Merge pull request #2277 from akortunov/terrain

Camera-related fixes

apps/openmw/mwrender/renderingmanager.cpp

@@ -311,7 +311,6 @@ namespace MWRender
         else
             mTerrain.reset(new Terrain::TerrainGrid(sceneRoot, mRootNode, mResourceSystem, mTerrainStorage, Mask_Terrain, Mask_PreCompile, Mask_Debug));
 
-        mTerrain->setDefaultViewer(mViewer->getCamera());
         mTerrain->setTargetFrameRate(Settings::Manager::getFloat("target framerate", "Cells"));
         mTerrain->setWorkQueue(mWorkQueue.get());
 

apps/openmw/mwrender/water.cpp

@@ -161,6 +161,23 @@ private:
     osg::Plane mPlane;
 };
 
+/// This callback on the Camera has the effect of a RELATIVE_RF_INHERIT_VIEWPOINT transform mode (which does not exist in OSG).
+/// We want to keep the View Point of the parent camera so we will not have to recreate LODs.
+class InheritViewPointCallback : public osg::NodeCallback
+{
+public:
+        InheritViewPointCallback() {}
+
+    virtual void operator()(osg::Node* node, osg::NodeVisitor* nv)
+    {
+        osgUtil::CullVisitor* cv = static_cast<osgUtil::CullVisitor*>(nv);
+        osg::ref_ptr<osg::RefMatrix> modelViewMatrix = new osg::RefMatrix(*cv->getModelViewMatrix());
+        cv->popModelViewMatrix();
+        cv->pushModelViewMatrix(modelViewMatrix, osg::Transform::ABSOLUTE_RF_INHERIT_VIEWPOINT);
+        traverse(node, nv);
+    }
+};
+
 /// Moves water mesh away from the camera slightly if the camera gets too close on the Z axis.
 /// The offset works around graphics artifacts that occurred with the GL_DEPTH_CLAMP when the camera gets extremely close to the mesh (seen on NVIDIA at least).
 /// Must be added as a Cull callback.
@@ -224,6 +241,7 @@ public:
         setReferenceFrame(osg::Camera::RELATIVE_RF);
         setSmallFeatureCullingPixelSize(Settings::Manager::getInt("small feature culling pixel size", "Water"));
         setName("RefractionCamera");
+        setCullCallback(new InheritViewPointCallback);
 
         setCullMask(Mask_Effect|Mask_Scene|Mask_Object|Mask_Static|Mask_Terrain|Mask_Actor|Mask_ParticleSystem|Mask_Sky|Mask_Sun|Mask_Player|Mask_Lighting);
         setNodeMask(Mask_RenderToTexture);
@@ -315,6 +333,7 @@ public:
         setReferenceFrame(osg::Camera::RELATIVE_RF);
         setSmallFeatureCullingPixelSize(Settings::Manager::getInt("small feature culling pixel size", "Water"));
         setName("ReflectionCamera");
+        setCullCallback(new InheritViewPointCallback);
 
         int reflectionDetail = Settings::Manager::getInt("reflection detail", "Water");
         reflectionDetail = std::min(4, std::max(isInterior ? 2 : 0, reflectionDetail));

apps/openmw/mwworld/cellpreloader.cpp

@@ -167,6 +167,44 @@ namespace MWWorld
         std::vector<osg::ref_ptr<const osg::Object> > mPreloadedObjects;
     };
 
+    class TerrainPreloadItem : public SceneUtil::WorkItem
+    {
+    public:
+        TerrainPreloadItem(const std::vector<osg::ref_ptr<Terrain::View> >& views, Terrain::World* world, const std::vector<osg::Vec3f>& preloadPositions)
+            : mAbort(false)
+            , mTerrainViews(views)
+            , mWorld(world)
+            , mPreloadPositions(preloadPositions)
+        {
+        }
+
+        void storeViews(double referenceTime)
+        {
+            for (unsigned int i=0; i<mTerrainViews.size() && i<mPreloadPositions.size(); ++i)
+                mWorld->storeView(mTerrainViews[i], referenceTime);
+        }
+
+        virtual void doWork()
+        {
+            for (unsigned int i=0; i<mTerrainViews.size() && i<mPreloadPositions.size() && !mAbort; ++i)
+            {
+                mTerrainViews[i]->reset();
+                mWorld->preload(mTerrainViews[i], mPreloadPositions[i], mAbort);
+            }
+        }
+
+        virtual void abort()
+        {
+            mAbort = true;
+        }
+
+    private:
+        std::atomic<bool> mAbort;
+        std::vector<osg::ref_ptr<Terrain::View> > mTerrainViews;
+        Terrain::World* mWorld;
+        std::vector<osg::Vec3f> mPreloadPositions;
+    };
+
     /// Worker thread item: update the resource system's cache, effectively deleting unused entries.
     class UpdateCacheItem : public SceneUtil::WorkItem
     {
@@ -288,6 +326,9 @@ namespace MWWorld
             }
 
