/* -*-c++-*- */
/* osgEarth - Geospatial SDK for OpenSceneGraph
 * Copyright 2020 Pelican Mapping
 * http://osgearth.org
 *
 * osgEarth is free software; you can redistribute it and/or modify
 * it under the terms of the GNU Lesser General Public License as published by
 * the Free Software Foundation; either version 2 of the License, or
 * (at your option) any later version.
 *
 * This program 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
 * GNU Lesser General Public License for more details.
 *
 * You should have received a copy of the GNU Lesser General Public License
 * along with this program.  If not, see <http://www.gnu.org/licenses/>
 */

#ifndef OSGEARTHSYMBOLOGY_ALTITUDE_SYMBOL_H
#define OSGEARTHSYMBOLOGY_ALTITUDE_SYMBOL_H 1

#include <osgEarth/Symbol>
#include <osgEarth/Expression>

namespace osgEarth
{
    /**
     * Symbol that conveys information about altitude and terrain interaction
     */
    class OSGEARTH_EXPORT AltitudeSymbol : public Symbol
    {
    public:
        /**
         * Controls if/how models are clamped to the terrain
         */
        enum Clamping
        {
            /** Do not clamp Z values to the terrain (but still apply the offset, if applicable) */
            CLAMP_NONE,

            /** Sample the terrain under the point, and set the feature's Z to the terrain height,
                ignoring and discarding the feature's original Z value. */
            CLAMP_TO_TERRAIN,

            /** Sample the terrain under the point, and ADD the terrain height to the feature's 
                pre-existing Z value. */
            CLAMP_RELATIVE_TO_TERRAIN,

            /** The feature has a attribute value that describes its height above "height zero",
                which is typically the ellipsoid or MSL. While this will not actually modify the
                feature's geometry, it will install ... */
            CLAMP_ABSOLUTE
        };

        /**
         * Clamping technique - when and where to do clamping.
         */
        enum Technique
        {
            /** Clamp geometry to the map model's elevation data. */
            TECHNIQUE_MAP,

            /** Clamp geometry to the terrain's scene graph. */
            TECHNIQUE_SCENE,

            /** Clamp geometry to the terrain as they are rendered by the GPU. */
            TECHNIQUE_GPU,

            /** Clamp geometry at draw time using projective texturing. */
            TECHNIQUE_DRAPE
        };

        /**
         * Binding - at what granularity the clamping is performed
         */
        enum Binding
        {
            /** Clamp every vertex independently */
            BINDING_VERTEX,

            /** Clamp to the centroid of the entire geometry */
            BINDING_CENTROID
        };

    public:
        META_Object(osgEarth, AltitudeSymbol);

        AltitudeSymbol(const AltitudeSymbol& rhs,const osg::CopyOp& copyop=osg::CopyOp::SHALLOW_COPY);
        AltitudeSymbol( const Config& conf =Config() );

        /** How to clamp instances to the terrain (default is CLAMP_NONE) */
        optional<Clamping>& clamping() { return _clamping; }
        const optional<Clamping>& clamping() const { return _clamping; }

        /** Method of terrain following to use (default is TECHNIQUE_MAP) */
        optional<Technique>& technique() { return _technique; }
        const optional<Technique>& technique() const { return _technique; }

        /** Terrain resolution at which to perform clamping (in map units) */
        optional<float>& clampingResolution() { return _resolution; }
        const optional<float>& clampingResolution() const { return _resolution; }

        /** Granularity at which to clamp a geometry */
        optional<Binding>& binding() { return _binding; }
        const optional<Binding>& binding() const { return _binding; }

        /** Vertical offset of geometry after clamping */
        optional<NumericExpression>& verticalOffset() { return _verticalOffset; }
        const optional<NumericExpression>& verticalOffset() const { return _verticalOffset; }

        /** Vertical scale factor to apply to geometry's Z after clamping. */
        optional<NumericExpression>& verticalScale() { return _verticalScale; }
        const optional<NumericExpression>& verticalScale() const { return _verticalScale; }

    public:
        virtual Config getConfig() const;
        virtual void mergeConfig( const Config& conf );
        static void parseSLD(const Config& c, class Style& style);

    protected:
        virtual ~AltitudeSymbol() { }

        optional<Clamping>           _clamping;
        optional<Technique>          _technique;
        optional<Binding>            _binding;
        optional<float>              _resolution;
        optional<NumericExpression>  _verticalOffset;
        optional<NumericExpression>  _verticalScale;
    };
} // namespace osgEarth

#endif // OSGEARTH_SYMBOLOGY_SYMBOL_H