Oh one other thing. It is actually incorrect to say that this is not compatible with Catmull Clark. It actually is, so long as the partially welded objects are coplaner, and are not actually going to end up curved.

This is how I make my walls in my room generator script. I cut holes for windows and the resulting set of polygons use the fewest possible number of vertices. Some are partially welded but it doesn't matter because they are all in the same plane.

Subdivision does not apply or matter when polygons are arranged in a plane.

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Renderosity forum reply notifications are wonky. If I read a follow-up in a thread, but I don't myself reply, then notifications no longer happen AT ALL on that thread. So if I seem to be ignoring a question, that's why. (Updated September 23, 2019)