Swing/TableColumnReorderingIcon のバックアップ(No.1)

class ColumnDragLayerUI extends LayerUI<JScrollPane> {
  private final Rectangle draggableRect = new Rectangle();

  @Override public void installUI(JComponent c) {
    super.installUI(c);
    if (c instanceof JLayer) {
      ((JLayer<?>) c).setLayerEventMask(
          AWTEvent.MOUSE_EVENT_MASK | AWTEvent.MOUSE_MOTION_EVENT_MASK);
    }
  }

  @Override public void uninstallUI(JComponent c) {
    if (c instanceof JLayer) {
      ((JLayer<?>) c).setLayerEventMask(0);
    }
    super.uninstallUI(c);
  }

  @Override public void paint(Graphics g, JComponent c) {
    super.paint(g, c);
    if (!draggableRect.isEmpty()) {
      Graphics2D g2 = (Graphics2D) g.create();
      // g2.fill(draggableRect);
      Icon icon = new DragAreaIcon();
      int x = (int) (draggableRect.getCenterX() - icon.getIconWidth() / 2d);
      int y = draggableRect.y + 1;
      icon.paintIcon(c, g2, x, y);
      g2.dispose();
    }
  }

  @Override protected void processMouseEvent(
      MouseEvent e, JLayer<? extends JScrollPane> l) {
    super.processMouseEvent(e, l);
    Component c = e.getComponent();
    if (c instanceof JTableHeader) {
      JTableHeader header = (JTableHeader) c;
      if (e.getID() == MouseEvent.MOUSE_PRESSED) {
        Point pt = e.getPoint();
        updateIconAndCursor(header, pt, l);
      } else if (e.getID() == MouseEvent.MOUSE_RELEASED) {
        header.setCursor(Cursor.getPredefinedCursor(Cursor.DEFAULT_CURSOR));
        draggableRect.setSize(0, 0);
      }
    }
  }

  @Override protected void processMouseMotionEvent(
      MouseEvent e, JLayer<? extends JScrollPane> l) {
    Component c = e.getComponent();
    if (c instanceof JTableHeader) {
      JTableHeader header = (JTableHeader) c;
      if (e.getID() == MouseEvent.MOUSE_DRAGGED) {
        TableColumn draggedColumn = header.getDraggedColumn();
        if (!draggableRect.isEmpty() && draggedColumn != null) {
          EventQueue.invokeLater(() -> {
            int modelIndex = draggedColumn.getModelIndex();
            int viewIndex = header.getTable().convertColumnIndexToView(modelIndex);
            Rectangle rect = header.getHeaderRect(viewIndex);
            rect.x += header.getDraggedDistance();
            draggableRect.setRect(SwingUtilities.convertRectangle(header, rect, l));
            header.repaint(rect);
          });
        } else {
          e.consume(); // Refuse to start drag
        }
      } else if (e.getID() == MouseEvent.MOUSE_MOVED) {
        Point pt = e.getPoint();
        updateIconAndCursor(header, pt, l);
        header.repaint();
      }
    } else {
      c.setCursor(Cursor.getPredefinedCursor(Cursor.DEFAULT_CURSOR));
      draggableRect.setSize(0, 0);
    }
  }

  private void updateIconAndCursor(JTableHeader header, Point pt, JLayer<?> l) {
    Rectangle r = header.getHeaderRect(header.columnAtPoint(pt));
    r.height /= 2;
    if (r.contains(pt)) {
      header.setCursor(Cursor.getPredefinedCursor(Cursor.HAND_CURSOR));
      draggableRect.setRect(SwingUtilities.convertRectangle(header, r, l));
    } else {
      header.setCursor(Cursor.getPredefinedCursor(Cursor.DEFAULT_CURSOR));
      draggableRect.setSize(0, 0);
    }
  }
}