GtkEv'sFunctionality

All the code presented so far implements the GtkWidget and GtkObject interfaces. GtkEv does have some unique functionality; namely, it responds to events on its event window by adding text describing the event to its buffer, and queueing a redraw. To do this, it overrides the default "event" signal handler.

Here is GtkEv's event method:

static gint   
gtk_ev_event (GtkWidget        *widget,
              GdkEvent         *event)
{
  GtkEv* ev;

  g_return_val_if_fail(widget != NULL, FALSE);
  g_return_val_if_fail(GTK_IS_EV(widget), FALSE);

  ev = GTK_EV(widget);

  if (event->any.window == widget->window)
    {
      if (GTK_WIDGET_CLASS(parent_class)->event)
        return (* GTK_WIDGET_CLASS(parent_class)->event) (widget, event);
      else
        return FALSE;
    }
  else
    {
      gchar* text;

      /* The event is either on ev->event_window, or it is a key event 
       * passed down to us from the toplevel GtkWindow
       */

      text = event_to_text(event);
      
      gtk_ev_push_text(ev, text);

      g_free(text);

      /* If it was a motion event, make sure we get more */
      if (event->type == GDK_MOTION_NOTIFY)
        {
          gdk_window_get_pointer(ev->event_window, NULL, NULL, NULL);
        }

      /* We didn't "handle" the event, just listened in on it. */
      return FALSE;
    }
}
      

Notice that the window method of the event is used to distinguish events that occur on widget->window from events that occur on the event subwindow. Some events will be received from a different window entirely; for example, key events actually occur on a toplevel window, and are passed to GtkEv if GtkEv has the focus.

event_to_text() is a lengthy but trivial function that creates a string describing the event; gtk_ev_push_text() pushes the text onto the front of the buffer and queues a redraw. The implementation of these functions is part of the complete GtkEv code listing, in Appendix E.