Various updates to operations related to cull traversal.

include/osg/fast_back_stack

@@ -0,0 +1,67 @@
+//C++ header - Open Scene Graph - Copyright (C) 1998-2001 Robert Osfield
+//Distributed under the terms of the GNU Library General Public License (LGPL)
+//as published by the Free Software Foundation.
+
+#ifndef OSG_FAST_BACK_STACK
+#define OSG_FAST_BACK_STACK 1
+
+namespace osg {
+
+/** Simple stack implementation that keeps the back() cached locally for fast access
+  * rather than at the back of the vector which is the traditional stack implementation.
+  * A conventional std::vector<> stores the rest of the stack. The fast_back_stack
+  * although contains a stl container it only implments the back push_back(),pop_back()
+  * and back() methods so is not as general purpose as stl stack implementation.
+  * The focus of the fast_back_stack is purly to maximize the speed at which the
+  * back can be accessed.*/
+  
+template<class T>
+class fast_back_stack
+{
+    public:
+    
+        inline fast_back_stack():_value(),_stack(),_size(0) {}
+
+        inline fast_back_stack(const T& value):_value(value),_stack(),_size(1) {}
+
+        inline void clear() { _stack.clear(); _size = 0; }
+
+        inline bool empty() const { return _size==0; }
+
+        inline unsigned int size() const { return _size; }
+
+        inline T& back() { return _value; }
+
+        inline const T& back() const { return _value; }
+
+        inline void push_back(const T& value)
+        {
+            if (_size>0)
+            {
+                _stack.push_back(_value);
+            }
+            _value = value;
+            ++_size;
+        }
+        
+        inline void pop_back()
+        {
+            if (_size>0)
+            {
+                if (!_stack.empty())
+                {
+                    _value = _stack.back();
+                    _stack.pop_back();
+                }
+                --_size;
+            } // else error condition.
+        }
+        
+        T              _value;
+        std::vector<T> _stack;
+        unsigned int   _size;
+};
+
+}
+
+#endif