Canvas cleanup and restructuring

- Add some methods for easier using the Canvas from C++
 - Add some documentation to Nasal

simgear/props/PropertyBasedMgr.cxx

@@ -45,6 +45,49 @@ namespace simgear
         _elements[i]->update(delta_time_sec);
   }
 
+  //----------------------------------------------------------------------------
+  PropertyBasedElementPtr
+  PropertyBasedMgr::createElement(const std::string& name)
+  {
+    SGPropertyNode* node = _props->addChild(_name_elements, 0, false);
+    if( !name.empty() )
+      node->setStringValue("name", name);
+
+    return getElement( node->getIndex() );
+  }
+
+  //----------------------------------------------------------------------------
+  PropertyBasedElementPtr PropertyBasedMgr::getElement(size_t index) const
+  {
+    if( index >= _elements.size() )
+      return PropertyBasedElementPtr();
+
+    return _elements[index];
+  }
+
+  //----------------------------------------------------------------------------
+  const SGPropertyNode* PropertyBasedMgr::getPropertyRoot() const
+  {
+    return _props;
+  }
+
+  //----------------------------------------------------------------------------
+  PropertyBasedMgr::PropertyBasedMgr( SGPropertyNode_ptr props,
+                                      const std::string& name_elements,
+                                      ElementFactory element_factory ):
+    _props( props ),
+    _name_elements( name_elements ),
+    _element_factory( element_factory )
+  {
+
+  }
+
+  //----------------------------------------------------------------------------
+  PropertyBasedMgr::~PropertyBasedMgr()
+  {
+
+  }
+
   //----------------------------------------------------------------------------
   void PropertyBasedMgr::childAdded( SGPropertyNode * parent,
                                      SGPropertyNode * child )
@@ -103,27 +146,4 @@ namespace simgear
       _elements[index].reset();
   }
 
-  //----------------------------------------------------------------------------
-  const SGPropertyNode* PropertyBasedMgr::getPropertyRoot() const
-  {
-    return _props;
-  }
-
-  //----------------------------------------------------------------------------
-  PropertyBasedMgr::PropertyBasedMgr( SGPropertyNode_ptr props,
-                                      const std::string& name_elements,
-                                      ElementFactory element_factory ):
-    _props( props ),
-    _name_elements( name_elements ),
-    _element_factory( element_factory )
-  {
-
-  }
-
-  //----------------------------------------------------------------------------
-  PropertyBasedMgr::~PropertyBasedMgr()
-  {
-
-  }
-
 } // namespace simgear

simgear/props/PropertyBasedMgr.hxx

@@ -39,12 +39,19 @@ namespace simgear
 
       virtual void update (double delta_time_sec);
 
-      virtual void childAdded( SGPropertyNode * parent,
-                               SGPropertyNode * child );
-      virtual void childRemoved( SGPropertyNode * parent,
-                                 SGPropertyNode * child );
+      /**
+       * Create a new PropertyBasedElement
+       *
+       * @param name    Name of the new element
+       */
+      PropertyBasedElementPtr createElement(const std::string& name = "");
 
-      virtual void elementCreated(PropertyBasedElementPtr element) {}
+      /**
+       * Get an existing PropertyBasedElement by its index
+       *
+       * @param index   Index of element node in property tree
+       */
+      PropertyBasedElementPtr getElement(size_t index) const;
 
       virtual const SGPropertyNode* getPropertyRoot() const;
 
@@ -75,6 +82,13 @@ namespace simgear
                         ElementFactory element_factory );
       virtual ~PropertyBasedMgr() = 0;
 
+      virtual void childAdded( SGPropertyNode * parent,
+                               SGPropertyNode * child );
+      virtual void childRemoved( SGPropertyNode * parent,
+                                 SGPropertyNode * child );
+
+      virtual void elementCreated(PropertyBasedElementPtr element) {}
+
   };
 
 } // namespace simgear