AsyncBoxView


1   /*
2    * @(#)AsyncBoxView.java    1.16 03/12/19
3    *
4    * Copyright 2004 Sun Microsystems, Inc. All rights reserved.
5    * SUN PROPRIETARY/CONFIDENTIAL. Use is subject to license terms.
6    */
7   package javax.swing.text;
8   
9   import java.util.*;
10  import java.awt.*;
11  import javax.swing.SwingUtilities  ;
12  import javax.swing.event.DocumentEvent  ;
13  
14  /**
15   * A box that does layout asynchronously.  This
16   * is useful to keep the GUI event thread moving by
17   * not doing any layout on it.  The layout is done
18   * on a granularity of operations on the child views.
19   * After each child view is accessed for some part
20   * of layout (a potentially time consuming operation) 
21   * the remaining tasks can be abandoned or a new higher 
22   * priority task (i.e. to service a synchronous request 
23   * or a visible area) can be taken on.
24   * <p>
25   * While the child view is being accessed
26   * a read lock is aquired on the associated document 
27   * so that the model is stable while being accessed.
28   *
29   * @author  Timothy Prinzing
30   * @version 1.16 12/19/03
31   * @since   1.3
32   */
33  public class AsyncBoxView extends View   {
34  
35      /**
36       * Construct a box view that does asynchronous layout.
37       *
38       * @param elem the element of the model to represent
39       * @param axis the axis to tile along.  This can be
40       *  either X_AXIS or Y_AXIS.
41       */
42      public AsyncBoxView(Element   elem, int axis) {
43      super(elem);
44      stats = new ArrayList();
45      this.axis = axis;
46      locator = new ChildLocator();
47      flushTask = new FlushTask();
48      minorSpan = Short.MAX_VALUE;
49      estimatedMajorSpan = false;
50      }
51  
52      /**
53       * Fetch the major axis (the axis the children
54       * are tiled along).  This will have a value of
55       * either X_AXIS or Y_AXIS.
56       */
57      public int getMajorAxis() {
58      return axis;
59      }
60  
61      /**
62       * Fetch the minor axis (the axis orthoginal 
63       * to the tiled axis).  This will have a value of
64       * either X_AXIS or Y_AXIS.
65       */
66      public int getMinorAxis() {
67      return (axis == X_AXIS) ? Y_AXIS : X_AXIS;
68      }
69  
70      /**
71       * Get the top part of the margin around the view.
72       */
73      public float getTopInset() {
74      return topInset;
75      }
76  
77      /**
78       * Set the top part of the margin around the view.
79       *
80       * @param i the value of the inset
81       */
82      public void setTopInset(float i) {
83      topInset = i;
84      }
85  
86      /**
87       * Get the bottom part of the margin around the view.
88       */
89      public float getBottomInset() {
90      return bottomInset;
91      }
92  
93      /**
94       * Set the bottom part of the margin around the view.
95       *
96       * @param i the value of the inset
97       */
98      public void setBottomInset(float i) {
99      bottomInset = i;
100     }
101     
102     /**
103      * Get the left part of the margin around the view.
104      */
105     public float getLeftInset() {
106     return leftInset;
107     }
108 
109     /**
110      * Set the left part of the margin around the view.
111      *
112      * @param i the value of the inset
113      */
114     public void setLeftInset(float i) {
115     leftInset = i;
116     }
117 
118     /**
119      * Get the right part of the margin around the view.
120      */
121     public float getRightInset() {
122     return rightInset;
123     }
124 
125     /**
126      * Set the right part of the margin around the view.
127      *
128      * @param i the value of the inset
129      */
130     public void setRightInset(float i) {
131     rightInset = i;
132     }
133     
134     /**
135      * Fetch the span along an axis that is taken up by the insets.
136      *
137      * @param axis the axis to determine the total insets along,
138      *  either X_AXIS or Y_AXIS.
139      * @since 1.4
140      */
141     protected float getInsetSpan(int axis) {
142     float margin = (axis == X_AXIS) ? 
