speeds up optimizer (#3162)

We can expect marginally improved loading times with this PR. Drawable, Transform and Node counts in stats panels are expected to remain unchanged - this PR does not add new scene graph optimisations, it just increases the speed with which we apply existing ones.

1. We add explicit `NodeVisitor::apply` overrides for commonly encountered node types to avoid additional virtual function calls per node associated with the default `apply` implementation.
2. We skip pushing `StateSet`s when  `_mergeAlphaBlending` is enabled or the `StateSet` contains no relevant state.
3. We add a specialised variant of `CollectLowestTransformsVisitor::addTransform` accepting `MatrixTransform` to avoid matrix copies and multiplications.

components/sceneutil/optimizer.cpp

@@ -171,7 +171,7 @@ class CollectLowestTransformsVisitor : public BaseOptimizerVisitor
             setTraversalMode(osg::NodeVisitor::TRAVERSE_PARENTS);
         }
 
-        void apply(osg::Node& node) override
+        void apply(osg::Group& node) override
         {
             if (node.getNumParents())
             {
@@ -180,7 +180,7 @@ class CollectLowestTransformsVisitor : public BaseOptimizerVisitor
             else
             {
                 // for all current objects mark a nullptr transform for them.
-                registerWithCurrentObjects(0);
+                registerWithCurrentObjects(static_cast<osg::Transform*>(nullptr));
             }
         }
 
@@ -198,15 +198,19 @@ class CollectLowestTransformsVisitor : public BaseOptimizerVisitor
             // for all current objects associated this transform with them.
             registerWithCurrentObjects(&transform);
         }
-
+        void apply(osg::MatrixTransform& transform) override
-        void apply(osg::Geode& geode) override
         {
-            traverse(geode);
+            // for all current objects associated this transform with them.
+            registerWithCurrentObjects(&transform);
         }
 
-        void apply(osg::Billboard& geode) override
+        void apply(osg::Node& node) override
+        {
+            traverse(node);
+        }
+
+        void apply(osg::Geometry& geode) override
         {
-            traverse(geode);
         }
 
         void collectDataFor(osg::Node* node)
@@ -293,7 +297,19 @@ class CollectLowestTransformsVisitor : public BaseOptimizerVisitor
 
             ObjectStruct():_canBeApplied(true),_moreThanOneMatrixRequired(false) {}
 
-            void add(osg::Transform* transform, bool canOptimize)
+            inline const osg::Matrix& getMatrix(osg::MatrixTransform* transform)
+            {
+                return transform->getMatrix();
+            }
+            osg::Matrix getMatrix(osg::Transform* transform)
+            {
+                osg::Matrix matrix;
+                transform->computeLocalToWorldMatrix(matrix, 0);
+                return matrix;
+            }
+            
+            template<typename T>
+            void add(T* transform, bool canOptimize)
             {
                 if (transform)
                 {
@@ -301,12 +317,10 @@ class CollectLowestTransformsVisitor : public BaseOptimizerVisitor
                     else if (transform->getReferenceFrame()!=osg::Transform::RELATIVE_RF) _moreThanOneMatrixRequired=true;
                     else
                     {
-                        if (_transformSet.empty()) transform->computeLocalToWorldMatrix(_firstMatrix,0);
+                        if (_transformSet.empty()) _firstMatrix = getMatrix(transform);
                         else
                         {
-                            osg::Matrix matrix;
+                            if (_firstMatrix!=getMatrix(transform)) _moreThanOneMatrixRequired=true;
-                            transform->computeLocalToWorldMatrix(matrix,0);
-                            if (_firstMatrix!=matrix) _moreThanOneMatrixRequired=true;
                         }
                     }
                 }
@@ -327,8 +341,8 @@ class CollectLowestTransformsVisitor : public BaseOptimizerVisitor
             TransformSet    _transformSet;
         };
 
-
+        template <typename T>
-        void registerWithCurrentObjects(osg::Transform* transform)
+        void registerWithCurrentObjects(T* transform)
         {
             for(ObjectList::iterator itr=_currentObjectList.begin();
                 itr!=_currentObjectList.end();
@@ -633,19 +647,23 @@ osg::Array* cloneArray(osg::Array* array, osg::VertexBufferObject*& vbo, const o
     return array;
 }
 
-void Optimizer::FlattenStaticTransformsVisitor::apply(osg::Drawable& drawable)
+void Optimizer::FlattenStaticTransformsVisitor::apply(osg::Geometry& geometry)
 {
-    osg::Geometry *geometry = drawable.asGeometry();
+    if(isOperationPermissibleForObject(&geometry))
-    if((geometry) && (isOperationPermissibleForObject(&drawable)))
     {
         osg::VertexBufferObject* vbo = nullptr;
-        if(geometry->getVertexArray() && geometry->getVertexArray()->referenceCount() > 1)
+        if(geometry.getVertexArray() && geometry.getVertexArray()->referenceCount() > 1)
-            geometry->setVertexArray(cloneArray(geometry->getVertexArray(), vbo, geometry));
+            geometry.setVertexArray(cloneArray(geometry.getVertexArray(), vbo, &geometry));
-        if(geometry->getNormalArray() && geometry->getNormalArray()->referenceCount() > 1)
+        if(geometry.getNormalArray() && geometry.getNormalArray()->referenceCount() > 1)
-            geometry->setNormalArray(cloneArray(geometry->getNormalArray(), vbo, geometry));
+            geometry.setNormalArray(cloneArray(geometry.getNormalArray(), vbo, &geometry));
-        if(geometry->getTexCoordArray(7) && geometry->getTexCoordArray(7)->referenceCount() > 1) // tangents
+        if(geometry.getTexCoordArray(7) && geometry.getTexCoordArray(7)->referenceCount() > 1) // tangents
-            geometry->setTexCoordArray(7, cloneArray(geometry->getTexCoordArray(7), vbo, geometry));
+            geometry.setTexCoordArray(7, cloneArray(geometry.getTexCoordArray(7), vbo, &geometry));
     }
+    _drawableSet.insert(&geometry);
+}
+
+void Optimizer::FlattenStaticTransformsVisitor::apply(osg::Drawable& drawable)
+{
     _drawableSet.insert(&drawable);
 }
 
