/*
 * Copyright (c) 1997, 2013, Oracle and/or its affiliates. All rights reserved.
 * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
 *
 * This code is free software; you can redistribute it and/or modify it
 * under the terms of the GNU General Public License version 2 only, as
 * published by the Free Software Foundation.  Oracle designates this
 * particular file as subject to the "Classpath" exception as provided
 * by Oracle in the LICENSE file that accompanied this code.
 *
 * This code 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
 * version 2 for more details (a copy is included in the LICENSE file that
 * accompanied this code).
 *
 * You should have received a copy of the GNU General Public License version
 * 2 along with this work; if not, write to the Free Software Foundation,
 * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.
 *
 * Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA
 * or visit www.oracle.com if you need additional information or have any
 * questions.
 */

package javax.swing;

import java.awt.*;
import java.awt.event.*;
import java.awt.peer.ComponentPeer;
import java.beans.Transient;
import javax.swing.plaf.ViewportUI;

import javax.swing.event.*;
import javax.swing.border.*;
import javax.accessibility.*;

import java.io.Serializable;

The "viewport" or "porthole" through which you see the underlying
information. When you scroll, what moves is the viewport. It is like
peering through a camera's viewfinder. Moving the viewfinder upwards
brings new things into view at the top of the picture and loses
things that were at the bottom.

By default, JViewport is opaque. To change this, use the
setOpaque method.

NOTE:We have implemented a faster scrolling algorithm that
does not require a buffer to draw in. The algorithm works as follows:
The view and parent view and checked to see if they are
JComponents,
if they aren't, stop and repaint the whole viewport.
If the viewport is obscured by an ancestor, stop and repaint the whole
viewport.
Compute the region that will become visible, if it is as big as
the viewport, stop and repaint the whole view region.
Obtain the ancestor Window's graphics and
do a copyArea on the scrolled region.
Message the view to repaint the newly visible region.
The next time paint is invoked on the viewport, if the clip region
is smaller than the viewport size a timer is kicked off to repaint the
whole region.

In general this approach is much faster. Compared to the backing store
approach this avoids the overhead of maintaining an offscreen buffer and
having to do two copyAreas.
Compared to the non backing store case this
approach will greatly reduce the painted region.

This approach can cause slower times than the backing store approach
when the viewport is obscured by another window, or partially offscreen.
When another window
obscures the viewport the copyArea will copy garbage and a
paint event will be generated by the system to inform us we need to
paint the newly exposed region. The only way to handle this is to
repaint the whole viewport, which can cause slower performance than the
backing store case. In most applications very rarely will the user be
scrolling while the viewport is obscured by another window or offscreen,
so this optimization is usually worth the performance hit when obscured.

Warning: Swing is not thread safe. For more
information see Swing's Threading
Policy.

Warning:
Serialized objects of this class will not be compatible with
future Swing releases. The current serialization support is
appropriate for short term storage or RMI between applications running
the same version of Swing.  As of 1.4, support for long term storage
of all JavaBeans™
has been added to the java.beans package. Please see XMLEncoder. 
Author:
Hans Muller, Philip Milne
See Also:
JScrollPane/**
 * The "viewport" or "porthole" through which you see the underlying
 * information. When you scroll, what moves is the viewport. It is like
 * peering through a camera's viewfinder. Moving the viewfinder upwards
 * brings new things into view at the top of the picture and loses
 * things that were at the bottom.
 * <p>
 * By default, <code>JViewport</code> is opaque. To change this, use the
 * <code>setOpaque</code> method.
 * <p>
 * <b>NOTE:</b>We have implemented a faster scrolling algorithm that
 * does not require a buffer to draw in. The algorithm works as follows:
 * <ol><li>The view and parent view and checked to see if they are
 * <code>JComponents</code>,
 * if they aren't, stop and repaint the whole viewport.
 * <li>If the viewport is obscured by an ancestor, stop and repaint the whole
 * viewport.
 * <li>Compute the region that will become visible, if it is as big as
 * the viewport, stop and repaint the whole view region.
 * <li>Obtain the ancestor <code>Window</code>'s graphics and
 * do a <code>copyArea</code> on the scrolled region.
 * <li>Message the view to repaint the newly visible region.
 * <li>The next time paint is invoked on the viewport, if the clip region
 * is smaller than the viewport size a timer is kicked off to repaint the
 * whole region.
 * </ol>
 * In general this approach is much faster. Compared to the backing store
 * approach this avoids the overhead of maintaining an offscreen buffer and
 * having to do two <code>copyArea</code>s.
 * Compared to the non backing store case this
 * approach will greatly reduce the painted region.
 * <p>
 * This approach can cause slower times than the backing store approach
 * when the viewport is obscured by another window, or partially offscreen.
 * When another window
 * obscures the viewport the copyArea will copy garbage and a
 * paint event will be generated by the system to inform us we need to
 * paint the newly exposed region. The only way to handle this is to
 * repaint the whole viewport, which can cause slower performance than the
 * backing store case. In most applications very rarely will the user be
 * scrolling while the viewport is obscured by another window or offscreen,
 * so this optimization is usually worth the performance hit when obscured.
 * <p>
 * <strong>Warning:</strong> Swing is not thread safe. For more
 * information see <a
 * href="package-summary.html#threading">Swing's Threading
 * Policy</a>.
 * <p>
 * <strong>Warning:</strong>
 * Serialized objects of this class will not be compatible with
 * future Swing releases. The current serialization support is
 * appropriate for short term storage or RMI between applications running
 * the same version of Swing.  As of 1.4, support for long term storage
 * of all JavaBeans&trade;
 * has been added to the <code>java.beans</code> package.
 * Please see {@link java.beans.XMLEncoder}.
 *
 * @author Hans Muller
 * @author Philip Milne
 * @see JScrollPane
 */
public class JViewport extends JComponent implements Accessible
{
    
See Also:
getUIClassID
JComponent.readObject/**
     * @see #getUIClassID
     * @see #readObject
     */
    private static final String uiClassID = "ViewportUI";

    
Property used to indicate window blitting should not be done.
/** Property used to indicate window blitting should not be done.
     */
    static final Object EnableWindowBlit = "EnableWindowBlit";

    
True when the viewport dimensions have been determined.
The default is false.
/**
     * True when the viewport dimensions have been determined.
     * The default is false.
     */
    protected boolean isViewSizeSet = false;

    
The last viewPosition that we've painted, so we know how
much of the backing store image is valid.
/**
     * The last <code>viewPosition</code> that we've painted, so we know how
     * much of the backing store image is valid.
     */
    protected Point lastPaintPosition = null;

    
True when this viewport is maintaining an offscreen image of its
contents, so that some scrolling can take place using fast "bit-blit"
operations instead of by accessing the view object to construct the
display.  The default is false.
See Also:
setScrollMode
Deprecated:
As of Java 2 platform v1.3/**
     * True when this viewport is maintaining an offscreen image of its
     * contents, so that some scrolling can take place using fast "bit-blit"
     * operations instead of by accessing the view object to construct the
     * display.  The default is <code>false</code>.
     *
     * @deprecated As of Java 2 platform v1.3
     * @see #setScrollMode
     */
    @Deprecated
    protected boolean backingStore = false;

    
The view image used for a backing store. /** The view image used for a backing store. */
    transient protected Image backingStoreImage = null;

    
The scrollUnderway flag is used for components like
JList.  When the downarrow key is pressed on a
JList and the selected
cell is the last in the list, the scrollpane autoscrolls.
Here, the old selected cell needs repainting and so we need
a flag to make the viewport do the optimized painting
only when there is an explicit call to
setViewPosition(Point).
When setBounds is called through other routes,
the flag is off and the view repaints normally.  Another approach
would be to remove this from the JViewport
class and have the JList manage this case by using
setBackingStoreEnabled.  The default is
false.
/**
     * The <code>scrollUnderway</code> flag is used for components like
     * <code>JList</code>.  When the downarrow key is pressed on a
     * <code>JList</code> and the selected
     * cell is the last in the list, the <code>scrollpane</code> autoscrolls.
     * Here, the old selected cell needs repainting and so we need
     * a flag to make the viewport do the optimized painting
     * only when there is an explicit call to
     * <code>setViewPosition(Point)</code>.
     * When <code>setBounds</code> is called through other routes,
     * the flag is off and the view repaints normally.  Another approach
     * would be to remove this from the <code>JViewport</code>
     * class and have the <code>JList</code> manage this case by using
     * <code>setBackingStoreEnabled</code>.  The default is
     * <code>false</code>.
     */
    protected boolean scrollUnderway = false;

    /*
     * Listener that is notified each time the view changes size.
     */
    private ComponentListener viewListener = null;

