# Ping pong position using lerp

Hi!

I’m trying to make some objects move from position A to position B and then back to position A. I’m using lerp with ping pong to achive that, but it doesn’t work as the objects continue moving and never get back to position A. This is my code:

``````    private float positionDisplacement;

private void Start()
{
positionDisplacement = Random.Range(-50f, 50f);
}

private void Update()
{
transform.position = new Vector3(Mathf.Lerp(transform.position.x, transform.position.x + positionDisplacement, Mathf.PingPong(Time.deltaTime, 1f)),
Mathf.Lerp(transform.position.y, transform.position.y + positionDisplacement, Mathf.PingPong(Time.deltaTime, 1f)),
Mathf.Lerp(transform.position.z, transform.position.z + positionDisplacement, Mathf.PingPong(Time.deltaTime, 1f)));
}
``````

yes it will not come back since the the transform.position.x/y/z is changed . consider record your original position at first then do the ping pong.The following code should work.

``````    private Vector3 positionDisplacement;
private Vector3 positionOrigin;
private float _timePassed;
private void Start(){
float randomDistance = Random.Range(-50f, 50f);
positionDisplacement = new Vector3(randomDistance,randomDistance,randomDistance);
positionOrigin = transform.position;
}

private void Update(){
_timePassed += Time.deltaTime;
transform.position = Vector3.Lerp(positionOrigin, positionOrigin + positionDisplacement,
Mathf.PingPong(_timePassed, 1));
}
``````

use liner equation with time.
B(t) = P0 + t(P1 – P0) = (1-t) P0 + tP

for example;

``````float _time = 0;
Transform PointA:
Transform PointB:
void update(){

_time += time.deltatime;

transform.position = GetNewPosition(_time);

}

Vector3 GetNewPosition(float t){
somevector = PointA + t(PointB – PointA) = (1-t) PointA + tPointB
return somevector
``````

}

this may not be error free. but this is how i did it

here is a code that should work, you need to assig the target in the oinspector

``````bool goingRight = true;
public float speed = 1;

public Vector3 endPosition;
Vector3 startPosition;

void Awake()
{
startPosition = transform.position;
}

private void Update()
{
transform.position = Vector3.Lerp(startPosition, endPosition, amount);

amount = speed ^Time.deltaTime;
if(amount >= 1 || amount <= 0) { speed = -speed; }
}
``````