I start mapping any file textures to reflection. In addition, I'm mostly not able to plug *anything* into the Reflection Glossiness parameter successfully - it just has no effect.

https://drive.google.com/file/d/1geA...ew?usp=sharing

Any help appreciated!

[CrispyDuck]

Another image showing what happens when a file texture interacts with the lights. All these lights have 0.0000 on their light cutoff threshold. Problem is more apparent as the threshold goes up, or as the intensity goes down.
Have updated Vray Next with nightly builds, updated graphics card drivers, updated Maya 2020. Reset all render settings.

[hermit.crab]

CrispyDuck This is how the Light cut-off threshold works. Setting its value to 0 on the provided scene eliminates the issue. Make sure it's zero; sometimes the number after the decimal point is not seen.

[CrispyDuck]

hermit.crab thanks for responding, but I don't think it solves my issue. Please see the attached image showing what happens when I've set all the lights to 0.0000 light cutoff threshold and have a file texture on the reflective plane. You can see that there is some really unpredictable interaction between the file texture mapped to the diffuse channel and the reflection. This interaction depends on the angle of incidence, the fresnel IOR, light intensity and size of the light etc but I've tested pretty thoroughly and it's still happening. I'm attaching a scene with a locked off camera to test render from. testing_floor.mb.zip

[Uniel]

Hi,

I played around with your scene to see if I could find something out. Unfortunately I’m just seeing the same result as you do. However I noticed that this doesn’t neccessarily have to do with the texture. I get the same result without a texture and with a really dark color in the diffuse channel, like black, or close to black.
The only thing I could come up with to work around this, would be to render with brighter lights (this seems to get rid of the cut-offs), save as a 32-bit image, and use an exposure adjustment in photoshop to lower the exposure. Not a very elegant solution. :/

Also I saw that you used an extremely low glossiness value, first I thought that that might be the issue, but I could get the same cut-off errors with much higher glossiness as well, so that wasn’t it, unfortunately.

I’m also curious what the developers have to say about this.

[hermit.crab]

Indeed, there is something the matter. It seems that lights are still cut regardless of the zero cut-off value. I've logged an issue about the matter (internal bug-tracker id: VMAX-9916) for our developers to investigate. The cut's border depends on the size and intensity of the light so raising either will place the cut out of the screen and can be used as a workaround.