Optimize terrain QuadTree build

components/terrain/quadtreenode.cpp

@@ -71,16 +71,6 @@ QuadTreeNode::~QuadTreeNode()
 {
 }
 
-QuadTreeNode* QuadTreeNode::getParent()
-{
-    return mParent;
-}
-
-QuadTreeNode *QuadTreeNode::getChild(unsigned int i)
-{
-    return static_cast<QuadTreeNode*>(Group::getChild(i));
-}
-
 QuadTreeNode *QuadTreeNode::getNeighbour(Direction dir)
 {
     return mNeighbours[dir];

components/terrain/quadtreenode.hpp

@@ -35,10 +35,19 @@ namespace Terrain
         QuadTreeNode(QuadTreeNode* parent, ChildDirection dir, float size, const osg::Vec2f& center);
         virtual ~QuadTreeNode();
 
-        QuadTreeNode* getParent();
-
-        QuadTreeNode* getChild(unsigned int i);
-        using osg::Group::getNumChildren;
+        inline QuadTreeNode* getParent() { return mParent; }
+        inline QuadTreeNode* getChild(unsigned int i) { return static_cast<QuadTreeNode*>(Group::getChild(i)); }
+        inline unsigned int getNumChildren() const { return _children.size(); }
+
+        // osg::Group::addChild() does a lot of unrelated stuff, but we just really want to add a child node.
+        void addChild(QuadTreeNode* child)
+        {
+            // QuadTree node should not contain more than 4 child nodes.
+            // Reserve enough space if this node is supposed to have child nodes.
+            _children.reserve(4);
+            _children.push_back(child);
+            child->addParent(this);
+        };
 
         /// Returns our direction relative to the parent node, or Root if we are the root node.
         ChildDirection getDirection() { return mDirection; }

components/terrain/quadtreeworld.cpp

@@ -158,9 +158,12 @@ public:
         osg::BoundingBox boundingBox;
         for (unsigned int i=0; i<4; ++i)
         {
-            QuadTreeNode* child = addChild(parent, static_cast<ChildDirection>(i), halfSize);
+            osg::ref_ptr<QuadTreeNode> child = addChild(parent, static_cast<ChildDirection>(i), halfSize);
             if (child)
+            {
                 boundingBox.expandBy(child->getBoundingBox());
+                parent->addChild(child);
+            }
         }
 
         if (!boundingBox.valid())
@@ -169,7 +172,7 @@ public:
             parent->setBoundingBox(boundingBox);
     }
 
-    QuadTreeNode* addChild(QuadTreeNode* parent, ChildDirection direction, float size)
+    osg::ref_ptr<QuadTreeNode> addChild(QuadTreeNode* parent, ChildDirection direction, float size)
     {
         float halfSize = size/2.f;
         osg::Vec2f center;
@@ -194,7 +197,6 @@ public:
         osg::ref_ptr<QuadTreeNode> node = new QuadTreeNode(parent, direction, size, center);
         node->setLodCallback(parent->getLodCallback());
         node->setViewDataMap(mViewDataMap);
-        parent->addChild(node);
 
         if (node->getSize() > mMinSize)
         {