I had someone else approach me with a file that didn't work today, this time because it was using obround shapes. Implementing them I found that the way I was handling polygons wasn't robust enough to properly deal with lots of intersecting polygons, so I changed that hole logic.

It's quite likely this logic will still break, but it seems to at least be more robust than before. There are still several gerber primitives that I haven't added support for yet, hopefully I'll get around to them on the weekend.