canvas::Element: add getter for parent element.

simgear/canvas/elements/CanvasElement.cxx

@@ -85,6 +85,12 @@ namespace canvas
     return boost::static_pointer_cast<Element>(_self.lock());
   }
 
+  //----------------------------------------------------------------------------
+  ElementPtr Element::getParent()
+  {
+    return _parent ? _parent->getWeakPtr().lock() : ElementPtr();
+  }
+
   //----------------------------------------------------------------------------
   void Element::update(double dt)
   {

simgear/canvas/elements/CanvasElement.hxx

@@ -84,6 +84,7 @@ namespace canvas
       virtual void onDestroy();
 
       ElementWeakPtr getWeakPtr() const;
+      ElementPtr getParent();
 
       /**
        * Called every frame to update internal state