OpenSceneGraph/include/osg/Drawable

//C++ header - Open Scene Graph - Copyright (C) 1998-2002 Robert Osfield
//Distributed under the terms of the GNU Library General Public License (LGPL)
//as published by the Free Software Foundation.

#ifndef OSG_DRAWABLE
#define OSG_DRAWABLE 1

#include <osg/BoundingBox>
#include <osg/State>
#include <osg/Types>
#include <osg/NodeVisitor>
#include <osg/Shape>

#include <vector>
#include <map>
#include <set>

namespace osg {

class Vec2;
class Vec3;
class Vec4;
class UByte4;
class Geometry;

// this is define to alter the way display lists are compiled inside the
// the draw method, it has been found that the NVidia drivers fail completely
// to optimize COMPILE_AND_EXECUTE in fact make it go slower than for no display 
// lists, but optimize a separate COMPILE very well?!  Define it as default
// the use of a sperate COMPILE, then glCallList rather than use COMPILE_AND_EXECUTE.

#define USE_SEPARATE_COMPILE_AND_EXECUTE

/** Pure virtual base class for drawable Geometry.  Contains no drawing primitives
    directly, these are provided by subclasses such as osg::Geometry. State attributes 
    for a Drawable are maintained in StateSet which the Drawable maintains
    a referenced counted pointer to.  Both Drawable's and StateSet's can 
    be shared for optimal memory usage and graphics performance.
*/
class SG_EXPORT Drawable : public Object
{
    public:

        Drawable();

        /** Copy constructor using CopyOp to manage deep vs shallow copy.*/
        Drawable(const Drawable& drawable,const CopyOp& copyop=CopyOp::SHALLOW_COPY);

        virtual bool isSameKindAs(const Object* obj) const { return dynamic_cast<const Drawable*>(obj)!=NULL; }
        virtual const char* libraryName() const { return "osg"; }
        virtual const char* className() const { return "Drawable"; }

        /** convert 'this' into a Geometry pointer if Drawable is a Geometry, otherwise return 0.
          * Equivalent to dynamic_cast<Geometry*>(this).*/
        virtual Geometry* asGeometry() { return 0; }
        /** convert 'const this' into a const Geometry pointer if Drawable is a Geometry, otherwise return 0.
          * Equivalent to dynamic_cast<const Geometry*>(this).*/
        virtual const Geometry* asGeometry() const { return 0; }


        /** A vector of osg::Node pointers which is used to store the parent(s) of drawable.*/
        typedef std::vector<Node*> ParentList;

        /** Get the parent list of drawable. */
        inline const ParentList& getParents() const { return _parents; }

        /** Get the a copy of parent list of node. A copy is returned to 
          * prevent modification of the parent list.*/
        inline ParentList getParents() { return _parents; }

        /** Get a single parent of Drawable.
          * @param i index of the parent to get.
          * @return the parent i.
          */
        inline Node* getParent(unsigned int i)  { return _parents[i]; }
        /** Get a single const parent of Drawable.
          * @param i index of the parent to get.
          * @return the parent i.
          */
        inline const Node* getParent(unsigned int i) const  { return _parents[i]; }

        /**
         * Get the number of parents of node.
         * @return the number of parents of this node.
         */
        inline unsigned int getNumParents() const { return _parents.size(); }



        /** Set the StateSet attached to the Drawable.
            Previously attached StateSet are automatically unreferenced on 
            assignment of a new drawstate.*/
        inline void setStateSet(StateSet *state) { _stateset = state; }
        
        /** Get the attached StateSet.*/
        inline StateSet* getStateSet() { return _stateset.get();}

        /** Get the attached const StateSet.*/
        inline const StateSet* getStateSet() const { return _stateset.get();}

        /** Get the attached const StateSet, 
          * if one is not already attach create one, 
          * attach it to the drawable and return a pointer to it.*/
        StateSet* getOrCreateStateSet();


        /** Dirty the bounding box, forcing a computeBound() on the next call
          * to getBound(). Should be called in the internal geometry of the Drawable
          * is modified.*/        
        void dirtyBound();