    /* Only one <code>ChangeEvent</code> is needed per
     * <code>JViewport</code> instance since the
     * event's only (read-only) state is the source property.  The source
     * of events generated here is always "this".
     */
    private transient ChangeEvent changeEvent = null;

    
Use graphics.copyArea to implement scrolling.
This is the fastest for most applications.
See Also:
setScrollMode
Since:
1.3/**
      * Use <code>graphics.copyArea</code> to implement scrolling.
      * This is the fastest for most applications.
      *
      * @see #setScrollMode
      * @since 1.3
      */
    public static final int BLIT_SCROLL_MODE = 1;

    
Draws viewport contents into an offscreen image.
This was previously the default mode for JTable.
This mode may offer advantages over "blit mode"
in some cases, but it requires a large chunk of extra RAM.
See Also:
setScrollMode
Since:
1.3/**
      * Draws viewport contents into an offscreen image.
      * This was previously the default mode for <code>JTable</code>.
      * This mode may offer advantages over "blit mode"
      * in some cases, but it requires a large chunk of extra RAM.
      *
      * @see #setScrollMode
      * @since 1.3
      */
    public static final int BACKINGSTORE_SCROLL_MODE = 2;

    
This mode uses the very simple method of redrawing the entire
contents of the scrollpane each time it is scrolled.
This was the default behavior in Swing 1.0 and Swing 1.1.
Either of the other two options will provide better performance
in most cases.
See Also:
setScrollMode
Since:
1.3/**
      * This mode uses the very simple method of redrawing the entire
      * contents of the scrollpane each time it is scrolled.
      * This was the default behavior in Swing 1.0 and Swing 1.1.
      * Either of the other two options will provide better performance
      * in most cases.
      *
      * @see #setScrollMode
      * @since 1.3
      */
    public static final int SIMPLE_SCROLL_MODE = 0;

    
See Also:
setScrollMode
Since:
1.3/**
      * @see #setScrollMode
      * @since 1.3
      */
    private int scrollMode = BLIT_SCROLL_MODE;

    //
    // Window blitting:
    //
    // As mentioned in the javadoc when using windowBlit a paint event
    // will be generated by the system if copyArea copies a non-visible
    // portion of the view (in other words, it copies garbage). We are
    // not guaranteed to receive the paint event before other mouse events,
    // so we can not be sure we haven't already copied garbage a bunch of
    // times to different parts of the view. For that reason when a blit
    // happens and the Component is obscured (the check for obscurity
    // is not supported on all platforms and is checked via ComponentPeer
    // methods) the ivar repaintAll is set to true. When paint is received
    // if repaintAll is true (we previously did a blit) it is set to
    // false, and if the clip region is smaller than the viewport
    // waitingForRepaint is set to true and a timer is started. When
    // the timer fires if waitingForRepaint is true, repaint is invoked.
    // In the mean time, if the view is asked to scroll and waitingForRepaint
    // is true, a blit will not happen, instead the non-backing store case
    // of scrolling will happen, which will reset waitingForRepaint.
    // waitingForRepaint is set to false in paint when the clip rect is
    // bigger (or equal) to the size of the viewport.
    // A Timer is used instead of just a repaint as it appeared to offer
    // better performance.


    
This is set to true in setViewPosition
if doing a window blit and the viewport is obscured.
/**
     * This is set to true in <code>setViewPosition</code>
     * if doing a window blit and the viewport is obscured.
     */
    private transient boolean repaintAll;

    
This is set to true in paint, if repaintAll
is true and the clip rectangle does not match the bounds.
If true, and scrolling happens the
repaint manager is not cleared which then allows for the repaint
previously invoked to succeed.
/**
     * This is set to true in paint, if <code>repaintAll</code>
     * is true and the clip rectangle does not match the bounds.
     * If true, and scrolling happens the
     * repaint manager is not cleared which then allows for the repaint
     * previously invoked to succeed.
     */
    private transient boolean waitingForRepaint;

    
Instead of directly invoking repaint, a Timer
is started and when it fires, repaint is invoked.
/**
     * Instead of directly invoking repaint, a <code>Timer</code>
     * is started and when it fires, repaint is invoked.
     */
    private transient Timer repaintTimer;

    
Set to true in paintView when paint is invoked.
/**
     * Set to true in paintView when paint is invoked.
     */
    private transient boolean inBlitPaint;

    
Whether or not a valid view has been installed.
/**
     * Whether or not a valid view has been installed.
     */
    private boolean hasHadValidView;

    
When view is changed we have to synchronize scrollbar values
with viewport (see the BasicScrollPaneUI#syncScrollPaneWithViewport method).
This flag allows to invoke that method while ScrollPaneLayout#layoutContainer
is running.
/**
     * When view is changed we have to synchronize scrollbar values
     * with viewport (see the BasicScrollPaneUI#syncScrollPaneWithViewport method).
     * This flag allows to invoke that method while ScrollPaneLayout#layoutContainer
     * is running.
     */
    private boolean viewChanged;

    
Creates a JViewport. /** Creates a <code>JViewport</code>. */
    public JViewport() {
        super();
        setLayout(createLayoutManager());
        setOpaque(true);
        updateUI();
        setInheritsPopupMenu(true);
    }



    
Returns the L&F object that renders this component.
Returns:
a ViewportUI object
Since:
1.3/**
     * Returns the L&amp;F object that renders this component.
     *
     * @return a <code>ViewportUI</code> object
     * @since 1.3
     */
    public ViewportUI getUI() {
        return (ViewportUI)ui;
    }


    
Sets the L&F object that renders this component.
Params:
ui –  the ViewportUI L&F object
See Also:
UIDefaults.getUI
@beaninfo

       bound: true
      hidden: true
   attribute: visualUpdate true
 description: The UI object that implements the Component's LookAndFeel.
Since:
1.3/**
     * Sets the L&amp;F object that renders this component.
     *
     * @param ui  the <code>ViewportUI</code> L&amp;F object
     * @see UIDefaults#getUI
     * @beaninfo
     *        bound: true
     *       hidden: true
     *    attribute: visualUpdate true
     *  description: The UI object that implements the Component's LookAndFeel.
     * @since 1.3
     */
    public void setUI(ViewportUI ui) {
        super.setUI(ui);
    }


    
Resets the UI property to a value from the current look and feel.
See Also:
updateUI.updateUI/**
     * Resets the UI property to a value from the current look and feel.
     *
     * @see JComponent#updateUI
     */
    public void updateUI() {
        setUI((ViewportUI)UIManager.getUI(this));
    }


    
Returns a string that specifies the name of the L&F class
that renders this component.
See Also:
JComponent.getUIClassID
UIDefaults.getUI
Returns:
the string "ViewportUI"/**
     * Returns a string that specifies the name of the L&amp;F class
     * that renders this component.
     *
     * @return the string "ViewportUI"
     *
     * @see JComponent#getUIClassID
     * @see UIDefaults#getUI
     */
    public String getUIClassID() {
        return uiClassID;
    }


    
Sets the JViewport's one lightweight child,
which can be null.
(Since there is only one child which occupies the entire viewport,
the constraints and index
arguments are ignored.)
Params:
child –       the lightweight child of the viewport
constraints – the constraints to be respected
index –       the index
See Also:
setView/**
     * Sets the <code>JViewport</code>'s one lightweight child,
     * which can be <code>null</code>.
     * (Since there is only one child which occupies the entire viewport,
     * the <code>constraints</code> and <code>index</code>
     * arguments are ignored.)
     *
     * @param child       the lightweight <code>child</code> of the viewport
     * @param constraints the <code>constraints</code> to be respected
     * @param index       the index
     * @see #setView
     */
    protected void addImpl(Component child, Object constraints, int index) {
      setView(child);
    }


    
Removes the Viewports one lightweight child.
See Also:
setView/**
     * Removes the <code>Viewport</code>s one lightweight child.
     *
     * @see #setView
     */
    public void remove(Component child) {
        child.removeComponentListener(viewListener);
        super.remove(child);
    }

    
Scrolls the view so that Rectangle
within the view becomes visible.

This attempts to validate the view before scrolling if the
view is currently not valid - isValid returns false.
To avoid excessive validation when the containment hierarchy is
being created this will not validate if one of the ancestors does not
have a peer, or there is no validate root ancestor, or one of the
ancestors is not a Window or Applet.

