subtract in region%

Sets the region to the subtraction of itself minus the given region. In other words, a point is removed from the region if it is included in the given region. (The given region may contain points that are not in the current region; such points are ignored.)

This region's DC and given region's DC must be the same.

The result is always reliable for unsmoothed drawing. For smoothed drawing, the result is consistent across platforms and devices, but it is never a true subtraction. A subtraction corresponds to combining the sub-paths of this region with the reversed sub-paths of the given region, then intersecting the result with this region. This fails as a true subtraction, because the boundary of loops (with either 'odd-even or 'winding filling) is ambiguous.

• (send a-region subtract rgn) -> void
     rgn : region% object