        /** get bounding box of geoset. 
          * Note, now made virtual to make it possible to implement user-drawn
          * objects albeit so what crudely, to be improved later.
          */
        inline const BoundingBox& getBound() const
        {
            if( !_bbox_computed)
                computeBound();
            return _bbox;
        }


    	/** Set the Shape of the drawable. The shape can be used to
	  * speed up collision detection or as a guide for produral
	  * geometry generation - see osg::ProduralGeometry.*/
    	inline void setShape(Shape* shape) { _shape = shape; }

    	/** Get the Shape of the Drawable.*/
    	inline Shape* getShape() { return _shape.get(); }
	
    	/** Get the const Shape of the const Drawable.*/
    	inline const Shape* getShape() const { return _shape.get(); }



        /** Set the drawable to it can or cannot be used in conjunction with OpenGL
          * display lists.  With set to true, calls to Drawable::setUseDisplayList,
          * whereas when set to false, no display lists can be created and calls
          * to setUseDisplayList are ignored, and a warning is produced.  The later
          * is typically used to guard against the switching on of display lists
          * on objects with dynamic internal data such as continuous Level of Detail
          * algorithms.*/
        void setSupportsDisplayList(bool flag);
      
        /** Get whether display lists are supported for this drawable instance.*/  
        inline bool getSupportsDisplayList() const { return _supportsDisplayList; }


        /** When set to true, force the draw method to use OpenGL Display List for rendering.
            If false rendering directly.  If the display list has not been already
            compile the next call to draw will automatically create the display list.*/
        void setUseDisplayList(bool flag);

        /** Return whether OpenGL display lists are being used for rendering.*/
        inline bool getUseDisplayList() const { return _useDisplayList; }

        /** Force a recompile on next draw() of any OpenGL display list associated with this geoset.*/
        void dirtyDisplayList();



        /** draw OpenGL primitives. 
          * If the drawable has _useDisplayList set to true then use an OpenGL display
          * list, automatically compiling one if required.
          * Otherwise call drawImplementation().
          * Note, draw method should *not* be overridden in subclasses as it 
          * manages the optional display list.
          */
        inline void draw(State& state);
        
        /** Immediately compile this drawable into an OpenGL Display List.
            Note I, operation is ignored if _useDisplayList to false.
            Note II, compile is not intended to be overridden in subclasses.*/
        void compile(State& state);


        struct AppCallback : public osg::Referenced
        {
                /** do customized app code.*/
                virtual void app(osg::NodeVisitor *visitor, osg::Drawable* drawable) = 0;
        };

        /** Set the AppCallback which allows users to attach customize the undating of an object during the app traversal.*/
        void setAppCallback(AppCallback* ac);
        
        /** Get the non const AppCallback.*/
        AppCallback* getAppCallback() { return _appCallback.get(); }
        
        /** Get the const AppCallback.*/
        const AppCallback* getAppCallback() const { return _appCallback.get(); }


        struct CullCallback : public osg::Referenced
        {
                /** do customized cull code.*/
                virtual bool cull(osg::NodeVisitor *visitor, osg::Drawable* drawable, osg::State *state=NULL) const = 0;
        };

        /** Set the CullCallback which allows users to attach customize the culling of Drawable during the cull traversal.*/
        void setCullCallback(CullCallback* cc) { _cullCallback=cc; }
        
        /** Get the non const CullCallback.*/
        CullCallback* getCullCallback() { return _cullCallback.get(); }
        
        /** Get the const CullCallback.*/
        const CullCallback* getCullCallback() const { return _cullCallback.get(); }


        /** Callback attached to an Drawable which allows the users to customize the drawing of an exist Drawable object.
          * The draw callback is implement as a replacement to the Drawable's own drawImplementation() method, if the
          * the user intends to decorate the exist draw code then simple call the drawable->drawImplementation() from
          * with the callbacks drawImplementation() method.  This allows the users to do both pre and post callbacks
          * without fuss and can even diable the inner draw in required.*/
        struct DrawCallback : public osg::Referenced
        {
            /** do customized draw code.*/
            virtual void drawImplementation(State& state,const osg::Drawable* drawable) const = 0;
        };

