Here is a section of wall with an arch in it - one of the room components I generate from a script. Every polygon is a quad - everything - the arch frame, the all parts, the baseboard, and the crown molding. But every possible common vertex has been welded. This results in lots and lots of partially welded polygons. But in each case, I was careful to only do it if they are coplanar.

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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)