Calculates the union of two rectangles.
The union of rectangles @src1 and @src2 is the smallest rectangle which
includes both @src1 and @src2 within it.
It is allowed for @dest to be the same as either @src1 or @src2.
Note that this function does not ignore 'empty' rectangles (ie. with
zero width or height).
Calculates the union of two rectangles. The union of rectangles @src1 and @src2 is the smallest rectangle which includes both @src1 and @src2 within it. It is allowed for @dest to be the same as either @src1 or @src2.
Note that this function does not ignore 'empty' rectangles (ie. with zero width or height).