Added the ability to release OpenGL objects in PagedLOD subgrphs that are no longer being rendered.

include/osg/PagedLOD

@@ -63,6 +63,7 @@ class OSG_EXPORT PagedLOD : public LOD
             float                           _priorityScale;
             double                          _timeStamp;
             int                             _frameNumber;
+            int                             _frameNumberOfLastReleaseGLObjects;
             osg::ref_ptr<osg::Referenced>   _databaseRequest;
         };
 
@@ -122,6 +123,10 @@ class OSG_EXPORT PagedLOD : public LOD
           * Return true if children are removed, false otherwise. */
         virtual bool removeExpiredChildren(double expiryTime, int expiryFrame, NodeList& removedChildren);
 
+        /** Release the GL Objects of the children from the PagedLOD which haven't been visited since specified expiry time and expiry frame number.
+          * Return true if any children have release called upon them, false otherwise. */
+        virtual bool releaseGLObjectsOnExpiredChildren(double releaseTime, int releaseFrame);
+        
     protected :
     
         virtual ~PagedLOD();

include/osgDB/DatabasePager

@@ -216,6 +216,24 @@ class OSGDB_EXPORT DatabasePager : public osg::NodeVisitor::DatabaseRequestHandl
           * before being removed.*/
         int getExpiryFrames() const { return _expiryFrames; }
 
+
+        /** Set the amount of time that a subgraph's OpenGL objects will be kept without being visited in the cull traversal
+          * before being released.*/
+        void setReleaseDelay(double releaseDelay);
+        
+        /** Get the amount of time that a subgraph's OpenGL objects will be kept without being visited in the cull traversal
+          * before being released.*/
+        double getReleaseDelay() const { return _releaseDelay; }
+
+        /** Set the number of frames that a subgraph's OpenGL objects will be kept without being visited in the cull traversal
+          * before being released.*/
+        void setReleaseFrames(int releaseFrames) { _releaseFrames = releaseFrames; }
+        
+        /** Get the number of frames that a subgraph's OpenGL objects will be kept without being visited in the cull traversal
+          * before being released.*/
+        int getReleaseFrames() const { return _releaseFrames; }
+
+
         /** Set whether the removed subgraphs should be deleted in the database thread or not.*/
         void setDeleteRemovedSubgraphsInDatabaseThread(bool flag) { _deleteRemovedSubgraphsInDatabaseThread = flag; }
         
@@ -534,6 +552,9 @@ class OSGDB_EXPORT DatabasePager : public osg::NodeVisitor::DatabaseRequestHandl
         double                          _expiryDelay;
         int                             _expiryFrames;
 
+        double                          _releaseDelay;
+        int                             _releaseFrames;
+
         ActiveGraphicsContexts          _activeGraphicsContexts;
         // CompileGraphicsContexts         _compileGraphicsContexts;