wn_active(_c)

	status.i4.v = wn_active(window_id.i4.r)

	status.i4.v = wn_active_c(window_id.i4.v)

	This routine sets the active window for graphical operations using
	"wn_xxxx" routines to the specified window.  This call must be
	preceded by calls to wn_view(_c) and wn_world(_c).

	window_id	window ID (use WN_BACKGROUND for background window)

	This function returns ACNET status values as follows:

	OK			success
	CBS_INVARG		invalid ID value
	CBS_INVID		this window doesn't exist
	CBS_NOSETUP		scaling for this window hasn't been established

	This function requires the following include files:

	cbslib_h, acnet_errors_h

	Related functions:

	wn_get_active, wn_view(_c), wn_world(_c), wn_get_active_screen,
	intro_graphics_windows

	C/C++ usage:

	int	window_id;
	int	status;

	status = wn_active_c(window_id);