        /** Set the DrawCallback which allows users to attach customize the drawing of existing Drawable object.*/
        void setDrawCallback(DrawCallback* dc) { _drawCallback=dc; dirtyDisplayList(); }
        
        /** Get the non const DrawCallback.*/
        DrawCallback* getDrawCallback() { return _drawCallback.get(); }
        
        /** Get the const DrawCallback.*/
        const DrawCallback* getDrawCallback() const { return _drawCallback.get(); }



        /** draw directly ignoring an OpenGL display list which could be attached.
          * This is the internal draw method which does the drawing itself,
          * and is the method to override when deriving from Drawable.
          */
        virtual void drawImplementation(State& state) const = 0;



        /** use deleteDisplayList instead of glDeleteList to allow
          * OpenGL display list to cached until they can be deleted
          * by the OpenGL context in which they were created, specified
          * by contextID.*/
        static void deleteDisplayList(uint contextID,uint globj);
        
        /** flush all the cached display list which need to be deleted
          * in the OpenGL context related to contextID.*/
        static void flushDeletedDisplayLists(uint contextID);


        enum AttributeType
        {
            VERTICES,
            NORMALS,
            COLORS,
            TEXTURE_COORDS,
            TEXTURE_COORDS_0    = TEXTURE_COORDS,
            TEXTURE_COORDS_1    = TEXTURE_COORDS_0+1,
            TEXTURE_COORDS_2    = TEXTURE_COORDS_0+2,
            TEXTURE_COORDS_3    = TEXTURE_COORDS_0+3,
            TEXTURE_COORDS_4    = TEXTURE_COORDS_0+4,
            TEXTURE_COORDS_5    = TEXTURE_COORDS_0+5,
            TEXTURE_COORDS_6    = TEXTURE_COORDS_0+6,
            TEXTURE_COORDS_7    = TEXTURE_COORDS_0+7 
            // only eight texture coord examples provided here, but underlying code can handle any no of texure units,
            // simply co them as (TEXTURE_COORDS_0+unit).
        };
        
        class AttributeFunctor
        {
        public:
        
            virtual ~AttributeFunctor() {}
            
            virtual void apply(AttributeType,unsigned int,GLbyte*) {}
            virtual void apply(AttributeType,unsigned int,GLshort*) {}
            virtual void apply(AttributeType,unsigned int,GLint*) {}

            virtual void apply(AttributeType,unsigned int,GLubyte*) {}
            virtual void apply(AttributeType,unsigned int,GLushort*) {}
            virtual void apply(AttributeType,unsigned int,GLuint*) {}

            virtual void apply(AttributeType,unsigned int,float*) {}
            virtual void apply(AttributeType,unsigned int,Vec2*) {}
            virtual void apply(AttributeType,unsigned int,Vec3*) {}
            virtual void apply(AttributeType,unsigned int,Vec4*) {}
            virtual void apply(AttributeType,unsigned int,UByte4*) {}
        };
        
        
        /** return true if the Drawable subclass supports accept(AttributeFunctor&).*/
        virtual bool supports(AttributeFunctor&) const { return false; }

        /** accept an AttributeFunctor and call its methods to tell it about the interal attributes that this Drawable has.
          * return true if functor handled by drawable, return false on failure of drawable to generate functor calls.*/
        virtual void accept(AttributeFunctor&) {}
        

        class ConstAttributeFunctor
        {
        public:
        
            virtual ~ConstAttributeFunctor() {}
            
            virtual void apply(AttributeType,const unsigned int,const GLbyte*) {}
            virtual void apply(AttributeType,const unsigned int,const GLshort*) {}
            virtual void apply(AttributeType,const unsigned int,const GLint*) {}

            virtual void apply(AttributeType,const unsigned int,const GLubyte*) {}
            virtual void apply(AttributeType,const unsigned int,const GLushort*) {}
            virtual void apply(AttributeType,const unsigned int,const GLuint*) {}

            virtual void apply(AttributeType,const unsigned int,const float*) {}
            virtual void apply(AttributeType,const unsigned int,const Vec2*) {}
            virtual void apply(AttributeType,const unsigned int,const Vec3*) {}
            virtual void apply(AttributeType,const unsigned int,const Vec4*) {}
            virtual void apply(AttributeType,const unsigned int,const UByte4*) {}
        };

