pTex + Modo VRay question

[wilson66]

My question is related to 3DCoat and Modo+VRAY. I am trying to create a simple pTex texture in 3DCoat and render it using VRay in Modo.

Its not really working though, since I am not sure about the workflow, haven't used the pTex features in 3DCoat yet (maybe there is someone in this forum who has used that functionality in 3DCoat).

What I did: created a simple sphere in Modo and exported it using OBJ format. Imported it into 3DCoat using the 'Paint w/ PTEX' button in the startup window. Painted a couple of strokes onto the sphere.

Then I exported a PTEX file using Textures -> Export -> Color to PTEX.

I then imported the new OBJ into Modo (3DCoat exports it automatically), assigned a new material and a V-Ray PTEX material layer, then assigned the new PTEX file I exported.

Unfortunately, VRAY does not render the texture. The sphere just renders white.

Can anyone give me a hint how to properly work with PTEX files exported from 3DCoat and rendering them in Modo+VRAY?

[vladimir.nedev]

So I tried this workflow and was able to make it work with a few caveats.
First you need to select "Export low-poly mesh" when exporting the obj file in 3D-Coat. It seems this is the mesh resolution at which the ptex texture is painted.
Then you need to check "Reverse vertex order" in the V-Ray Ptex texture in modo. Maybe it's possible to reverse the vertex order when exporting
the mesh/texture from 3d coat but I didn't find a way to do that.

Then you have a few more limitations that are not 3D-Coat specific. You can't use modo's subdivision on the imported mesh. This is because
the modo API doesn't provide the original quads from which a subdivided triangle originated.
If you want to enable subdivision on the mesh, use the V-Ray geometry properties.
The reverse vertex order option in the V-Ray Ptex texture doesn't work with the OpenSubd subdivision method though, we will have to fix this eventually.
But you can use V-Ray's dynamic subdivision.

Greetings,
Vladimir Nedev

[vladimir.nedev]

Actually you can flip the vertices in 3D-Coat from Textures -> Export -> Flip ptex quads. With this checked, the exported ptex file will be correct and you
won't have to check "Reverse vertex order" in the V-Ray Ptex interface. And you will be able to use OpenSubdiv from the V-Ray geometry properties.

Greetings,
Vladimir Nedev

[wilson66]

Actually you can flip the vertices in 3D-Coat from Textures -> Export -> Flip ptex quads. With this checked, the exported ptex file will be correct and you
won't have to check "Reverse vertex order" in the V-Ray Ptex interface. And you will be able to use OpenSubdiv from the V-Ray geometry properties.

Sorry for my late reply, there was a family tragedy going on that needed my full attention.

Thanks for your quick help Vladimir! I got it to work using your instructions.

It does not make sense to put a V-RAY Material layer into the same material group as the PTex layer, right? The texture renders fine when using a standard Modo material, but vanishes when I add a V-RAY Material.

[vladimir.nedev]

Sorry to hear about your family problems.

You can use the ptex texture for any kind of texture effect. When you add the V-Ray material though, you have to change the "texture effect" of the ptex
texture from "Diffuse Color" to "vmtl Diffuse Color" ( it's in the V-Ray Material Channels). That's a caveat other people had problems with too.
I am still not sure whether to make "diffuse color" and "vmtl diffuse color" interchangeable as it may create some other problems.

Greetings,
Vladimir Nedev