Make a game object face another game object when instantiated

Question

I am making a 2D asteroids game and I am trying to add an alien ship that shoots at the player (which is called 'ship') once every 2 seconds. I can get the alien ship to drop the bullet every 2 seconds, but can not get the bullet to move towards the ship. The bullet is a prefab. Can someone please explain how I would get the bullet prefab to move toward the ships position when instantiated?

This is the script to make the alien ship shoot the bullet:

 using UnityEngine;
 using System.Collections;

 public class AlienShootScript : MonoBehaviour 
 {
     public GameObject AlienBulletPrefab;
     public Transform Ship;
 
     void Start () 
     {
         StartCoroutine (onCoroutine()); 
     }
 
     IEnumerator onCoroutine()
     {
         while(true) 
         { 
             Instantiate (AlienBulletPrefab, transform.position, transform.LookAt (Ship.transform.position));
             yield return new WaitForSeconds(2f);
         }
     }
     
     void Update () 
     {
     
     }
 }

and here is the script for the bullet prefab that is supposed to shoot at the player:

 using UnityEngine;
 using System.Collections;
 
 public class AlienBulletScript : MonoBehaviour 
 {
     public float Thrust;
     public Rigidbody2D rb;
     public GameObject Ship;
 
     void Start () 
     {
         rb = GetComponent<Rigidbody2D> ();
     }
     
     void Update () 
     {
         rb.AddRelativeForce (Vector3.up * Thrust);
     }
 }

Thrust is set to 10.

Answer 1

Answer by Jessespike · Aug 21, 2015 at 06:09 PM

I'm not a Physics expert. But I think there's two ways you can go about this. Depending whether the rigidBody is kinematic or not.

 void Start () 
 {
     rb = GetComponent<Rigidbody2D> ();

     /*if isKinematic is false*/
     rb.AddRelativeForce (GetComponent<Transform>().forward * Thrust);
 }


 /*if isKinematic is true*/
 void FixedUpdate () 
 {
     Transform bulletTransform = GetComponent<Transform>();
     rb.MovePosition(bulletTransform + (bulletTransform.forward * Thrust));
 }

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Answer 2

transform.LookAt property should do the job. Try changing the code like below:

AlienShootScript:

  using UnityEngine;
  using System.Collections;
  public class AlienShootScript : MonoBehaviour 
  {
      public GameObject AlienBulletPrefab;
      public Transform Ship;
  
      void Start () 
      {
          StartCoroutine (onCoroutine()); 
      }
  
      IEnumerator onCoroutine()
      {
          while(true) 
          { 
              GameObject bullet = Instantiate (AlienBulletPrefab);
              bullet.GetComponent<AlienBulletScript>().AdjustPositionByLookingAt(Ship.transform.position);
              yield return new WaitForSeconds(2f);
          }
      }
      
      void Update () 
      {
      
      }
  }

and here is AlienBulletScript :

  using UnityEngine;
  using System.Collections;
  
  public class AlienBulletScript : MonoBehaviour 
  {
      public float Thrust;
      public Rigidbody2D rb;
      public GameObject Ship;
      Vector3 shipPosition; // or instead of this variable get position from `Ship` variable just above it.
 
      void Start () 
      {
          rb = GetComponent<Rigidbody2D> ();
      }
      
      void Update () 
      {
          rb.AddRelativeForce (Vector3.up * Thrust);
          // or
         // float step = Thrust* Time.deltaTime;
         // transform.position = Vector3.MoveTowards(transform.position, shipPosition, step);
      }
 
      public void AdjustPositionByLookingAt(Vector3 src) 
      {
          transform.LookAt(src);
          shipPosition = src;
      }
 
  }

Make a game object face another game object when instantiated

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