[Micheus]

Fill the selected n-gon faces (typically after Remove hole or pipe caps) with quads. The new mesh follows the curvature of the surrounding faces. The option dialog offers Rotation, Split, Curvature and Relax; the first two choose the layout of the new edge loops, the last two only move vertices.

Since no single method gives good quads for every outline, several approaches are combined:

• Regular rings are filled with an A x B grid (Coons patch plus a Hermite lift from the neighbouring faces, then tangential relax).
• Re-entrant corners are found from the hole angle at each border vertex and closed first, innermost first, with new edges that continue the surrounding edge loops; the remaining regular area is then filled as above.
• Corners that do not fit that pattern are cut by a cost-based search for the best diagonal.
• Six-sided pieces may use a three-quad star around a valence-3 vertex.
• Rings with an odd number of edges get one central triangle joined to three quad regions, since a quad-only fill is impossible.

* Comments were left for convenience to help understand each part since there are some different approach in order to try
cover the situation as possible.

NOTE: Fill the selected n-gon faces (typically after Remove hole or pipe caps) with quads.

[Micheus]

Here is a video showing some commands: Wings3D: Quad fill plugin

Some cases under evaluation. The re-entrance one was the most annoying, but I was very pleased with the result: