public void updateItemDisplay(
    Model itemModel, float amount, float xoff, float yoff
  ) {
    ItemStack match = null ;
    
    for (ItemStack s : stackFX) if (s.itemModel == itemModel) match = s ;
    if (amount < 1) { if (match != null) stackFX.remove(match) ; return ; }
    if (match == null) stackFX.add(match = new ItemStack(itemModel)) ;
    
    match.updateAmount((int) amount) ;
    match.position.set(
      position.x + xoff,
      position.y + yoff,
      position.z
    ) ;
  }