public static extern int IntersectRect(ref WinRect lpDestRect, ref WinRect lpSrc1Rect, ref WinRect lpSrc2Rect);
public static extern int GetClientRect(IntPtr hwnd, ref WinRect lpRect);
public static extern int OffsetRect(ref WinRect lpRect, int x, int y);
public static extern int InvalidateRect(IntPtr hwnd, ref WinRect lpRect, bool bErase);
public static extern int GetWindowRect(IntPtr hwnd, ref WinRect lpRect);