Swing bug?: scrolling BLIT_SCROLL_MODE painting JTextArea components hangs

Question

java version "1.5.0_04"
Hello,
When drawing JComponent Text Areas and dynamically scrolling, Java gets confused, gets the shivers and freezes when the viewport cannot get its arms around the canvas. ;)
Possible problem at JViewport.scrollRectToVisible().
When painting non-text area components eg. graphics circles, it is ok.
Have provided example code. This code is based on the ScrollDemo2 example provided in the Sun Java
Tutorial
thanks,
Anil Philip
juwo LLC
Usage: run program and repeatedly click the left mouse button near right boundary to create a new JComponent node each time and to force scrolling area to increase in size to the right.
When the first node crosses the left boundary, then the scroll pane gets confused, gets the shivers and hangs.
The other scroll modes are a bit better - but very slow leaving the toolbar (in the oroginal application) unpainted sometimes.
* to show possible bug when in the default BLIT_SCROLL_MODE and with JTextArea components.
* author: Anil Philip. juwo LLC. http://juwo.com
* Usage: run program and repeatedly click the left mouse button near right boundary to
* create a new JComponent node each time and to force scrolling area to increase in size to the right.
* When the first node crosses the left boundary, then the scroll pane gets confused, gets the shivers
and hangs.
* The other scroll modes are a bit better - but very slow leaving the toolbar (in the oroginal
application)
* unpainted sometimes.
* This code is based on the ScrollDemo2 example provided in the Sun Java Tutorial (written by John
Vella, a tutorial reader).
import javax.swing.*;
import javax.swing.border.EtchedBorder;
import java.awt.*;
import java.awt.event.*;
import java.util.*;
/* ScrollDemo2WithBug.java is a 1.5 application that requires no other files. */
public class ScrollDemo2WithBug extends JPanel {
private Dimension area; //indicates area taken up by graphics
private Vector circles; //coordinates used to draw graphics
private Vector components;
private JPanel drawingPane;
public ScrollDemo2WithBug() {
super(new BorderLayout());
area = new Dimension(0, 0);
circles = new Vector();
components = new Vector();
//Set up the instructions.
JLabel instructionsLeft = new JLabel(
"Click left mouse button to place a circle.");
JLabel instructionsRight = new JLabel(
"Click right mouse button to clear drawing area.");
JPanel instructionPanel = new JPanel(new GridLayout(0, 1));
instructionPanel.add(instructionsLeft);
instructionPanel.add(instructionsRight);
//Set up the drawing area.
drawingPane = new DrawingPane();
drawingPane.setBackground(Color.white);
drawingPane.setPreferredSize(new Dimension(200, 200));
//Put the drawing area in a scroll pane.
JScrollPane scroller = new JScrollPane(drawingPane);
// scroller.getViewport().setScrollMode(JViewport.SIMPLE_SCROLL_MODE);
if(scroller.getViewport().getScrollMode() == JViewport.BACKINGSTORE_SCROLL_MODE)
System.out.println("BACKINGSTORE_SCROLL_MODE");
if(scroller.getViewport().getScrollMode() == JViewport.BLIT_SCROLL_MODE)
System.out.println("BLIT_SCROLL_MODE");
if(scroller.getViewport().getScrollMode() == JViewport.SIMPLE_SCROLL_MODE)
System.out.println("SIMPLE_SCROLL_MODE");
//Lay out this demo.
add(instructionPanel, BorderLayout.PAGE_START);
add(scroller, BorderLayout.CENTER);
/** The component inside the scroll pane. */
public class DrawingPane extends JPanel implements MouseListener {
private class VisualNode {
int x = 0;
int y = 0;
int id = 0;
public VisualNode(int id, int x, int y) {
this.id = id;
this.x = x;
this.y = y;
title.setLineWrap(true);
title.setAlignmentY(Component.TOP_ALIGNMENT);
titlePanel.add(new JButton("Hi!"));
titlePanel.add(title);
nodePanel.add(titlePanel);
nodePanel.setBorder(BorderFactory
.createEtchedBorder(EtchedBorder.RAISED));
box.add(nodePanel);
ScrollDemo2WithBug.this.drawingPane.add(box);
Box box = Box.createVerticalBox();
Box titlePanel = Box.createHorizontalBox();
JTextArea title = new JTextArea(1, 10); // 1 rows x 10 cols
Box nodePanel = Box.createVerticalBox();
public void paintNode(Graphics g) {
int ix = (int) x + ScrollDemo2WithBug.this.getInsets().left;
int iy = (int) y + ScrollDemo2WithBug.this.getInsets().top;
title.setText(id + " (" + ix + "," + iy + ") ");
box.setBounds(ix, iy, box.getPreferredSize().width, box
.getPreferredSize().height);
int n = 0;
DrawingPane() {
this.setLayout(null);
addMouseListener(this);
protected void paintComponent(Graphics g) {
super.paintComponent(g);
g.fill3DRect(10, 10, 25, 25, true);
Point point;
for (int i = 0; i < circles.size(); i++) {
point = (Point) circles.elementAt(i);
VisualNode node = (VisualNode) components.get(i);
node.paintNode(g);
//Handle mouse events.