143         getLeftInset() + getRightInset() : getTopInset() + getBottomInset();
144     return margin;
145     }
146 
147     /**
148      * Set the estimatedMajorSpan property that determines if the
149      * major span should be treated as being estimated.  If this
150      * property is true, the value of setSize along the major axis 
151      * will change the requirements along the major axis and incremental 
152      * changes will be ignored until all of the children have been updated
153      * (which will cause the property to automatically be set to false).
154      * If the property is false the value of the majorSpan will be
155      * considered to be accurate and incremental changes will be
156      * added into the total as they are calculated.
157      *
158      * @since 1.4
159      */
160     protected void setEstimatedMajorSpan(boolean isEstimated) {
161     estimatedMajorSpan = isEstimated;
162     }
163 
164     /**
165      * Is the major span currently estimated?
166      *
167      * @since 1.4
168      */
169     protected boolean getEstimatedMajorSpan() {
170     return estimatedMajorSpan;
171     }
172 
173     /**
174      * Fetch the object representing the layout state of
175      * of the child at the given index.
176      *
177      * @param index the child index.  This should be a
178      *   value >= 0 and < getViewCount().
179      */
180     protected ChildState getChildState(int index) {
181     synchronized(stats) {
182         if ((index >= 0) && (index < stats.size())) {
183         return (ChildState) stats.get(index);
184         }
185         return null;
186     }
187     }
188 
189     /**
190      * Fetch the queue to use for layout.
191      */
192     protected LayoutQueue   getLayoutQueue() {
193     return LayoutQueue.getDefaultQueue();
194     }
195 
196     /**
197      * New ChildState records are created through
198      * this method to allow subclasses the extend
199      * the ChildState records to do/hold more
200      */
201     protected ChildState createChildState(View   v) {
202     return new ChildState(v);
203     }
204 
205     /**
206      * Requirements changed along the major axis.
207      * This is called by the thread doing layout for 
208      * the given ChildState object when it has completed
209      * fetching the child views new preferences.
210      * Typically this would be the layout thread, but
211      * might be the event thread if it is trying to update
212      * something immediately (such as to perform a 
213      * model/view translation).
214      * <p>
215      * This is implemented to mark the major axis as having 
216      * changed so that a future check to see if the requirements
217      * need to be published to the parent view will consider
218      * the major axis.  If the span along the major axis is 
219      * not estimated, it is updated by the given delta to reflect
220      * the incremental change.  The delta is ignored if the 
221      * major span is estimated.
222      */
223     protected synchronized void majorRequirementChange(ChildState cs, float delta) {
224     if (estimatedMajorSpan == false) {
225         majorSpan += delta;
226     }
227     majorChanged = true;
228     }
229 
230     /**
231      * Requirements changed along the minor axis.
232      * This is called by the thread doing layout for 
233      * the given ChildState object when it has completed
234      * fetching the child views new preferences.
235      * Typically this would be the layout thread, but
236      * might be the GUI thread if it is trying to update
237      * something immediately (such as to perform a 
238      * model/view translation).
239      */
240     protected synchronized void minorRequirementChange(ChildState cs) {
241     minorChanged = true;
242     }
243 
244     /**
245      * Publish the changes in preferences upward to the parent
246      * view.  This is normally called by the layout thread.
247      */
248     protected void flushRequirementChanges() {
249     AbstractDocument   doc = (AbstractDocument  ) getDocument();
250     try {
251         doc.readLock();
252 
253         View   parent = null;
254         boolean horizontal = false;
255         boolean vertical = false;
256 
257         synchronized(this) {
258         // perform tasks that iterate over the children while
259         // preventing the collection from changing.
