Multiple Colliders in Collision

Question

I have an object that has a front collider, left collider and right collider. When a collision occurs, I notice that there are situations where the front collider and left collider/right collider has collided with the object. I need to somehow figure out which collider made contact "first". Is there anyway to do this? The reason I need this is because I have different code that needs to run depending on which collider made contact first.

Answer 1

You can always use OnColliderEnter (or OnCollisionEnter2D), and store the first collision. So consider something like this:

Collider FirstCollider;
int CollisionCount;

void OnCollisionEnter(Collider collider)
{
     if (FirstCollider == null)
         FirstCollider = collider;

     CollisionCount++;
}

void OnCollisionExit(Collider collider)
{
     CollisionCount--;

     if (CollisionCount == 0)
        FirstCollider = null;
}

You would want to make sure none of your colliders are colliding before you set FirstCollider back to null.

I haven't tested it, but I figure it should work.

Answer 2

Actually and hopefully you did attach all three colliders on same gameObject. What you have to do is create 3 children gameObject and attach one collider to one child. In that way you can detect what you want.

Attach a Jon's script to each collider then in my OnCollisionEnter you can from which collider collision is occured through tag, any attribute or even with gameObject's name. Like,

void OnCollisionEnter( Collision col)
{
    Debug.Log("Collided with: " + name);
}

Update:

If your only problem is to avoid your own colliders then one of the many solutions is to assign a separate layer for your character for example layer name is Player.

• Add layer as

• Assign it to parent and children.
• Goto Edit -> Project Settings -> Physics, in collision matrix, remove check from Player to Player like,

In this way your player colliders will never fire any event on their own collision.

Answer 3

I'd just like to add, for completeness, that you could always try using a single collider for your GameObject, then infer what side it was on from the collision point.

You can access the point like so:

void OnCollisionEnter(Collision collision) {

    foreach(var contact in collision.contacts) {

        Vector3 pointOfImpact = contact.point;

    }

}