Вопрос по GTK+

#include <gtk/gtk.h>

gboolean on_configure( GtkWidget *widget,  GdkEventConfigure *event,
                gpointer   data )
{
    g_message ("Configure %d %d", event->x, event->y);
    return FALSE;
}

int main( int   argc,
          char *argv[] )
{
    GtkWidget *window;
    GtkWidget *button;
    
    gtk_init (&argc, &argv);
    
    window = gtk_window_new (GTK_WINDOW_TOPLEVEL);
    
    gtk_container_set_border_width (GTK_CONTAINER (window), 10);
    
    g_signal_connect (G_OBJECT(window), "configure-event", G_CALLBACK(on_configure), NULL);
    
    button = gtk_button_new_with_label ("Hello World");

    gtk_container_add (GTK_CONTAINER (window), button);
    
    gtk_widget_show_all (window);
    
    gtk_main ();
    
    return 0;
}