        /** return true if the Drawable subclass supports accept(ConstAttributeFunctor&).*/
        virtual bool supports(ConstAttributeFunctor&) const { return false; }

        /** accept an AttributeFunctor and call its methods to tell it about the interal attributes that this Drawable has.
          * return true if functor handled by drawable, return false on failure of drawable to generate functor calls.*/
        virtual void accept(ConstAttributeFunctor&) const {}


        class PrimitiveFunctor
        {
        public:
            
            virtual ~PrimitiveFunctor() {}

            virtual void setVertexArray(unsigned int count,const Vec3* vertices) = 0;
            
            virtual void drawArrays(GLenum mode,GLint first,GLsizei count) = 0;
            virtual void drawElements(GLenum mode,GLsizei count,const GLubyte* indices) = 0;
            virtual void drawElements(GLenum mode,GLsizei count,const GLushort* indices) = 0;
            virtual void drawElements(GLenum mode,GLsizei count,const GLuint* indices) = 0;
            
            virtual void begin(GLenum mode) = 0;
            virtual void vertex(const Vec3& vert) = 0;
            virtual void vertex(float x,float y,float z) = 0;
            virtual void end() = 0;
            
        };
        
        /** return true if the Drawable subclass supports accept(PrimitiveFunctor&).*/
        virtual bool supports(PrimitiveFunctor&) const { return false; }

        /** accept a PrimtiveFunctor and call its methods to tell it about the interal primtives that this Drawable has.
          * return true if functor handled by drawable, return false on failure of drawable to generate functor calls.
          * Note, PrimtiveFunctor only provide const access of the primtives, as primitives may be procedurally generated
          * so one cannot modify it.*/
        virtual void accept(PrimitiveFunctor&) const {}

    protected:

        Drawable& operator = (const Drawable&) { return *this;}

        virtual ~Drawable();

        /** compute the bounding box of the drawable. Method must be 
            implemented by subclasses.*/
        virtual bool computeBound() const;
        
        void addParent(osg::Node* node);
        void removeParent(osg::Node* node);

        ParentList _parents;
        friend class Node;
        friend class Geode;

        ref_ptr<StateSet>       _stateset;

        mutable BoundingBox     _bbox;
        mutable bool            _bbox_computed;
        
        ref_ptr<Shape>       	_shape;

        bool                    _supportsDisplayList;
        bool                    _useDisplayList;

        typedef std::vector<uint> GLObjectList;
        mutable GLObjectList _globjList;

        ref_ptr<AppCallback>    _appCallback;
        ref_ptr<DrawCallback>   _drawCallback;
        ref_ptr<CullCallback>   _cullCallback;
        
        // static cache of deleted display lists which can only 
        // by completely deleted once the appropriate OpenGL context
        // is set.
        typedef std::map<uint,std::set<uint> > DeletedDisplayListCache;
        static DeletedDisplayListCache s_deletedDisplayListCache;

};

inline void Drawable::draw(State& state)
{
    if (_useDisplayList)
    {

        // get the contextID (user defined ID of 0 upwards) for the 
        // current OpenGL context.
        uint contextID = state.getContextID();

        // fill in array if required.
        while (_globjList.size()<=contextID) _globjList.push_back(0);

        // get the globj for the current contextID.
        uint& globj = _globjList[contextID];

        // call the globj if already set otherwise compile and execute.
        if( globj != 0 )
        {
            glCallList( globj );
        }
        else if (_useDisplayList)
        {
#ifdef USE_SEPARATE_COMPILE_AND_EXECUTE
            globj = glGenLists( 1 );
            glNewList( globj, GL_COMPILE );
            if (_drawCallback.valid())
                _drawCallback->drawImplementation(state,this);
            else 
                drawImplementation(state);
            glEndList();
            
            glCallList( globj);
#else
            globj = glGenLists( 1 );
            glNewList( globj, GL_COMPILE_AND_EXECUTE );
            if (_drawCallback.valid())
                _drawCallback->drawImplementation(state,this);
            else 
                drawImplementation(state);                
            glEndList();
#endif
        }

