How to create collider between two circle in 2D

Question

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I have created a mesh of first image and i want the collider between the pink shaded region

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After writing the following Script i got collider in second image

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    void InnerOuterCircle () {

    vertice = new List<Vector3> ();
    triangle = new List<int> ();

    for (int x = 0; x <= angle; x ++) {

        vertice.Add(new Vector3(Mathf.Cos(x * Mathf.Deg2Rad) * innerRadius,Mathf.Sin(x * Mathf.Deg2Rad) * innerRadius));
        vertice.Add(new Vector3(Mathf.Cos(x * Mathf.Deg2Rad) * outerRadius,Mathf.Sin(x * Mathf.Deg2Rad) * outerRadius));

    }

    for (int x = 0; x < vertice.Count - 2; x += 2) {

        triangle.Add (x + 0);
        triangle.Add (x + 2);
        triangle.Add (x + 1);

        triangle.Add (x + 2);
        triangle.Add (x + 3);
        triangle.Add (x + 1);

    }

    Mesh mesh = new Mesh ();

    MeshFilter filter = GetComponent<MeshFilter> ();
    filter.mesh = mesh;

    mesh.vertices = vertice.ToArray ();
    mesh.triangles = triangle.ToArray ();

    PolygonCollider2D collider = gameObject.AddComponent<PolygonCollider2D> ();
    Vector2[] edgePoints = new Vector2[vertice.Count];
    for (int i = 0; i < vertice.Count; i++) {
        edgePoints [i] = vertice [i];
    }
    collider.points = edgePoints;
}

Answer 1

Assuming it's possible to do custom collision detection logic in Unity, collision detection between circles is rather simple; just use the Pythagorean theorem on the vector between their centers:

bool TestCirclesCollision(double x1, double y1, double r1, double x2, double y2, double r2)
{
    // Pythagorean theorem to compute distance between two points
    var dx = x2 - x1;
    var dy = y2 - y1;
    var distance = Math.Sqrt(dx * dx + dy * dy);

    // compare to combined radii of two circles
    // return true if collision, otherwise false
    return distance <= r1 + r2;
}

If the circles have holes in them at their centers, you would add an additional test to make sure they're not too close, same as the existing radius test but with a >= instead of a <= on the inner:

return distance <= r1outer + r2outer && distance >= r1inner + r2inner;