As an aside, I greatly improved the Tiled map loading system I wrote for Unity.

Eeek! Okay, so building a PolygonColldier2D is really slow, because it runs decomposition every time you insert a new polygon!

So I modified the code so it took my loaded collision polygons and then ran a simple swept-line combiner.

That's a lot better. Let's see what the performance is now.

Okay I can live with that!