    }
    else
    {
        // draw object as nature intended..
        if (_drawCallback.valid())
            _drawCallback->drawImplementation(state,this);
        else 
            drawImplementation(state);
    }
};

template<class T>
class TriangleFunctor : public Drawable::PrimitiveFunctor, public T
{
public:

    TriangleFunctor()
    {
        _vertexArraySize=0;
        _vertexArrayPtr=0;
        _modeCache=0;
    }
    
    virtual ~TriangleFunctor() {}

    virtual void setVertexArray(unsigned int count,const Vec3* vertices)
    {
        _vertexArraySize = count;
        _vertexArrayPtr = vertices;
    }

    virtual void drawArrays(GLenum mode,GLint first,GLsizei count)
    {
        if (_vertexArrayPtr==0 && count==0) return;
    
        switch(mode)
        {
            case(GL_TRIANGLES):
            {
                const Vec3* vlast = &_vertexArrayPtr[first+count];
                for(const Vec3* vptr=&_vertexArrayPtr[first];vptr<vlast;vptr+=3)
                    operator()(*(vptr),*(vptr+1),*(vptr+2));
                break;
            }
            case(GL_TRIANGLE_STRIP):
            {
                const Vec3* vptr = &_vertexArrayPtr[first];
                for(GLsizei i=2;i<count;++i,++vptr)
                {
		    if ((i%2)) operator()(*(vptr),*(vptr+2),*(vptr+1));
		    else       operator()(*(vptr),*(vptr+1),*(vptr+2));
                }
                break;
            }
            case(GL_QUADS):
            {
                const Vec3* vptr = &_vertexArrayPtr[first];
                for(GLsizei i=3;i<count;i+=4,vptr+=4)
                {
                    operator()(*(vptr),*(vptr+1),*(vptr+2));
                    operator()(*(vptr),*(vptr+2),*(vptr+3));
                }
                break;
            }
            case(GL_QUAD_STRIP):
            {
                const Vec3* vptr = &_vertexArrayPtr[first];
                for(GLsizei i=3;i<count;i+=2,vptr+=2)
                {
                    operator()(*(vptr),*(vptr+1),*(vptr+2));
                    operator()(*(vptr+1),*(vptr+3),*(vptr+2));
                }
                break;
            }
            case(GL_POLYGON): // treat polygons as GL_TRIANGLE_FAN
            case(GL_TRIANGLE_FAN):
            {
                const Vec3* vfirst = &_vertexArrayPtr[first];
                const Vec3* vptr = vfirst+1;
                for(GLsizei i=2;i<count;++i,++vptr)
                {
                    operator()(*(vfirst),*(vptr),*(vptr+1));
                }
                break;
            }
            case(GL_POINTS):
            case(GL_LINES):
            case(GL_LINE_STRIP):
            case(GL_LINE_LOOP):
            default:
                // can't be converted into to triangles.
                break;
        }
    }
    
    virtual void drawElements(GLenum mode,GLsizei count,const GLubyte* indices)
    {
        if (indices==0 || count==0) return;
    
        typedef const GLubyte* IndexPointer;
    
