title: Retrieving Gtk::Widget's relative position: get_allocation() doesn't work
body: <p>I need to retrieve the position of a <code>Gtk::Widget</code> relative to its parent, a <code>Gtk::Table</code>. Most sources (e.g. <a href="http://library.gnome.org/devel/gtk-faq/stable/x642.html" rel="nofollow noreferrer">http://library.gnome.org/devel/gtk-faq/stable/x642.html</a>) say that one needs to call <code>Gtk::Widget::get_allocation()</code>. However, the returned <code>Gtk::Allocation</code> object always contains <code>x = -1</code>, <code>y = -1</code>, <code>width = 1</code>, <code>height = 1</code>.</p>
  
  <p>I have to note that this happens before the <code>Gtk::Table</code> object is actually exposed and rendered. A call to <code>show_all_children()</code> or <code>check_resize()</code>, which I would expect to recalculate child widget geometry, doesn't help.</p>
  
  <p>What am I doing wrong? Thanks in advance.</p>