int UnionRect( LPRECT lpRect1, LPRECT lpRect2 );
lpRect1
Points to a RECT or CRect that contains a source rectangle.
lpRect2
Points to a RECT or CRect that contains a source rectangle.
Makes the dimensions of CRect equal to the union of the two source rectangles. The union is the smallest rectangle that contains both source rectangles.
Windows ignores the dimensions of an empty rectangle; that is, a rectangle that has no height or has no width.
TRUE if the union is not empty; FALSE if the union is empty.
::UnionRect, CRect::operator |=, CRect::operator |