        switch(mode)
        {
            case(GL_TRIANGLES):
            {
                IndexPointer ilast = &indices[count];
                for(IndexPointer  iptr=indices;iptr<ilast;iptr+=3)
                    operator()(_vertexArrayPtr[*iptr],_vertexArrayPtr[*(iptr+1)],_vertexArrayPtr[*(iptr+2)]);
                break;
            }
            case(GL_TRIANGLE_STRIP):
            {
                IndexPointer iptr = indices;
                for(GLsizei i=2;i<count;++i,++iptr)
                {
		    if ((i%2)) operator()(_vertexArrayPtr[*(iptr)],_vertexArrayPtr[*(iptr+2)],_vertexArrayPtr[*(iptr+1)]);
		    else       operator()(_vertexArrayPtr[*(iptr)],_vertexArrayPtr[*(iptr+1)],_vertexArrayPtr[*(iptr+2)]);
                }
                break;
            }
            case(GL_QUADS):
            {
                IndexPointer iptr = indices;
                for(GLsizei i=3;i<count;i+=4,iptr+=4)
                {
                    operator()(_vertexArrayPtr[*(iptr)],_vertexArrayPtr[*(iptr+1)],_vertexArrayPtr[*(iptr+2)]);
                    operator()(_vertexArrayPtr[*(iptr)],_vertexArrayPtr[*(iptr+2)],_vertexArrayPtr[*(iptr+3)]);
                }
                break;
            }
            case(GL_QUAD_STRIP):
            {
                IndexPointer iptr = indices;
                for(GLsizei i=3;i<count;i+=2,iptr+=2)
                {
                    operator()(_vertexArrayPtr[*(iptr)],_vertexArrayPtr[*(iptr+1)],_vertexArrayPtr[*(iptr+2)]);
                    operator()(_vertexArrayPtr[*(iptr+1)],_vertexArrayPtr[*(iptr+3)],_vertexArrayPtr[*(iptr+2)]);
                }
                break;
            }
            case(GL_POLYGON): // treat polygons as GL_TRIANGLE_FAN
            case(GL_TRIANGLE_FAN):
            {
                IndexPointer iptr = indices;
                const Vec3& vfirst = _vertexArrayPtr[*iptr];
                ++iptr;
                for(GLsizei i=2;i<count;++i,++iptr)
                {
                    operator()(vfirst,_vertexArrayPtr[*(iptr)],_vertexArrayPtr[*(iptr+1)]);
                }
                break;
            }
            case(GL_POINTS):
            case(GL_LINES):
            case(GL_LINE_STRIP):
            case(GL_LINE_LOOP):
            default:
                // can't be converted into to triangles.
                break;
        }
    }    

    virtual void drawElements(GLenum mode,GLsizei count,const GLushort* indices)
    {
        if (indices==0 || count==0) return;
    
        typedef const GLushort* IndexPointer;
    
        switch(mode)
        {
            case(GL_TRIANGLES):
            {
                IndexPointer ilast = &indices[count];
                for(IndexPointer  iptr=indices;iptr<ilast;iptr+=3)
                {
                    operator()(_vertexArrayPtr[*iptr],_vertexArrayPtr[*(iptr+1)],_vertexArrayPtr[*(iptr+2)]);
                }    
                break;
            }
            case(GL_TRIANGLE_STRIP):
            {
                IndexPointer iptr = indices;
                for(GLsizei i=2;i<count;++i,++iptr)
                {
		    if ((i%2)) operator()(_vertexArrayPtr[*(iptr)],_vertexArrayPtr[*(iptr+2)],_vertexArrayPtr[*(iptr+1)]);
		    else       operator()(_vertexArrayPtr[*(iptr)],_vertexArrayPtr[*(iptr+1)],_vertexArrayPtr[*(iptr+2)]);
                }
                break;
            }
            case(GL_QUADS):
            {
                IndexPointer iptr = indices;
                for(GLsizei i=3;i<count;i+=4,iptr+=4)
                {
                    operator()(_vertexArrayPtr[*(iptr)],_vertexArrayPtr[*(iptr+1)],_vertexArrayPtr[*(iptr+2)]);
                    operator()(_vertexArrayPtr[*(iptr)],_vertexArrayPtr[*(iptr+2)],_vertexArrayPtr[*(iptr+3)]);
                }
                break;
            }
            case(GL_QUAD_STRIP):
            {
                IndexPointer iptr = indices;
                for(GLsizei i=3;i<count;i+=2,iptr+=2)
                {
                    operator()(_vertexArrayPtr[*(iptr)],_vertexArrayPtr[*(iptr+1)],_vertexArrayPtr[*(iptr+2)]);
                    operator()(_vertexArrayPtr[*(iptr+1)],_vertexArrayPtr[*(iptr+3)],_vertexArrayPtr[*(iptr+2)]);
                }
                break;
            }
            case(GL_POLYGON): // treat polygons as GL_TRIANGLE_FAN
            case(GL_TRIANGLE_FAN):
            {
                IndexPointer iptr = indices;
                const Vec3& vfirst = _vertexArrayPtr[*iptr];
                ++iptr;
                for(GLsizei i=2;i<count;++i,++iptr)
                {
                    operator()(vfirst,_vertexArrayPtr[*(iptr)],_vertexArrayPtr[*(iptr+1)]);
                }
                break;
            }
            case(GL_POINTS):
            case(GL_LINES):
            case(GL_LINE_STRIP):
            case(GL_LINE_LOOP):
            default:
                // can't be converted into to triangles.
                break;
        }
    }    

