Re: Overriding on_motion_notify_event

[José Alburquerque <jaalburquerque cox net>]

On Aug 16, 2010, at 7:36 PM, Thomas Clark <thechewanater gmail com> wrote:

> I'm trying to override the virtual function on_motion_notify_event in a
> Gtk::DrawingArea, but the function never seems to be called. I don't get why,
> since DrawingArea inherits from Widget.  So, when does a motion notify event ever occur?
> 
> Here's a minimal example of what I mean:
> 
> #include <iostream>
> #include <gtkmm.h>
> 
> class Area: public Gtk::DrawingArea
> {
> public:
>  Area () {}
> private:
>  //never called?
>  virtual bool on_motion_notify_event (GdkEventMotion *event)
>  {
>    std::cout << event->x << '\t' << event->y << '\n';
>  }
> };
> 
> int main (int argc, char **argv)
> {
>  Gtk::Main test (argc, argv);
>  Gtk::Window window (Gtk::WINDOW_TOPLEVEL);
>  Area area;
> 
>  window.add (area);
>  window.show_all ();
> 
>  test.run (window);
> }

The C API "motion-notify-event" docs[1] suggests that the Gdk::POINTER_MOTION_MASK of the Gdk::Window needs to be set to get those events.  This can be done by using Gtk::Widget::add_events() or Gtk::Widget::set_events(), or by getting the Gdk::Window and setting the mask using Gdk::Window::set_events().

[1] http://library.gnome.org/devel/gtk/stable/GtkWidget.html#GtkWidget-motion-notify-event

--
José