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 * published by the Free Software Foundation.  Oracle designates this

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 * 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).

 *

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 * 2 along with this work; if not, write to the Free Software Foundation,

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package javax.swing;

import sun.swing.JLightweightFrame;

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.

 * <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™

 * 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 #getUIClassID

     * @see #readObject

     */

    private static final String uiClassID = "ViewportUI";

    /** 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.

     */

    protected boolean isViewSizeSet = false;

    /**

     * 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 <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. */

    transient protected Image backingStoreImage = null;

    /**

     * 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 <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 <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 #setScrollMode

      * @since 1.3

      */

    public static final int SIMPLE_SCROLL_MODE = 0;

    /**

      * @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 <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 <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 <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.

     */

    private transient boolean inBlitPaint;

    /**

     * 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.

     */

    private boolean viewChanged;

    /** Creates a <code>JViewport</code>. */

    public JViewport() {

        super();

        setLayout(createLayoutManager());

        setOpaque(true);

        updateUI();

        setInheritsPopupMenu(true);

    }

    /**

     * Returns the L&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.

     *

     * @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 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.

     *

     * @return the string "ViewportUI"

     *

     * @see JComponent#getUIClassID

     * @see UIDefaults#getUI

     */

    public String getUIClassID() {

        return uiClassID;

    }

    /**

     * 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 <code>Viewport</code>s one lightweight child.

     *

     * @see #setView

     */

    public void remove(Component child) {

        child.removeComponentListener(viewListener);

        super.remove(child);

    }

    @Override

    public void addNotify() {

        super.addNotify();

        // JLightweightFrame does not support BLIT_SCROLL_MODE, so it should be replaced

        Window rootWindow = SwingUtilities.getWindowAncestor(this);

        if (rootWindow instanceof JLightweightFrame

                && getScrollMode() == BLIT_SCROLL_MODE) {

            setScrollMode(BACKINGSTORE_SCROLL_MODE);

        }

    }

    /**

     * 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 <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;

        }