Summary:
Add a join_scene method to all the textures to allow the join_mesh function to include textures. Rename the join_mesh function to join_meshes_as_scene.
For TexturesAtlas, we now interpolate if the user attempts to have the resolution vary across the batch. This doesn't look great if the resolution is already very low.
For TexturesUV, a rectangle packing function is required, this does something simple.
Reviewed By: gkioxari
Differential Revision: D23188773
fbshipit-source-id: c013db061a04076e13e90ccc168a7913e933a9c5