Note that this method will not scroll outside of the
valid viewport; for example, if contentRect is larger
than the viewport, scrolling will be confined to the viewport's
bounds.
Params:
contentRect – the Rectangle to display
See Also:
JComponent.isValidateRoot
Component.isValid
Component.getPeer/**
     * Scrolls the view so that <code>Rectangle</code>
     * within the view becomes visible.
     * <p>
     * This attempts to validate the view before scrolling if the
     * view is currently not valid - <code>isValid</code> returns false.
     * To avoid excessive validation when the containment hierarchy is
     * being created this will not validate if one of the ancestors does not
     * have a peer, or there is no validate root ancestor, or one of the
     * ancestors is not a <code>Window</code> or <code>Applet</code>.
     * <p>
     * Note that this method will not scroll outside of the
     * valid viewport; for example, if <code>contentRect</code> is larger
     * than the viewport, scrolling will be confined to the viewport's
     * bounds.
     *
     * @param contentRect the <code>Rectangle</code> to display
     * @see JComponent#isValidateRoot
     * @see java.awt.Component#isValid
     * @see java.awt.Component#getPeer
     */
    public void scrollRectToVisible(Rectangle contentRect) {
        Component view = getView();

        if (view == null) {
            return;
        } else {
            if (!view.isValid()) {
                // If the view is not valid, validate. scrollRectToVisible
                // may fail if the view is not valid first, contentRect
                // could be bigger than invalid size.
                validateView();
            }
            int dx, dy;

            dx = positionAdjustment(getWidth(), contentRect.width, contentRect.x);
            dy = positionAdjustment(getHeight(), contentRect.height, contentRect.y);

            if (dx != 0 || dy != 0) {
                Point viewPosition = getViewPosition();
                Dimension viewSize = view.getSize();
                int startX = viewPosition.x;
                int startY = viewPosition.y;
                Dimension extent = getExtentSize();

                viewPosition.x -= dx;
                viewPosition.y -= dy;
                // Only constrain the location if the view is valid. If the
                // the view isn't valid, it typically indicates the view
                // isn't visible yet and most likely has a bogus size as will
                // we, and therefore we shouldn't constrain the scrolling
                if (view.isValid()) {
                    if (getParent().getComponentOrientation().isLeftToRight()) {
                        if (viewPosition.x + extent.width > viewSize.width) {
                            viewPosition.x = Math.max(0, viewSize.width - extent.width);
                        } else if (viewPosition.x < 0) {
                            viewPosition.x = 0;
                        }
                    } else {
                        if (extent.width > viewSize.width) {
                            viewPosition.x = viewSize.width - extent.width;
                        } else {
                            viewPosition.x = Math.max(0, Math.min(viewSize.width - extent.width, viewPosition.x));
                        }
                    }
                    if (viewPosition.y + extent.height > viewSize.height) {
                        viewPosition.y = Math.max(0, viewSize.height -
                                                  extent.height);
                    }
                    else if (viewPosition.y < 0) {
                        viewPosition.y = 0;
                    }
                }
                if (viewPosition.x != startX || viewPosition.y != startY) {
                    setViewPosition(viewPosition);
                    // NOTE: How JViewport currently works with the
                    // backing store is not foolproof. The sequence of
                    // events when setViewPosition
                    // (scrollRectToVisible) is called is to reset the
                    // views bounds, which causes a repaint on the
                    // visible region and sets an ivar indicating
                    // scrolling (scrollUnderway). When
                    // JViewport.paint is invoked if scrollUnderway is
                    // true, the backing store is blitted.  This fails
                    // if between the time setViewPosition is invoked
                    // and paint is received another repaint is queued
                    // indicating part of the view is invalid. There
                    // is no way for JViewport to notice another
                    // repaint has occurred and it ends up blitting
                    // what is now a dirty region and the repaint is
                    // never delivered.
                    // It just so happens JTable encounters this
                    // behavior by way of scrollRectToVisible, for
                    // this reason scrollUnderway is set to false
                    // here, which effectively disables the backing
                    // store.
                    scrollUnderway = false;
                }
            }
        }
    }

    
Ascends the Viewport's parents stopping when
a component is found that returns
true to isValidateRoot.
If all the Component's  parents are visible,
validate will then be invoked on it. The
RepaintManager is then invoked with
removeInvalidComponent. This
is the synchronous version of a revalidate.
/**
     * Ascends the <code>Viewport</code>'s parents stopping when
     * a component is found that returns
     * <code>true</code> to <code>isValidateRoot</code>.
     * If all the <code>Component</code>'s  parents are visible,
     * <code>validate</code> will then be invoked on it. The
     * <code>RepaintManager</code> is then invoked with
     * <code>removeInvalidComponent</code>. This
     * is the synchronous version of a <code>revalidate</code>.
     */
    private void validateView() {
        Component validateRoot = SwingUtilities.getValidateRoot(this, false);

        if (validateRoot == null) {
            return;
        }

        // Validate the root.
        validateRoot.validate();

        // And let the RepaintManager it does not have to validate from
        // validateRoot anymore.
        RepaintManager rm = RepaintManager.currentManager(this);

        if (rm != null) {
            rm.removeInvalidComponent((JComponent)validateRoot);
        }
    }

     /*  Used by the scrollRectToVisible method to determine the
      *  proper direction and amount to move by. The integer variables are named
      *  width, but this method is applicable to height also. The code assumes that
      *  parentWidth/childWidth are positive and childAt can be negative.
      */
    private int positionAdjustment(int parentWidth, int childWidth, int childAt)    {

        //   +-----+
        //   | --- |     No Change
        //   +-----+
        if (childAt >= 0 && childWidth + childAt <= parentWidth)    {
            return 0;
        }

        //   +-----+
        //  ---------   No Change
        //   +-----+
        if (childAt <= 0 && childWidth + childAt >= parentWidth) {
            return 0;
        }

        //   +-----+          +-----+
        //   |   ----    ->   | ----|
        //   +-----+          +-----+
        if (childAt > 0 && childWidth <= parentWidth)    {
            return -childAt + parentWidth - childWidth;
        }

        //   +-----+             +-----+
        //   |  --------  ->     |--------
        //   +-----+             +-----+
        if (childAt >= 0 && childWidth >= parentWidth)   {
            return -childAt;
        }

        //   +-----+          +-----+
        // ----    |     ->   |---- |
        //   +-----+          +-----+
        if (childAt <= 0 && childWidth <= parentWidth)   {
            return -childAt;
        }

        //   +-----+             +-----+
        //-------- |      ->   --------|
        //   +-----+             +-----+
        if (childAt < 0 && childWidth >= parentWidth)    {
            return -childAt + parentWidth - childWidth;
        }

        return 0;
    }


    
The viewport "scrolls" its child (called the "view") by the
normal parent/child clipping (typically the view is moved in
the opposite direction of the scroll).  A non-null border,
or non-zero insets, isn't supported, to prevent the geometry
of this component from becoming complex enough to inhibit
subclassing.  To create a JViewport with a border,
add it to a JPanel that has a border.
Note:  If border is non-null, this
method will throw an exception as borders are not supported on
a JViewPort.
Params:
border – the Border to set
Throws:
IllegalArgumentException – this method is not implemented/**
     * The viewport "scrolls" its child (called the "view") by the
     * normal parent/child clipping (typically the view is moved in
     * the opposite direction of the scroll).  A non-<code>null</code> border,
     * or non-zero insets, isn't supported, to prevent the geometry
     * of this component from becoming complex enough to inhibit
     * subclassing.  To create a <code>JViewport</code> with a border,
     * add it to a <code>JPanel</code> that has a border.
     * <p>Note:  If <code>border</code> is non-<code>null</code>, this
     * method will throw an exception as borders are not supported on
     * a <code>JViewPort</code>.
     *
     * @param border the <code>Border</code> to set
     * @exception IllegalArgumentException this method is not implemented
     */
    public final void setBorder(Border border) {
        if (border != null) {
            throw new IllegalArgumentException("JViewport.setBorder() not supported");
        }
    }


    
Returns the insets (border) dimensions as (0,0,0,0), since borders
are not supported on a JViewport.
See Also:
setBorder
Returns:
a Rectangle of zero dimension and zero origin/**
     * Returns the insets (border) dimensions as (0,0,0,0), since borders
     * are not supported on a <code>JViewport</code>.
     *
     * @return a <code>Rectangle</code> of zero dimension and zero origin
     * @see #setBorder
     */
    public final Insets getInsets() {
        return new Insets(0, 0, 0, 0);
    }

