From Geoff Michel, added normal definition for tesselation

include/osgUtil/Tesselator

@@ -77,6 +77,14 @@ class OSGUTIL_EXPORT Tesselator : public osg::Referenced
           * as well as Polygons so as to not break old codes relying on this function name. */
         void retesselatePolygons(osg::Geometry &cxgeom);
 
+        /** Define the normal to the tesselated polygon - this provides a hint how to
+         *  tesselate the contours; see gluTessNormal in red book or man pages.
+         *  GWM July 2005. Can improve teselation
+         *  "For example, if you know that all polygons lie in the x-y plane, 
+         *   call gluTessNormal(tess, 0.0, 0.0, 1.0) before rendering any polygons."
+         */
+        void setTesselationNormal(const osg::Vec3 norm) { tessNormal=norm;}
+
         osg::Geometry::PrimitiveSetList  getContours() { return _Contours;}
 
         typedef std::vector<osg::Vec3*> VertexPointList;
@@ -225,6 +233,9 @@ class OSGUTIL_EXPORT Tesselator : public osg::Referenced
 
         /** count number of primitives in a geometry to get right no. of norms/colurs etc for per_primitive attributes. */
         unsigned int _index;
+
+        /** the gluTessNormal for tesselation hint */
+        osg::Vec3 tessNormal;
 };
 
 }

src/osgUtil/Tesselator.cpp

@@ -35,8 +35,6 @@ Tesselator::~Tesselator()
     reset();
 }
 
-
-
 void Tesselator::beginTesselation()
 {
     reset();
@@ -48,6 +46,7 @@ void Tesselator::beginTesselation()
     gluTessCallback(_tobj, GLU_TESS_END_DATA,    (GLU_TESS_CALLBACK) endCallback);
     gluTessCallback(_tobj, GLU_TESS_COMBINE_DATA,(GLU_TESS_CALLBACK) combineCallback);
     gluTessCallback(_tobj, GLU_TESS_ERROR_DATA,  (GLU_TESS_CALLBACK) errorCallback);
+    if (tessNormal.length()>0.0) gluTessNormal(_tobj, tessNormal.x(), tessNormal.y(), tessNormal.z());
 
     gluTessBeginPolygon(_tobj,this);
 }