int pascal WinInvertRect(HWND hWnd, LPRECT r)

  This function reverses the attribute bytes contained within the
screen area contained in rectangle r. This function is useful for
doing things like highlighting certains areas on the screen. Please
note that no clipping is performed by this function. It is a low
level function to invert the attributes of an area of the screen.

Parameters
  hWnd is a handle to a window.
  r is a pointer to a RECT structure.

Returns
  Nothing.