How to make a smooth movement in XNA?

Question

I'm trying to make a nice controls for my game, but I can't achieve enough SMOOTHNESS.

if (kbState.GetPressedKeys().Length != 0 && _direction != Vector2.Zero)
    {
        _direction.Normalize();
        _position += _direction * (_speed * (float)gameTime.ElapsedGameTime.TotalSeconds);
    }
    else
        _direction = Vector2.Zero;

    if (kbState.IsKeyDown(Keys.W))
    {
        _direction += new Vector2(0, -1f);
    }
    if (kbState.IsKeyDown(Keys.S))
    {
        _direction += new Vector2(0, 1);
    }

    if (kbState.IsKeyDown(Keys.D))
    {
        _direction += new Vector2(1, 0);
    }

    if (kbState.IsKeyDown(Keys.A))
    {
        _direction += new Vector2(-1, 0);
    }

There is the code. Could you help me a little and give an advice how to make character stop smoothly. I tried many options, but could'nt find any that fit.

Answer 1

Here is how I usually simulate friction:

    Vector2 Velocity;
    float Friction; // In pixels / second^2

    void ApplyFriction() {
        if (Velocity.X > 0) Velocity.X -= Friction;
        if (Velocity.X < 0) Velocity.X = 0;
    }

You then put the function at the end of your character's presumed Update() method.

If you want constant movement, you can set Friction to 0 until you want it enabled again (as in, when you want your character to stop). (y)

PROTIP: You can transform this in a Gravity function by turning the code into Velocity.Y += GravitySpeed; if (Velocity.Y > TerminalVelocity) Velocity.Y = TerminalVelocity!

Answer 2

You need velocity Assuming fixed time step:

if(noKeysPressed)
{
    _velocity =* 0.5f; //adjust ratio to your needs
}
else
{
    //change velocity how you want
}

_position += velocity; //modify position even if no key is pressed