From Farshid Lashkari, "Another update. I added a LIMIT_NEAREST enum which implements your previous suggestion of rejecting bounding volumes further from the nearest existing intersection. I only implemented this for LineSegmentIntersector. I'd appreciate it if you could double check the math I added to LineSegmentIntersector::intersects() for checking if the bounding sphere is further away. The results of this are promising. I'm getting noticeable performance increase for line intersections with scenes containing many drawables.

"

include/osgUtil/IntersectionVisitor

@@ -42,8 +42,17 @@ class Intersector : public osg::Referenced
             MODEL
         };
 
+        enum IntersectionLimit
+        {
+            NO_LIMIT,
+            LIMIT_ONE_PER_DRAWABLE,
+            LIMIT_ONE,
+            LIMIT_NEAREST
+        };
+
         Intersector(CoordinateFrame cf=MODEL):
             _coordinateFrame(cf),
+            _intersectionLimit(NO_LIMIT),
             _disabledCount(0) {}
 
 
@@ -51,6 +60,9 @@ class Intersector : public osg::Referenced
 
         CoordinateFrame getCoordinateFrame() const { return _coordinateFrame; }
 
+        void setIntersectionLimit(IntersectionLimit limit) { _intersectionLimit = limit; }
+
+        IntersectionLimit getIntersectionLimit() const { return _intersectionLimit; }
 
         virtual Intersector* clone(osgUtil::IntersectionVisitor& iv) = 0;
 
@@ -70,9 +82,12 @@ class Intersector : public osg::Referenced
 
         inline void decrementDisabledCount() { if (_disabledCount>0) --_disabledCount; }
 
+        inline bool reachedLimit() { return _intersectionLimit == LIMIT_ONE && containsIntersections(); }
+
    protected:
 
         CoordinateFrame _coordinateFrame;
+        IntersectionLimit _intersectionLimit;
         unsigned int    _disabledCount;
 
 };

include/osgUtil/LineSegmentIntersector

@@ -91,7 +91,7 @@ class OSGUTIL_EXPORT LineSegmentIntersector : public Intersector
 
         virtual void reset();
 
-        virtual bool containsIntersections() { return !_intersections.empty(); }
+        virtual bool containsIntersections() { return !getIntersections().empty(); }
 
     protected:
 

include/osgUtil/PlaneIntersector

@@ -86,7 +86,7 @@ class OSGUTIL_EXPORT PlaneIntersector : public Intersector
 
         virtual void reset();
 
-        virtual bool containsIntersections() { return !_intersections.empty(); }
+        virtual bool containsIntersections() { return !getIntersections().empty(); }
 
     protected:
 

include/osgUtil/PolytopeIntersector

@@ -109,7 +109,7 @@ class OSGUTIL_EXPORT PolytopeIntersector : public Intersector
 
         virtual void reset();
 
-        virtual bool containsIntersections() { return !_intersections.empty(); }
+        virtual bool containsIntersections() { return !getIntersections().empty(); }
 
     protected:
 

src/osgUtil/LineSegmentIntersector.cpp

@@ -63,6 +63,7 @@ namespace LineSegmentIntersectorUtils
         int         _index;
         float       _ratio;
         bool        _hit;
+        bool        _limitOneIntersection;
 
         TriangleIntersections _intersections;
 
@@ -72,6 +73,7 @@ namespace LineSegmentIntersectorUtils
             _index = 0;
             _ratio = 0.0f;
             _hit = false;
+            _limitOneIntersection = false;
         }
 
         void set(const osg::Vec3d& start, osg::Vec3d& end, float ratio=FLT_MAX)
@@ -90,6 +92,8 @@ namespace LineSegmentIntersectorUtils
         {
             ++_index;
 
+            if (_limitOneIntersection && _hit) return;
+
             if (v1==v2 || v2==v3 || v1==v3) return;
 
             osg::Vec3 v12 = v2-v1;
@@ -238,6 +242,7 @@ Intersector* LineSegmentIntersector::clone(osgUtil::IntersectionVisitor& iv)
     {
         osg::ref_ptr<LineSegmentIntersector> lsi = new LineSegmentIntersector(_start, _end);
         lsi->_parent = this;
+        lsi->_intersectionLimit = this->_intersectionLimit;
         return lsi.release();
     }
 
@@ -271,11 +276,13 @@ Intersector* LineSegmentIntersector::clone(osgUtil::IntersectionVisitor& iv)
 
     osg::ref_ptr<LineSegmentIntersector> lsi = new LineSegmentIntersector(_start * inverse, _end * inverse);
     lsi->_parent = this;
+    lsi->_intersectionLimit = this->_intersectionLimit;
     return lsi.release();
 }
 
 bool LineSegmentIntersector::enter(const osg::Node& node)
 {
+    if (reachedLimit()) return false;
     return !node.isCullingActive() || intersects( node.getBound() );
 }
 