260         synchronized(stats) {
261             int n = getViewCount();
262             if ((n > 0) && (minorChanged || estimatedMajorSpan)) {
263             LayoutQueue   q = getLayoutQueue();
264             ChildState min = getChildState(0);
265             ChildState pref = getChildState(0);
266             float span = 0f;
267             for (int i = 1; i < n; i++) {
268                 ChildState cs = getChildState(i);
269                 if (minorChanged) {
270                 if (cs.min > min.min) {
271                     min = cs;
272                 }
273                 if (cs.pref > pref.pref) {
274                     pref = cs;
275                 }
276                 }
277                 if (estimatedMajorSpan) {
278                 span += cs.getMajorSpan();
279                 }
280             }
281 
282             if (minorChanged) {
283                 minRequest = min;
284                 prefRequest = pref;
285             }
286             if (estimatedMajorSpan) {
287                 majorSpan = span;
288                 estimatedMajorSpan = false;
289                 majorChanged = true;
290             }
291             }
292         }
293 
294         // message preferenceChanged 
295         if (majorChanged || minorChanged) {
296             parent = getParent();
297             if (parent != null) {
298             if (axis == X_AXIS) {
299                 horizontal = majorChanged;
300                 vertical = minorChanged;
301             } else {
302                 vertical = majorChanged;
303                 horizontal = minorChanged;
304             }
305             }
306             majorChanged = false;
307             minorChanged = false;
308         }
309         }
310 
311         // propagate a preferenceChanged, using the
312         // layout thread.
313         if (parent != null) {
314         parent.preferenceChanged(this, horizontal, vertical);
315             
316         // probably want to change this to be more exact.
317         Component c = getContainer();
318         if (c != null) {
319             c.repaint();
320         }
321         }
322     } finally {
323         doc.readUnlock();
324     }
325     }
326 
327     /**
328      * Calls the superclass to update the child views, and
329      * updates the status records for the children.  This
330      * is expected to be called while a write lock is held
331      * on the model so that interaction with the layout
332      * thread will not happen (i.e. the layout thread 
333      * acquires a read lock before doing anything). 
334      *
335      * @param offset the starting offset into the child views >= 0
336      * @param length the number of existing views to replace >= 0
337      * @param views the child views to insert
338      */
339     public void replace(int offset, int length, View  [] views) {
340     synchronized(stats) {
341         // remove the replaced state records
342         for (int i = 0; i < length; i++) {
343                 ChildState cs = (ChildState)stats.remove(offset);
344                 float csSpan = cs.getMajorSpan();
345 
346                 cs.getChildView().setParent(null);
347                 if (csSpan != 0) {
348                     majorRequirementChange(cs, -csSpan);
349                 }
350         }
351 
352         // insert the state records for the new children
353         LayoutQueue   q = getLayoutQueue();
354         if (views != null) {
355         for (int i = 0; i < views.length; i++) {
356             ChildState s = createChildState(views[i]);
357             stats.add(offset + i, s);
358             q.addTask(s);
359         }
360         }
361 
362         // notify that the size changed
363         q.addTask(flushTask);
364     }
365     }
366 
367     /**
368      * Loads all of the children to initialize the view.
369      * This is called by the <a HREF="#setParent">setParent</a> 
370      * method.  Subclasses can reimplement this to initialize 
371      * their child views in a different manner.  The default
372      * implementation creates a child view for each 
373      * child element.
374      * <p>
375      * Normally a write-lock is held on the Document while
376      * the children are being changed, which keeps the rendering
377      * and layout threads safe.  The exception to this is when 
378      * the view is initialized to represent an existing element
379      * (via this method), so it is synchronized to exclude 
380      * preferenceChanged while we are initializing.
381      *
382      * @param f the view factory
383      * @see #setParent
384      */
385     protected void loadChildren(ViewFactory   f) {
386     Element   e = getElement();
387     int n = e.getElementCount();
388     if (n > 0) {
389         View  [] added = new View  [n];
390         for (int i = 0; i < n; i++) {
391         added[i] = f.create(e.getElement(i));
392         }
393         replace(0, 0, added);
394     }
395     }
396 
397     /**
398      * Fetches the child view index representing the given position in
399      * the model.  This is implemented to fetch the view in the case
400      * where there is a child view for each child element.
401      *
402      * @param pos the position >= 0
403      * @return  index of the view representing the given position, or 
404      *   -1 if no view represents that position
405      */
406     protected synchronized int getViewIndexAtPosition(int pos, Position.Bias   b) {
407     boolean isBackward = (b == Position.Bias.Backward);
408     pos = (isBackward) ? Math.max(0, pos - 1) : pos;
409     Element   elem = getElement();
410     return elem.getElementIndex(pos);
411     }
412 
413     /**
414      * Update the layout in response to receiving notification of
415      * change from the model.  This is implemented to note the 
416      * change on the ChildLocator so that offsets of the children
417      * will be correctly computed.
