openPBR in LookDevX and metalness

[oglu]

Are there any known issues with metalness and the openPBR shader in LookDevX (matx) ?
I cant get it to work with textures.

[oglu]

Here is a scene file showing the issue.
If you render with Arnold it look fine.

[petya.georgieva]

Heyya
Typically metalness expects a float and if you switch your texture to a float node type it works. That being said, I can see in newer builds we can render color3 textures in metalness while in the regular USD context so it seems like something is missed for MaterialX documents and I've logged that for review.

Overall, if we add the support for color3, the look would likely be the same as float as that seems to be what the material expects and the conversion would be mostly for utility. I see there's a difference with Arnold but I'm not sure that's entirely desired and I'll tell you once we've had a better look. But my suggestion would be to use float type.

[oglu]

Thanks for the answer. I thought it would work like in Arnold if i use only the red channel of the image.

Edit: If i switch the node to float it does render but does look different to what Arnold is rendering.

[petya.georgieva]

Yeah, it seems Arnold is indeed taking the red channel which in the case with a coloured texture is different than the overall intensity (which is what we use in V-Ray).
An oversight in my original answer was that you had connected the red channel which is a float. I've logged it and we'll see what can be done but my original recommendation remains. Overall metalness expects float type textures with values from 0 to 1 which would usually mean black and white textures. I can see some merit in using colored textures to isolate specific masks via the red green or blue channel but I'm unsure if that's the use case you're going for or how common of a workflow it would be. Also it seems to me that Arnold isn't reading any of the other channels (green or blue)

Any arguments for colored textures or other aspects of this are welcome here so the solutions can be better defined for the team

[oglu]

If i use a black and white image its working as expected if i set the node to flaot.
As a metalness is usually only black and white this does work for me.