This is rarely needed, but a very useful optimization in this case:

static void
model_changed_callback (Model     *model,
                        GtkWidget *view)
{
  if (model->width != view->requisition.width ||
      model->height != view_requisition.height)
    {
      gtk_widget_queue_resize (widget);
    }
  else
    {
      gtk_widget_queue_draw (widget);
    }
}

Will attach a trivial patch.