title: How to set bg image of a window in a GTK3 application
body: <p>I found this way:</p>
  
  <pre><code>GdkPixmap *backPixMap = gdk_pixmap_create_from_xpm ( window , NULL , NULL , fileName );
  gdk_window_set_back_pixmap( GTK_WIDGET( window )-&gt;window , backPixMap , FALSE );
  </code></pre>
  
  <p>but it seems that GdkPixmap is obsolete now...</p>
  
  <p>So, with GTK3, how can I set the background image of a GtkWindow?</p>