gluLookAt

class Camera
{
    public:
        Camera()
           : pos( 0, 0, 5 ),
             dir( 0, 0, -1 ),
             up( 0, 1, 0 )
        {
        }

        sf::Vector3f pos;
        sf::Vector3f dir;
        sf::Vector3f up;

        void Display()
        {
            gluLookAt( pos.x, pos.y, pos.z,
                       pos.x + dir.x, pos.y + dir.y, pos.z + dir.z,
                       up.x, up.y, up.z );
        }
};

// Update
{
    // I know this should be a seperate function, but it was easier to just put it here. :P
    #define Distance(a,b) std::sqrt( std::pow( b.x - a.x, 2 ) + std::pow( b.y - a.y, 2 ) + std::pow( b.z - a.z, 2 ) )

    float speed = 1;
    sf::Vector3f amount( cam.dir.x * speed, cam.dir.y * speed, cam.dir.z * speed );

    if ( sf::Keyboard::IsKeyPressed( sf::Keyboard::W ) )
    {
        cam.pos += amount;
    }
    if ( sf::Keyboard::IsKeyPressed( sf::Keyboard::S ) )
    {
        cam.pos -= amount;
    }
}