public void mouseReleased(MouseEvent e) {
final int W = 100;
final int H = 100;
boolean changed = false;
if (SwingUtilities.isRightMouseButton(e)) {
//This will clear the graphic objects.
circles.removeAllElements();
area.width = 0;
area.height = 0;
changed = true;
} else {
int x = e.getX() - W / 2;
int y = e.getY() - H / 2;
if (x < 0)
x = 0;
if (y < 0)
y = 0;
Point point = new Point(x, y);
VisualNode node = new VisualNode(circles.size(), point.x,
point.y);
// add(node);
components.add(node);
circles.addElement(point);
drawingPane.scrollRectToVisible(new Rectangle(x, y, W, H));
int this_width = (x + W + 2);
if (this_width > area.width) {
area.width = this_width;
changed = true;
int this_height = (y + H + 2);
if (this_height > area.height) {
area.height = this_height;
changed = true;
if (changed) {
//Update client's preferred size because
//the area taken up by the graphics has
//gotten larger or smaller (if cleared).
drawingPane.setPreferredSize(area);
//Let the scroll pane know to update itself
//and its scrollbars.
drawingPane.revalidate();
drawingPane.repaint();
public void mouseClicked(MouseEvent e) {
public void mouseEntered(MouseEvent e) {
public void mouseExited(MouseEvent e) {
public void mousePressed(MouseEvent e) {
* Create the GUI and show it. For thread safety, this method should be
* invoked from the event-dispatching thread.
private static void createAndShowGUI() {
//Make sure we have nice window decorations.
JFrame.setDefaultLookAndFeelDecorated(true);
//Create and set up the window.
JFrame frame = new JFrame("ScrollDemo2");
frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
//Create and set up the content pane.
JComponent newContentPane = new ScrollDemo2WithBug();
newContentPane.setOpaque(true); //content panes must be opaque
frame.setContentPane(newContentPane);
//Display the window.
frame.setSize(800, 600);
frame.pack();
frame.setVisible(true);
public static void main(String[] args) {
//Schedule a job for the event-dispatching thread:
//creating and showing this application's GUI.
javax.swing.SwingUtilities.invokeLater(new Runnable() {
public void run() {
createAndShowGUI();
}

Answer 1

I changed the name so you can run this as-is without name clashing. It works okay now.
import javax.swing.*;
import javax.swing.border.EtchedBorder;
import java.awt.*;
import java.awt.event.*;
import java.util.*;
public class SD2 extends JPanel {
    public SD2() {
        super(new BorderLayout());
        //Set up the instructions.
        JLabel instructionsLeft = new JLabel(
                "Click left mouse button to place a circle.");
        JLabel instructionsRight = new JLabel(
                "Click right mouse button to clear drawing area.");
        JPanel instructionPanel = new JPanel(new GridLayout(0, 1));
        instructionPanel.add(instructionsLeft);
        instructionPanel.add(instructionsRight);
        //Set up the drawing area.
        DrawingPane drawingPane = new DrawingPane(this);
        drawingPane.setBackground(Color.white);
        drawingPane.setPreferredSize(new Dimension(200, 200));
        //Put the drawing area in a scroll pane.
        JScrollPane scroller = new JScrollPane(drawingPane);
        // scroller.getViewport().setScrollMode(JViewport.SIMPLE_SCROLL_MODE);
        if(scroller.getViewport().getScrollMode() == JViewport.BACKINGSTORE_SCROLL_MODE)
            System.out.println("BACKINGSTORE_SCROLL_MODE");
        if(scroller.getViewport().getScrollMode() == JViewport.BLIT_SCROLL_MODE)
            System.out.println("BLIT_SCROLL_MODE");
        if(scroller.getViewport().getScrollMode() == JViewport.SIMPLE_SCROLL_MODE)
            System.out.println("SIMPLE_SCROLL_MODE");
        //Lay out this demo.
        add(instructionPanel, BorderLayout.PAGE_START);
        add(scroller, BorderLayout.CENTER);
     * Create the GUI and show it. For thread safety, this method should be
     * invoked from the event-dispatching thread.
    private static void createAndShowGUI() {
        //Make sure we have nice window decorations.
        JFrame.setDefaultLookAndFeelDecorated(true);
        //Create and set up the window.
        JFrame frame = new JFrame("ScrollDemo2");
        frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
        //Create and set up the content pane.