    
Returns an Insets object containing this
JViewports inset values.  The passed-in
Insets object will be reinitialized, and
all existing values within this object are overwritten.
Params:
insets – the Insets object which can be reused
See Also:
getInsets
Returns:
this viewports inset values
@beaninfo

  expert: true/**
     * Returns an <code>Insets</code> object containing this
     * <code>JViewport</code>s inset values.  The passed-in
     * <code>Insets</code> object will be reinitialized, and
     * all existing values within this object are overwritten.
     *
     * @param insets the <code>Insets</code> object which can be reused
     * @return this viewports inset values
     * @see #getInsets
     * @beaninfo
     *   expert: true
     */
    public final Insets getInsets(Insets insets) {
        insets.left = insets.top = insets.right = insets.bottom = 0;
        return insets;
    }


    private Graphics getBackingStoreGraphics(Graphics g) {
        Graphics bsg = backingStoreImage.getGraphics();
        bsg.setColor(g.getColor());
        bsg.setFont(g.getFont());
        bsg.setClip(g.getClipBounds());
        return bsg;
    }


    private void paintViaBackingStore(Graphics g) {
        Graphics bsg = getBackingStoreGraphics(g);
        try {
            super.paint(bsg);
            g.drawImage(backingStoreImage, 0, 0, this);
        } finally {
            bsg.dispose();
        }
    }

    private void paintViaBackingStore(Graphics g, Rectangle oClip) {
        Graphics bsg = getBackingStoreGraphics(g);
        try {
            super.paint(bsg);
            g.setClip(oClip);
            g.drawImage(backingStoreImage, 0, 0, this);
        } finally {
            bsg.dispose();
        }
    }

    
The JViewport overrides the default implementation of
this method (in JComponent) to return false.
This ensures
that the drawing machinery will call the Viewport's
paint
implementation rather than messaging the JViewport's
children directly.
Returns:
false/**
     * The <code>JViewport</code> overrides the default implementation of
     * this method (in <code>JComponent</code>) to return false.
     * This ensures
     * that the drawing machinery will call the <code>Viewport</code>'s
     * <code>paint</code>
     * implementation rather than messaging the <code>JViewport</code>'s
     * children directly.
     *
     * @return false
     */
    public boolean isOptimizedDrawingEnabled() {
        return false;
    }

    
Returns true if scroll mode is a BACKINGSTORE_SCROLL_MODE to cause painting to originate from JViewport, or one of its ancestors. Otherwise returns false. 
See Also:
JComponent.isPaintingOrigin()
Returns:
true if if scroll mode is a BACKINGSTORE_SCROLL_MODE./**
     * Returns true if scroll mode is a {@code BACKINGSTORE_SCROLL_MODE} to cause
     * painting to originate from {@code JViewport}, or one of its
     * ancestors. Otherwise returns {@code false}.
     *
     * @return true if if scroll mode is a {@code BACKINGSTORE_SCROLL_MODE}.
     * @see JComponent#isPaintingOrigin()
     */
    protected boolean isPaintingOrigin() {
        return scrollMode == BACKINGSTORE_SCROLL_MODE;
    }


    
Only used by the paint method below.
/**
     * Only used by the paint method below.
     */
    private Point getViewLocation() {
        Component view = getView();
        if (view != null) {
            return view.getLocation();
        }
        else {
            return new Point(0,0);
        }
    }

    
Depending on whether the backingStore is enabled,
either paint the image through the backing store or paint
just the recently exposed part, using the backing store
to "blit" the remainder.

The term "blit" is the pronounced version of the PDP-10
BLT (BLock Transfer) instruction, which copied a block of
bits. (In case you were curious.)

Params:
g – the Graphics context within which to paint/**
     * Depending on whether the <code>backingStore</code> is enabled,
     * either paint the image through the backing store or paint
     * just the recently exposed part, using the backing store
     * to "blit" the remainder.
     * <blockquote>
     * The term "blit" is the pronounced version of the PDP-10
     * BLT (BLock Transfer) instruction, which copied a block of
     * bits. (In case you were curious.)
     * </blockquote>
     *
     * @param g the <code>Graphics</code> context within which to paint
     */
    public void paint(Graphics g)
    {
        int width = getWidth();
        int height = getHeight();

        if ((width <= 0) || (height <= 0)) {
            return;
        }

        if (inBlitPaint) {
            // We invoked paint as part of copyArea cleanup, let it through.
            super.paint(g);
            return;
        }

        if (repaintAll) {
            repaintAll = false;
            Rectangle clipB = g.getClipBounds();
            if (clipB.width < getWidth() ||
                clipB.height < getHeight()) {
                waitingForRepaint = true;
                if (repaintTimer == null) {
                    repaintTimer = createRepaintTimer();
                }
                repaintTimer.stop();
                repaintTimer.start();
                // We really don't need to paint, a future repaint will
                // take care of it, but if we don't we get an ugly flicker.
            }
            else {
                if (repaintTimer != null) {
                    repaintTimer.stop();
                }
                waitingForRepaint = false;
            }
        }
        else if (waitingForRepaint) {
            // Need a complete repaint before resetting waitingForRepaint
            Rectangle clipB = g.getClipBounds();
            if (clipB.width >= getWidth() &&
                clipB.height >= getHeight()) {
                waitingForRepaint = false;
                repaintTimer.stop();
            }
        }

        if (!backingStore || isBlitting() || getView() == null) {
            super.paint(g);
            lastPaintPosition = getViewLocation();
            return;
        }

        // If the view is smaller than the viewport and we are not opaque
        // (that is, we won't paint our background), we should set the
        // clip. Otherwise, as the bounds of the view vary, we will
        // blit garbage into the exposed areas.
        Rectangle viewBounds = getView().getBounds();
        if (!isOpaque()) {
            g.clipRect(0, 0, viewBounds.width, viewBounds.height);
        }

        if (backingStoreImage == null) {
            // Backing store is enabled but this is the first call to paint.
            // Create the backing store, paint it and then copy to g.
            // The backing store image will be created with the size of
            // the viewport. We must make sure the clip region is the
            // same size, otherwise when scrolling the backing image
            // the region outside of the clipped region will not be painted,
            // and result in empty areas.
            backingStoreImage = createImage(width, height);
            Rectangle clip = g.getClipBounds();
            if (clip.width != width || clip.height != height) {
                if (!isOpaque()) {
                    g.setClip(0, 0, Math.min(viewBounds.width, width),
                              Math.min(viewBounds.height, height));
                }
                else {
                    g.setClip(0, 0, width, height);
                }
                paintViaBackingStore(g, clip);
            }
            else {
                paintViaBackingStore(g);
            }
        }
        else {
            if (!scrollUnderway || lastPaintPosition.equals(getViewLocation())) {
                // No scrolling happened: repaint required area via backing store.
                paintViaBackingStore(g);
            } else {
                // The image was scrolled. Manipulate the backing store and flush it to g.
                Point blitFrom = new Point();
                Point blitTo = new Point();
                Dimension blitSize = new Dimension();
                Rectangle blitPaint = new Rectangle();

                Point newLocation = getViewLocation();
                int dx = newLocation.x - lastPaintPosition.x;
                int dy = newLocation.y - lastPaintPosition.y;
                boolean canBlit = computeBlit(dx, dy, blitFrom, blitTo, blitSize, blitPaint);
                if (!canBlit) {
                    // The image was either moved diagonally or
                    // moved by more than the image size: paint normally.
                    paintViaBackingStore(g);
                } else {
                    int bdx = blitTo.x - blitFrom.x;
                    int bdy = blitTo.y - blitFrom.y;

                    // Move the relevant part of the backing store.
                    Rectangle clip = g.getClipBounds();
                    // We don't want to inherit the clip region when copying
                    // bits, if it is inherited it will result in not moving
                    // all of the image resulting in garbage appearing on
                    // the screen.
                    g.setClip(0, 0, width, height);
                    Graphics bsg = getBackingStoreGraphics(g);
                    try {
                        bsg.copyArea(blitFrom.x, blitFrom.y, blitSize.width, blitSize.height, bdx, bdy);

                        g.setClip(clip.x, clip.y, clip.width, clip.height);
                        // Paint the rest of the view; the part that has just been exposed.
                        Rectangle r = viewBounds.intersection(blitPaint);
                        bsg.setClip(r);
                        super.paint(bsg);

                        // Copy whole of the backing store to g.
                        g.drawImage(backingStoreImage, 0, 0, this);
                    } finally {
                        bsg.dispose();
                    }
                }
            }
        }
        lastPaintPosition = getViewLocation();
        scrollUnderway = false;
    }


    
Sets the bounds of this viewport.  If the viewport's width
or height has changed, fire a StateChanged event.
Params:
x – left edge of the origin
y – top edge of the origin
w – width in pixels
h – height in pixels
See Also:
JComponent.reshape(int, int, int, int)/**
     * Sets the bounds of this viewport.  If the viewport's width
     * or height has changed, fire a <code>StateChanged</code> event.
     *
     * @param x left edge of the origin
     * @param y top edge of the origin
     * @param w width in pixels
     * @param h height in pixels
     *
     * @see JComponent#reshape(int, int, int, int)
     */
    public void reshape(int x, int y, int w, int h) {
        boolean sizeChanged = (getWidth() != w) || (getHeight() != h);
        if (sizeChanged) {
            backingStoreImage = null;
        }
        super.reshape(x, y, w, h);
        if (sizeChanged || viewChanged) {
            viewChanged = false;

            fireStateChanged();
        }
    }


    
Used to control the method of scrolling the viewport contents.
You may want to change this mode to get maximum performance for your
use case.
Params:
mode – one of the following values:

