Getting all collisions with gameobject that script is attached to

Questions & Answers
1

Hello, I am attempting to get all the collisions with the sphere in the picture in order to get the mean normal. Because I am checking in the collection other.contacts, the length of the contacts array is always 1, because it is checking the one wall to see what is colliding with it, which is only my one sphere. I want to check everything that is colliding with the sphere, i.e. the two walls. Is there a way to do from a single OnCollisionStay2D call? In other words, get all collisions on this gameobject, not the other colliding object. The following code always logs “NumContacts: 1, Normal: (the normal of the longer wall)”. Thanks.

    void OnCollisionStay2D(Collision2D other)
    {
        Vector2 vecNormal = Vector2.zero;

        foreach (ContactPoint2D contact in other.contacts)
        {
            vecNormal += contact.normal;
        }

        vecNormal /= other.contacts.Length;
        jumpNormal = vecNormal;
        Debug.Log("NumContacts: " + other.contacts.Length + ", Normal: " + jumpNormal);
    }

50520-physicsscreen.png
50520-physicsscreen.png1385×860 68.1 KB

2

Collisions are always between two bodies only, and also only a single contact per collision (not just in Unity, but in any Physics Engine I know). The reason is simple: checking for collisions and resolving them is really hard.
But the case pictured above is usually handled correctly. It is calculated as two distinct collisions, one with each wall. Since the first collision doesn’t change the component of the ball’s velocity that is used to calculate the second collision, the result should be correct.

If you need the mean normal for some internal logic, you will have to write something yourself, like on collision checking for intersections with other objects, maybe with Physics.SpherecastAll().