418      *
419      * @param ec changes to the element this view is responsible
420      *  for (may be null if there were no changes).
421      * @param e the change information from the associated document
422      * @param a the current allocation of the view
423      * @see #insertUpdate
424      * @see #removeUpdate
425      * @see #changedUpdate     
426      */
427     protected void updateLayout(DocumentEvent.ElementChange   ec, 
428                     DocumentEvent   e, Shape a) {
429     if (ec != null) {
430         // the newly inserted children don't have a valid
431         // offset so the child locator needs to be messaged
432         // that the child prior to the new children has 
433         // changed size.
434         int index = Math.max(ec.getIndex() - 1, 0);
435         ChildState cs = getChildState(index);
436         locator.childChanged(cs);
437     }
438     }
439 
440     // --- View methods ------------------------------------
441 
442     /**
443      * Sets the parent of the view.
444      * This is reimplemented to provide the superclass
445      * behavior as well as calling the <code>loadChildren</code>
446      * method if this view does not already have children.  
447      * The children should not be loaded in the 
448      * constructor because the act of setting the parent
449      * may cause them to try to search up the hierarchy
450      * (to get the hosting Container for example).
451      * If this view has children (the view is being moved
452      * from one place in the view hierarchy to another), 
453      * the <code>loadChildren</code> method will not be called.
454      *
455      * @param parent the parent of the view, null if none
456      */
457     public void setParent(View   parent) {
458     super.setParent(parent);
459     if ((parent != null) && (getViewCount() == 0)) {
460         ViewFactory   f = getViewFactory();
461         loadChildren(f);
462     }
463     }
464 
465     /**
466      * Child views can call this on the parent to indicate that
467      * the preference has changed and should be reconsidered
468      * for layout.  This is reimplemented to queue new work
469      * on the layout thread.  This method gets messaged from
470      * multiple threads via the children.
471      *
472      * @param child the child view
473      * @param width true if the width preference has changed
474      * @param height true if the height preference has changed
475      * @see javax.swing.JComponent#revalidate
476      */
477     public synchronized void preferenceChanged(View   child, boolean width, boolean height) {
478     if (child == null) {
479         getParent().preferenceChanged(this, width, height);
480     } else {
481         if (changing != null) {
482         View   cv = changing.getChildView();
483         if (cv == child) {
484             // size was being changed on the child, no need to
485             // queue work for it.
486             changing.preferenceChanged(width, height);
487             return;
488         }
489         }
490         int index = getViewIndex(child.getStartOffset(), 
491                      Position.Bias.Forward);
492         ChildState cs = getChildState(index);
493         cs.preferenceChanged(width, height);
494         LayoutQueue   q = getLayoutQueue();
495         q.addTask(cs);
496         q.addTask(flushTask);
497     }
498     }
499 
500     /**
501      * Sets the size of the view.  This should cause 
502      * layout of the view if the view caches any layout
503      * information.
504      * <p>
505      * Since the major axis is updated asynchronously and should be 
506      * the sum of the tiled children the call is ignored for the major 
507      * axis.  Since the minor axis is flexible, work is queued to resize 
508      * the children if the minor span changes.
509      *
510      * @param width the width >= 0
511      * @param height the height >= 0
512      */
513     public void setSize(float width, float height) {
514     setSpanOnAxis(X_AXIS, width);
515     setSpanOnAxis(Y_AXIS, height);
516     }
517 
518     /**
519      * Retrieves the size of the view along an axis.  
520      *
521      * @param axis may be either <code>View.X_AXIS</code> or
522      *      <code>View.Y_AXIS</code>
523      * @return the current span of the view along the given axis, >= 0
524      */
525     float getSpanOnAxis(int axis) {
526     if (axis == getMajorAxis()) {
527         return majorSpan;
528     }
529     return minorSpan;
530     }
531 
532     /**
533      * Sets the size of the view along an axis.  Since the major
534      * axis is updated asynchronously and should be the sum of the
535      * tiled children the call is ignored for the major axis.  Since
536      * the minor axis is flexible, work is queued to resize the
537      * children if the minor span changes.
