Unity判断顺时针或者逆时针旋转

    Vector2 curPos;
    Vector2 lastPos;
    Vector2 centerInScreen;

 void Update()
    {
         curPos = eventData.position;

        centerInScreen = RectTransformUtility.WorldToScreenPoint(null,         transform.position);
        Debug.Log("centerInScreen: " + centerInScreen);

        float deltaAngle = GetDeltaRadians();
        Debug.Log("deltaAngle: " + deltaAngle);
        RotateUI(deltaAngle * Mathf.Rad2Deg);
        lastPos = curPos;
    }

    public float GetDeltaRadians()
    {
        var a = GetLastRadians(centerInScreen);
        var b = GetRadians(centerInScreen);
        var d = Mathf.Repeat(a - b, Mathf.PI * 2.0f);
        Debug.Log("a: " + a + "  b: " + b + "  d: " + d);
        if (d > Mathf.PI)
        {
            d -= Mathf.PI * 2.0f;
        }

        return d;
    }

    public float GetLastRadians(Vector2 pivot)
    {
        return Mathf.Atan2(lastPos.x - pivot.x, lastPos.y - pivot.y);
    }
    /// 
This will return the angle between the finger and the reference point, relative to the screen.
    public float GetRadians(Vector2 pivot)
    {
        return Mathf.Atan2(curPos.x - pivot.x, curPos.y - pivot.y);
    }