             mPreloadCells.erase(found);
+
+            if (cell->isExterior() && mTerrainPreloadItem && mTerrainPreloadItem->isDone())
+                mTerrainPreloadItem->storeViews(0.0);
         }
     }
 
@@ -329,6 +370,12 @@ namespace MWWorld
             mWorkQueue->addWorkItem(mUpdateCacheItem, true);
             mLastResourceCacheUpdate = timestamp;
         }
+
+        if (mTerrainPreloadItem && mTerrainPreloadItem->isDone())
+        {
+            mTerrainPreloadItem->storeViews(timestamp);
+            mTerrainPreloadItem = nullptr;
+        }
     }
 
     void CellPreloader::setExpiryDelay(double expiryDelay)
@@ -366,38 +413,6 @@ namespace MWWorld
         mUnrefQueue = unrefQueue;
     }
 
-    class TerrainPreloadItem : public SceneUtil::WorkItem
-    {
-    public:
-        TerrainPreloadItem(const std::vector<osg::ref_ptr<Terrain::View> >& views, Terrain::World* world, const std::vector<osg::Vec3f>& preloadPositions)
-            : mAbort(false)
-            , mTerrainViews(views)
-            , mWorld(world)
-            , mPreloadPositions(preloadPositions)
-        {
-        }
-
-        virtual void doWork()
-        {
-            for (unsigned int i=0; i<mTerrainViews.size() && i<mPreloadPositions.size() && !mAbort; ++i)
-            {
-                mWorld->preload(mTerrainViews[i], mPreloadPositions[i], mAbort);
-                mTerrainViews[i]->reset(0);
-            }
-        }
-
-        virtual void abort()
-        {
-            mAbort = true;
-        }
-
-    private:
-        std::atomic<bool> mAbort;
-        std::vector<osg::ref_ptr<Terrain::View> > mTerrainViews;
-        Terrain::World* mWorld;
-        std::vector<osg::Vec3f> mPreloadPositions;
-    };
-
     void CellPreloader::setTerrainPreloadPositions(const std::vector<osg::Vec3f> &positions)
     {
         if (mTerrainPreloadItem && !mTerrainPreloadItem->isDone())
@@ -418,8 +433,6 @@ namespace MWWorld
                     mTerrainViews.push_back(mTerrain->createView());
             }
 
-            // TODO: provide some way of giving the preloaded view to the main thread when we enter the cell
-            // right now, we just use it to make sure the resources are preloaded
             mTerrainPreloadPositions = positions;
             mTerrainPreloadItem = new TerrainPreloadItem(mTerrainViews, mTerrain, positions);
             mWorkQueue->addWorkItem(mTerrainPreloadItem);

apps/openmw/mwworld/cellpreloader.hpp

@@ -31,6 +31,7 @@ namespace MWRender
 namespace MWWorld
 {
     class CellStore;
+    class TerrainPreloadItem;
 
     class CellPreloader
     {
@@ -105,7 +106,7 @@ namespace MWWorld
 
         std::vector<osg::ref_ptr<Terrain::View> > mTerrainViews;
         std::vector<osg::Vec3f> mTerrainPreloadPositions;
-        osg::ref_ptr<SceneUtil::WorkItem> mTerrainPreloadItem;
+        osg::ref_ptr<TerrainPreloadItem> mTerrainPreloadItem;
         osg::ref_ptr<SceneUtil::WorkItem> mUpdateCacheItem;
     };
 

components/terrain/quadtreenode.cpp

@@ -114,9 +114,10 @@ void QuadTreeNode::traverse(osg::NodeVisitor &nv)
     if (!hasValidBounds())
         return;
 
-    ViewData* vd = getView(nv);
+    bool needsUpdate = true;
+    ViewData* vd = getView(nv, needsUpdate);
 
