static extern int CombineRgn(IntPtr hrgnDest, IntPtr hrgnSrc1,

Private Shared Function CombineRgn(ByVal hrgnDest As IntPtr,

public enum CombineRgnStyles:int

    static extern int CombineRgn(IntPtr hrgnDest, IntPtr hrgnSrc1,IntPtr hrgnSrc2, int fnCombineMode);

            CombineRgn(r3,r1,r2,0);