How do i get some objects to ignore collision with a specific object?

Suppose that i have few objects outside a huge box. The box and all the objects have collider components on them. I want those objects to be able to enter the box (without any change to their velocity) and once they enter, they should get collided back into the box whenever they collide with the huge box.

I.e. i want to ignore the first collision so that objects can enter.

How can i achieve this?

holy heck tysm man

TAG

 void OnCollisionEnter(Collision collision)
  {
      if (collision.gameObject.tag == "theobjectToIgnore")
      {
          Physics.IgnoreCollision(theobjectToIgnore.collider, collider);
      }

LAYER

 void OnCollisionEnter(Collision collision)
  {
      if (collision.gameObject.layer == "theobjectToIgnore")
      {
          Physics.IgnoreCollision(theobjectToIgnore.collider, collider);
      }

: )

How would one start the script for the following? I'm not great at code and have tried finding the answer but have had no luck. Any help with that would be very much appreciated!

 void OnCollisionEnter(Collision collision)
   {
       if (collision.gameObject.tag == "theobjectToIgnore")
       {
           Physics.IgnoreCollision(theobjectToIgnore.collider, collider);
       }

This is not a solution. Calling IgnoreCollision in OnCollisionEnter does not cancel the initial collision, so objects still receive collision impulses.

This helped me, once I changed all the Physics etc. to 2D. I'm not working with shooters, but basically need enemies to ignore everything but the player on their patrols in my game.

$$anonymous$$y variation with the updated syntax put in my Unity:

 public string TagToIgnore = "Ignored";
     
 void OnCollisionEnter2D(Collision2D collision){
         if(collision.gameObject.tag == TagToIgnore ){
             Physics2D.IgnoreCollision( collision.gameObject.GetComponent<Collider2D>(), GetComponent<Collider2D>());
       }
 } 

I just dump copies of this little diddy on my objects for each tag I want them to ignore. Not the most efficient, but simple and reusable.

Thanks man, works perfectly.

 using UnityEngine;
 
 public class playerMovementHorizontal : MonoBehaviour {
     public Rigidbody2D rb2d;
     public float speed;
 
     private void Update() {
         rb2d.velocity = new Vector2(Input.GetAxis("Horizontal") * speed, rb2d.velocity.y);
         Debug.Log(transform.position);
     }
 
     private void OnCollisionEnter2D(Collision2D col2d) {
         if (col2d.collider.name == "GroundCheck") {
             Physics2D.IgnoreCollision(col2d.collider, col2d.otherCollider);
         }
     }
 }

Simple, concise, extensible. Thanks, just what I needed to find!

This works perfect, thanks.

I am slightly confused as to how this works. I have managed to make this work on some objects, but it doesn't work on others.

I am using this for a bullet, and here is my code:

 public class BulletControllerModified : MonoBehaviour
 {
     public float bulletSpeed;
     public Rigidbody2D theRigidBody;
 
     public Vector2 moveDir;
     
     public GameObject impactEffect;
 
     //maybe needed for BulletIgnore tag
     //public GameObject bullet;
 
     public int damageAmount = 3;
 
     // Start is called before the first frame update
     void Start()
     {
         //ignoring collision with BulletIgnore tag
         GameObject bullet = GameObject.FindGameObjectWithTag("BulletIgnore");
         Physics2D.IgnoreCollision(bullet.GetComponent<Collider2D>(), GetComponent<Collider2D>());
     }
 

Have tried to use Physics.IgnoreCollision, it doesn't work. The projectiles still collide with the player.

Here's the part of the script. No errors or anything.

 void OnCollisionEnter2D(Collision2D coll)
 {
     if (coll.gameObject.tag == "projectile")
     {
         Transform bullet = Instantiate(bulletPrefab) as Transform;
         Physics.IgnoreCollision(bullet.collider, collider);
     }

And have no idea of how the matrix you mentioned works

No bulletPrefab is a GameObject. How do i assign it as a Transform? (i'm guessing it has to be the transform of the projectiles). But the script is on the same object as the player collider yeah.

No. It did not work. The same thing as before; the player collides with the projectiles.

I should have looked at your code or read your question more carefully. IgnoreCollision() is for 3D colliders. You are making a 2D system. From a look at the reference (not by experience), it appears that you will have to put the bullets on a different layer. You can then use Physics2D.IgnoreLayerCollision(). Sorry for not getting it right up front. You can also set what layers collide using:

  Edit > Project Settings > Physics2D

YES! It works. Using the matrix to ignore collision between the two layers. Thanks for help.

The second Ball should be collision.

Assu$$anonymous$$g this code is on the barrier, the OnCollisionEnter declaration is grabbing the Ball as an object named "collision".

The line should be:

 Physics.IgnoreCollision(collision.collider, collider);