        JComponent newContentPane = new SD2();
        newContentPane.setOpaque(true);      //content panes must be opaque
        frame.setContentPane(newContentPane);
        //Display the window.
        frame.setSize(800, 600);
        frame.pack();
        frame.setVisible(true);
    public static void main(String[] args) {
        //Schedule a job for the event-dispatching thread:
        //creating and showing this application's GUI.
        javax.swing.SwingUtilities.invokeLater(new Runnable() {
            public void run() {
                createAndShowGUI();
/** The component inside the scroll pane. */
class DrawingPane extends JPanel implements MouseListener {
    SD2 sd2;
    private Dimension area;     //indicates area taken up by graphics
    private Vector circles;     //coordinates used to draw graphics
    private Vector components;
    int n = 0;
    final int
        W = 100,
        H = 100;
    DrawingPane(SD2 sd2) {
        this.sd2 = sd2;
        area = new Dimension(0, 0);
        circles = new Vector();
        components = new Vector();
        this.setLayout(null);
        addMouseListener(this);
     * The 'paint' method is a Container method and it passes its
     * Graphics context, g, to each of its Component children which
     * use it to draw themselves into the parent. JComponent overrides
     * this Container 'paint' method and in it calls this method in
     * addition to others - see api. So the children of DrawingPane will
     * each paint themselves. Here you can do custom painting/rendering.
     * But this is not the place to ask components to paint themselves.
     * That would get swing very confused...
    protected void paintComponent(Graphics g) {
        super.paintComponent(g);
        g.fill3DRect(10, 10, 25, 25, true);
        g.setColor(Color.red);
        Point point;
        for (int i = 0; i < circles.size(); i++) {
            point = (Point) circles.elementAt(i);
            g.fillOval(point.x-2, point.y-2, 4, 4);
    //Handle mouse events.
    public void mousePressed(MouseEvent e) {
        if (SwingUtilities.isRightMouseButton(e)) {
            //This will clear the graphic objects.
            circles.removeAllElements();
            components.removeAllElements();
            removeAll();                    // to clear the components
            area.width = 0;
            area.height = 0;
            setPreferredSize(area);
            revalidate();
            repaint();
        } else {
            int x = e.getX() - W / 2;
            int y = e.getY() - H / 2;
            if (x < 0)
                x = 0;
            if (y < 0)
                y = 0;
            Point point = new Point(x, y);
            VisualNode node = new VisualNode(this, circles.size(), point.x, point.y);
            // add(node);
            components.add(node);       // not needed
            circles.addElement(point);
            checkBoundries(x, y, node);
    private void checkBoundries(int x, int y, VisualNode node) {
        boolean changed = false;
        // since we used the setPreferredSize property to set the size
        // of each box we'll have to use it again to let the JScrollPane
        // know what size we need to show all our child components
        int this_width = (x + node.box.getPreferredSize().width + 2);
        if (this_width > area.width) {
            area.width = this_width;
            changed = true;
        int this_height = (y + node.box.getPreferredSize().height + 2);
        if (this_height > area.height) {
            area.height = this_height;
            changed = true;
        if (changed) {
            //Update client's preferred size because
            //the area taken up by the graphics has
            //gotten larger or smaller (if cleared).
            setPreferredSize(area);
            scrollRectToVisible(new Rectangle(x, y, W, H));
            //Let the scroll pane know to update itself
            //and its scrollbars.
            revalidate();
        repaint();
    public void mouseReleased(MouseEvent e) { }
    public void mouseClicked(MouseEvent e)  { }
    public void mouseEntered(MouseEvent e)  { }
    public void mouseExited(MouseEvent e)   { }
* We are adding components to DrawingPanel so there is no need to get
* into the paint methods of DrawingPane. Components are designed to draw
* themseleves when their parent container passes them a Graphics context
* and asks them to paint themselves into the parent.
class VisualNode {
    DrawingPane drawPane;
    int x;
    int y;
    int id;
    Box box;
    public VisualNode(DrawingPane dp, int id, int x, int y) {
        drawPane = dp;
        this.id = id;
        this.x = x;
        this.y = y;
        box = Box.createVerticalBox();
        Box titlePanel = Box.createHorizontalBox();
        JTextArea title = new JTextArea(1, 10);     // 1 rows x 10 cols
        Box nodePanel = Box.createVerticalBox();
        title.setLineWrap(true);
        title.setAlignmentY(Component.TOP_ALIGNMENT);
        titlePanel.add(new JButton("Hi!"));
        titlePanel.add(title);
        nodePanel.add(titlePanel);
        nodePanel.setBorder(BorderFactory.createEtchedBorder(EtchedBorder.RAISED));
        box.add(nodePanel);
        // here we are adding a component to drawPane so there is really
        // no need to keep this VisualNode in a collection
        drawPane.add(box);
        int ix = (int) x + drawPane.getInsets().left;
        int iy = (int) y + drawPane.getInsets().top;
        title.setText(id + " (" + ix + "," + iy + ") ");
        // since we are using the preferredSize property to setBounds here
        // we'll need access to it (via box) for the scrollPane in DrawPane
        // so we expose box as a member variable
        box.setBounds(ix, iy, box.getPreferredSize().width,
                              box.getPreferredSize().height);
}