@Override
  public void computeEnabled() {
    Project proj = canvas.getProject();
    Circuit circ = canvas.getCircuit();
    Selection sel = canvas.getSelection();
    boolean selEmpty = sel.isEmpty();
    boolean canChange = proj.getLogisimFile().contains(circ);
    boolean clipExists = !Clipboard.isEmpty();
    boolean selHasRemovable = false;
    for (CanvasObject o : sel.getSelected()) {
      if (!(o instanceof AppearanceElement)) {
        selHasRemovable = true;
      }
    }
    boolean canRaise;
    boolean canLower;
    if (!selEmpty && canChange) {
      Map<CanvasObject, Integer> zs = ZOrder.getZIndex(sel.getSelected(), canvas.getModel());
      int zmin = Integer.MAX_VALUE;
      int zmax = Integer.MIN_VALUE;
      int count = 0;
      for (Map.Entry<CanvasObject, Integer> entry : zs.entrySet()) {
        if (!(entry.getKey() instanceof AppearanceElement)) {
          count++;
          int z = entry.getValue().intValue();
          if (z < zmin) zmin = z;
          if (z > zmax) zmax = z;
        }
      }
      int maxPoss = AppearanceCanvas.getMaxIndex(canvas.getModel());
      if (count > 0 && count <= maxPoss) {
        canRaise = zmin <= maxPoss - count;
        canLower = zmax >= count;
      } else {
        canRaise = false;
        canLower = false;
      }
    } else {
      canRaise = false;
      canLower = false;
    }
    boolean canAddCtrl = false;
    boolean canRemCtrl = false;
    Handle handle = sel.getSelectedHandle();
    if (handle != null && canChange) {
      CanvasObject o = handle.getObject();
      canAddCtrl = o.canInsertHandle(handle.getLocation()) != null;
      canRemCtrl = o.canDeleteHandle(handle.getLocation()) != null;
    }

    setEnabled(LogisimMenuBar.CUT, selHasRemovable && canChange);
    setEnabled(LogisimMenuBar.COPY, !selEmpty);
    setEnabled(LogisimMenuBar.PASTE, canChange && clipExists);
    setEnabled(LogisimMenuBar.DELETE, selHasRemovable && canChange);
    setEnabled(LogisimMenuBar.DUPLICATE, !selEmpty && canChange);
    setEnabled(LogisimMenuBar.SELECT_ALL, true);
    setEnabled(LogisimMenuBar.RAISE, canRaise);
    setEnabled(LogisimMenuBar.LOWER, canLower);
    setEnabled(LogisimMenuBar.RAISE_TOP, canRaise);
    setEnabled(LogisimMenuBar.LOWER_BOTTOM, canLower);
    setEnabled(LogisimMenuBar.ADD_CONTROL, canAddCtrl);
    setEnabled(LogisimMenuBar.REMOVE_CONTROL, canRemCtrl);
  }