 JViewport.BLIT_SCROLL_MODE
 JViewport.BACKINGSTORE_SCROLL_MODE
 JViewport.SIMPLE_SCROLL_MODE
See Also:
BLIT_SCROLL_MODE
BACKINGSTORE_SCROLL_MODE
SIMPLE_SCROLL_MODE
@beaninfo

       bound: false
 description: Method of moving contents for incremental scrolls.
        enum: BLIT_SCROLL_MODE JViewport.BLIT_SCROLL_MODE
              BACKINGSTORE_SCROLL_MODE JViewport.BACKINGSTORE_SCROLL_MODE
              SIMPLE_SCROLL_MODE JViewport.SIMPLE_SCROLL_MODE
Since:
1.3/**
      * Used to control the method of scrolling the viewport contents.
      * You may want to change this mode to get maximum performance for your
      * use case.
      *
      * @param mode one of the following values:
      * <ul>
      * <li> JViewport.BLIT_SCROLL_MODE
      * <li> JViewport.BACKINGSTORE_SCROLL_MODE
      * <li> JViewport.SIMPLE_SCROLL_MODE
      * </ul>
      *
      * @see #BLIT_SCROLL_MODE
      * @see #BACKINGSTORE_SCROLL_MODE
      * @see #SIMPLE_SCROLL_MODE
      *
      * @beaninfo
      *        bound: false
      *  description: Method of moving contents for incremental scrolls.
      *         enum: BLIT_SCROLL_MODE JViewport.BLIT_SCROLL_MODE
      *               BACKINGSTORE_SCROLL_MODE JViewport.BACKINGSTORE_SCROLL_MODE
      *               SIMPLE_SCROLL_MODE JViewport.SIMPLE_SCROLL_MODE
      *
      * @since 1.3
      */
    public void setScrollMode(int mode) {
        scrollMode = mode;
        backingStore = mode == BACKINGSTORE_SCROLL_MODE;
    }

    
Returns the current scrolling mode.
See Also:
setScrollMode
Returns:
the scrollMode property
Since:
1.3/**
      * Returns the current scrolling mode.
      *
      * @return the <code>scrollMode</code> property
      * @see #setScrollMode
      * @since 1.3
      */
    public int getScrollMode() {
        return scrollMode;
    }

    
Returns true if this viewport is maintaining
an offscreen image of its contents.
Returns:
true if scrollMode is
   BACKINGSTORE_SCROLL_MODE
Deprecated:
As of Java 2 platform v1.3, replaced by
            getScrollMode()./**
     * Returns <code>true</code> if this viewport is maintaining
     * an offscreen image of its contents.
     *
     * @return <code>true</code> if <code>scrollMode</code> is
     *    <code>BACKINGSTORE_SCROLL_MODE</code>
     *
     * @deprecated As of Java 2 platform v1.3, replaced by
     *             <code>getScrollMode()</code>.
     */
    @Deprecated
    public boolean isBackingStoreEnabled() {
        return scrollMode == BACKINGSTORE_SCROLL_MODE;
    }


    
If true if this viewport will maintain an offscreen
image of its contents.  The image is used to reduce the cost
of small one dimensional changes to the viewPosition.
Rather than repainting the entire viewport we use
Graphics.copyArea to effect some of the scroll.
Params:
enabled – if true, maintain an offscreen backing store
Deprecated:
As of Java 2 platform v1.3, replaced by
            setScrollMode()./**
     * If true if this viewport will maintain an offscreen
     * image of its contents.  The image is used to reduce the cost
     * of small one dimensional changes to the <code>viewPosition</code>.
     * Rather than repainting the entire viewport we use
     * <code>Graphics.copyArea</code> to effect some of the scroll.
     *
     * @param enabled if true, maintain an offscreen backing store
     *
     * @deprecated As of Java 2 platform v1.3, replaced by
     *             <code>setScrollMode()</code>.
     */
    @Deprecated
    public void setBackingStoreEnabled(boolean enabled) {
        if (enabled) {
            setScrollMode(BACKINGSTORE_SCROLL_MODE);
        } else {
            setScrollMode(BLIT_SCROLL_MODE);
        }
    }

    private boolean isBlitting() {
        Component view = getView();
        return (scrollMode == BLIT_SCROLL_MODE) &&
               (view instanceof JComponent) && view.isOpaque();
    }


    
Returns the JViewport's one child or null.
See Also:
setView
Returns:
the viewports child, or null if none exists/**
     * Returns the <code>JViewport</code>'s one child or <code>null</code>.
     *
     * @return the viewports child, or <code>null</code> if none exists
     *
     * @see #setView
     */
    public Component getView() {
        return (getComponentCount() > 0) ? getComponent(0) : null;
    }

    
Sets the JViewport's one lightweight child
(view), which can be null.
Params:
view – the viewport's new lightweight child
See Also:
getView/**
     * Sets the <code>JViewport</code>'s one lightweight child
     * (<code>view</code>), which can be <code>null</code>.
     *
     * @param view the viewport's new lightweight child
     *
     * @see #getView
     */
    public void setView(Component view) {

        /* Remove the viewport's existing children, if any.
         * Note that removeAll() isn't used here because it
         * doesn't call remove() (which JViewport overrides).
         */
        int n = getComponentCount();
        for(int i = n - 1; i >= 0; i--) {
            remove(getComponent(i));
        }

        isViewSizeSet = false;

        if (view != null) {
            super.addImpl(view, null, -1);
            viewListener = createViewListener();
            view.addComponentListener(viewListener);
        }

        if (hasHadValidView) {
            // Only fire a change if a view has been installed.
            fireStateChanged();
        }
        else if (view != null) {
            hasHadValidView = true;
        }

        viewChanged = true;

        revalidate();
        repaint();
    }


    
If the view's size hasn't been explicitly set, return the
preferred size, otherwise return the view's current size.
If there is no view, return 0,0.
Returns:
a Dimension object specifying the size of the view/**
     * If the view's size hasn't been explicitly set, return the
     * preferred size, otherwise return the view's current size.
     * If there is no view, return 0,0.
     *
     * @return a <code>Dimension</code> object specifying the size of the view
     */
    public Dimension getViewSize() {
        Component view = getView();

        if (view == null) {
            return new Dimension(0,0);
        }
        else if (isViewSizeSet) {
            return view.getSize();
        }
        else {
            return view.getPreferredSize();
        }
    }


    
Sets the size of the view.  A state changed event will be fired.
Params:
newSize – a Dimension object specifying the new
         size of the view/**
     * Sets the size of the view.  A state changed event will be fired.
     *
     * @param newSize a <code>Dimension</code> object specifying the new
     *          size of the view
     */
    public void setViewSize(Dimension newSize) {
        Component view = getView();
        if (view != null) {
            Dimension oldSize = view.getSize();
            if (!newSize.equals(oldSize)) {
                // scrollUnderway will be true if this is invoked as the
                // result of a validate and setViewPosition was previously
                // invoked.
                scrollUnderway = false;
                view.setSize(newSize);
                isViewSizeSet = true;
                fireStateChanged();
            }
        }
    }

    
Returns the view coordinates that appear in the upper left
hand corner of the viewport, or 0,0 if there's no view.
Returns:
a Point object giving the upper left coordinates/**
     * Returns the view coordinates that appear in the upper left
     * hand corner of the viewport, or 0,0 if there's no view.
     *
     * @return a <code>Point</code> object giving the upper left coordinates
     */
    public Point getViewPosition() {
        Component view = getView();
        if (view != null) {
            Point p = view.getLocation();
            p.x = -p.x;
            p.y = -p.y;
            return p;
        }
        else {
            return new Point(0,0);
        }
    }


    
Sets the view coordinates that appear in the upper left
hand corner of the viewport, does nothing if there's no view.
Params:
p –  a Point object giving the upper left coordinates/**
     * Sets the view coordinates that appear in the upper left
     * hand corner of the viewport, does nothing if there's no view.
     *
     * @param p  a <code>Point</code> object giving the upper left coordinates
     */
    public void setViewPosition(Point p)
    {
        Component view = getView();
        if (view == null) {
            return;
        }

        int oldX, oldY, x = p.x, y = p.y;

