Bug OnTriggerEnter2D triggered despite being ignored in the layer collision matrix.

The layers are checked when two things come into contact. If it says they cannot, a contact is not created and therefore nothing will happen which obviously includes subsequent callbacks.

If you're changing the setting in script while callbacks are happening, it won't change callbacks yet to happen as they all happen together at the end of the simulation step. Same if you were to change the layer during callbacks. Changing this ensures that new contacts will behave as you've requested and existing contacts will be adjusted to be allowed or not allowed. This won't affect callbacks that are being performed from the simulation step.

Beyond that, there's no reason and this has never been reported.

NOTE: You only need to check one direction here as it'll automatically be a bi-direction check of layer vs layer.

 

Sorry, the descripton is a tad confusing. Know that parent child relationships are of no concern to physics, it never sees them. It is simply concerned about when two colliders potentially overlap, it then checks their layer masks to see if they can. No transform hierarchies are involved and it's super simple what happens and it doesn't involve anything to do with Unity (the Box2D physics system) in reality.

In terms of callbacks after the simulation has run; when two colliders come into contact, a callback happens on the Collider2D GameObject as well as the Rigidbody2D GameObject if it's not on the same GameObject (parent) and the same happens for the other Collider2D/Rigidbody2D involved in the contact.

 

If you have a simple reproduction project then please feel free to share it and I can take a look for you.

 

Unfortunately I cannot access a bug report until QA have processed it or at least until they are around next week. I just wanted access to the test project really. Regardless, thanks for the instructions, I'll give this a go setting up shortly.

It wouldn't anyway. The child collider is attached to the Rigidbody2D. Sibling colliders (colliders attached to the same Rigidbody2D) cannot ever come into contact with each other. Different Rigidbody2D can of course. That said, you're debugging the check which says if those layers are allowed to come into contact which isn't a statement of whether the colliders in question could ever be allowed to contact; those two things are not the same.

So you must've set these Rigidbody2D to use full kinematic contacts. If not, you're contacting something else. Kinematic/Kinematic do not come into contact unless you ask for it.

 

Okay so I just created a test project following your instructions and I too get that callback but I get it because the two child colliders are on Layer "B" and following your instructions, only Layer "A" and Layer "B" cannot come into contact. This is correct behaviour.

However, if you place this callback on the Rigidbody2D (the collider there didn't collide) then using "gameObject.layer" isn't anything to do with the two colliders coming into contact.

See what I said above:

Unfortunately, because trigger callbacks only tell you the "other" collider, you have no way of knowing which one on "this" side actually collided. You've made that even worse in your case because you're assuming it's the one on the "Parent" GameObject which is likely isn't.

Solution:
Change it to not be a trigger and use the "Collision2D" structure instead, that gives you both sides and because it's Kinematic, you won't get a collision response.

Using the following method on a script on the "Parent" GameObject now correctly produces "false" as the output:

Code (CSharp):

1.     void OnCollisionEnter2D(Collision2D collision)
2.     {
3.         Debug.Log($"Test: {Physics2D.GetIgnoreLayerCollision(collision.collider.gameObject.layer, collision.gameObject.layer)}.");
4.     }
5.  

Also, would you please request that the bug case be closed?