A flat region in the XY plane: everything its boundary encloses, less everything any of its
holes encloses. The boundary and each hole are a range of x, y pairs without the first point
repeated, in either winding; a boundary that crosses itself keeps every loop it makes.
A flat region in the XY plane: everything its boundary encloses, less everything any of its holes encloses. The boundary and each hole are a range of
x, ypairs without the first point repeated, in either winding; a boundary that crosses itself keeps every loop it makes.