When triangulating meshes, the UV unwrapper was previously using a
heuristic to split quads into triangles. If one of the internal angles
is greater than 180degrees, a so-called "reflex angle", the heuristic
was giving a poor choice of split.
Instead of using a special case for quads, this change routes everything
through the generic n-gon `BLI_polyfill_beautify` method instead.
Reviewed By: Brecht Van Lommel
Differential Revision: https://developer.blender.org/D16505
When n-gons share vertices, their triangulation can be non-manifold,
even if the original mesh is manifold.
The UV Unwrapper does not currently work with non-manifold meshes.
This workaround attempts to modify the triangulation of n-gons in
the UV unwrapper to preserve the manifold property.
This change replaces the previous fix for quads, and extends it
to all n-gons.
See T84078 as motivation for this change.
Differential Revision: https://developer.blender.org/D16521
Provide reasonable defaults for UV unwrap for triangles with zero area:
* Three vertices are arranged in a line.
* Two vertices are at the same 3D location.
* All three vertices are at the same 3D location.
Change fixes quads / ngons which have triangulations with zero area.
Change fixes both "Angle Based" method and "Conformal" method.
Differential Revision: https://developer.blender.org/D15922
