> Does MetaPost have a clever way of determining whether a point z is
> "inside" a closed path (cycle) p?
You might play with the `is_clockwise' macro from the `mf2pt1.mp' file
(in the mf2pt1 package). It has a different purpose, and you have to
simplify it a lot to start from a given point, but the used algorithm
should work just fine.
Werner