union in region%

Sets the region to the union of itself with the given region.

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

The result is always reliable for unsmoothed drawing. For smoothed drawing, a union corresponds to combining the sub-paths of each region into one path, using an 'odd-even fill if either of the region uses an 'odd-even fill (otherwise using a 'winding fill). Consequently, while the result is consistent across platforms and devices, it is a true union only for certain input regions. For example, it is a true union for non-overlapping atomic and union regions. It is also a true union for atomic and union regions (potentially overlapping) that are all clockwise and use 'winding fill.

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