Unity之UI正对相机

 //World space的canvas画布需要一直相向相机，cameraAr为相机
Vector3 targetPos = canvas.transform.position + cameraAr.transform.rotation * Vector3.forward;
        Vector3 targetOrientation = cameraAr.transform.rotation * Vector3.up;
        canvas.transform.LookAt(targetPos, targetOrientation);