I made a quick ptex test using 3dc 3.2.04 Linux 64 and Pixar's PrMan 15.0.
Even though it works at first glance, it is currently un-usable with an external renderer.
Here is what I found :
ptex is only usable on subdivision surfaces (catmull-clark or loop), but PrMan and 3dCoat treat them differently :
PrMan subdivides the faces at render-time using either a catmull-clark or loop scheme.
3dCoat pre-subdivides them with a different-looking scheme to allow you to paint on flat polys.There should be an option in the import dialog to choose your subdivision scheme.
3dCoat exports ptex tiles per subdivided faces instead of per un-subdivided face.
If a face has been subdivided once, the final ptex tile for that face should be made of 4 3dCoat faces stictched together into one texture.
If you look at the ptex paint demo on youtube, you can see around 1:16 that faces are subdivided but represent a single texture tile.
There is currently no way to garantee that connectivity data will be preserved accross the pipeline.
I'll explain :Say you model something in Maya. Maya has its own data representation (vertex/face ids and connectivity).
You export that model to an obj file to import it in 3dCoat. The order in wich the vertices are written to this file is likely to change, compared to Maya's original structure.
You import the obj in 3dCoat : the vertex/face ids and connectivity data is likely to change again based on the way it is stored internaly.
You paint until you are happy, export the ptex files.
You plug that ptex file into your shader and the faces are all over the place, because the faceids / connectivity data are not the same as the original mesh.
[*]The solution :
Import a fed files with the mesh so that 3dCoat may be able to either use the same ids/connectivity or remap it's own internal data structure when exporting the ptex files.
fed files are simple text files containing the connectivity info for each face in the mesh. They are described in the ptx SDK.
My test ptex files from 3dCoat looked incorrect color-wise, although they loaded fine in Pixar's ptxview utility.
I am still very interested in seeing this work in 3dCoat and remain available for further discussion / testing.
Thanks