@@ -673,6 +691,11 @@ void Optimizer::FlattenStaticTransformsVisitor::apply(osg::Transform& transform)
     _transformStack.pop_back();
 }
 
+void Optimizer::FlattenStaticTransformsVisitor::apply(osg::MatrixTransform& transform)
+{
+    apply(static_cast<osg::Transform&>(transform));
+}
+
 bool Optimizer::FlattenStaticTransformsVisitor::removeTransforms(osg::Node* nodeWeCannotRemove)
 {
     CollectLowestTransformsVisitor cltv(_optimizer);
@@ -1112,10 +1135,13 @@ bool isAbleToMerge(const osg::Geometry& g1, const osg::Geometry& g2)
 }
 
 
-void Optimizer::MergeGeometryVisitor::pushStateSet(osg::StateSet *stateSet)
+bool Optimizer::MergeGeometryVisitor::pushStateSet(osg::StateSet *stateSet)
 {
+    if (_mergeAlphaBlending || !stateSet || stateSet->getRenderBinMode() & osg::StateSet::INHERIT_RENDERBIN_DETAILS)
+        return false;
     _stateSetStack.push_back(stateSet);
     checkAlphaBlendingActive();
+    return true;
 }
 
 void Optimizer::MergeGeometryVisitor::popStateSet()
@@ -1145,15 +1171,14 @@ void Optimizer::MergeGeometryVisitor::checkAlphaBlendingActive()
 
 void Optimizer::MergeGeometryVisitor::apply(osg::Group &group)
 {
-    if (group.getStateSet())
+    bool pushed = pushStateSet(group.getStateSet());
-        pushStateSet(group.getStateSet());
 
     if (!_alphaBlendingActive || _mergeAlphaBlending)
         mergeGroup(group);
 
     traverse(group);
 
-    if (group.getStateSet())
+    if (pushed)
         popStateSet();
 }
 

components/sceneutil/optimizer.hpp

@@ -285,9 +285,11 @@ class Optimizer
                     BaseOptimizerVisitor(optimizer, FLATTEN_STATIC_TRANSFORMS) {}
 
                 void apply(osg::Node& geode) override;
+                void apply(osg::Geometry& drawable) override;
                 void apply(osg::Drawable& drawable) override;
                 void apply(osg::Billboard& geode) override;
-                void apply(osg::Transform& transform) override;
+                void apply(osg::Transform& transform) override final;
+                void apply(osg::MatrixTransform& transform) override;
 
                 bool removeTransforms(osg::Node* nodeWeCannotRemove);
 
@@ -316,6 +318,7 @@ class Optimizer
                     BaseOptimizerVisitor(optimizer, FLATTEN_STATIC_TRANSFORMS) {}
 
                 void apply(osg::MatrixTransform& transform) override;
+                void apply(osg::Geometry&) override { }
 
                 bool removeTransforms(osg::Node* nodeWeCannotRemove);
 
@@ -338,6 +341,7 @@ class Optimizer
                     BaseOptimizerVisitor(optimizer, REMOVE_REDUNDANT_NODES) {}
 
                 void apply(osg::Group& group) override;
+                void apply(osg::Geometry&) override { }
 
                 void removeEmptyNodes();
 
@@ -358,6 +362,7 @@ class Optimizer
                 void apply(osg::Transform& transform) override;
                 void apply(osg::LOD& lod) override;
                 void apply(osg::Switch& switchNode) override;
+                void apply(osg::Geometry&) override { }
 
                 bool isOperationPermissible(osg::Node& node);
 
@@ -376,6 +381,7 @@ class Optimizer
 
             bool isOperationPermissible(osg::Group& node);
 
+            void apply(osg::Geometry&) override { }
             void apply(osg::Group& group) override;
             void apply(osg::LOD& lod) override;
             void apply(osg::Switch& switchNode) override;
@@ -409,10 +415,10 @@ class Optimizer
                     return _targetMaximumNumberOfVertices;
                 }
 
-                void pushStateSet(osg::StateSet* stateSet);
+                bool pushStateSet(osg::StateSet* stateSet);
                 void popStateSet();
                 void checkAlphaBlendingActive();
-
+                void apply(osg::Geometry&) override { }
                 void apply(osg::Group& group) override;
                 void apply(osg::Billboard&) override { /* don't do anything*/ }