For a problem that is theoretically binary (either in, or out?) filling polys can have really fiddly corner (literally!) cases.

Thanks for the WIP screenshots; they made me feel much better about my own slicers/rasterisers.

(there's probably a trick I'm missing*, but so far I've had the most robust results for 3D booleans by chasing fiddly overlaps/intersections on lower facets, all the way down to 0-D if necessary)

* like working directly with cubics, à la Jim Blinn?