-    if ((mLodCallback && mLodCallback->isSufficientDetail(this, distance(vd->getEyePoint()))) || !getNumChildren())
+    if ((mLodCallback && mLodCallback->isSufficientDetail(this, distance(vd->getViewPoint()))) || !getNumChildren())
         vd->add(this, true);
     else
         osg::Group::traverse(nv);
@@ -142,26 +143,22 @@ ViewDataMap *QuadTreeNode::getViewDataMap()
     return mViewDataMap;
 }
 
-ViewData* QuadTreeNode::getView(osg::NodeVisitor &nv)
+ViewData* QuadTreeNode::getView(osg::NodeVisitor &nv, bool& needsUpdate)
 {
+    ViewData* vd = NULL;
     if (nv.getVisitorType() == osg::NodeVisitor::CULL_VISITOR)
     {
         osgUtil::CullVisitor* cv = static_cast<osgUtil::CullVisitor*>(&nv);
-        ViewData* vd = mViewDataMap->getViewData(cv->getCurrentCamera());
+        vd = mViewDataMap->getViewData(cv->getCurrentCamera(), nv.getViewPoint(), needsUpdate);
-        vd->setEyePoint(nv.getViewPoint());
-        return vd;
     }
     else // INTERSECTION_VISITOR
     {
+        osg::Vec3f viewPoint = nv.getViewPoint();
         static osg::ref_ptr<osg::Object> dummyObj = new osg::DummyObject;
-        ViewData* vd = mViewDataMap->getViewData(dummyObj.get());
+        vd = mViewDataMap->getViewData(dummyObj.get(), viewPoint, needsUpdate);
-        ViewData* defaultView = mViewDataMap->getDefaultView();
+        needsUpdate = true;
-        if (defaultView->hasEyePoint())
-            vd->setEyePoint(defaultView->getEyePoint());
-        else
-            vd->setEyePoint(nv.getEyePoint());
-        return vd;
     }
+    return vd;
 }
 
 void QuadTreeNode::setBoundingBox(const osg::BoundingBox &boundingBox)

components/terrain/quadtreenode.hpp

@@ -85,7 +85,7 @@ namespace Terrain
         ViewDataMap* getViewDataMap();
 
         /// Create or retrieve a view for the given traversal.
-        ViewData* getView(osg::NodeVisitor& nv);
+        ViewData* getView(osg::NodeVisitor& nv, bool& needsUpdate);
 
     private:
         QuadTreeNode* mParent;

components/terrain/quadtreeworld.cpp

@@ -247,7 +247,7 @@ QuadTreeWorld::~QuadTreeWorld()
 }
 
 
-void traverse(QuadTreeNode* node, ViewData* vd, osg::NodeVisitor* nv, LodCallback* lodCallback, const osg::Vec3f& eyePoint, bool visible, float maxDist)
+void traverse(QuadTreeNode* node, ViewData* vd, osg::NodeVisitor* nv, LodCallback* lodCallback, const osg::Vec3f& viewPoint, bool visible, float maxDist)
 {
     if (!node->hasValidBounds())
         return;
@@ -255,7 +255,7 @@ void traverse(QuadTreeNode* node, ViewData* vd, osg::NodeVisitor* nv, LodCallbac
     if (nv && nv->getVisitorType() == osg::NodeVisitor::CULL_VISITOR)
         visible = visible && !static_cast<osgUtil::CullVisitor*>(nv)->isCulled(node->getBoundingBox());
 
-    float dist = node->distance(eyePoint);
+    float dist = node->distance(viewPoint);
     if (dist > maxDist)
         return;
 
@@ -266,7 +266,7 @@ void traverse(QuadTreeNode* node, ViewData* vd, osg::NodeVisitor* nv, LodCallbac
     else
     {
         for (unsigned int i=0; i<node->getNumChildren(); ++i)
-            traverse(node->getChild(i), vd, nv, lodCallback, eyePoint, visible, maxDist);
+            traverse(node->getChild(i), vd, nv, lodCallback, viewPoint, visible, maxDist);
     }
 }
 
