Colliders/Triggers going through each other

Question

I'm making a game, similar to the game Cartoon Wars (don't know if you've heard of it) and Plants vs Zombies. You set down your troops and they attack your enemy's base, while your enemy is attacking yours.

It is working fine, except for one problem. When the enemies or defenders get stacked up to each other, and one of them dies, it registers to the other side that their target has been killed and they continue walking right past the enemies in front of them. Basically, they think that since they killed one guy, the rest in front of them are dead, too.

Here's my code for the Defenders (the Attacker code is basically the same. I have Kinematic Rigidbody2Ds and Box Collider2Ds with Triggers set on them). using UnityEngine; using System.Collections;

public class Defenders : MonoBehaviour {

  public int cost = 50;
  
  private float defenderSpeed;
  private Animator anim;
  private bool standGuard;
  private GameObject defenderTarget;
  
  void Start () {
      defenderSpeed = .5f;
      anim = GetComponent<Animator>();
  }
  
  void Update () {
      transform.Translate (Vector3.right * defenderSpeed * Time.deltaTime);
      if (!defenderTarget) {
          defenderSpeed = .5f;
          anim.SetBool ("isAttacking", false);
      }
  }
  
  
  
  void OnTriggerEnter2D(Collider2D collider) {
      GameObject obj = collider.gameObject;
      defenderTarget = obj;
      
      if (obj.GetComponent<Attacker>()) {
          defenderSpeed = 0f;
          anim.SetBool ("isAttacking", true);
      }
  }
  
  
  void OnMouseDown() {
      if (standGuard == true) {
          anim.SetBool ("standGuard", false);
          standGuard = false;
      } else if (standGuard == false) {
          anim.SetBool ("standGuard", true);
          standGuard = true;
      }
  }
  
  
  
  public void StrikeCurrentTarget (float damage) {
      if (defenderTarget) {
          Health health = defenderTarget.GetComponent<Health>();
          if (health) {
              health.DealDamage (damage);
          }
      }
  }
  
  public void Attack (GameObject obj) {
      defenderTarget = obj;
  }

}

Is there a way that I can make the unit check to make sure there isn't another unit in front of him before carrying on?

Answer 1

I'll try a quickie example, but you should be prepared to research such well-documented design techniques on your own.

In a more complicated Finite State Machine, you'd use some variable like an enum to track which state(s) your agents are currently in.

 public enum AgentState { idle, patrol, attack }
 public AgentState currentState;
 //...
 switch ( currentState ) {
   case AgentState.idle : DoIdleBehavior(); break;
   // etc...
 }

In this example, because there are only two states (lookForTargets and attackTarget) you can safely determine the state based on whether a currentTarget variable is null or populated. You'll need a way to detect and select the "best target" among detected agents.

 // where Agent is the name of some script your characters derive from
 private Agent currentTarget;
     
 // it really makes the most sense to discover all nearby objects, 
 // check whether they're agents, 
 // verify that they belong to the same lane,
 // then sort through those agents to select the nearest one.
 // Failure to do so may allow the "wrong" agent to get selected
 // which might lead to all sorts of problems.

 // This isn't hard, but there are many valid ways to do this so I'm leaving it to you.
 // You could use OnTriggerStay() but I would recommend Physics.OverlapSphere()
 // which bypasses triggers altogether, and conveniently
 // hands you a collection of all detected objects.
     
 // don't look for a target if you already have one
 if (currentTarget == null) {
   // do whatever you're gonna do to discover and select the best agent, then...
   Agent otherAgent = (other.gameObject.GetComponent<Agent>() as Agent;
   if (otherAgent != null) currentTarget = otherAgent;
 }

 // now, if you have a target, attack it until the target is no longer valid
 // somewhere in your attack method...
 if (currentTarget.health <= 0) {
   GameObject.Destroy( currentTarget.gameObject );
   currentTarget = null;
 }

You'll then allow your look-for-targets code to run again, starting the cycle over.

Then, you'd probably want a way for friendly agents to detect each other too, so they can "wait" on friendlies in front of them. "Waiting" should really constitute a third state, so you might need to have a more complicated FSM after all...

http://docs.unity3d.com/ScriptReference/Physics.OverlapSphere.html

Colliders/Triggers going through each other

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