Unity2d Camara smooth zoom issue

Question

want to know that how mathf.movetowards works, i tried to play around it and have some issues. i want to make the camera moves from player to target places along with zooming upon triggered and vise versa, while smooth follow(camera changes target) works, smooth zooming doesn't work. i place the movetowards code to ontriggerenter/exit, but it doesn't work as intended as it only zoom for frames. However, if i place it at update side, the zooming doesn't work at al.

code provided for more infomation.

public class Disable : MonoBehaviour {
GameObject player;
GameObject Camera;
public Transform placeHolder;
public float smoothTime = 2f;
public float adjustSize;
public float originalSize = 6.5f;
public float targetOrtho;


public Vector3 velocity;


void Awake()
{
    player = GameObject.FindGameObjectWithTag("Player");
    Camera = GameObject.FindGameObjectWithTag("MainCamera");



}
private void Start()
{
    targetOrtho = originalSize;
}

void Update()
{
    Camera.GetComponent<Camera>().orthographicSize = Mathf.MoveTowards(Camera.GetComponent<Camera>().orthographicSize, targetOrtho, smoothTime * Time.deltaTime); //doesn't work

}

void OnTriggerEnter2D(Collider2D other)
{
    if (other.gameObject == player)
    {

        Camera.GetComponent<Camera2DFollow>().target = placeHolder;
       targetOrtho = adjustSize;
       //Camera.GetComponent<Camera>().orthographicSize = adjustSize; //works but only changes the size without smooth
       //Camera.GetComponent<Camera>().orthographicSize = Mathf.MoveTowards(Camera.GetComponent<Camera>().orthographicSize, adjustSize, smoothTime * Time.deltaTime); //works but only did for a few frames( not completely)


    }
}


void OnTriggerExit2D(Collider2D other)
{

    Camera.GetComponent<Camera2DFollow>().target = null;
    targetOrtho = originalSize;
    //Camera.GetComponent<Camera>().orthographicSize = originalSize; //works but only changes the size without smooth
    //Camera.GetComponent<Camera>().orthographicSize = Mathf.MoveTowards(Camera.GetComponent<Camera>().orthographicSize, originalSize, smoothTime * Time.deltaTime); //works but only did for a few frames (not completely)
}

Answer 1

want to know that how mathf.movetowards works

Anytime you want to know how part of Unity's C# API works, you can look it up in the published source code:

// Moves a value /current/ towards /target/.
static public float MoveTowards(float current, float target, float maxDelta)
{
    if (Mathf.Abs(target - current) <= maxDelta)
        return target;
    return current + Mathf.Sign(target - current) * maxDelta;
}

As you can see, MoveTowards is just a math function: it takes in some numbers, and returns a computed number.

It does not have any knowledge about what you want to do with that number. It doesn't receive a reference to any object that you want it to update, which is why you have to assign the return value yourself:

Camera.GetComponent<Camera>().orthographicSize = Mathf.MoveTowards(...

This assignment happens exactly once: the frame when this line of code is run. It does not kick off a background process that will keep updating the object frame over frame. If that's the behaviour you want, then it's your job to write that code:

Coroutine zoomTween;

IEnumerator ZoomCoroutine(Camera camera, float targetSize, float duration) {
    float startSize = camera.orthographicSize;

    for(float t = 0f; t < duration; t += Time.deltaTime) {
        float blend = t/duration;
        // A SmoothStep rather than a Lerp might look good here too.
        camera.orthographicSize = Mathf.Lerp(startSize, targetSize, blend); 

        // Wait one frame, then resume.
        yield return null;
    }

    // Finish up our transition, and mark our work done.
    camera.orthographicSize = targetSize;
    zoomTween = null;
}

void ZoomTo(Camera camera, float targetSize, float duration) {
    // Check if we're already in a zoom transition, and stop it to ensure we don't double-up.
    if(zoomTween != null)
        StopCoroutine(zoomTween);

    // Kick off a new zoom transition that can keep going on future frames.
    zoomTween = StartCoroutine(ZoomCoroutine(camera, targetSize, duration));
}

Then when you want to change zoom, you just call ZoomTo() with your desired parameters.