Nice, I haven't come across this library before. One minor suggestion: You could remove all of the corner and border special cases for overlap testing by makin

Nice, I haven't come across this library before. One minor suggestion: You could remove all of the corner and border special cases for overlap testing by making the grid 2 columns wider and 2 rows taller, offsetting all coordinates by 1, and pretending that the outer "border" on all sides of this slightly larger grid is covered with black cells.