538      *
539      * @param axis may be either <code>View.X_AXIS</code> or
540      *      <code>View.Y_AXIS</code>
541      * @param span the span to layout to >= 0
542      */
543     void setSpanOnAxis(int axis, float span) {
544     float margin = getInsetSpan(axis);
545     if (axis == getMinorAxis()) {
546         float targetSpan = span - margin;
547         if (targetSpan != minorSpan) {
548         minorSpan = targetSpan;
549 
550         // mark all of the ChildState instances as needing to
551         // resize the child, and queue up work to fix them.
552         int n = getViewCount();
553         if (n != 0) {
554             LayoutQueue   q = getLayoutQueue();
555             for (int i = 0; i < n; i++) {
556             ChildState cs = getChildState(i);
557             cs.childSizeValid = false;
558             q.addTask(cs);
559             }
560             q.addTask(flushTask);
561         }
562         }
563     } else {
564         // along the major axis the value is ignored 
565         // unless the estimatedMajorSpan property is
566         // true.
567         if (estimatedMajorSpan) {
568         majorSpan = span - margin;
569         }
570     }
571     }
572 
573     /**
574      * Render the view using the given allocation and
575      * rendering surface.
576      * <p>
577      * This is implemented to determine whether or not the
578      * desired region to be rendered (i.e. the unclipped 
579      * area) is up to date or not.  If up-to-date the children
580      * are rendered.  If not up-to-date, a task to build
581      * the desired area is placed on the layout queue as
582      * a high priority task.  This keeps by event thread
583      * moving by rendering if ready, and postponing until
584      * a later time if not ready (since paint requests
585      * can be rescheduled).
586      *
587      * @param g the rendering surface to use
588      * @param alloc the allocated region to render into
589      * @see View#paint
590      */
591     public void paint(Graphics g, Shape alloc) {
592     synchronized (locator) {
593         locator.setAllocation(alloc);
594         locator.paintChildren(g);
595     }
596     }
597 
598     /**
599      * Determines the preferred span for this view along an
600      * axis.
601      *
602      * @param axis may be either View.X_AXIS or View.Y_AXIS
603      * @return   the span the view would like to be rendered into >= 0.
604      *           Typically the view is told to render into the span
605      *           that is returned, although there is no guarantee.  
606      *           The parent may choose to resize or break the view.
607      * @exception IllegalArgumentException for an invalid axis type
608      */
609     public float getPreferredSpan(int axis) {
610     float margin = getInsetSpan(axis);
611     if (axis == this.axis) {
612         return majorSpan + margin;
613     }
614     if (prefRequest != null) {
615         View   child = prefRequest.getChildView();
616         return child.getPreferredSpan(axis) + margin;
617     }
618 
619     // nothing is known about the children yet
620     return margin + 30;
621     }
622 
623     /**
624      * Determines the minimum span for this view along an
625      * axis.
626      *
627      * @param axis may be either View.X_AXIS or View.Y_AXIS
628      * @return  the span the view would like to be rendered into >= 0.
629      *           Typically the view is told to render into the span
630      *           that is returned, although there is no guarantee.  
631      *           The parent may choose to resize or break the view.
632      * @exception IllegalArgumentException for an invalid axis type
633      */
634     public float getMinimumSpan(int axis) {
635     if (axis == this.axis) {
636         return getPreferredSpan(axis);
637     }
638     if (minRequest != null) {
639         View   child = minRequest.getChildView();
640         return child.getMinimumSpan(axis);
641     }
642 
643     // nothing is known about the children yet
644     if (axis == X_AXIS) {
645         return getLeftInset() + getRightInset() + 5;
646     } else {
647         return getTopInset() + getBottomInset() + 5;
648     }
649     }
650 
651     /**
652      * Determines the maximum span for this view along an
653      * axis.
654      *
655      * @param axis may be either View.X_AXIS or View.Y_AXIS
656      * @return   the span the view would like to be rendered into >= 0.
