Only damage one object with "Enemy" tag

Question

Im making a tower defense game and i need my cannon to pick a target (first enemy that enters it's range) and shoot at it until it dies while ignoring other enemies, then pick a new target. Right now my turret damages every enemy with the tag "Enemy" that enters it's range.

My cannon code:

 var level = 1;
 var damage = level;
 var attackspeed = 1;
 var isshooting = 0;
 var currentenemy : GameObject;
 
 function Start () {
 
 }
 
 function Update () {
   
 }
 function OnTriggerEnter (other : Collider) {
 
 if(other.gameObject.CompareTag("Enemy")){
 
 print("damaged the enemy");
 other.gameObject.SendMessage("OnDamage", damage);
 }
 }

And my Enemy code:

 var health=10;
  
 function OnDamage(damage:int)
 {
 print(damage);
 health = health - damage;
 if(health <- 0)
 {
 Destroy(gameObject);
 }
 }

Answer 1

Since i'm not experienced that much in javascript i'll provide the code in C#. First you need to implement a list of targets , and the target acquisition mechanism. Here's a simple implementation for it (possible syntax errors may be present but the general concept is solid.)

 List<Transform> enemiesInRange = new List<Transform>(); // All the enemis in range
 Transform lockedEnemy = null; // Enemy that we're targeting
 float firingInterval = 2f; // Fire every 2 seconds.
 float elapsedTime = 0f; // Time measuring variable.

 void OnTriggerEnter(Collider other) {
   // if enemy enters range
   if(other.gameObject.CompareTag("Enemy")) {
   // and we have no lock on enemy
   if (lockedEnemy == null) {
     // lock on the entering enemy
     lockedEnemy = other.transform; // other.gameObject.transform;
   }
   // Add it to the list of enemies
   enemiesInRange.Add(other.transform);
   }
 }
 
 void OnTriggerLeave(Collider other) {
    if (lockedEnemy == other.transform) {
    // if the enemy leaving the range is the one we're targeting remove it from the enemies in range
    lockedEnemy = null;
    // Reset the aiming timer
    elapsedTime = 0;
    }

    enemiesInRange.Remove(other.transform);
    // reacquire target from the enemies in range (the first one in the list).
    if (enemiesInRange.Count > 0) {
     lockedEnemy = enemiesInRange[0];
     } else {
      // if no enemies are in range , set the locked enemy to null
      lockedEnemy = null;
     }
    }
  }

 void Update() {
  // if we have locked in enemy.
  if (lockedEnemy != null) {
    // increase the timer
    elapsedTime += Time.deltaTime;
    // if enough time has passed , fire
    if (elapsedTime > firingInterval) {
      // Fire!
      lockedEnemy.gameObject.SendMessage("OnDamage", damage);
      // Reset the time measuring to start firing
      elapsedTime = 0;
    }
  }
 }

Answer 2

All the enemies are being damaged because you're telling it to damage them whenever one enters the range.

 function OnTriggerEnter (other : Collider)
 {
     if(other.gameObject.CompareTag("Enemy"))
     {
         print("damaged the enemy");
         other.gameObject.SendMessage("OnDamage", damage);
     }
 }

OnTriggerEnter does exactly what it says, it runs when something enters a trigger. The code inside it will only be activated when your enemy enters the area and this snippit of code doesn't actually use currentEnemy anywhere.

You could set OnTriggerEnter to set the currentEnemy to the new one that has entered if it doesn't currently have a target like this:

 function OnTriggerEnter (other : Collider)
 {
     if(other.gameObject.CompareTag("Enemy"))
     {
         if(currentEnemy == null)
         {
             currentEnemy = other;
         }
     }
 }

This however wouldn't automatically assign the new enemy when currentEnemy is defeated. I suggest that to work around these issues you look in to using Coroutines as they allow you to loop tasks like damaging an enemy on a time of your choosing. Your code for damaging "currentEnemy" would be placed inside your couroutine.

As for picking a new enemy, you need some way of calculating which enemy to target after your current target dies. I would suggest working out a way of calculating which enemy is furthest along the path, unless you're satisfied with the turret only being able to see an enemy that enters the trigger.

Only damage one object with "Enemy" tag

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