        /* Collect the old x,y values for the views location
         * and do the song and dance to avoid allocating
         * a Rectangle object if we don't have to.
         */
        if (view instanceof JComponent) {
            JComponent c = (JComponent)view;
            oldX = c.getX();
            oldY = c.getY();
        }
        else {
            Rectangle r = view.getBounds();
            oldX = r.x;
            oldY = r.y;
        }

        /* The view scrolls in the opposite direction to mouse
         * movement.
         */
        int newX = -x;
        int newY = -y;

        if ((oldX != newX) || (oldY != newY)) {
            if (!waitingForRepaint && isBlitting() && canUseWindowBlitter()) {
                RepaintManager rm = RepaintManager.currentManager(this);
                // The cast to JComponent will work, if view is not
                // a JComponent, isBlitting will return false.
                JComponent jview = (JComponent)view;
                Rectangle dirty = rm.getDirtyRegion(jview);
                if (dirty == null || !dirty.contains(jview.getVisibleRect())) {
                    rm.beginPaint();
                    try {
                        Graphics g = JComponent.safelyGetGraphics(this);
                        flushViewDirtyRegion(g, dirty);
                        view.setLocation(newX, newY);
                        Rectangle r = new Rectangle(
                            0, 0, getWidth(), Math.min(getHeight(), jview.getHeight()));
                        g.setClip(r);
                        // Repaint the complete component if the blit succeeded
                        // and needsRepaintAfterBlit returns true.
                        repaintAll = (windowBlitPaint(g) &&
                                      needsRepaintAfterBlit());
                        g.dispose();
                        rm.notifyRepaintPerformed(this, r.x, r.y, r.width, r.height);
                        rm.markCompletelyClean((JComponent)getParent());
                        rm.markCompletelyClean(this);
                        rm.markCompletelyClean(jview);
                    } finally {
                        rm.endPaint();
                    }
                }
                else {
                    // The visible region is dirty, no point in doing copyArea
                    view.setLocation(newX, newY);
                    repaintAll = false;
                }
            }
            else {
                scrollUnderway = true;
                // This calls setBounds(), and then repaint().
                view.setLocation(newX, newY);
                repaintAll = false;
            }
            // we must validate the hierarchy to not break the hw/lw mixing
            revalidate();
            fireStateChanged();
        }
    }


    
Returns a rectangle whose origin is getViewPosition
and size is getExtentSize.
This is the visible part of the view, in view coordinates.
Returns:
a Rectangle giving the visible part of
         the view using view coordinates./**
     * Returns a rectangle whose origin is <code>getViewPosition</code>
     * and size is <code>getExtentSize</code>.
     * This is the visible part of the view, in view coordinates.
     *
     * @return a <code>Rectangle</code> giving the visible part of
     *          the view using view coordinates.
     */
    public Rectangle getViewRect() {
        return new Rectangle(getViewPosition(), getExtentSize());
    }


    
Computes the parameters for a blit where the backing store image
currently contains oldLoc in the upper left hand corner
and we're scrolling to newLoc.
The parameters are modified
to return the values required for the blit.
Params:
dx –  the horizontal delta
dy –  the vertical delta
blitFrom – the Point we're blitting from
blitTo – the Point we're blitting to
blitSize – the Dimension of the area to blit
blitPaint – the area to blit
Returns:
 true if the parameters are modified and we're ready to blit;
         false otherwise/**
     * Computes the parameters for a blit where the backing store image
     * currently contains <code>oldLoc</code> in the upper left hand corner
     * and we're scrolling to <code>newLoc</code>.
     * The parameters are modified
     * to return the values required for the blit.
     *
     * @param dx  the horizontal delta
     * @param dy  the vertical delta
     * @param blitFrom the <code>Point</code> we're blitting from
     * @param blitTo the <code>Point</code> we're blitting to
     * @param blitSize the <code>Dimension</code> of the area to blit
     * @param blitPaint the area to blit
     * @return  true if the parameters are modified and we're ready to blit;
     *          false otherwise
     */
    protected boolean computeBlit(
        int dx,
        int dy,
        Point blitFrom,
        Point blitTo,
        Dimension blitSize,
        Rectangle blitPaint)
    {
        int dxAbs = Math.abs(dx);
        int dyAbs = Math.abs(dy);
        Dimension extentSize = getExtentSize();

        if ((dx == 0) && (dy != 0) && (dyAbs < extentSize.height)) {
            if (dy < 0) {
                blitFrom.y = -dy;
                blitTo.y = 0;
                blitPaint.y = extentSize.height + dy;
            }
            else {
                blitFrom.y = 0;
                blitTo.y = dy;
                blitPaint.y = 0;
            }

            blitPaint.x = blitFrom.x = blitTo.x = 0;

            blitSize.width = extentSize.width;
            blitSize.height = extentSize.height - dyAbs;

            blitPaint.width = extentSize.width;
            blitPaint.height = dyAbs;

            return true;
        }

        else if ((dy == 0) && (dx != 0) && (dxAbs < extentSize.width)) {
            if (dx < 0) {
                blitFrom.x = -dx;
                blitTo.x = 0;
                blitPaint.x = extentSize.width + dx;
            }
            else {
                blitFrom.x = 0;
                blitTo.x = dx;
                blitPaint.x = 0;
            }

            blitPaint.y = blitFrom.y = blitTo.y = 0;

            blitSize.width = extentSize.width - dxAbs;
            blitSize.height = extentSize.height;

            blitPaint.width = dxAbs;
            blitPaint.height = extentSize.height;

            return true;
        }

        else {
            return false;
        }
    }


    
Returns the size of the visible part of the view in view coordinates.
Returns:
a Dimension object giving the size of the view/**
     * Returns the size of the visible part of the view in view coordinates.
     *
     * @return a <code>Dimension</code> object giving the size of the view
     */
    @Transient
    public Dimension getExtentSize() {
        return getSize();
    }


    
Converts a size in pixel coordinates to view coordinates.
Subclasses of viewport that support "logical coordinates"
will override this method.
Params:
size –  a Dimension object using pixel coordinates
Returns:
a Dimension object converted to view coordinates/**
     * Converts a size in pixel coordinates to view coordinates.
     * Subclasses of viewport that support "logical coordinates"
     * will override this method.
     *
     * @param size  a <code>Dimension</code> object using pixel coordinates
     * @return a <code>Dimension</code> object converted to view coordinates
     */
    public Dimension toViewCoordinates(Dimension size) {
        return new Dimension(size);
    }

    
Converts a point in pixel coordinates to view coordinates.
Subclasses of viewport that support "logical coordinates"
will override this method.
Params:
p –  a Point object using pixel coordinates
Returns:
a Point object converted to view coordinates/**
     * Converts a point in pixel coordinates to view coordinates.
     * Subclasses of viewport that support "logical coordinates"
     * will override this method.
     *
     * @param p  a <code>Point</code> object using pixel coordinates
     * @return a <code>Point</code> object converted to view coordinates
     */
    public Point toViewCoordinates(Point p) {
        return new Point(p);
    }


    
Sets the size of the visible part of the view using view coordinates.
Params:
newExtent –  a Dimension object specifying
         the size of the view/**
     * Sets the size of the visible part of the view using view coordinates.
     *
     * @param newExtent  a <code>Dimension</code> object specifying
     *          the size of the view
     */
    public void setExtentSize(Dimension newExtent) {
        Dimension oldExtent = getExtentSize();
        if (!newExtent.equals(oldExtent)) {
            setSize(newExtent);
            fireStateChanged();
        }
    }

    
A listener for the view.

