public void Update()
 {
     if (Time.time - last_display_time > DISPLAY_PERIOD)
     {
         if (to_display.Count > 0)
         {
             EnableDisplay();
             CatAchievement current = to_display.Dequeue();
             text.text         = current.name;
             last_display_time = Time.time;
         }
         else
         {
             DisableDisplay();
         }
     }
 }
 public void OnUnlock(CatAchievement achievement)
 {
     to_display.Enqueue(achievement);
 }