intersection
Description:
Computes the intersection of the two given rectangles.

The intersection in the image above is the blue outline.
If the two rectangles do not intersect, res
will contain a degenerate rectangle with origin in (0, 0) and a size of 0.
Parameters:
this |
a Rect |
b |
a Rect |
res |
return location for a Rect |
Returns:
`true` if the two rectangles intersect |