657      *           Typically the view is told to render into the span
658      *           that is returned, although there is no guarantee.  
659      *           The parent may choose to resize or break the view.
660      * @exception IllegalArgumentException for an invalid axis type
661      */
662     public float getMaximumSpan(int axis) {
663     if (axis == this.axis) {
664         return getPreferredSpan(axis);
665     }
666     return Integer.MAX_VALUE;
667     }
668 
669 
670     /** 
671      * Returns the number of views in this view.  Since
672      * the default is to not be a composite view this
673      * returns 0.
674      *
675      * @return the number of views >= 0
676      * @see View#getViewCount
677      */
678     public int getViewCount() {
679     synchronized(stats) {
680         return stats.size();
681     }
682     }
683 
684     /** 
685      * Gets the nth child view.  Since there are no
686      * children by default, this returns null.
687      *
688      * @param n the number of the view to get, >= 0 && < getViewCount()
689      * @return the view
690      */
691     public View   getView(int n) {
692     ChildState cs = getChildState(n);
693     if (cs != null) {
694         return cs.getChildView();
695     }
696     return null;
697     }
698 
699     /**
700      * Fetches the allocation for the given child view. 
701      * This enables finding out where various views
702      * are located, without assuming the views store
703      * their location.  This returns null since the
704      * default is to not have any child views.
705      *
706      * @param index the index of the child, >= 0 && < getViewCount()
707      * @param a  the allocation to this view.
708      * @return the allocation to the child
709      */
710     public Shape getChildAllocation(int index, Shape a) {
711     Shape ca = locator.getChildAllocation(index, a);
712     return ca;
713     }
714 
715     /**
716      * Returns the child view index representing the given position in
717      * the model.  By default a view has no children so this is implemented
718      * to return -1 to indicate there is no valid child index for any
719      * position.
720      *
721      * @param pos the position >= 0
722      * @return  index of the view representing the given position, or 
723      *   -1 if no view represents that position
724      * @since 1.3
725      */
726     public int getViewIndex(int pos, Position.Bias   b) {
727         return getViewIndexAtPosition(pos, b);
728     }
729 
730     /**
731      * Provides a mapping from the document model coordinate space
732      * to the coordinate space of the view mapped to it.
733      *
734      * @param pos the position to convert >= 0
735      * @param a the allocated region to render into
736      * @param b the bias toward the previous character or the
737      *  next character represented by the offset, in case the 
738      *  position is a boundary of two views. 
739      * @return the bounding box of the given position is returned
740      * @exception BadLocationException  if the given position does
741      *   not represent a valid location in the associated document
742      * @exception IllegalArgumentException for an invalid bias argument
743      * @see View#viewToModel
744      */
745     public Shape modelToView(int pos, Shape a, Position.Bias   b) throws BadLocationException   {
746     int index = getViewIndex(pos, b);
747     Shape ca = locator.getChildAllocation(index, a);
748 
749     // forward to the child view, and make sure we don't
750     // interact with the layout thread by synchronizing
751     // on the child state.
752     ChildState cs = getChildState(index);
753     synchronized (cs) {
754         View   cv = cs.getChildView();
755         Shape v = cv.modelToView(pos, ca, b);
756         return v;
757     }
758     }
759 
760     /**
761      * Provides a mapping from the view coordinate space to the logical
762      * coordinate space of the model.  The biasReturn argument will be
763      * filled in to indicate that the point given is closer to the next
764      * character in the model or the previous character in the model.
765      * <p>
766      * This is expected to be called by the GUI thread, holding a 
767      * read-lock on the associated model.  It is implemented to
768      * locate the child view and determine it's allocation with a
769      * lock on the ChildLocator object, and to call viewToModel
770      * on the child view with a lock on the ChildState object 
771      * to avoid interaction with the layout thread.
772      *
773      * @param x the X coordinate >= 0
774      * @param y the Y coordinate >= 0
775      * @param a the allocated region to render into
776      * @return the location within the model that best represents the
777      *  given point in the view >= 0.  The biasReturn argument will be
778      * filled in to indicate that the point given is closer to the next
779      * character in the model or the previous character in the model.