Warning:
Serialized objects of this class will not be compatible with
future Swing releases. The current serialization support is
appropriate for short term storage or RMI between applications running
the same version of Swing.  As of 1.4, support for long term storage
of all JavaBeans™
has been added to the java.beans package. Please see XMLEncoder. /**
     * A listener for the view.
     * <p>
     * <strong>Warning:</strong>
     * Serialized objects of this class will not be compatible with
     * future Swing releases. The current serialization support is
     * appropriate for short term storage or RMI between applications running
     * the same version of Swing.  As of 1.4, support for long term storage
     * of all JavaBeans&trade;
     * has been added to the <code>java.beans</code> package.
     * Please see {@link java.beans.XMLEncoder}.
     */
    protected class ViewListener extends ComponentAdapter implements Serializable
    {
        public void componentResized(ComponentEvent e) {
            fireStateChanged();
            revalidate();
        }
    }

    
Creates a listener for the view.
Returns:
a ViewListener/**
     * Creates a listener for the view.
     * @return a <code>ViewListener</code>
     */
    protected ViewListener createViewListener() {
        return new ViewListener();
    }


    
Subclassers can override this to install a different
layout manager (or null) in the constructor.  Returns
the LayoutManager to install on the JViewport.
Returns:
a LayoutManager/**
     * Subclassers can override this to install a different
     * layout manager (or <code>null</code>) in the constructor.  Returns
     * the <code>LayoutManager</code> to install on the <code>JViewport</code>.
     *
     * @return a <code>LayoutManager</code>
     */
    protected LayoutManager createLayoutManager() {
        return ViewportLayout.SHARED_INSTANCE;
    }


    
Adds a ChangeListener to the list that is
notified each time the view's
size, position, or the viewport's extent size has changed.
Params:
l – the ChangeListener to add
See Also:
removeChangeListener
setViewPosition
setViewSize
setExtentSize/**
     * Adds a <code>ChangeListener</code> to the list that is
     * notified each time the view's
     * size, position, or the viewport's extent size has changed.
     *
     * @param l the <code>ChangeListener</code> to add
     * @see #removeChangeListener
     * @see #setViewPosition
     * @see #setViewSize
     * @see #setExtentSize
     */
    public void addChangeListener(ChangeListener l) {
        listenerList.add(ChangeListener.class, l);
    }

    
Removes a ChangeListener from the list that's notified each
time the views size, position, or the viewports extent size
has changed.
Params:
l – the ChangeListener to remove
See Also:
addChangeListener/**
     * Removes a <code>ChangeListener</code> from the list that's notified each
     * time the views size, position, or the viewports extent size
     * has changed.
     *
     * @param l the <code>ChangeListener</code> to remove
     * @see #addChangeListener
     */
    public void removeChangeListener(ChangeListener l) {
        listenerList.remove(ChangeListener.class, l);
    }

    
Returns an array of all the ChangeListeners added
to this JViewport with addChangeListener().
Returns:
all of the ChangeListeners added or an empty
        array if no listeners have been added
Since:
1.4/**
     * Returns an array of all the <code>ChangeListener</code>s added
     * to this JViewport with addChangeListener().
     *
     * @return all of the <code>ChangeListener</code>s added or an empty
     *         array if no listeners have been added
     * @since 1.4
     */
    public ChangeListener[] getChangeListeners() {
        return listenerList.getListeners(ChangeListener.class);
    }

    
Notifies all ChangeListeners when the views
size, position, or the viewports extent size has changed.
See Also:
addChangeListener
removeChangeListener
EventListenerList/**
     * Notifies all <code>ChangeListeners</code> when the views
     * size, position, or the viewports extent size has changed.
     *
     * @see #addChangeListener
     * @see #removeChangeListener
     * @see EventListenerList
     */
    protected void fireStateChanged()
    {
        Object[] listeners = listenerList.getListenerList();
        for (int i = listeners.length - 2; i >= 0; i -= 2) {
            if (listeners[i] == ChangeListener.class) {
                if (changeEvent == null) {
                    changeEvent = new ChangeEvent(this);
                }
                ((ChangeListener)listeners[i + 1]).stateChanged(changeEvent);
            }
        }
    }

    
Always repaint in the parents coordinate system to make sure
only one paint is performed by the RepaintManager.
Params:
tm –   maximum time in milliseconds before update
x –    the x coordinate (pixels over from left)
y –    the y coordinate (pixels down from top)
w –    the width
h –   the height
See Also:
Component.update(Graphics)/**
     * Always repaint in the parents coordinate system to make sure
     * only one paint is performed by the <code>RepaintManager</code>.
     *
     * @param     tm   maximum time in milliseconds before update
     * @param     x    the <code>x</code> coordinate (pixels over from left)
     * @param     y    the <code>y</code> coordinate (pixels down from top)
     * @param     w    the width
     * @param     h   the height
     * @see       java.awt.Component#update(java.awt.Graphics)
     */
    public void repaint(long tm, int x, int y, int w, int h) {
        Container parent = getParent();
        if(parent != null)
            parent.repaint(tm,x+getX(),y+getY(),w,h);
        else
            super.repaint(tm,x,y,w,h);
    }


    
Returns a string representation of this JViewport.
This method
is intended to be used only for debugging purposes, and the
content and format of the returned string may vary between
implementations. The returned string may be empty but may not
be null.
Returns:
 a string representation of this JViewport/**
     * Returns a string representation of this <code>JViewport</code>.
     * This method
     * is intended to be used only for debugging purposes, and the
     * content and format of the returned string may vary between
     * implementations. The returned string may be empty but may not
     * be <code>null</code>.
     *
     * @return  a string representation of this <code>JViewport</code>
     */
    protected String paramString() {
        String isViewSizeSetString = (isViewSizeSet ?
                                      "true" : "false");
        String lastPaintPositionString = (lastPaintPosition != null ?
                                          lastPaintPosition.toString() : "");
        String scrollUnderwayString = (scrollUnderway ?
                                       "true" : "false");

        return super.paramString() +
        ",isViewSizeSet=" + isViewSizeSetString +
        ",lastPaintPosition=" + lastPaintPositionString +
        ",scrollUnderway=" + scrollUnderwayString;
    }

    //
    // Following is used when doBlit is true.
    //

    
Notifies listeners of a property change. This is subclassed to update
the windowBlit property.
(The putClientProperty property is final).
Params:
propertyName – a string containing the property name
oldValue – the old value of the property
newValue –  the new value of the property/**
     * Notifies listeners of a property change. This is subclassed to update
     * the <code>windowBlit</code> property.
     * (The <code>putClientProperty</code> property is final).
     *
     * @param propertyName a string containing the property name
     * @param oldValue the old value of the property
     * @param newValue  the new value of the property
     */
    protected void firePropertyChange(String propertyName, Object oldValue,
                                      Object newValue) {
        super.firePropertyChange(propertyName, oldValue, newValue);
        if (propertyName.equals(EnableWindowBlit)) {
            if (newValue != null) {
                setScrollMode(BLIT_SCROLL_MODE);
            } else {
                setScrollMode(SIMPLE_SCROLL_MODE);
            }
        }
    }

    
Returns true if the component needs to be completely repainted after
a blit and a paint is received.
/**
     * Returns true if the component needs to be completely repainted after
     * a blit and a paint is received.
     */
    private boolean needsRepaintAfterBlit() {
        // Find the first heavy weight ancestor. isObscured and
        // canDetermineObscurity are only appropriate for heavy weights.
        Component heavyParent = getParent();

        while (heavyParent != null && heavyParent.isLightweight()) {
            heavyParent = heavyParent.getParent();
        }

        if (heavyParent != null) {
            ComponentPeer peer = heavyParent.getPeer();

            if (peer != null && peer.canDetermineObscurity() &&
                                !peer.isObscured()) {
                // The peer says we aren't obscured, therefore we can assume
                // that we won't later be messaged to paint a portion that
                // we tried to blit that wasn't valid.
                // It is certainly possible that when we blited we were
                // obscured, and by the time this is invoked we aren't, but the
                // chances of that happening are pretty slim.
                return false;
            }
        }
        return true;
    }

    private Timer createRepaintTimer() {
        Timer timer = new Timer(300, new ActionListener() {
            public void actionPerformed(ActionEvent ae) {
                // waitingForRepaint will be false if a paint came down
                // with the complete clip rect, in which case we don't
                // have to cause a repaint.
                if (waitingForRepaint) {
                    repaint();
                }
            }
        });
        timer.setRepeats(false);
        return timer;
    }

    
If the repaint manager has a dirty region for the view, the view is
asked to paint.
Params:
g –  the Graphics context within which to paint/**
     * If the repaint manager has a dirty region for the view, the view is
     * asked to paint.
     *
     * @param g  the <code>Graphics</code> context within which to paint
     */
    private void flushViewDirtyRegion(Graphics g, Rectangle dirty) {
        JComponent view = (JComponent) getView();
        if(dirty != null && dirty.width > 0 && dirty.height > 0) {
            dirty.x += view.getX();
            dirty.y += view.getY();
            Rectangle clip = g.getClipBounds();
            if (clip == null) {
                // Only happens in 1.2
                g.setClip(0, 0, getWidth(), getHeight());
            }
            g.clipRect(dirty.x, dirty.y, dirty.width, dirty.height);
            clip = g.getClipBounds();
            // Only paint the dirty region if it is visible.
            if (clip.width > 0 && clip.height > 0) {
                paintView(g);
            }
        }
    }

