public void setUpVariables(){
        xShip = (window.getWidth()/2) - (ship.getWidth()/6);
        yShip = 600-ship.getHeight()/3;
        attackSpeed = 24; //lower is faster;
        moveSpeed = 3;
        difficulty = 3;
        health = 3;
        invulnerabiltyTime = 750; //1 sec in ms
        currentBackground = 0;
    }