@@ -286,6 +293,8 @@ void LineSegmentIntersector::leave()
 
 void LineSegmentIntersector::intersect(osgUtil::IntersectionVisitor& iv, osg::Drawable* drawable)
 {
+    if (reachedLimit()) return;
+
     osg::Vec3d s(_start), e(_end);
     if ( !intersectAndClip( s, e, drawable->getBound() ) ) return;
 
@@ -354,6 +363,7 @@ void LineSegmentIntersector::intersect(osgUtil::IntersectionVisitor& iv, osg::Dr
 
     osg::TriangleFunctor<LineSegmentIntersectorUtils::TriangleIntersector> ti;
     ti.set(s,e);
+    ti._limitOneIntersection = (_intersectionLimit == LIMIT_ONE_PER_DRAWABLE || _intersectionLimit == LIMIT_ONE);
     drawable->accept(ti);
 
     if (ti._hit)
@@ -371,6 +381,14 @@ void LineSegmentIntersector::intersect(osgUtil::IntersectionVisitor& iv, osg::Dr
             // remap ratio into _start, _end range
             double remap_ratio = ((s-_start).length() + ratio * (e-s).length() )/(_end-_start).length();
 
+            if ( _intersectionLimit == LIMIT_NEAREST && !getIntersections().empty() )
+            {
+                if (remap_ratio >= getIntersections().begin()->ratio )
+                    break;
+                else
+                    getIntersections().clear();
+            }
+
             LineSegmentIntersectorUtils::TriangleIntersection& triHit = thitr->second;
 
             Intersection hit;
@@ -450,6 +468,12 @@ bool LineSegmentIntersector::intersects(const osg::BoundingSphere& bs)
 
     if (r1>=1.0 && r2>=1.0) return false;
 
+    if (_intersectionLimit == LIMIT_NEAREST && !getIntersections().empty())
+    {
+        double ratio = (sm.length() - bs._radius) / sqrt(a);
+        if (ratio >= getIntersections().begin()->ratio) return false;
+    }
+
     // passed all the rejection tests so line must intersect bounding sphere, return true.
     return true;
 }

src/osgUtil/PlaneIntersector.cpp

@@ -359,6 +359,7 @@ namespace PlaneIntersectorUtils
         osg::ref_ptr<osg::RefMatrix>        _matrix;
         bool _recordHeightsAsAttributes;
         osg::ref_ptr<osg::EllipsoidModel>   _em;
+        bool _limitOneIntersection;
 
         PolylineConnector _polylineConnector;
 
@@ -366,6 +367,7 @@ namespace PlaneIntersectorUtils
         TriangleIntersector()
         {
             _hit = false;
+            _limitOneIntersection = false;
         }
 
         void set(const osg::Plane& plane, const osg::Polytope& polytope, osg::RefMatrix* matrix, bool recordHeightsAsAttributes, osg::EllipsoidModel* em)
@@ -440,6 +442,8 @@ namespace PlaneIntersectorUtils
         inline void operator () (const osg::Vec3& v1,const osg::Vec3& v2,const osg::Vec3& v3, bool)
         {
 
+            if (_limitOneIntersection && _hit) return;
+
             double d1 = _plane.distance(v1);
             double d2 = _plane.distance(v2);
             double d3 = _plane.distance(v3);
@@ -590,6 +594,7 @@ Intersector* PlaneIntersector::clone(osgUtil::IntersectionVisitor& iv)
     {
         osg::ref_ptr<PlaneIntersector> pi = new PlaneIntersector(_plane, _polytope);
         pi->_parent = this;
+        pi->_intersectionLimit = this->_intersectionLimit;
         pi->_recordHeightsAsAttributes = _recordHeightsAsAttributes;
         pi->_em = _em;
         return pi.release();
@@ -628,6 +633,7 @@ Intersector* PlaneIntersector::clone(osgUtil::IntersectionVisitor& iv)
 
     osg::ref_ptr<PlaneIntersector> pi = new PlaneIntersector(plane, transformedPolytope);
     pi->_parent = this;
+    pi->_intersectionLimit = this->_intersectionLimit;
     pi->_recordHeightsAsAttributes = _recordHeightsAsAttributes;
     pi->_em = _em;
     return pi.release();
@@ -635,6 +641,7 @@ Intersector* PlaneIntersector::clone(osgUtil::IntersectionVisitor& iv)
 
 bool PlaneIntersector::enter(const osg::Node& node)
 {
+    if (reachedLimit()) return false;
     return !node.isCullingActive() ||
            ( _plane.intersect(node.getBound())==0 && _polytope.contains(node.getBound()) );
 }
@@ -650,6 +657,7 @@ void PlaneIntersector::intersect(osgUtil::IntersectionVisitor& iv, osg::Drawable
 {
     // OSG_NOTICE<<"PlaneIntersector::intersect(osgUtil::IntersectionVisitor& iv, osg::Drawable* drawable)"<<std::endl;
 
+    if (reachedLimit()) return;
     if ( _plane.intersect( drawable->getBound() )!=0 ) return;
     if ( !_polytope.contains( drawable->getBound() ) ) return;
 