@@ -367,7 +367,8 @@ void loadRenderingNode(ViewData::Entry& entry, ViewData* vd, int vertexLodMod, C
 
 void QuadTreeWorld::accept(osg::NodeVisitor &nv)
 {
-    if (nv.getVisitorType() != osg::NodeVisitor::CULL_VISITOR && nv.getVisitorType() != osg::NodeVisitor::INTERSECTION_VISITOR)
+    bool isCullVisitor = nv.getVisitorType() == osg::NodeVisitor::CULL_VISITOR;
+    if (!isCullVisitor && nv.getVisitorType() != osg::NodeVisitor::INTERSECTION_VISITOR)
     {
         if (nv.getName().find("AcceptedByComponentsTerrainQuadTreeWorld") != std::string::npos)
         {
@@ -382,26 +383,40 @@ void QuadTreeWorld::accept(osg::NodeVisitor &nv)
         return;
     }
 
-    ViewData* vd = mRootNode->getView(nv);
+    bool needsUpdate = false;
+    ViewData* vd = mRootNode->getView(nv, needsUpdate);
 
-    if (nv.getVisitorType() == osg::NodeVisitor::CULL_VISITOR)
+    if (needsUpdate)
     {
-        osgUtil::CullVisitor* cv = static_cast<osgUtil::CullVisitor*>(&nv);
+        vd->reset();
-
+        if (isCullVisitor)
-        osg::UserDataContainer* udc = cv->getCurrentCamera()->getUserDataContainer();
-        if (udc && udc->getNumDescriptions() >= 2 && udc->getDescriptions()[0] == "NoTerrainLod")
         {
-            std::istringstream stream(udc->getDescriptions()[1]);
+            osgUtil::CullVisitor* cv = static_cast<osgUtil::CullVisitor*>(&nv);
-            int x,y;
+
-            stream >> x;
+            osg::UserDataContainer* udc = cv->getCurrentCamera()->getUserDataContainer();
-            stream >> y;
+            if (udc && udc->getNumDescriptions() >= 2 && udc->getDescriptions()[0] == "NoTerrainLod")
-            traverseToCell(mRootNode.get(), vd, x,y);
+            {
+                std::istringstream stream(udc->getDescriptions()[1]);
+                int x,y;
+                stream >> x;
+                stream >> y;
+                traverseToCell(mRootNode.get(), vd, x,y);
+            }
+            else
+                traverse(mRootNode.get(), vd, cv, mRootNode->getLodCallback(), cv->getViewPoint(), true, mViewDistance);
         }
         else
-            traverse(mRootNode.get(), vd, cv, mRootNode->getLodCallback(), cv->getViewPoint(), true, mViewDistance);
+            mRootNode->traverse(nv);
+    }
+    else if (isCullVisitor)
+    {
+        // view point is the same, but must still update visible status in case the camera has rotated
+        for (unsigned int i=0; i<vd->getNumEntries(); ++i)
+        {
+            ViewData::Entry& entry = vd->getEntry(i);
+            entry.set(entry.mNode, !static_cast<osgUtil::CullVisitor*>(&nv)->isCulled(entry.mNode->getBoundingBox()));
+        }
     }
-    else
-        mRootNode->traverse(nv);
 
     for (unsigned int i=0; i<vd->getNumEntries(); ++i)
     {
@@ -416,14 +431,23 @@ void QuadTreeWorld::accept(osg::NodeVisitor &nv)
             {
                 mCompositeMapRenderer->setImmediate(static_cast<CompositeMap*>(udc->getUserData()));
                 udc->setUserData(nullptr);
+
             }
             entry.mRenderingNode->accept(nv);
         }
     }
 
-    vd->reset(nv.getTraversalNumber());
+    if (!isCullVisitor)
+        vd->reset(); // we can't reuse intersection views in the next frame because they only contain what is touched by the intersection ray.
 
-    mRootNode->getViewDataMap()->clearUnusedViews(nv.getTraversalNumber());
+    vd->markUnchanged();
+
+    double referenceTime = nv.getFrameStamp() ? nv.getFrameStamp()->getReferenceTime() : 0.0;
+    if (referenceTime != 0.0)
+    {
+        vd->setLastUsageTimeStamp(referenceTime);
+        mViewDataMap->clearUnusedViews(referenceTime);
+    }
 }
 
 void QuadTreeWorld::ensureQuadTreeBuilt()
@@ -473,18 +497,30 @@ View* QuadTreeWorld::createView()
     return new ViewData;
 }
 