    
Used when blitting.
Params:
g –  the Graphics context within which to paint
Returns:
true if blitting succeeded; otherwise false/**
     * Used when blitting.
     *
     * @param g  the <code>Graphics</code> context within which to paint
     * @return true if blitting succeeded; otherwise false
     */
    private boolean windowBlitPaint(Graphics g) {
        int width = getWidth();
        int height = getHeight();

        if ((width == 0) || (height == 0)) {
            return false;
        }

        boolean retValue;
        RepaintManager rm = RepaintManager.currentManager(this);
        JComponent view = (JComponent) getView();

        if (lastPaintPosition == null ||
            lastPaintPosition.equals(getViewLocation())) {
            paintView(g);
            retValue = false;
        } else {
            // The image was scrolled. Manipulate the backing store and flush
            // it to g.
            Point blitFrom = new Point();
            Point blitTo = new Point();
            Dimension blitSize = new Dimension();
            Rectangle blitPaint = new Rectangle();

            Point newLocation = getViewLocation();
            int dx = newLocation.x - lastPaintPosition.x;
            int dy = newLocation.y - lastPaintPosition.y;
            boolean canBlit = computeBlit(dx, dy, blitFrom, blitTo, blitSize,
                                          blitPaint);
            if (!canBlit) {
                paintView(g);
                retValue = false;
            } else {
                // Prepare the rest of the view; the part that has just been
                // exposed.
                Rectangle r = view.getBounds().intersection(blitPaint);
                r.x -= view.getX();
                r.y -= view.getY();

                blitDoubleBuffered(view, g, r.x, r.y, r.width, r.height,
                                   blitFrom.x, blitFrom.y, blitTo.x, blitTo.y,
                                   blitSize.width, blitSize.height);
                retValue = true;
            }
        }
        lastPaintPosition = getViewLocation();
        return retValue;
    }

    //
    // NOTE: the code below uses paintForceDoubleBuffered for historical
    // reasons.  If we're going to allow a blit we've already accounted for
    // everything that paintImmediately and _paintImmediately does, for that
    // reason we call into paintForceDoubleBuffered to diregard whether or
    // not setDoubleBuffered(true) was invoked on the view.
    //

    private void blitDoubleBuffered(JComponent view, Graphics g,
                                    int clipX, int clipY, int clipW, int clipH,
                                    int blitFromX, int blitFromY, int blitToX, int blitToY,
                                    int blitW, int blitH) {
        // NOTE:
        //   blitFrom/blitTo are in JViewport coordinates system
        //     not the views coordinate space.
        //   clip* are in the views coordinate space.
        RepaintManager rm = RepaintManager.currentManager(this);
        int bdx = blitToX - blitFromX;
        int bdy = blitToY - blitFromY;

        Composite oldComposite = null;
        // Shift the scrolled region
        if (g instanceof Graphics2D) {
            Graphics2D g2d = (Graphics2D) g;
            oldComposite = g2d.getComposite();
            g2d.setComposite(AlphaComposite.Src);
        }
        rm.copyArea(this, g, blitFromX, blitFromY, blitW, blitH, bdx, bdy,
                    false);
        if (oldComposite != null) {
            ((Graphics2D) g).setComposite(oldComposite);
        }
        // Paint the newly exposed region.
        int x = view.getX();
        int y = view.getY();
        g.translate(x, y);
        g.setClip(clipX, clipY, clipW, clipH);
        view.paintForceDoubleBuffered(g);
        g.translate(-x, -y);
    }

    
Called to paint the view, usually when blitPaint
can not blit.
Params:
g – the Graphics context within which to paint/**
     * Called to paint the view, usually when <code>blitPaint</code>
     * can not blit.
     *
     * @param g the <code>Graphics</code> context within which to paint
     */
    private void paintView(Graphics g) {
        Rectangle clip = g.getClipBounds();
        JComponent view = (JComponent)getView();

        if (view.getWidth() >= getWidth()) {
            // Graphics is relative to JViewport, need to map to view's
            // coordinates space.
            int x = view.getX();
            int y = view.getY();
            g.translate(x, y);
            g.setClip(clip.x - x, clip.y - y, clip.width, clip.height);
            view.paintForceDoubleBuffered(g);
            g.translate(-x, -y);
            g.setClip(clip.x, clip.y, clip.width, clip.height);
        }
        else {
            // To avoid any problems that may result from the viewport being
            // bigger than the view we start painting from the viewport.
            try {
                inBlitPaint = true;
                paintForceDoubleBuffered(g);
            } finally {
                inBlitPaint = false;
            }
        }
    }

    
Returns true if the viewport is not obscured by one of its ancestors,
or its ancestors children and if the viewport is showing. Blitting
when the view isn't showing will work,
or rather copyArea will work,
but will not produce the expected behavior.
/**
     * Returns true if the viewport is not obscured by one of its ancestors,
     * or its ancestors children and if the viewport is showing. Blitting
     * when the view isn't showing will work,
     * or rather <code>copyArea</code> will work,
     * but will not produce the expected behavior.
     */
    private boolean canUseWindowBlitter() {
        if (!isShowing() || (!(getParent() instanceof JComponent) &&
                             !(getView() instanceof JComponent))) {
            return false;
        }
        if (isPainting()) {
            // We're in the process of painting, don't blit. If we were
            // to blit we would draw on top of what we're already drawing,
            // so bail.
            return false;
        }

        Rectangle dirtyRegion = RepaintManager.currentManager(this).
                                getDirtyRegion((JComponent)getParent());

        if (dirtyRegion != null && dirtyRegion.width > 0 &&
            dirtyRegion.height > 0) {
            // Part of the scrollpane needs to be repainted too, don't blit.
            return false;
        }

        Rectangle clip = new Rectangle(0,0,getWidth(),getHeight());
        Rectangle oldClip = new Rectangle();
        Rectangle tmp2 = null;
        Container parent;
        Component lastParent = null;
        int x, y, w, h;

        for(parent = this; parent != null && isLightweightComponent(parent); parent = parent.getParent()) {
            x = parent.getX();
            y = parent.getY();
            w = parent.getWidth();
            h = parent.getHeight();

            oldClip.setBounds(clip);
            SwingUtilities.computeIntersection(0, 0, w, h, clip);
            if(!clip.equals(oldClip))
                return false;

            if(lastParent != null && parent instanceof JComponent &&
               !((JComponent)parent).isOptimizedDrawingEnabled()) {
                Component comps[] = parent.getComponents();
                int index = 0;

                for(int i = comps.length - 1 ;i >= 0; i--) {
                    if(comps[i] == lastParent) {
                        index = i - 1;
                        break;
                    }
                }

                while(index >= 0) {
                    tmp2 = comps[index].getBounds(tmp2);

                    if(tmp2.intersects(clip))
                        return false;
                    index--;
                }
            }
            clip.x += x;
            clip.y += y;
            lastParent = parent;
        }
        if (parent == null) {
            // No Window parent.
            return false;
        }
        return true;
    }


/////////////////
// Accessibility support
////////////////

    
Gets the AccessibleContext associated with this JViewport.
For viewports, the AccessibleContext takes the form of an
AccessibleJViewport.
A new AccessibleJViewport instance is created if necessary.
Returns:
an AccessibleJViewport that serves as the
        AccessibleContext of this JViewport/**
     * Gets the AccessibleContext associated with this JViewport.
     * For viewports, the AccessibleContext takes the form of an
     * AccessibleJViewport.
     * A new AccessibleJViewport instance is created if necessary.
     *
     * @return an AccessibleJViewport that serves as the
     *         AccessibleContext of this JViewport
     */
    public AccessibleContext getAccessibleContext() {
        if (accessibleContext == null) {
            accessibleContext = new AccessibleJViewport();
        }
        return accessibleContext;
    }

    
This class implements accessibility support for the
JViewport class.  It provides an implementation of the
Java Accessibility API appropriate to viewport user-interface elements.

Warning:
Serialized objects of this class will not be compatible with
future Swing releases. The current serialization support is
appropriate for short term storage or RMI between applications running
the same version of Swing.  As of 1.4, support for long term storage
of all JavaBeans™
has been added to the java.beans package. Please see XMLEncoder. /**
     * This class implements accessibility support for the
     * <code>JViewport</code> class.  It provides an implementation of the
     * Java Accessibility API appropriate to viewport user-interface elements.
     * <p>
     * <strong>Warning:</strong>
     * Serialized objects of this class will not be compatible with
     * future Swing releases. The current serialization support is
     * appropriate for short term storage or RMI between applications running
     * the same version of Swing.  As of 1.4, support for long term storage
     * of all JavaBeans&trade;
     * has been added to the <code>java.beans</code> package.
     * Please see {@link java.beans.XMLEncoder}.
     */
    protected class AccessibleJViewport extends AccessibleJComponent {
        
Get the role of this object.
Returns:
an instance of AccessibleRole describing the role of
the object/**
         * Get the role of this object.
         *
         * @return an instance of AccessibleRole describing the role of
         * the object
         */
        public AccessibleRole getAccessibleRole() {
            return AccessibleRole.VIEWPORT;
        }
    } // inner class AccessibleJViewport
}