Added PolytopeVisitor to SphereSegment.cpp to help cull down to only drawables

that intersect with the frustum of the SphereSegment. PolytopeVisitor may
eventually be pulled out to be more generally used along the lines of osgUtil::IntersectVisitor.

src/osgSim/SphereSegment.cpp

@@ -2,6 +2,8 @@
 #include <osg/Notify>
 #include <osg/CullFace>
 #include <osg/LineWidth>
+#include <osg/Transform>
+#include <osg/io_utils>
 
 #include <algorithm>
 
@@ -961,9 +963,129 @@ void SphereSegment::setAllColors(const osg::Vec4& c)
     setSideColor(c);
 }
 
+////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////
+//
+// SphereSegment interesection code.
+
+class PolytopeVisitor : public osg::NodeVisitor
+{
+    public:
+    
+        typedef std::pair<osg::Matrix, osg::Polytope> MatrixPolytopePair;
+        typedef std::vector<MatrixPolytopePair> PolytopeStack;
+    
+        struct Hit
+        {
+            Hit(const osg::Matrix& matrix, osg::NodePath& nodePath, osg::Drawable* drawable):
+                _matrix(matrix),
+                _nodePath(nodePath),
+                _drawable(drawable) {}
+
+            osg::Matrix                 _matrix;
+            osg::NodePath               _nodePath;
+            osg::ref_ptr<osg::Drawable> _drawable;
+        };
+    
+        typedef std::vector<Hit> HitList;
+
+
+        PolytopeVisitor(const osg::Matrix& matrix, const osg::Polytope& polytope):
+            osg::NodeVisitor(osg::NodeVisitor::TRAVERSE_ACTIVE_CHILDREN)
+        {
+            _polytopeStack.push_back(MatrixPolytopePair());
+            _polytopeStack.back().first = matrix;
+            _polytopeStack.back().second.setAndTransformProvidingInverse(polytope, _polytopeStack.back().first);
+        }
+        
+        void reset()
+        {
+            _polytopeStack.clear();
+            _hits.clear();
+        }
+            
+        void apply(osg::Node& node)
+        {
+            if (_polytopeStack.back().second.contains(node.getBound()))
+            {
+                traverse(node);
+            }
+        }
+
+        void apply(osg::Transform& transform)
+        {
+            if (_polytopeStack.back().second.contains(transform.getBound()))
+            {
+                const osg::Polytope& polytope = _polytopeStack.front().second;
+
+                osg::Matrix matrix = _polytopeStack.back().first;
+                transform.computeLocalToWorldMatrix(matrix, this);
+                
+                _polytopeStack.push_back(MatrixPolytopePair());
+                _polytopeStack.back().first = matrix;
+                _polytopeStack.back().second.setAndTransformProvidingInverse(polytope, matrix);
+
+                traverse(transform);
+                
+                _polytopeStack.back();
+            }
+        }
+
+        void apply(osg::Geode& node)
+        {
+            if (_polytopeStack.back().second.contains(node.getBound()))
+            {
+                for(unsigned int i=0; i<node.getNumDrawables(); ++i)
+                {
+                    if (_polytopeStack.back().second.contains(node.getDrawable(i)->getBound()))
+                    {
+                        _hits.push_back(Hit(_polytopeStack.back().first,getNodePath(),node.getDrawable(i)));
+                    }
+
+                }
+            
+                traverse(node);
+            }
+        }
+
+        HitList& getHits() { return _hits; }
+
+    protected:
+        
+        PolytopeStack   _polytopeStack;
+        HitList         _hits;
+
+};
+
+
 SphereSegment::LineList SphereSegment::computeIntersection(osg::Node* subgraph, const osg::Matrixd& transform)
 {
     osg::notify(osg::NOTICE)<<"Creating line intersection between sphere segment and subgraph."<<std::endl;
     SphereSegment::LineList lines;
+    
+    osg::BoundingBox bb = getBoundingBox();
+
+    osg::Polytope polytope;
+    polytope.add(osg::Plane(1.0,0.0,0.0,-bb.xMin())); 
+    polytope.add(osg::Plane(-1.0,0.0,0.0,bb.xMax())); 
+    polytope.add(osg::Plane(0.0,1.0,0.0,-bb.yMin())); 
+    polytope.add(osg::Plane(0.0,-1.0,0.0,bb.yMax())); 
+    polytope.add(osg::Plane(0.0,0.0,1.0,-bb.zMin())); 
+    polytope.add(osg::Plane(0.0,0.0,-1.0,bb.zMax())); 
+    
+    osg::Plane pl;
+    pl.set(osg::Vec3(-1.0,0.0,0.0), bb.corner(0));
+    PolytopeVisitor polytopeVisitor(transform, polytope);
+    
+    subgraph->accept(polytopeVisitor);
+
+    if (polytopeVisitor.getHits().empty())
+    {
+        osg::notify(osg::NOTICE)<<"No hits found."<<std::endl;
+    }
+    else
+    {
+        osg::notify(osg::NOTICE)<<"Hits found. "<<polytopeVisitor.getHits().size()<<std::endl;
+    }
+
     return lines;
 }