Blender Git Loki

Fix #30159: Boolean modifier creating non-concave faces

Issue was caused by merging triangles into quads policy which used to think
triangulation of non-planar/non-concave quads happens by 1-3 diagonal which
isn't actually correct in some OpenGL implementations.

Added check for non-concave faces when merging triangles. It will work fine if
original faces are flat. In case if original faces aren't flat this check might
fail and triangulate face when it's not actually needed or merge triangles in
a way which leads to OpenGL artifacts.