// Use this for initialization
    protected override IntPtr Init()
    {
        FrictionJointDef jd = new FrictionJointDef(other.body, body.body);

        jd.Initialize(other.body, body.body, anchor);
        jd.maxForce  = maxForce;
        jd.maxTorque = maxTorque;
        return(API.CreateFrictionJoint(B2DWorld.instance.world, jd));
    }