Now that we have all the information required to build our game, let's start to change it. The first step is to change our world to a Euclidean torus with a fixed size. Here is a representation of a torus taken from the Wikipedia page:

To do this, we will need some information from inside the game, such as the world size. We will add the information inside the Game class as two integer values, height and width:

const int _x, const _y;

We will initialize them with the constructor. So now, we need parameters for this class:

Game(int x=800, int y=600);

We will need to change our constructor implementation a bit, as shown in the following code snippet:

Game::Game(int x, int y) : _window(sf::VideoMode(x,y),"03_Asteroid"),x(x),y(y){
     _player.setPosition(100,100);
}

Okay, now we can choose the size of the world, but how do we make it a torus? In reality, it's not complicated. We only need to check the position of each entity after moving them; and if they are out of the world...