unity 在没有碰撞物的情况下，射线生成物体

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 public Camera mainCamrea;
   public float h = 0;

    private void Update()
    {
        if (Input.GetKeyDown(KeyCode.Mouse0))
        {
            Ray ray = mainCamrea.ScreenPointToRay(Input.mousePosition);
            float dis = (h - ray.origin.y) / ray.direction.y;
            Vector3 pos = ray.origin + ray.direction * dis;
            Clone(pos);
        }
    }

    private void Clone(Vector3 pos)
    {
        GameObject cl = GameObject.CreatePrimitive(PrimitiveType.Sphere);
        cl.transform.position = pos;
    }