-void QuadTreeWorld::preload(View *view, const osg::Vec3f &eyePoint, std::atomic<bool> &abort)
+void QuadTreeWorld::preload(View *view, const osg::Vec3f &viewPoint, std::atomic<bool> &abort)
 {
     ensureQuadTreeBuilt();
 
     ViewData* vd = static_cast<ViewData*>(view);
-    traverse(mRootNode.get(), vd, nullptr, mRootNode->getLodCallback(), eyePoint, false, mViewDistance);
+    vd->setViewPoint(viewPoint);
+    traverse(mRootNode.get(), vd, nullptr, mRootNode->getLodCallback(), viewPoint, false, mViewDistance);
 
     for (unsigned int i=0; i<vd->getNumEntries() && !abort; ++i)
     {
         ViewData::Entry& entry = vd->getEntry(i);
         loadRenderingNode(entry, vd, mVertexLodMod, mChunkManager.get());
     }
+    vd->markUnchanged();
+}
+
+void QuadTreeWorld::storeView(const View* view, double referenceTime)
+{
+    osg::ref_ptr<osg::Object> dummy = new osg::DummyObject;
+    const ViewData* vd = static_cast<const ViewData*>(view);
+    bool needsUpdate = false;
+    ViewData* stored = mViewDataMap->getViewData(dummy, vd->getViewPoint(), needsUpdate);
+    stored->copyFrom(*vd);
+    stored->setLastUsageTimeStamp(referenceTime);
 }
 
 void QuadTreeWorld::reportStats(unsigned int frameNumber, osg::Stats *stats)
@@ -492,11 +528,6 @@ void QuadTreeWorld::reportStats(unsigned int frameNumber, osg::Stats *stats)
     stats->setAttribute(frameNumber, "Composite", mCompositeMapRenderer->getCompileSetSize());
 }
 
-void QuadTreeWorld::setDefaultViewer(osg::Object *obj)
-{
-    mViewDataMap->setDefaultViewer(obj);
-}
-
 void QuadTreeWorld::loadCell(int x, int y)
 {
     // fallback behavior only for undefined cells (every other is already handled in quadtree)

components/terrain/quadtreeworld.hpp

@@ -38,11 +38,10 @@ namespace Terrain
 
         View* createView();
         void preload(View* view, const osg::Vec3f& eyePoint, std::atomic<bool>& abort);
+        void storeView(const View* view, double referenceTime);
 
         void reportStats(unsigned int frameNumber, osg::Stats* stats);
 
-        virtual void setDefaultViewer(osg::Object* obj);
-
     private:
         void ensureQuadTreeBuilt();
 

components/terrain/terraingrid.cpp

@@ -15,7 +15,7 @@ class MyView : public View
 public:
     osg::ref_ptr<osg::Node> mLoaded;
 
-    virtual void reset(unsigned int frame) {}
+    virtual void reset() {}
 };
 
 TerrainGrid::TerrainGrid(osg::Group* parent, osg::Group* compileRoot, Resource::ResourceSystem* resourceSystem, Storage* storage, int nodeMask, int preCompileMask, int borderMask)

components/terrain/viewdata.cpp

@@ -5,9 +5,9 @@ namespace Terrain
 
 ViewData::ViewData()
     : mNumEntries(0)
-    , mFrameLastUsed(0)
+    , mLastUsageTimeStamp(0.0)
     , mChanged(false)
-    , mHasEyePoint(false)
+    , mHasViewPoint(false)
 {
 
 }
@@ -17,6 +17,15 @@ ViewData::~ViewData()
 
 }
 
+void ViewData::copyFrom(const ViewData& other)
+{
+    mNumEntries = other.mNumEntries;
+    mEntries = other.mEntries;
+    mChanged = other.mChanged;
+    mHasViewPoint = other.mHasViewPoint;
+    mViewPoint = other.mViewPoint;
+}
+
 void ViewData::add(QuadTreeNode *node, bool visible)
 {
     unsigned int index = mNumEntries++;
@@ -44,23 +53,23 @@ bool ViewData::hasChanged() const
     return mChanged;
 }
 
-bool ViewData::hasEyePoint() const
+bool ViewData::hasViewPoint() const
 {
-    return mHasEyePoint;
+    return mHasViewPoint;
 }
 
