philippe leprince

I get the exact same kind of result. The problem is that the vertex order of the obj file isn't set in stone. Maya's importer may re-order the vertices to make it fit with its internal data structures. The simplest solution would be to write a mapping importer that describes the face ids and use that in 3dCoat to paint and export the final file. it could be as simple as a text file storing the face indexes and the vertex positions as described in http://ptex.us/metakeys.html.

Hi Andrew, I did a quick test and the ptex files seem to be written correctly now ! Well Done ! There is still no way to garantee that the faceids in my scene are going to match 3dCoat's faceids, so the textures tiles are all over the place in my renderman renders. Ideally, we'd need to import meshes in a format that can store the faceids so that 3dCoat may export the ptex tiles with the same ids. AFAIK, OBJ can not store per-vertex or per-face variables. Are there any other formats we can import in 3dCoat ? Cheers.

the ptex format supports triangles in catmull-clark meshes. AFAIR, it will just just turn the triangle into 3 quads by adding a vertex at the center of the triangle and connecting it to the center of each edge. Those faces effectively pack 3 texture tiles and are classified as "subdivided".

You are welcome. Great. I might be wrong. I will test a bit more tomorrow. It is a bit hard to tell. I am attaching a couple of snapshots for you to see. Thanks. P.S. : The last snapshot is a display artefact I get when I turn on the low-poly view mode.

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