@@ -657,6 +665,7 @@ void PlaneIntersector::intersect(osgUtil::IntersectionVisitor& iv, osg::Drawable
 
     osg::TriangleFunctor<PlaneIntersectorUtils::TriangleIntersector> ti;
     ti.set(_plane, _polytope, iv.getModelMatrix(), _recordHeightsAsAttributes, _em.get());
+    ti._limitOneIntersection = (_intersectionLimit == LIMIT_ONE_PER_DRAWABLE || _intersectionLimit == LIMIT_ONE);
     drawable->accept(ti);
 
     ti._polylineConnector.consolidatePolylineLists();

src/osgUtil/PolytopeIntersector.cpp

@@ -88,6 +88,7 @@ namespace PolytopeIntersectorUtils
         PolytopePrimitiveIntersector() :
             _index(0),
              _dimensionMask( PolytopeIntersector::AllDims ),
+             _limitOneIntersection( false ),
             _candidates(20) {}
 
             void addIntersection(unsigned int index, const CandList_t& cands) {
@@ -130,6 +131,9 @@ namespace PolytopeIntersectorUtils
         {
             ++_index;
             if ((_dimensionMask & PolytopeIntersector::DimZero) == 0) return;
+
+            if (_limitOneIntersection && !intersections.empty()) return;
+
             for (PlaneList::const_iterator it=_planes.begin(); it!=_planes.end(); ++it)
             {
                 const osg::Plane& plane=*it;
@@ -147,6 +151,8 @@ namespace PolytopeIntersectorUtils
             ++_index;
             if ((_dimensionMask & PolytopeIntersector::DimOne) == 0) return;
 
+            if (_limitOneIntersection && !intersections.empty()) return;
+
             PlaneMask selector_mask = 0x1;
             PlaneMask inside_mask = 0x0;
             _candidates.clear();
@@ -210,6 +216,8 @@ namespace PolytopeIntersectorUtils
             ++_index;
             if ((_dimensionMask & PolytopeIntersector::DimTwo) == 0) return;
 
+            if (_limitOneIntersection && !intersections.empty()) return;
+
             PlaneMask selector_mask = 0x1;
             PlaneMask inside_mask = 0x0;
             _candidates.clear();
@@ -354,6 +362,8 @@ namespace PolytopeIntersectorUtils
 
         void setDimensionMask(unsigned int dimensionMask) { _dimensionMask = dimensionMask; }
 
+        void setLimitOneIntersection(bool limit) { _limitOneIntersection = limit; }
+
         void setPolytope(osg::Polytope& polytope, osg::Plane& referencePlane)
         {
             _referencePlane = referencePlane;
@@ -426,6 +436,7 @@ namespace PolytopeIntersectorUtils
         unsigned int _index;
 
         private:
+        bool _limitOneIntersection;
         unsigned int _dimensionMask;
         PlaneList _planes;                   ///< active planes extracted from polytope
         LinesList _lines;                    ///< all intersection lines of two polytope planes
@@ -492,6 +503,7 @@ Intersector* PolytopeIntersector::clone(osgUtil::IntersectionVisitor& iv)
     {
         osg::ref_ptr<PolytopeIntersector> pi = new PolytopeIntersector(_polytope);
         pi->_parent = this;
+        pi->_intersectionLimit = this->_intersectionLimit;
         pi->_dimensionMask = this->_dimensionMask;
         pi->_referencePlane = this->_referencePlane;
         return pi.release();
@@ -527,6 +539,7 @@ Intersector* PolytopeIntersector::clone(osgUtil::IntersectionVisitor& iv)
 
     osg::ref_ptr<PolytopeIntersector> pi = new PolytopeIntersector(transformedPolytope);
     pi->_parent = this;
+    pi->_intersectionLimit = this->_intersectionLimit;
     pi->_dimensionMask = this->_dimensionMask;
     pi->_referencePlane = this->_referencePlane;
     pi->_referencePlane.transformProvidingInverse(matrix);
@@ -535,6 +548,7 @@ Intersector* PolytopeIntersector::clone(osgUtil::IntersectionVisitor& iv)
 
 bool PolytopeIntersector::enter(const osg::Node& node)
 {
+    if (reachedLimit()) return false;
     return !node.isCullingActive() || _polytope.contains( node.getBound() );
 }
 
@@ -547,11 +561,14 @@ void PolytopeIntersector::leave()
 
 void PolytopeIntersector::intersect(osgUtil::IntersectionVisitor& iv, osg::Drawable* drawable)
 {
+    if (reachedLimit()) return;
+
     if ( !_polytope.contains( drawable->getBound() ) ) return;
 
     osg::TemplatePrimitiveFunctor<PolytopeIntersectorUtils::PolytopePrimitiveIntersector> func;
     func.setPolytope( _polytope, _referencePlane );
     func.setDimensionMask( _dimensionMask );
+    func.setLimitOneIntersection( _intersectionLimit == LIMIT_ONE_PER_DRAWABLE || _intersectionLimit == LIMIT_ONE );
 
     drawable->accept(func);