Is caret positioning in right-to-left oriented jtextpane corruptable?

Question

Dear all -
Below is a serious problem. I hope I can get help from you experts out there; otherwise, I think it is a bug that should be reported to the JDK developers.
I am writing an editor using my own keyboard layout to type in Arabic. To do so, I use jTextPane, and my own implementation of DocumentFilter (where I map English keys to Arabic letters). I start by i) setting the component orientation of jTextPane to be from RIGHT_TO_LEFT, and ii) attaching a caretListener to trace the caret's position.
The problem (I think it is a bug just like what is recorded here: http://bugs.adobe.com/jira/browse/SDK-16315):
Initially as I type text in Arabic, there is one-to-one correspondence between where I point my mouse and where the caret displays, basically, the same place. However, a problem occurs (and can always be re-produced) when I type a word towards the end of the line, follow it by a space character, and that space character causes the word to descend to the next line as a result of a wrap-around. Now, as I point my mouse to that first line again, the location where I click the mouse and the location where the caret flashes are no longer coincident! Also, the caret progression counter is reversed! That is, if there are 5 characters on Line 1, then whereas initially the caret starts from Position 0 on the right-hand side and increases as more text is added from right to left, it is now reversed where the the caret now increases from left to right for the first line, but correctly increases from right to left in the second line! yes funny stuff and very hard to describe to.
So, here is an example. I wrote the code below (JDK1.6_u10, on Netbeans 6.5 RC2) to make it easy to reproduce the problem. In the example, I have replaced the keys A, S, D, F and G with their Arabic corresponding letters alif, seen, daal, faa and jeem. Now, type these letters inside the double quotes (without the double quotes) including the two spaces please and watch out for the output: "asdfg asdfg ". Up until you type the last g and before you type space, all is perfect, and you should notice that the caret position correctly moves from 0 upwards in the printlines I provided. When you type that last space, the second word descends as a result of the wrap-around, and hell breaks loose! Notice that whereas the mouse and caret position are coincident on the second line, there is no way to fine-control the mouse position on the first line any more. Further, whereas adding text on the second line is intuitive (i.e., you can insert more text wherever you point your mouse, which is also where the caret would show up), for the first line, if you point the mouse any place over the written string, the caret displays in a different place, the any added text is added in the wrong place! All this because the caret counter is now reversed, which should never occur. Any ideas or fixes?
Thank you very much for reading.
Mohsen
package workshop.onframes;
import java.awt.ComponentOrientation;
import java.awt.Rectangle;
import javax.swing.event.CaretEvent;
import javax.swing.event.CaretListener;
import javax.swing.text.BadLocationException;
public class NewJFrame1 extends javax.swing.JFrame {
public NewJFrame1() {
initComponents();
jTextPane1.setComponentOrientation(ComponentOrientation.RIGHT_TO_LEFT);
CaretListener caretListener = new CaretListener() {
public void caretUpdate(CaretEvent e) {
int dot = e.getDot();
int mark = e.getMark();
if (dot == mark) {
try {
Rectangle cc = jTextPane1.modelToView(dot);
System.out.println("Caret text position: " + dot +
", view location (x, y): (" + cc.x + ", " + cc.y + ")");
} catch (BadLocationException ble) {
System.err.println("CTP: " + dot);
} else if (dot < mark) {
System.out.println("Selection from " + dot + " to " + mark);
} else {
System.out.println("Selection from " + mark + " to " + dot);
jTextPane1.addCaretListener(caretListener);
/** This method is called from within the constructor to
* initialize the form.
* WARNING: Do NOT modify this code. The content of this method is
* always regenerated by the Form Editor.
