gcc/libjava/classpath/javax/swing/ViewportLayout.java

/* ViewportLayout.java --
   Copyright (C) 2002, 2004, 2006 Free Software Foundation, Inc.

This file is part of GNU Classpath.

GNU Classpath is free software; you can redistribute it and/or modify
it under the terms of the GNU General Public License as published by
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02110-1301 USA.

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package javax.swing;

import java.awt.Component;
import java.awt.Container;
import java.awt.Dimension;
import java.awt.LayoutManager;
import java.awt.Point;
import java.awt.Rectangle;
import java.io.Serializable;

/**
 * The default layout for {@link JViewport}. The viewport makes its view the
 * same size as itself, but not smaller than its minimum size.
 *
 * If the port extends extends into space <em>past</em> the edge of the view,
 * this layout manager moves the port up or to the left, in view space, by the
 * amount of empty space (keep the lower and right edges lined up).
 *
 * @author  Andrew Selkirk
 * @author  Graydon Hoare
 * @author  Audrius Meskauskas (audriusa@Bioinformatics.org)
 */
public class ViewportLayout implements LayoutManager, Serializable
{
  private static final long serialVersionUID = -788225906076097229L;

  public ViewportLayout()
  {
    // Nothing to do here.
  }

  /**
   * The method is not used with this manager.
   */
  public void addLayoutComponent(String name, Component c)
  {
    // Nothing to do here.
  }

  /**
   * The method is not used with this manager.
   */
  public void removeLayoutComponent(Component c)
  {
    // Nothing to do here.
  }

  /**
   * Get the preferred layout size. If the view implements
   * {@link Scrollable}, this method returns
   * {@link Scrollable#getPreferredScrollableViewportSize}.
   * Otherwise, it returns {@link Component#getPreferredSize()}.
   *
   * @return the preferred layout size, as described about.
   */
  public Dimension preferredLayoutSize(Container parent)
  {
    JViewport vp = (JViewport)parent;
    Component view = vp.getView();
    if (view != null)
      {
        if (view instanceof Scrollable)
          return ((Scrollable)view).getPreferredScrollableViewportSize();
        return view.getPreferredSize();
      }
    else
      return new Dimension();
  }

  /**
   * Get the minimum layout size. Normally this method returns the value,
   * returned by the view method {@link Component#getMinimumSize()}.
   *
   * If the view is not set, the zero size is returned.
   *
   * @param parent the viewport
   * @return the minimum layout size.
   */
  public Dimension minimumLayoutSize(Container parent)
  {
    // These values have been determined by the Mauve test for this method.
    return new Dimension(4, 4);
  }

  /**
   * Layout the view and viewport to respect the following rules. These are not
   * precisely the rules described in sun's javadocs, but they are the rules
   * which sun's swing implementation follows, if you watch its behavior:
   * <ol>
   * <li>If the port is smaller than the view, leave the view at its current
   * size.</li>
   * <li>If the view is smaller than the port, the view is top aligned.</li>
   * <li>If the view tracks the port size, the view position is always zero and
   * the size equal to the viewport size</li>
   * <li>In {@link JViewport#setViewSize(Dimension)}, the view size is never
   * set smaller that its minimum size.</li>
   * </ol>
   *
   * @see JViewport#getViewSize
   * @see JViewport#setViewSize
   * @see JViewport#getViewPosition
   * @see JViewport#setViewPosition
   */
  public void layoutContainer(Container parent)
  {
    // The way to interpret this function is basically to ignore the names
    // of methods it calls, and focus on the variable names here. getViewRect
    // doesn't, for example, return the view; it returns the port bounds in
    // view space. Likwise setViewPosition doesn't reposition the view; it
    // positions the port, in view coordinates.

    JViewport port = (JViewport) parent;
    Component view = port.getView();

    if (view == null)
      return;

    // These dimensions and positions are in *view space*. Do not mix
    // variables in here from port space (eg. parent.getBounds()). This
    // function should be entirely in view space, because the methods on
    // the viewport require inputs in view space.

    Rectangle portBounds = port.getViewRect();
    Dimension viewPref = new Dimension(view.getPreferredSize());

    Point portLowerRight = new Point(portBounds.x + portBounds.width,
                                     portBounds.y + portBounds.height);

    // vertical implementation of the above rules
    if (view instanceof Scrollable)
      {
        Scrollable sView = (Scrollable) view;

        // If the view size matches viewport size, the port offset can
        // only be zero.
        if (sView.getScrollableTracksViewportWidth())
          {
            viewPref.width = portBounds.width;
            portBounds.x = 0;
          }
        if (sView.getScrollableTracksViewportHeight())
          {
            viewPref.height = portBounds.height;
            portBounds.y = 0;
          }
      }

     if (viewPref.width < portBounds.width)
       viewPref.width = portBounds.width;
     if (viewPref.height < portBounds.height)
       viewPref.height = portBounds.height;

    // If the view is larger than the port, the port is top and right
    // aligned.
    if (portLowerRight.x > viewPref.width)
      portBounds.x = 0;

    if (portLowerRight.y > viewPref.height)
      portBounds.y = 0;

    port.setViewSize(viewPref);
    port.setViewPosition(portBounds.getLocation());
  }

}