780      */
781     public int viewToModel(float x, float y, Shape a, Position.Bias  [] biasReturn) {
782     int pos;    // return position
783         int index;  // child index to forward to
784     Shape ca;   // child allocation
785     
786     // locate the child view and it's allocation so that
787     // we can forward to it.  Make sure the layout thread
788     // doesn't change anything by trying to flush changes
789     // to the parent while the GUI thread is trying to
790     // find the child and it's allocation.
791     synchronized (locator) {
792         index = locator.getViewIndexAtPoint(x, y, a);
793         ca = locator.getChildAllocation(index, a);
794     }
795 
796     // forward to the child view, and make sure we don't
797     // interact with the layout thread by synchronizing
798     // on the child state.
799     ChildState cs = getChildState(index);
800     synchronized (cs) {
801         View   v = cs.getChildView();
802         pos = v.viewToModel(x, y, ca, biasReturn);
803     }
804     return pos;
805     }
806 
807     /**
808      * Provides a way to determine the next visually represented model 
809      * location that one might place a caret.  Some views may not be visible,
810      * they might not be in the same order found in the model, or they just
811      * might not allow access to some of the locations in the model.
812      *
813      * @param pos the position to convert >= 0
814      * @param a the allocated region to render into
815      * @param direction the direction from the current position that can
816      *  be thought of as the arrow keys typically found on a keyboard;
817      *  this may be one of the following: 
818      *  <ul>
819      *  <code>SwingConstants.WEST</code>
820      *  <code>SwingConstants.EAST</code> 
821      *  <code>SwingConstants.NORTH</code>
822      *  <code>SwingConstants.SOUTH</code>  
823      *  </ul>
824      * @param biasRet an array contain the bias that was checked
825      * @return the location within the model that best represents the next
826      *  location visual position
827      * @exception BadLocationException
828      * @exception IllegalArgumentException if <code>direction</code> is invalid
829      */
830     public int getNextVisualPositionFrom(int pos, Position.Bias   b, Shape a, 
831                      int direction,
832                                          Position.Bias  [] biasRet) 
833                                                   throws BadLocationException   {
834         return Utilities.getNextVisualPositionFrom(
835                             this, pos, b, a, direction, biasRet);
836     }
837 
838     // --- variables -----------------------------------------
839 
840     /**
841      * The major axis against which the children are
842      * tiled.
843      */
844     int axis;
845 
846     /**
847      * The children and their layout statistics.
848      */
849     java.util.List   stats;
850 
851     /**
852      * Current span along the major axis.  This
853      * is also the value returned by getMinimumSize,
854      * getPreferredSize, and getMaximumSize along
855      * the major axis.
856      */
857     float majorSpan;
858 
859     /**
860      * Is the span along the major axis estimated?
861      */
862     boolean estimatedMajorSpan;
863 
864     /**
865      * Current span along the minor axis.  This
866      * is what layout was done against (i.e. things
867      * are flexible in this direction).
868      */
869     float minorSpan;
870 
871     /**
872      * Object that manages the offsets of the 
873      * children.  All locking for management of
874      * child locations is on this object.
875      */
876     protected ChildLocator locator;
877 
878     float topInset;
879     float bottomInset;
880     float leftInset;
881     float rightInset;
882 
883     ChildState minRequest;
884     ChildState prefRequest;
885     boolean majorChanged;
886     boolean minorChanged;
887     Runnable   flushTask;
888 
889     /**
890      * Child that is actively changing size.  This often
891      * causes a preferenceChanged, so this is a cache to
892      * possibly speed up the marking the state.  It also
893      * helps flag an opportunity to avoid adding to flush
894      * task to the layout queue.
895      */
896     ChildState changing;
897 
898     /**
899      * A class to manage the effective position of the
900      * child views in a localized area while changes are
901      * being made around the localized area.  The AsyncBoxView
902      * may be continuously changing, but the visible area
903      * needs to remain fairly stable until the layout thread
904      * decides to publish an update to the parent.
905      */
906     public class ChildLocator {
907 
908     /**
909      * construct a child locator.
