/* -*-c++-*- */
/* osgEarth - Dynamic map generation toolkit for OpenSceneGraph
 * Copyright 2015 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 OSGEARTH_TEXTURE_COMPOSITOR_H
#define OSGEARTH_TEXTURE_COMPOSITOR_H 1

#include <osgEarth/Common>
#include <osgEarth/ThreadingUtils>

namespace osgEarth
{
    /**
     * Utility class that tracks texture allocation units
     */
    class OSGEARTH_EXPORT TextureCompositor : public osg::Referenced
    {
    public:
        /**
         * Constructs a new compositor.
         */
        TextureCompositor();

        /** dtor */
        virtual ~TextureCompositor() { }

        /**
         * Requests a texture image unit that is not in use, and marks is as reserved.
         * You can release the reserved texture image unit by calling releaseTextureImageUnit().
         * @param out_unit  Reserved unit is written to this variable.
         * @param requestor Optional requestor string (for information purposes only)
         */
        bool reserveTextureImageUnit(
            int&        out_unit,
            const char* requestor =0L );

        /**
         * Releases a reserved texture image unit previously returned by reserveTextureImageUnit.
         */
        void releaseTextureImageUnit(int unit);

        /**
         * Marks a specific texture image as reserved. Only call this if your application
         * is known to use a particular texture image unit and you don't want osgEarth
         * touching it.
         *
         * Returns true upon success, and false if the unit has already been reserved.
         */
        bool setTextureImageUnitOffLimits(int unit);

    private:
        Threading::Mutex _reservedUnitsMutex;
        std::set<int>    _reservedUnits;
    };
}

#endif // OSGEARTH_TEXTURE_COMPOSITOR_H
