Fixed Time-Step

        // In the class
        bool isRunning;
        sf::Clock simulationTimer;
        const sf::Uint8 simulationRate;

        // The Loop
        sf::Uint32 rate = 0;
        simulationTimer.Reset();
        isRunning = true;

        while ( isRunning )
        {
            // Process to the next scene, if it's different
            // ...
            ScenePtr scene = scenes[ currentScene ];

            // Simulate only simulationRate times a second
            while ( rate > simulationRate )
            {
                // Events, update loop
                sf::Event event;
                while ( window.PollEvent( event ) )
                {
                    scene->Update( event );
                }
                scene->Update();

                rate -= ( 1000 / simulationRate );
            }

            // Render as much as possible
            // You could probably put this in the above loop, for battery
            scene->Draw( window );



            // Update the simulation rate...
            rate += simulationTimer.GetElapsedTime();
            simulationTimer.Reset();
        }