-void ViewData::setEyePoint(const osg::Vec3f &eye)
+void ViewData::setViewPoint(const osg::Vec3f &viewPoint)
 {
-    mEyePoint = eye;
+    mViewPoint = viewPoint;
-    mHasEyePoint = true;
+    mHasViewPoint = true;
 }
 
-const osg::Vec3f& ViewData::getEyePoint() const
+const osg::Vec3f& ViewData::getViewPoint() const
 {
-    return mEyePoint;
+    return mViewPoint;
 }
 
-void ViewData::reset(unsigned int frame)
+void ViewData::reset()
 {
     // clear any unused entries
     for (unsigned int i=mNumEntries; i<mEntries.size(); ++i)
@@ -69,8 +78,6 @@ void ViewData::reset(unsigned int frame)
     // reset index for next frame
     mNumEntries = 0;
     mChanged = false;
-
-    mFrameLastUsed = frame;
 }
 
 void ViewData::clear()
@@ -78,8 +85,9 @@ void ViewData::clear()
     for (unsigned int i=0; i<mEntries.size(); ++i)
         mEntries[i].set(nullptr, false);
     mNumEntries = 0;
-    mFrameLastUsed = 0;
+    mLastUsageTimeStamp = 0;
     mChanged = false;
+    mHasViewPoint = false;
 }
 
 bool ViewData::contains(QuadTreeNode *node)
@@ -112,17 +120,41 @@ bool ViewData::Entry::set(QuadTreeNode *node, bool visible)
     }
 }
 
-ViewData *ViewDataMap::getViewData(osg::Object *viewer)
+bool suitable(ViewData* vd, const osg::Vec3f& viewPoint, float& maxDist)
+{
+    return vd->hasViewPoint() && (vd->getViewPoint() - viewPoint).length2() < maxDist*maxDist;
+}
+
+ViewData *ViewDataMap::getViewData(osg::Object *viewer, const osg::Vec3f& viewPoint, bool& needsUpdate)
 {
     Map::const_iterator found = mViews.find(viewer);
+    ViewData* vd = nullptr;
     if (found == mViews.end())
     {
-        ViewData* vd = createOrReuseView();
+        vd = createOrReuseView();
         mViews[viewer] = vd;
-        return vd;
     }
     else
-        return found->second;
+        vd = found->second;
+
+    if (!suitable(vd, viewPoint, mReuseDistance))
+    {
+        for (Map::const_iterator other = mViews.begin(); other != mViews.end(); ++other)
+        {
+            if (suitable(other->second, viewPoint, mReuseDistance) && other->second->getNumEntries())
+            {
+                vd->copyFrom(*other->second);
+                needsUpdate = false;
+                return vd;
+            }
+        }
+        vd->setViewPoint(viewPoint);
+        needsUpdate = true;
+    }
+    else
+        needsUpdate = false;
+
+    return vd;
 }
 
 ViewData *ViewDataMap::createOrReuseView()
@@ -140,12 +172,12 @@ ViewData *ViewDataMap::createOrReuseView()
     }
 }
 
-void ViewDataMap::clearUnusedViews(unsigned int frame)
+void ViewDataMap::clearUnusedViews(double referenceTime)
 {
     for (Map::iterator it = mViews.begin(); it != mViews.end(); )
     {
         ViewData* vd = it->second;
-        if (vd->getFrameLastUsed() + 2 < frame)
+        if (vd->getLastUsageTimeStamp() + mExpiryDelay < referenceTime)
         {
             vd->clear();
             mUnusedViews.push_back(vd);
@@ -163,15 +195,4 @@ void ViewDataMap::clear()
     mViewVector.clear();
 }
 
-void ViewDataMap::setDefaultViewer(osg::Object *viewer)
-{
-    mDefaultViewer = viewer;
-}
-
-ViewData* ViewDataMap::getDefaultView()
-{
-    return getViewData(mDefaultViewer);
-}
-
-
 }

components/terrain/viewdata.hpp

@@ -21,12 +21,14 @@ namespace Terrain
 
         void add(QuadTreeNode* node, bool visible);
 
-        void reset(unsigned int frame);
+        void reset();
 
         void clear();
 
         bool contains(QuadTreeNode* node);
 
+        void copyFrom(const ViewData& other);
+
         struct Entry
         {
             Entry();
@@ -44,49 +46,55 @@ namespace Terrain
 
         Entry& getEntry(unsigned int i);
 
