/* -*-c++-*- OpenSceneGraph - Copyright (C) 1998-2006 Robert Osfield
 *
 * This library is open source and may be redistributed and/or modified under
 * the terms of the OpenSceneGraph Public License (OSGPL) version 0.0 or
 * (at your option) any later version.  The full license is in LICENSE file
 * included with this distribution, and on the openscenegraph.org website.
 *
 * This library is distributed in the hope that it will be useful,
 * but WITHOUT ANY WARRANTY; without even the implied warranty of
 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
 * OpenSceneGraph Public License for more details.
*/

#ifndef OSGSIM_HEIGHTABOVETERRAIN
#define OSGSIM_HEIGHTABOVETERRAIN 1

#include <osgUtil/IntersectionVisitor>

// include so we can get access to the DatabaseCacheReadCallback
#include <osgSim/LineOfSight>

namespace osgSim {

/** Helper class for setting up and acquiring height above terrain intersections with terrain.
  * By default assigns a osgSim::DatabaseCacheReadCallback that enables automatic loading
  * of external PagedLOD tiles to ensure that the highest level of detail is used in intersections.
  * This automatic loading of tiles is done by the intersection traversal that is done within
  * the computeIntersections(..) method, so can result in long intersection times when external
  * tiles have to be loaded.
  * The external loading of tiles can be disabled by removing the read callback, this is done by
  * calling the setDatabaseCacheReadCallback(DatabaseCacheReadCallback*) method with a value of 0.*/
class OSGSIM_EXPORT HeightAboveTerrain
{
    public :


        HeightAboveTerrain();


        /** Clear the internal HAT List so it contains no height above terrain tests.*/
        void clear();

        /** Add a height above terrain test point in the CoordinateFrame.*/
        unsigned int addPoint(const osg::Vec3d& point);

        /** Get the number of height above terrain tests.*/
        unsigned int getNumPoints() const { return _HATList.size(); }

        /** Set the source point of single height above terrain test.*/
        void setPoint(unsigned int i, const osg::Vec3d& point) { _HATList[i]._point = point; }

        /** Get the source point of single height above terrain test.*/
        const osg::Vec3d& getPoint(unsigned int i) const { return _HATList[i]._point; }

        /** Get the intersection height for a single height above terrain test.
          * Note, you must call computeIntersections(..) before you can query the HeightAboveTerrain.
          * If no intersections are found then height returned will be the height above mean sea level. */
        double getHeightAboveTerrain(unsigned int i) const  { return _HATList[i]._hat; }

        /** Set the lowest height that the should be tested for.
          * Defaults to -1000, i.e. 1000m below mean sea level. */
        void setLowestHeight(double lowestHeight) { _lowestHeight = lowestHeight; }

        /** Get the lowest height that the should be tested for.*/
        double getLowestHeight() const { return _lowestHeight; }

        /** Compute the HAT intersections with the specified scene graph.
          * The results are all stored in the form of a single height above terrain value per HAT test.
          * Note, if the topmost node is a CoordinateSystemNode then the input points are assumed to be geocentric,
          * with the up vector defined by the EllipsoidModel attached to the CoordinateSystemNode.
          * If the topmost node is not a CoordinateSystemNode then a local coordinates frame is assumed, with a local up vector. */
        void computeIntersections(osg::Node* scene, osg::Node::NodeMask traversalMask=0xffffffff);

        /** Compute the vertical distance between the specified scene graph and a single HAT point. */
        static double computeHeightAboveTerrain(osg::Node* scene, const osg::Vec3d& point, osg::Node::NodeMask traversalMask=0xffffffff);


        /** Clear the database cache.*/
        void clearDatabaseCache() { if (_dcrc.valid()) _dcrc->clearDatabaseCache(); }

        /** Set the ReadCallback that does the reading of external PagedLOD models, and caching of loaded subgraphs.
          * Note, if you have multiple LineOfSight or HeightAboveTerrain objects in use at one time then you should share a single
          * DatabaseCacheReadCallback between all of them. */
        void setDatabaseCacheReadCallback(DatabaseCacheReadCallback* dcrc);

        /** Get the ReadCallback that does the reading of external PagedLOD models, and caching of loaded subgraphs.*/
        DatabaseCacheReadCallback* getDatabaseCacheReadCallback() { return _dcrc.get(); }

    protected :

        struct HAT
        {
            HAT(const osg::Vec3d& point):
                _point(point),
                _hat(0.0) {}

            osg::Vec3d      _point;
            double          _hat;
        };

        typedef std::vector<HAT> HATList;


        double                                  _lowestHeight;
        HATList                                 _HATList;


        osg::ref_ptr<DatabaseCacheReadCallback> _dcrc;
        osgUtil::IntersectionVisitor            _intersectionVisitor;


};

}

#endif
