MultisortTableHeaderCellRenderer.java

/**
 * MultisortTableHeaderCellRenderer class written by Darryl from
 * https://tips4java.wordpress.com/2010/08/22/alpha-icons/
 *
 * Open licence code.
 */
package org.openpnp.gui;

import javax.swing.Icon;
import javax.swing.JTable;
import javax.swing.RowSorter;
import javax.swing.UIManager;

/**
 * An extension of <code>DefaultTableHeaderCellRenderer</code> that paints sort icons
 * on the header of each sorted column with varying opacity.
 * @author Darryl
 */
public class MultisortTableHeaderCellRenderer extends DefaultTableHeaderCellRenderer {

  private float alpha;

  /**
   * Constructs a <code>MultisortTableHeaderCellRenderer</code> with a default alpha of 0.5.
   */
  public MultisortTableHeaderCellRenderer() {
    this(0.5F);
  }

  /**
   * Constructs a <code>MultisortTableHeaderCellRenderer</code> with the specified alpha.
   * A lower value represents greater contrast between icons, while a higher value can make
   * more sort icons visible.
   * 
   * @param alpha the opacity, in the range 0.0F to 1.0F.  Recommended range: 0.5F to 0.7F.
   */
  public MultisortTableHeaderCellRenderer(float alpha) {
    this.alpha = alpha;
  }

  /**
   * Overridden to return an icon suitable to a sorted column, or null if the column is unsorted.
   * The icon for the primary sorted column is fully opaque, and the opacity is reduced by a
   * factor of <code>alpha</code> for each subsequent sort index.
   *
   * @param table the <code>JTable</code>.
   * @param column the column index.
   * @return the sort icon with appropriate opacity, or null if the column is unsorted.
   */
  @Override
  public Icon getIcon(JTable table, int column) {
    float computedAlpha = 1.0F;
    for (RowSorter.SortKey sortKey : table.getRowSorter().getSortKeys()) {
      if (table.convertColumnIndexToView(sortKey.getColumn()) == column) {
        switch (sortKey.getSortOrder()) {
          case ASCENDING:
            return new AlphaIcon(UIManager.getIcon("Table.ascendingSortIcon"), computedAlpha);
          case DESCENDING:
            return new AlphaIcon(UIManager.getIcon("Table.descendingSortIcon"), computedAlpha);
        }
      }
      computedAlpha *= alpha;
    }
    return null;
  }
}