How to subdivide edges of the pentagon so that when I'm making grid with faces I get perfect quads or almost all quads ?
This is more math-combinatorics question but is quite important for the mesh to have nice grid.
For example, if I press grid fill with this subdivion, Blender says to select two edge loops and I can't fill it with almost all quads.
If you look at how the Catmull-Clark subdivision algorithm does it, you can see it creates a five-pointed star:
Before:
After:
When you surround it with quad geometry, it still works the same:
Before:
After:
With Catmull-Clark smoothing:
If we look at this, we can see that this redirects the topology very nicely:
It is important to note, though, that in a few cases, you can change the way you divide it up to change the topological flow. Most times though, this is the easiest and most useful subdivision.
When I saw your edit and understood better what you were asking, the first thing I thought of was CGCookie's Retopoflow addon. You can purchase it on the Blender Market. This has a few algorithms to fill or "patch" areas like that. I looked at how it did that and came up with a few ideas:
I know that this doesn't answer your question directly, but it seems like the number one thing that the RetopoFlow does is reevaluate whether all of the vertices on each edge are necessary. It will add or remove vertices to adjust and produce cleaner topology.
In some cases, you can treat it like a quadrilateral. For example, if you have a pentagon like this:
You can treat the two right edges as one edge and still fill it like a quad:
It doesn't have to be symmetrical:
In addition, Retopoflow has a open pull request that has more sophisticated N-gon filling methods. You might be able to look through the source code to find what algorithms it uses. Here is a gif from the site of what this produces:
