Why is Vector3.MoveTowards only working on a single frame?

Question

I have three laptops in my scene and I am trying to bring them to front when I click on them. I am able to recognize which laptop is clicked by using the code below, but it doesn't move to the focus position in a single click: it moves only one frame so I have to keep clicking it.

void Update () {
        if (Input.GetMouseButtonDown (0)) {
            RaycastHit hit;
            Ray ray = Camera.main.ScreenPointToRay (Input.mousePosition);

            if (Physics.Raycast (ray, out hit)) {
                if (hit.transform.name == "Laptop 1") {

                    Debug.Log("Laptop 1 is clicked");
                    Laptop1Trans.position = Vector3.MoveTowards (Laptop1Trans.position, FocusPointTrans.position, moveSpeed);

                } else if (hit.transform.name == "Laptop 2") {
                    Debug.Log("Laptop 2 is clicked");
                } else if (hit.transform.name == "Laptop 3") {
                    Debug.Log("Laptop 3 is clicked");
                } else {
                }
            }
        }
    }

I tried moving the move part to a method but still same behaviour.

Are there any workaround?

Answer 1

It looks like you're trying to use MoveTowards in a fire-and-forget manner, like a tweening library: "Hey you, move over there gradually over the next several frames, without further supervision"

MoveTowards doesn't do that (It couldn't if it wanted to — it doesn't even know what object to move, all it has is some vectors). It's just a way to calculate one position: the place the object should be this frame after taking one step toward the destination.

To keep updating its position, you need a method that runs every frame until it reaches its destination, not just the frame you clicked. A Coroutine can do this quite well:

IEnumerator MoveTo(Transform mover, Vector3 destination, float speed) {
    // This looks unsafe, but Unity uses
    // en epsilon when comparing vectors.
    while(mover.position != destination) {
         mover.position = Vector3.MoveTowards(
             mover.position,
             destination,
             speed * Time.deltaTime);
         // Wait a frame and move again.
         yield return null;
    }
}

You can start this motion with:

StartCoroutine(MoveTo(clickedLaptop, FocusPointTrans.position, moveSpeed); 

Answer 2

Use Input.GetMouseButton instead. GetMouseButtonDown only returns true on one frame when the button was pressed down, while GetMouseButton returns true while the button is held down.