)
Create a rectangle spanned by the points a and b;
The rectangle contains the points
with x-coordinate between a.x and b.x, and
with y-coordinate between a.y and b.y, both inclusive.
If the distance between a.x and b.x is not representable
(which can happen if one or both is a double),
the actual right edge might be slightly off from max(a.x, b.x).
Similar for the y-coordinates and the bottom edge.