-        unsigned int getFrameLastUsed() const { return mFrameLastUsed; }
+        double getLastUsageTimeStamp() const { return mLastUsageTimeStamp; }
+        void setLastUsageTimeStamp(double timeStamp) { mLastUsageTimeStamp = timeStamp; }
 
         /// @return Have any nodes changed since the last frame
         bool hasChanged() const;
+        void markUnchanged() { mChanged = false; }
 
-        bool hasEyePoint() const;
+        bool hasViewPoint() const;
 
-        void setEyePoint(const osg::Vec3f& eye);
+        void setViewPoint(const osg::Vec3f& viewPoint);
-        const osg::Vec3f& getEyePoint() const;
+        const osg::Vec3f& getViewPoint() const;
 
     private:
         std::vector<Entry> mEntries;
         unsigned int mNumEntries;
-        unsigned int mFrameLastUsed;
+        double mLastUsageTimeStamp;
         bool mChanged;
-        osg::Vec3f mEyePoint;
+        osg::Vec3f mViewPoint;
-        bool mHasEyePoint;
+        bool mHasViewPoint;
+        float mReuseDistance;
     };
 
     class ViewDataMap : public osg::Referenced
     {
     public:
-        ViewData* getViewData(osg::Object* viewer);
+        ViewDataMap()
+            : mReuseDistance(300) // large value should be safe because the visibility of each node is still updated individually for each camera even if the base view was reused.
+                                  // this value also serves as a threshold for when a newly loaded LOD gets unloaded again so that if you hover around an LOD transition point the LODs won't keep loading and unloading all the time.
+            , mExpiryDelay(1.f)
+        {}
+
+        ViewData* getViewData(osg::Object* viewer, const osg::Vec3f& viewPoint, bool& needsUpdate);
 
         ViewData* createOrReuseView();
 
-        void clearUnusedViews(unsigned int frame);
+        void clearUnusedViews(double referenceTime);
 
         void clear();
 
-        void setDefaultViewer(osg::Object* viewer);
-
-        ViewData* getDefaultView();
-
     private:
         std::list<ViewData> mViewVector;
 
         typedef std::map<osg::ref_ptr<osg::Object>, ViewData*> Map;
         Map mViews;
 
-        std::deque<ViewData*> mUnusedViews;
+        float mReuseDistance;
+        float mExpiryDelay; // time in seconds for unused view to be removed
 
-        osg::ref_ptr<osg::Object> mDefaultViewer;
+        std::deque<ViewData*> mUnusedViews;
     };
 
 }

components/terrain/world.hpp

@@ -8,6 +8,7 @@
 #include <atomic>
 #include <memory>
 #include <set>
+#include <atomic>
 
 #include "defs.hpp"
 #include "cellborder.hpp"
@@ -48,7 +49,7 @@ namespace Terrain
         virtual ~View() {}
 
         /// Reset internal structure so that the next addition to the view will override the previous frame's contents.
-        virtual void reset(unsigned int frame) = 0;
+        virtual void reset() = 0;
     };
 
     /**
@@ -81,7 +82,7 @@ namespace Terrain
         /// @note Thread safe.
         virtual void clearAssociatedCaches();
 
-        /// Load a terrain cell at maximum LOD and store it in the View for later use.
+        /// Load a terrain cell and store it in the View for later use.
         /// @note Thread safe.
         virtual void cacheCell(View* view, int x, int y) {}
 
@@ -102,13 +103,15 @@ namespace Terrain
         virtual View* createView() { return nullptr; }
 
         /// @note Thread safe, as long as you do not attempt to load into the same view from multiple threads.
-        virtual void preload(View* view, const osg::Vec3f& eyePoint, std::atomic<bool>& abort) {}
+
+        virtual void preload(View* view, const osg::Vec3f& viewPoint, std::atomic<bool>& abort) {}
+
+        /// Store a preloaded view into the cache with the intent that the next rendering traversal can use it.
+        /// @note Not thread safe.
+        virtual void storeView(const View* view, double referenceTime) {}
 
         virtual void reportStats(unsigned int frameNumber, osg::Stats* stats) {}
 
-        /// Set the default viewer (usually a Camera), used as viewpoint for any viewers that don't use their own viewpoint.
-        virtual void setDefaultViewer(osg::Object* obj) {}
-
         virtual void setViewDistance(float distance) {}
 
         Storage* getStorage() { return mStorage; }