Moved rendering support into GraphisContext, osgViewer::Viewer/View, and

added frame stamp updating and update traversal to osgViewer::Scene/Viewer.

Updated osgcamera example to use new Viewer API calls instead of using local
rendering calls.

include/osg/GraphicsContext

@@ -136,6 +136,52 @@ class OSG_EXPORT GraphicsContext : public Referenced
         /** Decrement the usage count associate with a contextID. Once the contextID goes to 0 the contextID is then free to be reused.*/
         static void decrementContextIDUsageCount(unsigned int contextID);
     
+    public:
+    
+        /** Base class for implementing graphics operations.*/
+        struct OSG_EXPORT Operation : virtual public Referenced
+        {
+            Operation(const std::string& name, bool keep):
+                _name(name),
+                _keep(keep) {}
+                
+            /** Set the human readable name of the operation.*/
+            void setName(const std::string& name) { _name = name; }
+
+            /** Get the human readable name of the operation.*/
+            const std::string& getName() const { return _name; }
+        
+            /** Set whether the operation should be kept once its been applied.*/ 
+            void setKeep(bool keep) { _keep = keep; }
+
+            /** Get whether the operation should be kept once its been applied.*/ 
+            bool getKeep() const { return _keep; }
+
+            /** if this operation is a barrier then release it.*/
+            virtual void release() {}
+
+            /** Do the actual task of this operation.*/ 
+            virtual void operator () (GraphicsContext*) {}
+            
+            std::string _name;
+            bool        _keep;
+        };
+        
+        /** Add operation to end of OperationQueue.*/
+        void add(Operation* operation);
+        
+        /** Remove operation from OperationQueue.*/
+        void remove(Operation* operation);
+
+        /** Remove named operation from OperationQueue.*/
+        void remove(const std::string& name);
+
+        /** Remove all operations from OperationQueue.*/
+        void removeAllOperations();
+
+        /** Run the operations. */
+        void runOperations();
+
     public:
     
         /** Get the traits of the GraphicsContext.*/
@@ -242,6 +288,12 @@ class OSG_EXPORT GraphicsContext : public Referenced
         OpenThreads::Mutex      _mutex;
         OpenThreads::Thread*    _threadOfLastMakeCurrent;
         
+        typedef std::list< ref_ptr<Operation> > OperationQueue;
+        OpenThreads::Mutex          _operationsMutex;
+        osg::ref_ptr<osg::Block>    _operationsBlock;
+        OperationQueue              _operations;
+        osg::ref_ptr<Operation>     _currentOperation;
+
         ref_ptr<GraphicsThread> _graphicsThread;
         
 };