i’m not sure and hope that you can prove me wrong, but i think there is a problem with the uv-lookup within the imported mesh.
i suppose we have to think about what is stored in the xfile.
when exporting xfiles constructed with advanced texturing tools as in Maya, XSI,… then i think these uv coordinates are somehow baked onto the mesh (and then are just part of the vertices, i.e. uv-texturecoordinates).
so we have an arbitrary mesh made of vertices, which at least have
now i cannot think of a shader/node/algorithm which does the lookup task in a straight forward and therefore fast way.
this algorithm would have to search for the triangle including the uv coordinate. and this search task would be something more complex (it could search in the one-dimensional list of triangles, or a better solution could be more adaptive and include adjacency information of triangles to search into the right direction, which could be faster).
for now i think this sounds to be to complicated to just do it right now…
so i would suggest another module (doing something completely different), which you could be also possible to patch.
what about projecting a point onto the mesh. you can freely position the point in space and you can freely define the direction to project that point onto the mesh.
the only thing you need to do is to get that normal (which i think should be possible with the face index)
then you can constrain an object at an arbitrary mesh (even without uv texture coordinates) at that point.
what do you think?