How do I get an NPC to follow the player(and stop when it gets within range)

Question

I'm making a game where you have a friend follow you. I have a script that partly works, but when the friend exits the trigger, it won't follow the player.

How do I get the friend to follow the player once indefinitely, or until it hits the trigger again?

Here is the script:

public Transform friend;
private int movespeed;

public int speed;
public Rigidbody rb;

// Use this for initialization
void Start()
{
    speedup();
}

// Update is called once per frame
void Update()
{

    transform.LookAt(freind);
    Vector3 eulerAngles = transform.rotation.eulerAngles;
    eulerAngles.x = 0;
    eulerAngles.z = 0;
    transform.rotation = Quaternion.Euler(eulerAngles);

    rb.AddRelativeForce(0, 0, movespeed);

}

public void OnTriggerStay(Collider other)
{

    if (other.tag == "Player")
    {
        movespeed = 0;
    }
    else
    {
        speedup();
    }
}

public void speedup()
{
    movespeed = speed;
}

Answer 1

This code says:

"As long as I'm still in trigger contact with something...

...if that thing is tagged 'Player', set move speed to zero

...otherwise (ie. if that thing is tagged anything else), set move speed to speed"

It looks like you mean that last clause to say "if I'm no longer in trigger contact..." but if we weren't in trigger contact anymore, OnTriggerStay wouldn't even be called.

It looks like what you want is something more like:

bool isNearPlayer;

void OnTriggerEnter(Collider other) {
    if(other.gameObject.CompareTag("Player"))
        isNearPlayer = true;
}

void OnTriggerExit(Collider other) {
    if(other.gameObject.CompareTag("Player"))
         isNearPlayer = false;
}

This toggles a mode flag on & off when we enter & exit trigger range around the player. (Also note that using CompareTag is more efficient than comparing strings with ==)

Then you can use that mode flag in your FixedUpdate method:

if(isNearPlayer == false)
    rb.AddRelativeForce...

(Even better, since you already have a reference to the player object, you can check its range directly, without waiting to detect trigger contact: isNearPlayer = (transform.position - friend.Position).sqrMagnitude < stopRange * stopRange); )

Answer 2

I've found the answer! I just had to add an on Trigger exit statement with the speed up function inside:

public Transform freind;
private int movespeed;

public int speed;
public Rigidbody rb;
// Use this for initialization
void Start()
{
    speedup();
}

// Update is called once per frame
void Update()
{

    transform.LookAt(freind);
    Vector3 eulerAngles = transform.rotation.eulerAngles;
    eulerAngles.x = 0;
    eulerAngles.z = 0;
    transform.rotation = Quaternion.Euler(eulerAngles);

    rb.AddRelativeForce(0, 0, movespeed);

}

public void OnTriggerStay(Collider other)
{


    if (other.tag == "Player")
    {
        movespeed = 0;
    }

}
public void OnTriggerExit(Collider other)
{
    speedup();
}

public void speedup()
{
    movespeed = speed;
}