BOOL CreateEllipticRgnIndirect( LPRECT lpRect );
lpRect
Points to a RECT structure or CRect object that contains the coordinates of the upper-left and lower-right corners of the bounding rectangle of the ellipse.
Creates an elliptical region. The region is defined by lpRect and is stored in the CRgn object.
TRUE if the operation succeeded; otherwise FALSE.
CRgn::CreateEllipticRgn, ::CreateEllipticRgnIndirect