@SuppressWarnings("unchecked")
// <editor-fold defaultstate="collapsed" desc="Generated Code">
private void initComponents() {
jScrollPane3 = new javax.swing.JScrollPane();
jTextPane1 = new javax.swing.JTextPane();
setDefaultCloseOperation(javax.swing.WindowConstants.EXIT_ON_CLOSE);
jTextPane1.setFont(new java.awt.Font("Tahoma", 0, 24)); // NOI18N
jTextPane1.setAutoscrolls(false);
jTextPane1.addKeyListener(new java.awt.event.KeyAdapter() {
public void keyTyped(java.awt.event.KeyEvent evt) {
jTextPane1KeyTyped(evt);
jScrollPane3.setViewportView(jTextPane1);
javax.swing.GroupLayout layout = new javax.swing.GroupLayout(getContentPane());
getContentPane().setLayout(layout);
layout.setHorizontalGroup(
layout.createParallelGroup(javax.swing.GroupLayout.Alignment.LEADING)
.addGroup(layout.createSequentialGroup()
.addContainerGap()
.addComponent(jScrollPane3, javax.swing.GroupLayout.DEFAULT_SIZE, 159, Short.MAX_VALUE)
.addContainerGap())
layout.setVerticalGroup(
layout.createParallelGroup(javax.swing.GroupLayout.Alignment.LEADING)
.addGroup(layout.createSequentialGroup()
.addContainerGap()
.addComponent(jScrollPane3, javax.swing.GroupLayout.PREFERRED_SIZE, 85, javax.swing.GroupLayout.PREFERRED_SIZE)
.addContainerGap(javax.swing.GroupLayout.DEFAULT_SIZE, Short.MAX_VALUE))
pack();
}// </editor-fold>
private void jTextPane1KeyTyped(java.awt.event.KeyEvent evt) {
if (evt.getKeyChar() == 'a') {
evt.setKeyChar('\u0627');
} else if (evt.getKeyChar() == 's') {
evt.setKeyChar('\u0633');
} else if (evt.getKeyChar() == 'd') {
evt.setKeyChar('\u062f');
} else if (evt.getKeyChar() == 'f') {
evt.setKeyChar('\u0641');
} else if (evt.getKeyChar() == 'g') {
evt.setKeyChar('\u062c');
public
static void main(String args[]) {
java.awt.EventQueue.invokeLater(new Runnable() {
public void run() {
new NewJFrame1().setVisible(true);
// Variables declaration - do not modify
private javax.swing.JScrollPane jScrollPane3;
private javax.swing.JTextPane jTextPane1;
// End of variables declaration
}

Answer 1

Hi Mohsen,
I looked at it and indeed, I see what you describe. Sorry, but I can't shed any light. I tried to figure out what software component, or combination of components, is the cause of the problem. I see several candidates:
1) The JTextPane
2) The Document
3) RTL support
4) BIDI support
5) Interpretation (by any other software component) of the left and right arrow key
6) The font
To clarify number 6: I know virtually nothing of Arabic language (apart from it being written from right to left). I remember however that the actual representation of a letter is dependent of its position between other letters: front, middle and end. What I see to my astonishment is that it seems that the rendering is also aware of this phenomenon. When you insert an A between the S and D of ASDFG, the shape of the S changes. Quite magic.
I tried to add a second textpane with the same Document, but a different size, to see what would happen with number one if one types text in number two and vice versa.
In my first attempt, the font that you set on textpane one was gone after I set its document to number two. For me that is very strange. The font was set to the textpane, not to the document. The separation betweem Model and View seems not very clear in this case. So I now also set that font on the second textpane.
I will post the changed code so that you may experiment some more and hopefully will find the problem.
You might be interested in a thread on java dot net forums that discusses a memory leak for RTL [http://forums.java.net/jive/message.jspa?messageID=300344#300344]
Piet
import java.awt.ComponentOrientation;
import java.awt.EventQueue;
import java.awt.Font;
import java.awt.Rectangle;
import java.awt.event.KeyAdapter;
import java.awt.event.KeyEvent;
import javax.swing.GroupLayout;
import javax.swing.JFrame;
import javax.swing.JScrollPane;
import javax.swing.JTextPane;
import javax.swing.WindowConstants;
import javax.swing.event.CaretEvent;
import javax.swing.event.CaretListener;
import javax.swing.text.BadLocationException;
import javax.swing.text.Document;
public class NewJFrame1 extends JFrame {
    private static final long serialVersionUID = 1L;
    public NewJFrame1() {
     initComponents();
     // jTextPane1.setComponentOrientation(ComponentOrientation.RIGHT_TO_LEFT);
     this.applyComponentOrientation(ComponentOrientation.RIGHT_TO_LEFT);
     CaretListener caretListener = new CaretListener() {
         public void caretUpdate(CaretEvent e) {
          int dot = e.getDot();
          int mark = e.getMark();
          if (dot == mark) {
              try {
               Rectangle cc = jTextPane1.modelToView(dot);
               System.out.println("Caret text position: " + dot
                    + ", view location (x, y): (" + cc.x + ", "
                    + cc.y + ")");
              } catch (BadLocationException ble) {
               System.err.println("CTP: " + dot);
          } else if (dot < mark) {
              System.out.println("Selection from " + dot + " to " + mark);
          } else {
              System.out.println("Selection from " + mark + " to " + dot);
     jTextPane1.addCaretListener(caretListener);
    private KeyAdapter toArabic = new KeyAdapter() {
     public void keyTyped(KeyEvent evt) {
         jTextPane1KeyTyped(evt);
     * This method is called from within the constructor to initialize the form.
