/* -*-c++-*- */
/* osgEarth - Geospatial SDK for OpenSceneGraph
 * Copyright 2008-2014 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_FRAME_CLOCK
#define OSGEARTH_FRAME_CLOCK 1

#include "Common"
#include <chrono>
#include <atomic>

namespace osgEarth
{
    /**
     * Frame clock to keep track of time/frames independently of OSG
     */
    class OSGEARTH_EXPORT FrameClock
    {
    public:
        //! New frame clock
        FrameClock();

        //! Seconds since creation of this object
        double getTime() const;

        //! Current frame number. This will increment each time a
        //! cull() and update() pair are called in succession.
        unsigned getFrame() const;

        //! Register a cull traversal.
        void cull();

        //! Register an update traversal. If cull() was called before
        //! the last call to update(), this will increment the frame
        //! number and return true. Otherwise it returns false, which
        //! means that update() was already called for this frame and
        //! the frame number was not incremented.
        //! (i.e., multiple calls to update in one frame will only
        //! result in the frame number incrementing once.)
        bool update();

    private:
        using Time = std::chrono::time_point<std::chrono::steady_clock>;
        Time _zero;
        Time _tick;
        unsigned _frame;
        std::atomic_bool _newframe;
    };

} // namespace osgEarth


#endif // OSGEARTH_FRAME_CLOCK