Triangular textures in Ptex are stored as power-of-two images with triangular texels.
For ease of storage and access, the texels are divided into even and
odd texels and the odd texels are unfolded to form a rectangular image
as shown below. The main differences between the triangle and quad
- The resolutions must be symmetric powers of two. I.e. the images must be square.
- The adjacency data is identical to the quad case, but the adjacent face and edge values for the fourth edge of each face are ignored.
- Subfaces are not supported. (Non-quad faces in a quad mesh can be mapped with quad subfaces, but this is unnecessary with a triangle mesh.)