How do I get an object to face in the direction of its movement, not its force.

Questions & Answers
1

I have created an object that has a constant velocity going right across the screen, however, when it comes into contact with a wall, I want it to face the direction its moving, not the direction of its velocity. My inital thought was to create two variables position, and positionOld, my thought is that if you can get the direction of movement from the new frames position and the last frames position.

public class TurtleController : MonoBehaviour
{
private Rigidbody2D rb;
public float speed;
public Vector2 velocity;
public bool manual;
private Vector2 position;
private Vector2 positionOld;
// Start is called before the first frame update
void Start()
{
rb = GetComponent();
positionOld = Vector2.zero;
}

// Update is called once per frame
void Update()
{
    position = rb.position;
    Vector2 moveinput = new Vector2(Input.GetAxis("Horizontal")*speed, Input.GetAxis("Vertical")*speed);
    if (manual)
        rb.velocity = moveinput;
    else
        rb.velocity = velocity;
    float angle = Mathf.Atan2((position.y-positionOld.y), (position.x - positionOld.x)) * Mathf.Rad2Deg;
    transform.rotation = Quaternion.AngleAxis(angle, Vector3.forward);
   
    positionOld = position;
2

The direction an object is moving is it’s velocity. Velocity is the current speed and direction of movement. All you need to do is this:

transform.rotation = Quaternion.LookRotation(Vector3.forward,rb.velocity);

If you want to always face the direction of the keys you are pressing, use moveinput instead of rb.velocity