Blender Git Loki

adaptive_cloth: Mesh: is_edge_flippable(): works with across_seams

It is useful to know if the "3D edge" is flippable or not. This is
essentially done by going over all the `Edge` formed by the `Node`s of
the `Edge` and working with all those faces as a whole. Here we also
need to ensure that the edge is not on a seam. It actually might be
possible to optimize this and remove the boundary check entirely.