判断两条线段是否相交

/// <summary>
    /// 判断两条线段是否相交
    /// </summary>
    /// <param name="a1"></param>
    /// <param name="a2"></param>
    /// <param name="b1"></param>
    /// <param name="b2"></param>
    /// <returns></returns>
    public bool IsBanana(Vector2 a1, Vector2 a2, Vector2 b1, Vector2 b2)
    {
        if (Mathf.Min(a1.x, a2.x) > Mathf.Max(b1.x, b2.x) || Mathf.Max(a1.x, a2.x) < Mathf.Min(b1.x, b2.x) ||
            Mathf.Min(a1.y, a2.y) > Mathf.Max(b1.y, b2.y) || Mathf.Max(a1.y, a2.y) < Mathf.Min(b1.y, b2.y))
        {
            return false;
        }

        if (Math.Sign(Vector3.Cross(b1 - a1, a2 - a1).z) * Math.Sign(Vector3.Cross(b2 - a1, a2 - a1).z) > 0 ||
            Math.Sign(Vector3.Cross(b1 - a2, a1 - a2).z) * Math.Sign(Vector3.Cross(b2 - a2, a1 - a2).z) > 0 ||
            Math.Sign(Vector3.Cross(a1 - b1, b2 - b1).z) * Math.Sign(Vector3.Cross(a2 - b2, b2 - b1).z) > 0 ||
            Math.Sign(Vector3.Cross(a1 - b2, b1 - b2).z) * Math.Sign(Vector3.Cross(a2 - b2, b1 - b2).z) > 0)
        {
            return false;
        }

        return true;
    }