Determining Whether a Window Is on the Screen

You can check whether a window is up with the window is up function, wn_isup():

ULONG wn_isup(wnp)

WINDOWPTR wnp;        /* Pointer to window        */

A non-zero value is returned if the window is set on the screen; 0 is returned otherwise. wn_isup() does not determine whether a window is the current window or whether it is visible.