     * WARNING: Do NOT modify this code. The content of this method is always
     * regenerated by the Form Editor.
    // @SuppressWarnings("unchecked")
    // <editor-fold defaultstate="collapsed" desc="Generated Code">
    private void initComponents() {
     jScrollPane3 = new JScrollPane();
     jTextPane1 = new JTextPane();
     setDefaultCloseOperation(WindowConstants.EXIT_ON_CLOSE);
     jTextPane1.setFont(new Font("Tahoma", 0, 24)); // NOI18N
     jTextPane1.setAutoscrolls(false);
     jTextPane1.addKeyListener(toArabic);
     jScrollPane3.setViewportView(jTextPane1);
     GroupLayout layout = new GroupLayout(getContentPane());
     getContentPane().setLayout(layout);
     layout.setHorizontalGroup(layout.createParallelGroup(
          GroupLayout.Alignment.LEADING).addGroup(
          layout.createSequentialGroup().addContainerGap().addComponent(
               jScrollPane3, GroupLayout.DEFAULT_SIZE, 159,
               Short.MAX_VALUE).addContainerGap()));
     layout.setVerticalGroup(layout.createParallelGroup(
          GroupLayout.Alignment.LEADING).addGroup(
          layout.createSequentialGroup().addContainerGap().addComponent(
               jScrollPane3, GroupLayout.PREFERRED_SIZE, 85,
               GroupLayout.PREFERRED_SIZE).addContainerGap(
               GroupLayout.DEFAULT_SIZE, Short.MAX_VALUE)));
     pack();
    }// </editor-fold>
    private void jTextPane1KeyTyped(KeyEvent evt) {
     if (evt.getKeyChar() == 'a') {
         evt.setKeyChar('\u0627');
     } else if (evt.getKeyChar() == 's') {
         evt.setKeyChar('\u0633');
     } else if (evt.getKeyChar() == 'd') {
         evt.setKeyChar('\u062f');
     } else if (evt.getKeyChar() == 'f') {
         evt.setKeyChar('\u0641');
     } else if (evt.getKeyChar() == 'g') {
         evt.setKeyChar('\u062c');
    public static void main(String args[]) {
     EventQueue.invokeLater(new Runnable() {
         public void run() {
          final NewJFrame1 frameOne = new NewJFrame1();
          frameOne.setLocationRelativeTo(null);
          frameOne.setVisible(true);
          EventQueue.invokeLater(new Runnable() {
              public void run() {
               Document doc = frameOne.jTextPane1.getDocument();
               JTextPane textPane2 = new JTextPane();
               textPane2.setFont(new Font("Tahoma", 0, 24)); // NOI18N
               textPane2.setAutoscrolls(false);
               textPane2.setDocument(doc);
               textPane2.addKeyListener(frameOne.toArabic);
               JFrame frameTwo = new JFrame();
               frameTwo.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
               frameTwo.add(new JScrollPane(textPane2));
               frameTwo.setSize(400, 300);
               frameTwo.setLocationByPlatform(true);
               frameTwo.setVisible(true);
               frameTwo
                    .applyComponentOrientation(ComponentOrientation.RIGHT_TO_LEFT);
    // Variables declaration - do not modify
    private JScrollPane jScrollPane3;
    private JTextPane jTextPane1;
    // End of variables declaration
}