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The Waikato Environment for Knowledge Analysis (WEKA), a machine learning workbench. This version represents the developer version, the "bleeding edge" of development, you could say. New functionality gets added to this version.
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/*
 *   This program is free software: you can redistribute it and/or modify
 *   it under the terms of the GNU General Public License as published by
 *   the Free Software Foundation, either version 3 of the License, or
 *   (at your option) any later version.
 *
 *   This program is distributed in the hope that it will be useful,
 *   but WITHOUT ANY WARRANTY; without even the implied warranty of
 *   MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
 *   GNU General Public License for more details.
 *
 *   You should have received a copy of the GNU General Public License
 *   along with this program.  If not, see .
 */

/*
 *    WrapLayout.java
 *    Public domain code from Java Tips Weblog:
 *    https://tips4java.wordpress.com/about/
 */

package weka.gui;

import java.awt.*;
import javax.swing.JScrollPane;
import javax.swing.SwingUtilities;

/**
 * FlowLayout subclass that fully supports wrapping of components. 

 */
public class WrapLayout extends FlowLayout {
  private static final long serialVersionUID = 7055023419450383821L;
  private Dimension preferredLayoutSize;

  /**
   * Constructs a new WrapLayout with a left alignment and a
   * default 5-unit horizontal and vertical gap.
   */
  public WrapLayout() {
    super();
  }

  /**
   * Constructs a new FlowLayout with the specified alignment and a
   * default 5-unit horizontal and vertical gap. The value of the alignment
   * argument must be one of WrapLayout, WrapLayout,
   * or WrapLayout.
   * 
   * @param align the alignment value
   */
  public WrapLayout(int align) {
    super(align);
  }

  /**
   * Creates a new flow layout manager with the indicated alignment and the
   * indicated horizontal and vertical gaps.
   * 
   * The value of the alignment argument must be one of WrapLayout,
   * WrapLayout, or WrapLayout.
   * 
   * @param align the alignment value
   * @param hgap the horizontal gap between components
   * @param vgap the vertical gap between components
   */
  public WrapLayout(int align, int hgap, int vgap) {
    super(align, hgap, vgap);
  }

  /**
   * Returns the preferred dimensions for this layout given the visible
   * components in the specified target container.
   * 
   * @param target the component which needs to be laid out
   * @return the preferred dimensions to lay out the subcomponents of the
   *         specified container
   */
  @Override
  public Dimension preferredLayoutSize(Container target) {
    return layoutSize(target, true);
  }

  /**
   * Returns the minimum dimensions needed to layout the visible
   * components contained in the specified target container.
   * 
   * @param target the component which needs to be laid out
   * @return the minimum dimensions to lay out the subcomponents of the
   *         specified container
   */
  @Override
  public Dimension minimumLayoutSize(Container target) {
    Dimension minimum = layoutSize(target, false);
    minimum.width -= (getHgap() + 1);
    return minimum;
  }

  /**
   * Returns the minimum or preferred dimension needed to layout the target
   * container.
   *
   * @param target target to get layout size for
   * @param preferred should preferred size be calculated
   * @return the dimension to layout the target container
   */
  private Dimension layoutSize(Container target, boolean preferred) {
    synchronized (target.getTreeLock()) {
      // Each row must fit with the width allocated to the containter.
      // When the container width = 0, the preferred width of the container
      // has not yet been calculated so lets ask for the maximum.

      int targetWidth = target.getSize().width;
      Container container = target;

      while (container.getSize().width == 0 && container.getParent() != null) {
        container = container.getParent();
      }

      targetWidth = container.getSize().width;

      if (targetWidth == 0)
        targetWidth = Integer.MAX_VALUE;

      int hgap = getHgap();
      int vgap = getVgap();
      Insets insets = target.getInsets();
      int horizontalInsetsAndGap = insets.left + insets.right + (hgap * 2);
      int maxWidth = targetWidth - horizontalInsetsAndGap;

      // Fit components into the allowed width

      Dimension dim = new Dimension(0, 0);
      int rowWidth = 0;
      int rowHeight = 0;

      int nmembers = target.getComponentCount();

      for (int i = 0; i < nmembers; i++) {
        Component m = target.getComponent(i);

        if (m.isVisible()) {
          Dimension d = preferred ? m.getPreferredSize() : m.getMinimumSize();

          // Can't add the component to current row. Start a new row.

          if (rowWidth + d.width > maxWidth) {
            addRow(dim, rowWidth, rowHeight);
            rowWidth = 0;
            rowHeight = 0;
          }

          // Add a horizontal gap for all components after the first

          if (rowWidth != 0) {
            rowWidth += hgap;
          }

          rowWidth += d.width;
          rowHeight = Math.max(rowHeight, d.height);
        }
      }

      addRow(dim, rowWidth, rowHeight);

      dim.width += horizontalInsetsAndGap;
      dim.height += insets.top + insets.bottom + vgap * 2;

      // When using a scroll pane or the DecoratedLookAndFeel we need to
      // make sure the preferred size is less than the size of the
      // target containter so shrinking the container size works
      // correctly. Removing the horizontal gap is an easy way to do this.

      Container scrollPane =
        SwingUtilities.getAncestorOfClass(JScrollPane.class, target);

      if (scrollPane != null && target.isValid()) {
        dim.width -= (hgap + 1);
      }

      return dim;
    }
  }

  /*
   * A new row has been completed. Use the dimensions of this row to update the
   * preferred size for the container.
   *
   * @param dim update the width and height when appropriate
   * 
   * @param rowWidth the width of the row to add
   * 
   * @param rowHeight the height of the row to add
   */
  private void addRow(Dimension dim, int rowWidth, int rowHeight) {
    dim.width = Math.max(dim.width, rowWidth);

    if (dim.height > 0) {
      dim.height += getVgap();
    }

    dim.height += rowHeight;
  }
}