From Maceij Krol, "I have implement frame based expiration of PagedLOD children.

New attribute DatabasePager::_expiryFrames sets number of frames a PagedLOD child is kept in memory. The attribute is set with DatabasePager::setExpiryFrames method or OSG_EXPIRY_FRAMES environmental variable.

New attribute PagedLOD::PerRangeData::_
frameNumber contains frame number of last cull traversal.

Children of PagedLOD are expired when time _AND_ number of frames since last cull traversal exceed OSG_EXPIRY_DELAY _AND_ OSG_EXPIRY_FRAMES respectively. By default OSG_EXPIRY_FRAMES = 1 which means that nodes from last cull/rendering
traversal will not be expired even if last cull time exceeds OSG_EXPIRY_DELAY. Setting OSG_EXPIRY_FRAMES = 0 revokes previous behaviour of PagedLOD.

Setting OSG_EXPIRY_FRAMES > 0 fixes problems of children reloading in lazy rendering applications. Required behaviour is achieved by manipulating OSG_EXPIRY_DELAY and OSG_EXPIRY_FRAMES together.

Two interface changes are made:

DatabasePager::updateSceneGraph(double currentFrameTime) is replaced by DatabasePager::updateSceneGraph(const osg::FrameStamp &frameStamp). The previous method is in #if 0 clause in the header file. Robert, decide if You want to include it.

PagedLOD::removeExpiredChildren(double expiryTime, NodeList &removedChildren) is deprecated (warning is printed), when subclassing use PagedLOD::removeExpiredChildren(double expiryTime, int expiryFrame, NodeList &removedChildren) instead. "

src/osgDB/ImagePager.cpp

@@ -326,7 +326,7 @@ bool ImagePager::requiresUpdateSceneGraph() const
     return !(_completedQueue->_requestList.empty());
 }
 
-void ImagePager::updateSceneGraph(double currentFrameTime)
+void ImagePager::updateSceneGraph(const osg::FrameStamp &frameStamp)
 {
     OpenThreads::ScopedLock<OpenThreads::Mutex> lock(_completedQueue->_requestMutex);