JTree - Move nodes to the right

Question

I have a JTree with several node levels. I changed the icons for the root nodes to some bigger ones. The problem is, now that the icons are bigger than the default ones, that the vertical dashed lines and the corresponding child nodes are not centered below the root node icon.

See following picture:

My question is: Is it possible to move everything except the root nodes a little bit to the right side?

Answer 1

Set left margin in JTree and draw real root node icon separately in JLayer.

import java.awt.*;
import javax.swing.*;
import javax.swing.plaf.*;
import javax.swing.tree.*;

public class MiddleXOfRootNodeIconTest {
  public JComponent makeUI() {
    int ow = UIManager.getIcon("Tree.openIcon").getIconWidth();
    int iw = 32;

    Icon icon1 = new ColorIcon(Color.GREEN, new Dimension(ow, iw));
    Icon icon2 = new ColorIcon(new Color(0x550000AA, true), new Dimension(iw, iw));

    JTree tree = new JTree();
    tree.setBorder(BorderFactory.createEmptyBorder(1, 1 + iw / 2, 1, 1));
    //TEST:
    //tree.setBorder(BorderFactory.createMatteBorder(1, 1 + iw / 2, 1, 1, Color.RED));
    tree.setCellRenderer(new CompoundTreeCellRenderer(icon1, iw));
    LayerUI<JTree> layerUI = new LayerUI<JTree>() {
      @Override public void paint(Graphics g, JComponent c) {
        super.paint(g, c);
        Graphics2D g2 = (Graphics2D) g.create();
        icon2.paintIcon(c, g2, 1 + ow / 2, 1);
        g2.dispose();
      }
    };

    JPanel p = new JPanel(new GridLayout(1, 3));
    p.add(new JScrollPane(new JTree()));
    p.add(new JScrollPane(new JLayer<JTree>(tree, layerUI)));
    return p;
  }
  public static void main(String... args) {
    EventQueue.invokeLater(() -> {
      JFrame f = new JFrame();
      f.setDefaultCloseOperation(WindowConstants.EXIT_ON_CLOSE);
      f.getContentPane().add(new MiddleXOfRootNodeIconTest().makeUI());
      f.setSize(320, 240);
      f.setLocationRelativeTo(null);
      f.setVisible(true);
    });
  }
}
class CompoundTreeCellRenderer extends DefaultTreeCellRenderer {
  private static final Color ALPHA_ZERO = new Color(0x0, true);
  private final JPanel p = new JPanel(new GridBagLayout());
  private final GridBagConstraints ci = new GridBagConstraints();
  private final GridBagConstraints cl = new GridBagConstraints();
  private final JLabel icon = new JLabel();
  private final Icon gap1 = new ColorIcon(ALPHA_ZERO, new Dimension(2, 10));
  private final Icon gap2;
  private final Icon rootIcon;
  public CompoundTreeCellRenderer(Icon rootIcon, int iw) {
    super();
    Dimension d = new Dimension(2 + (iw - rootIcon.getIconWidth()) / 2, 10);
    this.rootIcon = rootIcon;
    //TEST: this.gap2 = new ColorIcon(Color.BLUE, d);
    this.gap2 = new ColorIcon(ALPHA_ZERO, d);
    this.setOpaque(false);
    p.setOpaque(false);
    ci.gridx = 0;
    ci.weightx = 1.0;
    cl.gridx = 1;
    cl.anchor = GridBagConstraints.WEST;
  }
  @Override public Component getTreeCellRendererComponent(
      JTree tree, Object value, boolean selected, boolean expanded,
      boolean leaf, int row, boolean hasFocus) {
    JLabel l = (JLabel) super.getTreeCellRendererComponent(
        tree, value, selected, expanded, leaf, row, hasFocus);
    l.setOpaque(false);
    p.removeAll();

    if (value.equals(tree.getModel().getRoot())) {
      icon.setIcon(rootIcon);
      l.setIcon(gap2);
    } else {
      icon.setIcon(l.getIcon());
      l.setIcon(gap1);
    }
    p.add(icon, ci);
    p.add(l, cl);
    return p;
  }
}
class ColorIcon implements Icon {
  private final Color color;
  private final Dimension dim;
  public ColorIcon(Color color, Dimension dim) {
    this.color = color;
    this.dim = dim;
  }
  @Override public void paintIcon(Component c, Graphics g, int x, int y) {
    Graphics2D g2 = (Graphics2D) g.create();
    g2.translate(x, y);
    g2.setColor(color);
    g2.fillRect(1, 1, dim.width - 2, dim.height - 2);
    g2.dispose();
  }
  @Override public int getIconWidth()  {
    return dim.width;
  }
  @Override public int getIconHeight() {
    return dim.height;
  }
}