    virtual void drawElements(GLenum mode,GLsizei count,const GLuint* indices)
    {
        if (indices==0 || count==0) return;
    
        typedef const GLuint* IndexPointer;
    
        switch(mode)
        {
            case(GL_TRIANGLES):
            {
                IndexPointer ilast = &indices[count];
                for(IndexPointer  iptr=indices;iptr<ilast;iptr+=3)
                    operator()(_vertexArrayPtr[*iptr],_vertexArrayPtr[*(iptr+1)],_vertexArrayPtr[*(iptr+2)]);
                break;
            }
            case(GL_TRIANGLE_STRIP):
            {
                IndexPointer iptr = indices;
                for(GLsizei i=2;i<count;++i,++iptr)
                {
		    if ((i%2)) operator()(_vertexArrayPtr[*(iptr)],_vertexArrayPtr[*(iptr+2)],_vertexArrayPtr[*(iptr+1)]);
		    else       operator()(_vertexArrayPtr[*(iptr)],_vertexArrayPtr[*(iptr+1)],_vertexArrayPtr[*(iptr+2)]);
                }
                break;
            }
            case(GL_QUADS):
            {
                IndexPointer iptr = indices;
                for(GLsizei i=3;i<count;i+=4,iptr+=4)
                {
                    operator()(_vertexArrayPtr[*(iptr)],_vertexArrayPtr[*(iptr+1)],_vertexArrayPtr[*(iptr+2)]);
                    operator()(_vertexArrayPtr[*(iptr)],_vertexArrayPtr[*(iptr+2)],_vertexArrayPtr[*(iptr+3)]);
                }
                break;
            }
            case(GL_QUAD_STRIP):
            {
                IndexPointer iptr = indices;
                for(GLsizei i=3;i<count;i+=2,iptr+=2)
                {
                    operator()(_vertexArrayPtr[*(iptr)],_vertexArrayPtr[*(iptr+1)],_vertexArrayPtr[*(iptr+2)]);
                    operator()(_vertexArrayPtr[*(iptr+1)],_vertexArrayPtr[*(iptr+3)],_vertexArrayPtr[*(iptr+2)]);
                }
                break;
            }
            case(GL_POLYGON): // treat polygons as GL_TRIANGLE_FAN
            case(GL_TRIANGLE_FAN):
            {
                IndexPointer iptr = indices;
                const Vec3& vfirst = _vertexArrayPtr[*iptr];
                ++iptr;
                for(GLsizei i=2;i<count;++i,++iptr)
                {
                    operator()(vfirst,_vertexArrayPtr[*(iptr)],_vertexArrayPtr[*(iptr+1)]);
                }
                break;
            }
            case(GL_POINTS):
            case(GL_LINES):
            case(GL_LINE_STRIP):
            case(GL_LINE_LOOP):
            default:
                // can't be converted into to triangles.
                break;
        }
    }    



    /** begin(..),vertex(..) & end() are convinience methods for adapting 
     *  non vertex array primitives to vertex array based primitives.
     * this is done to simplify the implementation of primtive functor
     * subclasses - users only need override drawArray and drawElements.*/
    inline void begin(GLenum mode)
    {
        _modeCache = mode;
        _vertexCache.clear();
    }

    inline void vertex(const Vec3& vert) { _vertexCache.push_back(vert); }
    inline void vertex(float x,float y,float z) { _vertexCache.push_back(osg::Vec3(x,y,z)); }
    inline void end()
    {
        if (!_vertexCache.empty())
        {
            setVertexArray(_vertexCache.size(),&_vertexCache.front());
            drawArrays(_modeCache,0,_vertexCache.size());
        }
    }

protected:


    unsigned int        _vertexArraySize;
    const Vec3*         _vertexArrayPtr;

    GLenum              _modeCache;
    std::vector<Vec3>   _vertexCache;

};


}

#endif