OpenSceneGraph/include/osg/Impostor

//C++ header - Open Scene Graph - Copyright (C) 1998-2001 Robert Osfield
//Distributed under the terms of the GNU Library General Public License (LGPL)
//as published by the Free Software Foundation.

#ifndef OSG_IMPOSTOR
#define OSG_IMPOSTOR 1

#include <osg/LOD>
#include <osg/ImpostorSprite>

namespace osg {

/** Impostor - is a form of Level Of Detail group node which allows both switching 
  * between children depending on distance from eye point and image caching.
  * 
  * The principle behind Imposters is that they cache an image of real geometry and then the image is drawn 
  * in subsequent frames instead of the real geometry.  Its a bit like a
  * Billboard *but* is updated at runtime and w.r.t view point.  By drawing
  * just the texture mapped quad you can cut down scene complexity and
  * improve performance.
  * 
  * For more details have a look at:
  * 
  *    http://grail.cs.washington.edu/projects/hic/
  * 
  * The OSG doesn't implement exactly the same technique as above, but its
  * should be a good starting place.  The OSG's impostors are much less
  * intrusive since you don't need to restructure your whole scene to use
  * them.
  *
  * All you need to do to use Impostors is to set up the visible
  * range values for each LOD child of the Impostor, as per osg::LOD,
  * and set an Impostor threshold to tell the renderer at what distance
  * the Impostor's image caching should cut in.  The osg::CullVisitor
  * automatically handles all the setting of pre-rendering stages to
  * calculate the required ImpostorSprites (which encapsulates the image
  * cache and quad), and updates them as the view point changes. If you 
  * use osg::SceneView/CullVisitor all the complexity of supporting 
  * Impostor will be nicely hidden away.
  *
  * TODO:
  * Various improvements are planned for the Impostor-
  * 1) Estimation of how many frames an ImpostorSprite will be reused, if
  * it won't be used more often than a minimum threshold then do not create
  * ImpostorSprite - use the real geometry.
  * 2) Sharing of texture memory between ImpostorSprites.
  * 3) Simple 3D geometry for ImpostorSprite's rather than Billboarding.
  * 4) Shrinking of the ImpostorSprite size to more closely fit the underlying
  * geometry.
  */
class SG_EXPORT Impostor : public LOD
{
    public :
        Impostor();

        META_Node(Impostor);

        typedef std::vector< ref_ptr<ImpostorSprite> > ImpostorSpriteList;

        /** Set the Impostor threshold distance.
          * For eye points further than this threshold the Imposter is used if appropriate,
          * otherwise the LOD children as chosen as per a standard LOD node.*/
        inline void setImpostorThreshold(float distance) { _impostorThreshold = distance; }
        
        /** Set the Impostor threshold distance relative to the node's bounding
          * sphere's radius.*/
        inline void setImpostorThresholdToBound(float ratio=1.0f) { _impostorThreshold = getBound().radius()*ratio; }

        /* Get the Impostor threshold distance.*/
        inline const float getImpostorThreshold() const { return _impostorThreshold; }

        /* Get the Impostor threshold distance squared.*/
        inline const float getImpostorThreshold2() const { return _impostorThreshold*_impostorThreshold; }

        /** Find the ImposterSprite which fits the current eye point best.*/
        ImpostorSprite* findBestImpostorSprite(const osg::Vec3& currLocalEyePoint);
        
        /** Add an ImpostorSprite to the Impostor.*/
        void addImpostorSprite(ImpostorSprite* is);

        /** Get the list of ImpostorSprites attached to this Impostor.*/
        inline ImpostorSpriteList& getImpostorSpriteList() { return _impostorSpriteList; }

        /** Get a const list of ImpostorSprites attached to this const Impostor.*/
        inline const ImpostorSpriteList& getImpostorSpriteList() const { return _impostorSpriteList; }

    protected :

        virtual ~Impostor() {}

        virtual const bool computeBound() const;
        
        ImpostorSpriteList  _impostorSpriteList;

        float _impostorThreshold;

};

};

#endif