This function creates the union of two rectangles. The union is the smallest rectangle that contains both source rectangles.
BOOL UnionRect( LPRECT lprcDst, const RECT* lprcSrc1, const RECT* lprcSrc2 );
Long pointer to the RECT structure that will receive a rectangle containing the rectangles pointed to by the lprcSrc1 and lprcSrc2 parameters.
Long pointer to the RECT structure that contains the first source rectangle.
Long pointer to the RECT structure that contains the second source rectangle.
Nonzero indicates that the specified structure contains a nonempty rectangle.
Zero indicates that the specified structure does not contain a nonempty rectangle.
To get extended error information, call GetLastError.