#ifndef OSGUTIL_DISPLAYLISTVISITOR
#define OSGUTIL_DISPLAYLISTVISITOR 1

#include <osg/NodeVisitor>
#include <osg/Geode>
#include <osg/State>

#include <osgUtil/Export>

namespace osgUtil {

/** Visitor for traversing scene graph and setting each osg::GeoSet's _useDisplayList flag, 
  * with option to immediately compile osg::GeoSet's OpenGL Display lists.
  * The mode of operation
  * of the visitor is controlled by setting the DisplayListMode either on visitor
  * constructor or via the setDisplayListMode() method.  DisplayListMode options are:
  * _displayListMode == SWITCH_ON_AND_COMPILE_DISPLAY_LISTS cals gset->compile() on
  * all Geode children. Note, the visitor must only be used within a valid 
  * OpenGL context as compile uses OpenGL calls.
  * _displayListMode == SWITCH_ON_DISPLAY_LISTS sets the Geode's children with 
  * gset->setUseDisplayList(true), this method does not directly create display list,
  * or uses OpenGL calls so if safe to use before a valid OpenGL context has been set up.
  * On the next redraw of the scene, the gset's draw methods will be called
  * which then will respond to their _useDisplayList being set by creating display lists
  * automatically.
  * _displayListMode == SWITCH_OFF_DISPLAY_LISTS sets the Geode's children with 
  * gset->setUseDisplayList(false), this method does not directly create display list,
  *  or uses OpenGL calls so if safe to use before a valid OpenGL context has been set up.
  */
class OSGUTIL_EXPORT DisplayListVisitor : public osg::NodeVisitor
{
    public:

        /** Operation modes of the DisplayListVisitor.*/
        enum DisplayListMode
        {
            SWITCH_ON_AND_COMPILE_DISPLAY_LISTS,
            COMPILE_ON_DISPLAY_LISTS,
            SWITCH_ON_DISPLAY_LISTS,
            SWITCH_OFF_DISPLAY_LISTS
        };

        /** Construct a CompileGeoSetsVisior to traverse all child,
          * with set specified display list mode.  Default mode is to
          * gset->setUseDisplayList(true).
          */
        DisplayListVisitor(DisplayListMode mode=SWITCH_ON_DISPLAY_LISTS);
        
        /** Set the operational mode of how the visitor should set up osg::GeoSet's.*/
        void setDisplayListMode(DisplayListMode mode) { _displayListMode = mode; }

        /** Get the operational mode.*/
        DisplayListMode getDisplayListMode() const { return _displayListMode; }
        
        /** Set the State to use during traversal. */
        void setState(osg::State* state)
        {
            _externalState = state;
            if (_externalState.valid()) _activeState = _externalState;
            else _activeState = _localState;
        }
        
        osg::State* getState()
        {
            return _activeState.get();
        }
        

        /** Simply traverse using standard NodeVisitor traverse method.*/
        virtual void apply(osg::Node& node)
        {
            traverse(node);
        }

        /** For each Geode visited set the display list usage according to the 
          * _displayListMode.
          */
        virtual void apply(osg::Geode& node);

    protected:

        DisplayListMode _displayListMode;
        
        /** local state is created in constructor and used as the default state during traversal.*/
        osg::ref_ptr<osg::State> _localState;
        /** external state is used to override the default state.*/
        osg::ref_ptr<osg::State> _externalState;
        /** active state is equal to _externalState when it is valid, otherwise defaults to _localState.*/
        osg::ref_ptr<osg::State> _activeState;

};

};

#endif