910      */
911     public ChildLocator() {
912         lastAlloc = new Rectangle();
913         childAlloc = new Rectangle();
914     }
915 
916     /**
917      * Notification that a child changed.  This can effect
918      * whether or not new offset calculations are needed.
919      * This is called by a ChildState object that has 
920      * changed it's major span.  This can therefore be
921      * called by multiple threads.
922      */
923         public synchronized void childChanged(ChildState cs) {
924         if (lastValidOffset == null) {
925         lastValidOffset = cs;
926         } else if (cs.getChildView().getStartOffset() < 
927                lastValidOffset.getChildView().getStartOffset()) {
928         lastValidOffset = cs;
929         }
930     }
931 
932     /**
933      * Paint the children that intersect the clip area.
934      */
935         public synchronized void paintChildren(Graphics g) {
936         Rectangle clip = g.getClipBounds();
937         float targetOffset = (axis == X_AXIS) ? 
938         clip.x - lastAlloc.x : clip.y - lastAlloc.y;
939         int index = getViewIndexAtVisualOffset(targetOffset);
940         int n = getViewCount();
941         float offs = getChildState(index).getMajorOffset();
942         for (int i = index; i < n; i++) {
943         ChildState cs = getChildState(i);
944         cs.setMajorOffset(offs);
945         Shape ca = getChildAllocation(i);
946         if (intersectsClip(ca, clip)) {
947             synchronized (cs) {
948             View   v = cs.getChildView();
949             v.paint(g, ca);
950             }
951         } else {
952             // done painting intersection
953             break;
954         }
955         offs += cs.getMajorSpan();
956         }
957     }
958 
959     /**
960      * Fetch the allocation to use for a child view.
961      * This will update the offsets for all children
962      * not yet updated before the given index.
963      */
964     public synchronized Shape getChildAllocation(int index, Shape a) {
965         if (a == null) {
966         return null;
967         }
968         setAllocation(a);
969         ChildState cs = getChildState(index);
970         if (lastValidOffset == null) {
971         lastValidOffset = getChildState(0);
972         }
973         if (cs.getChildView().getStartOffset() >
974         lastValidOffset.getChildView().getStartOffset()) {
975         // offsets need to be updated
976         updateChildOffsetsToIndex(index);
977         }
978         Shape ca = getChildAllocation(index);
979         return ca;
980     }
981 
982     /**
983      * Fetches the child view index at the given point.
984      * This is called by the various View methods that
985      * need to calculate which child to forward a message
986      * to.  This should be called by a block synchronized
987      * on this object, and would typically be followed
988      * with one or more calls to getChildAllocation that
989      * should also be in the synchronized block.
990      *
991      * @param x the X coordinate >= 0
992      * @param y the Y coordinate >= 0
993      * @param a the allocation to the View
994      * @return the nearest child index
995      */
996         public int getViewIndexAtPoint(float x, float y, Shape a) {
997         setAllocation(a);
998         float targetOffset = (axis == X_AXIS) ? x - lastAlloc.x : y - lastAlloc.y;
999         int index = getViewIndexAtVisualOffset(targetOffset);
1000        return index;
1001    }
1002
1003    /**
1004     * Fetch the allocation to use for a child view.
1005     * <em>This does not update the offsets in the ChildState
1006     * records.</em>
1007     */
1008    protected Shape getChildAllocation(int index) {
1009        ChildState cs = getChildState(index);
1010        if (! cs.isLayoutValid()) {
1011        cs.run();
1012        }
1013        if (axis == X_AXIS) {
1014        childAlloc.x = lastAlloc.x + (int) cs.getMajorOffset();
1015        childAlloc.y = lastAlloc.y + (int) cs.getMinorOffset();
1016        childAlloc.width = (int) cs.getMajorSpan();
1017        childAlloc.height = (int) cs.getMinorSpan();
1018        } else {
1019        childAlloc.y = lastAlloc.y + (int) cs.getMajorOffset();
1020        childAlloc.x = lastAlloc.x + (int) cs.getMinorOffset();
1021        childAlloc.height = (int) cs.getMajorSpan();
1022        childAlloc.width = (int) cs.getMinorSpan();
1023        }
1024            childAlloc.x += (int)getLeftInset()