From Chris Xennon, add support for billboard intersections + fix to addLineSegments.

Small addition from Robert Osfield of setLODSelectionMode(..) to control
the LOD selection behavior.

include/osgUtil/IntersectVisitor

@@ -110,6 +110,28 @@ class OSGUTIL_EXPORT IntersectVisitor : public osg::NodeVisitor
 
         bool hits();
 
+        enum LODSelectionMode
+        {
+            USE_HEIGHEST_LEVEL_OF_DETAIL,
+            USE_SEGMENT_START_POINT_AS_EYE_POINT_FOR_LOD_LEVEL_SELECTION
+        };
+        
+        void setLODSelectionMode(LODSelectionMode mode) { _lodSelectionMode = mode; }
+        LODSelectionMode getLODSelectionMode() const { return _lodSelectionMode; }
+
+        /** Set the eye point in local coordinates.
+          * This is a pseudo-EyePoint for billboarding and LOD purposes.
+          * It is copied from the Start point of the most-recently-added segment
+          * of the intersection ray set (IntersectState::_segList). */
+        void setEyePoint(const osg::Vec3& eye) { _pseudoEyePoint = eye; }
+
+        virtual osg::Vec3 getEyePoint() const { return _pseudoEyePoint; }
+
+
+        /** Get the distance from a point to the eye point, distance value in local coordinate system.
+          * This is calculated using the pseudo-EyePoint (above) when doing LOD calculcations. */
+        virtual float getDistanceToEyePoint(const osg::Vec3& pos, bool withLODScale) const;
+
         virtual void apply(osg::Node&);
         virtual void apply(osg::Geode& node);
         virtual void apply(osg::Billboard& node);
@@ -166,6 +188,9 @@ class OSGUTIL_EXPORT IntersectVisitor : public osg::NodeVisitor
 
         osg::NodePath               _nodePath;
         LineSegmentHitListMap       _segHitList;
+        
+        LODSelectionMode            _lodSelectionMode;
+        osg::Vec3                   _pseudoEyePoint;
 };
 
 }

src/osgUtil/IntersectVisitor.cpp

@@ -150,8 +150,15 @@ bool IntersectVisitor::IntersectState::isCulled(const BoundingBox& bb,LineSegmen
 
 IntersectVisitor::IntersectVisitor()
 {
+
     // overide the default node visitor mode.
     setTraversalMode(NodeVisitor::TRAVERSE_ACTIVE_CHILDREN);
+    
+    // Initialize eyepoint to 0,0,0
+    setEyePoint(Vec3(0.0f,0.0f,0.0f));
+
+    setLODSelectionMode(USE_HEIGHEST_LEVEL_OF_DETAIL); // orignal IntersectVisitor behavior
+    //setLODSelectionMode(USE_SEGMENT_START_POINT_AS_EYE_POINT_FOR_LOD_LEVEL_SELECTION);
 
     reset();
 }
@@ -174,6 +181,21 @@ void IntersectVisitor::reset()
 
 }
 
+float IntersectVisitor::getDistanceToEyePoint(const Vec3& pos, bool /*withLODScale*/) const
+{
+    if (_lodSelectionMode==USE_SEGMENT_START_POINT_AS_EYE_POINT_FOR_LOD_LEVEL_SELECTION)
+    {
+        // LODScale is not available to IntersectVisitor, so we ignore the withLODScale argument
+        //if (withLODScale) return (pos-getEyePoint()).length()*getLODScale();
+        //else return (pos-getEyePoint()).length();
+        return (pos-getEyePoint()).length();
+    }
+    else
+    {
+        return 0.0f;
+    }
+}
+
 
 bool IntersectVisitor::hits()
 {
@@ -198,16 +220,19 @@ void IntersectVisitor::addLineSegment(LineSegment* seg)
         return;
     }
 
+    IntersectState* cis = _intersectStateStack.back().get();
+    
+    setEyePoint(seg->start()); // set start of line segment to be pseudo EyePoint for billboarding and LOD purposes
+
     // first check to see if segment has already been added.
-    for(LineSegmentHitListMap::iterator itr = _segHitList.begin();
-        itr != _segHitList.end();
+    for(IntersectState::LineSegmentList::iterator itr = cis->_segList.begin();
+        itr != cis->_segList.end();
         ++itr)
     {
         if (itr->first == seg) return;
     }
 
     // create a new segment transformed to local coordintes.
-    IntersectState* cis = _intersectStateStack.back().get();
     LineSegment* ns = new LineSegment;
 
     if (cis->_inverse.valid()) ns->mult(*seg,*(cis->_inverse));
@@ -293,6 +318,7 @@ void IntersectVisitor::leaveNode()
 }
 
 
+
 void IntersectVisitor::apply(Node& node)
 {
     if (!enterNode(node)) return;
@@ -572,6 +598,23 @@ void IntersectVisitor::apply(Billboard& node)
 {
     if (!enterNode(node)) return;
 
+    // IntersectVisitor doesn't have getEyeLocal(), can we use NodeVisitor::getEyePoint()?
+    const Vec3& eye_local = getEyePoint();
+
+    for(unsigned int i = 0; i < node.getNumDrawables(); i++ )
+    {
+        const Vec3& pos = node.getPosition(i);
+        osg::ref_ptr<RefMatrix> billboard_matrix = new RefMatrix;
+        node.computeMatrix(*billboard_matrix,eye_local,pos);
+
+        pushMatrix(*billboard_matrix);
+
+        intersect(*node.getDrawable(i));
+	
+        popMatrix();
+
+    }
+
     leaveNode();
 }