# How to make enemies moving in a line oscillate between going left and going right at a certain trigger,How to make one enemy go left at a certain point and the following right

Hey guys,
this is the code I am having trouble with…
I am trying to build a TD game in which, as usual, multiple enemies of the same kind spawn and make their way to the finish line. I am trying to make one enemy go left, the next one right and then oscillate between the two, but instead once they all go into the same direction and they start to rapidly oscillate right at the exit going left, right, left, right etc…

``````public class Enemy_Movement_Normal_Speed : MonoBehaviour
{
public float moveSpeed = 2f;
public bool changeDir1;
public bool changeDirleft;
public Transform changeDir2;
public int changeDirectionDir1 = 1;

void FixedUpdate()
{
Vector3 vel = transform.forward * moveSpeed;    //move forward
vel.y = GetComponent<Rigidbody>().velocity.y;
GetComponent<Rigidbody>().velocity = vel;

if (changeDir1 == true && changeDirectionDir1 == 1) //move right at the junction
{
Vector3 vel2 = transform.right * moveSpeed;
vel2.y = GetComponent<Rigidbody>().velocity.y;
GetComponent<Rigidbody>().velocity = vel2;

//transform.LookAt(changeDir2)

Debug.Log(changeDirectionDir1);
}
if (changeDir1 == true && changeDirectionDir1 == 2) //move left at the junction
{
Vector3 vel2 = -transform.right * moveSpeed;
vel2.y = GetComponent<Rigidbody>().velocity.y;
GetComponent<Rigidbody>().velocity = vel2;

//transform.LookAt(changeDir2)

Debug.Log(changeDirectionDir1);
}
if (changeDirleft == true)  //move foward at different junction again,
//called left because it
//is like actually moving left, in game
//world however it's forward
{
Vector3 vel2 = transform.forward * moveSpeed;
vel2.y = GetComponent<Rigidbody>().velocity.y;
GetComponent<Rigidbody>().velocity = vel2;
}
}
public void OnTriggerEnter(Collider other)
{
if (other.CompareTag("Change Dir 1")) //is the enemy at the first junction?
{
changeDir1 = true;
changeDirectionDir1 += 1;   //this is supposed to go up once when they enter
// the trigger in order for the next one to move left
Debug.Log("Entered the first trigger");
}
if (other.CompareTag("Change Dir Left"))
{
changeDir1 = false;
changeDirleft = true;
Debug.Log("Entered the second trigger");
}
}
public void OnTriggerExit(Collider other)
{
if (other.CompareTag("Change Dir 1"))
{
changeDirectionDir1 -= 1; //subtract one again so that
//once one has left the junction the next one goes right again
}
}
}
``````

Sorry for the messy code, I am still a beginner ^^

Based on your code, I’m assuming that each enemy will have its own copy of this script, which means that each will have its own instance variables (see Instance variable - Wikipedia).

Instead, what you probably want is to have a single variable associated with each trigger zone that causes a direction change. In a Tower Defense game, I would probably have a single script that keeps track of and controls all enemies rather than making each enemy be in charge of its own movement, because that will help coordinate their movements at a high level. That manager script would have references to each enemy and each trigger, and when an enemy enters a trigger zone, the manager could ask the trigger which direction the enemy should go and tell the trigger that an enemy has reached it. The trigger could then update a variable that will make it respond with a different direction when the manager detects that the next enemy has reached it.

If you’d prefer to keep having enemies manage their own movement, you could make a new `TriggerZone` `MonoBehaviour` that keeps track of and updates the next desired enemy direction. Something like this:

``````public class TriggerZone : MonoBehaviour {
private float _enemyDirection = 1f;
public float GetNextEnemyDirectionAndUpdate () {
float nextDir = _enemyDirection;
_enemyDirection = -_enemyDirection;
return nextDir;
}
}

public class Enemy_Movement_Normal_Speed : MonoBehaviour {
private float _myDirection = 1f;

void FixedUpdate () {
// ... Move base on _myDirection
}

void OnTriggerEnter (Collider other) {
TriggerZone zone = other.GetComponent<TriggerZone>();
if (zone != null) {
_myDirection = zone.GetNextEnemyDirectionAndUpdate();
}
}
}
``````