static gboolean
 on_draw (GtkWidget *widget,
          cairo_t   *cr)
 {
   /* draw something here */
   return FALSE;
 }

 int main (int argc, char *argv[])
 {
   GtkWidget *window;

   gtk_init (&argc, &argv);

   window = gtk_window_new (GTK_WINDOW_TOPLEVEL);
   gtk_window_set_default_size (GTK_WINDOW (window), 300, 300);
   g_signal_connect (window, "draw", G_CALLBACK (on_draw), NULL);

   gtk_widget_show_all (window);
   gtk_main ();

   return 0;
 }