gcc/libjava/javax/swing/ViewportLayout.java

/* ViewportLayout.java --
   Copyright (C) 2002, 2004 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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02111-1307 USA.

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permission to link this library with independent modules to produce an
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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;

/**
 * ViewportLayout
 * @author	Andrew Selkirk
 * @author	Graydon Hoare
 */
public class ViewportLayout implements LayoutManager, Serializable
{
  static final long serialVersionUID = -788225906076097229L;

  public ViewportLayout() 
  {
  }
  public void addLayoutComponent(String name, Component c) 
  {
  }
  public void removeLayoutComponent(Component c) 
  {
  }
  public Dimension preferredLayoutSize(Container parent) 
  {
    JViewport vp = (JViewport)parent;
    Component view = vp.getView();
      return view.getPreferredSize();
  }
  public Dimension minimumLayoutSize(Container parent) 
  {
    JViewport vp = (JViewport)parent;
    Component view = vp.getView();
    return view.getMinimumSize();
  }

  /**
   * 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 larger than the view's minimum size, put the port
   * at view position <code>(0,0)</code> and make the view's size equal to
   * the port's.</li>
   *
   * <li>If the port is smaller than the view, leave the view at its
   * minimum size. also, do not move the port, <em>unless</em> the port
   * extends into space <em>past</em> the edge of the view. If so, move the
   * port up or to the left, in view space, by the amount of empty space
   * (keep the lower and right edges lined up)</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();

    // 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 = view.getPreferredSize();
    Dimension viewMinimum = view.getMinimumSize();
    Point portLowerRight = new Point(portBounds.x + portBounds.width,
                                     portBounds.y + portBounds.height);
        
    // vertical implementation of the above rules
    if (portBounds.height >= viewMinimum.height)
      {
        portBounds.y = 0;
        viewPref.height = portBounds.height;
      }
    else
      {
        viewPref.height = viewMinimum.height;
        int overextension = portLowerRight.y - viewPref.height;
        if (overextension > 0)
            portBounds.y -= overextension;
      }

    // horizontal implementation of the above rules
    if (portBounds.width >= viewMinimum.width)
      {
        portBounds.x = 0;
        viewPref.width = portBounds.width;
      }
    else
      {
        viewPref.width = viewMinimum.width;
        int overextension = portLowerRight.x - viewPref.width;
        if (overextension > 0)
            portBounds.x -= overextension;
      }

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