Adding multithreading to our games

We will now modify our Gravitris to paralyze the physics calculations from the rest of the program. We will need to change only two files: Game.hpp and Game.cpp.

In the header file, we will not only need to add the required header, but also change the prototype of the update_physics() function and finally add some attributes to the class. So here are the different steps to follow:

1. Add #include <SFML/System.hpp>, this will allow us to have access to all the classes needed.

2. Then, change the following code snippet:

   void updatePhysics(const sf::Time& deltaTime,const sf::Time& timePerFrame);

   to:

   void updatePhysics();

   The reason is that a thread is not able to pass any parameters to its wrapped function so we will use another solution: member variables.

3. Add the following variables into the Game class as private:

   sf::Thread _physicsThread;
   sf::Mutex _mutex;
   bool _isRunning;
   int _physicsFramePerSeconds;

   All these variables will be used by the physics thread...