通过Dot和Cross获取a到b的夹角

    //获取a到b的夹角，b到a的夹角
    public void DotAndCross() {
        a = CubeA.transform.position;
        b = CubeB.transform.position;
        Vector3 c = Vector3.Cross(a, b);//通过叉积求的A，B的法向量
        float angle = Vector3.Angle(a, b);//求得a,b的夹角(绝对值)

        //a到b的夹角
        //获取正负号
        float sign = Mathf.Sign(Vector3.Dot(c.normalized, Vector3.Cross(a.normalized, b.normalized)));
        float sign_angle = sign * angle;
        Debug.Log("a到b的夹角是" + sign_angle);

        //b到a的夹角
        //获取正负号
        sign = Mathf.Sign(Vector3.Dot(c.normalized, Vector3.Cross(b.normalized, a.normalized)));
       	sign_angle = sign * angle;
        Debug.Log("b到a的夹角是" + sign_angle);
    }