Paint Drag Preview

Question

Hi there,
Here's a challenging little problem I need to solve. Below is a test project whose sole purpose is to demonstrate, what I call, a "paintDragPreview". What I mean by this is show the drawn outline of a component as it is being dragged to another position on a JPanel. For purposes of simplicity and education, I'm not actually going to relocate the component in this test project. The component can stay where it is. I'm just going to use the normal FlowLayoutManager to place the component on a JPanel. In a larger project I am actually using an XYLayoutManager which allows me to place a component anywhere on the JPanel after I finish dragging it to another location.
For this test project, in order to draw an outline of a component, I needed layers of JPanels. One that has its layout manager set to OverlayLayout(...), another named WhiteBoard (where I place the component), and another on top of the WhiteBoard named glassPane. It is on the glassPane that I draw an outline of the component as it is being dragged across the WhiteBoard. So far, so good.
Here's the problem I face at this juncture and you can copy/paste, compile and run the code below to confirm the behaviour of this test project so far. As you place your mouse cursor over the LabelComponent the cursor changes to the crosshairs cursor indicating that the component can be moved. As you press the left mouse button the current coordinates of the LabelComponent is registered. As you begin to drag the component the glassPane draws a rectangle representing the component and repaints for every pixel that you drag the mouse. What is supposed to happen next is on the mouseReleased(..) the component becomes relocated in the new position. However, as I said before, I'm not taking this test project that far.
I just want to show that as the rectangle is drawn on the glassPane we loose sight of the LabelComponent. It disappears! We can't see anything below the glassPane! This is because we set the glassPane.setVisible(...) method to true while dragging and back to false upon mouseReleased(...). This is necessary in order to see what's being drawn on the glassPane. However, this is not the behaviour I want.
DESIRED BEHAVIOUR: I want to both see the component below the glassPane and also see the rectangle as it is being repainted as we drag the mouse across the WhiteBoard. I've played with the setOpaque(...) method for the glassPane but that doesn't seem to help much.
As a reference, I consulted the example for Glass Pane at the following URL: http://java.sun.com/docs/books/tutorial/uiswing/components/rootpane.html
When you run that example project you can still see the components below the Glass Pane the whole time while the red dot is being painted on the Glass Pane. I fail to see a difference between that example project and mine. Perhaps someone can help on this one?
Thanks,
Alan
//place in a seperate file
import javax.swing.*;
import java.awt.*;
import java.awt.event.*;
import java.awt.geom.*;
import javax.swing.event.*;
import javax.swing.border.*;
public class LabelComponent extends JLabel
  private JPanel parent;
  private boolean selected = true; 
  public LabelComponent()
    super();
  public LabelComponent(String text, JPanel parent)
    super(text);
    this.parent = parent;
    // Enable the events that you want to process.
    enableEvents(AWTEvent.MOUSE_MOTION_EVENT_MASK);
    enableEvents(AWTEvent.MOUSE_EVENT_MASK);
    //create a border for this object
    setBorder(new LineBorder(Color.blue, 2));
  public LabelComponent(JPanel parent)
    this.parent = parent;
    // Enable the events that you want to process.
    enableEvents(AWTEvent.MOUSE_MOTION_EVENT_MASK);
    enableEvents(AWTEvent.MOUSE_EVENT_MASK);
    //create a border for this object
    setBorder(new LineBorder(Color.blue, 2));
  public JPanel getParent()
    return parent;
  private void changeBorderColor(Color color)
    setBorder(new LineBorder(color, 2));
  public void processMouseEvent(MouseEvent evt)
    //In order so that coordinates appear properly on JCanvas ruler
    //as if TextComponent was any other Shape object, we're going
    //to adjust the values for X & Y of the MouseEvent before
    //passing it on.
    Rectangle rect = getBounds();
    Double xOffset = new Double(rect.getX());
    Double yOffset = new Double(rect.getY());
    evt.translatePoint(xOffset.intValue(), yOffset.intValue());
    if(selected)
      parent.dispatchEvent(evt);      
    else
      super.processMouseEvent(evt);
  public void processMouseMotionEvent(MouseEvent evt)
    //In order so that coordinates appear properly on JCanvas ruler
    //as if TextComponent was any other Shape object, we're going
    //to adjust the values for X & Y of the MouseEvent before
    //passing it on.
    Rectangle rect = getBounds();
    Double xOffset = new Double(rect.getX());
    Double yOffset = new Double(rect.getY());
    evt.translatePoint(xOffset.intValue(), yOffset.intValue());
    if(selected)
      parent.dispatchEvent(evt);      
    else
      super.processMouseEvent(evt);
  public Cursor getCursor() {
        if(selected)
           return new Cursor(Cursor.MOVE_CURSOR);
         else
            return new Cursor(Cursor.TEXT_CURSOR);
  public void setSelected(boolean value)
    System.out.println("TextComponent.setSelected() == " + value);
    if(value)
      changeBorderColor(Color.blue);
    else
      changeBorderColor(Color.black);
    selected = value;   
  public boolean isSelected()
    return selected;
* place in a seperate file
import java.awt.*;
import java.awt.event.*;
import javax.swing.*;
import javax.swing.event.*;
import javax.swing.border.*;
public class OverlayTest extends JFrame
  JPanel whiteboard = new JPanel();
  MyGlassPane glass = new MyGlassPane(whiteboard);
  public static void main(String[] args)
    OverlayTest ot = new OverlayTest();
    ot.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
    ot.init();
  public void init()
    setSize(300, 300);
    Container contentPane = getContentPane();
    contentPane.setLayout(new OverlayLayout(contentPane));
    whiteboard.setLayout(new FlowLayout());
    glass.setLayout(null);   
    LabelComponent label = new LabelComponent("MyComponent", whiteboard);
    whiteboard.add(label);
    whiteboard.addMouseListener(new MouseAdapter()
            public void mousePressed(MouseEvent e)
              glass.mousePressed(e);
            public void mouseReleased(MouseEvent e)
              glass.mouseReleased(e);
    whiteboard.addMouseMotionListener(new MouseMotionAdapter()
            public void mouseDragged(MouseEvent e)
              //System.out.println("whiteboard.mouseDragged");
              glass.mouseDragged(e);
            public void mouseMoved(MouseEvent e)
              //System.out.println("whiteboard.mouseMoved");
              glass.mouseMoved(e);
    contentPane.add(whiteboard);
    contentPane.add(glass);
    setVisible(true);
  class MyGlassPane extends JPanel implements MouseListener, MouseMotionListener
    boolean shouldDrawRect = false;
    Rectangle rect = null;   
    int XOffset = 0;
    int YOffset = 0;
    CBListener listener = null;
    public MyGlassPane(Container whiteboard)
        listener = new CBListener(this, whiteboard);
        addMouseListener(listener);
        addMouseMotionListener(listener);
    public void setDrawRect(boolean value)
      shouldDrawRect = value;
    public boolean areBoundsSet()
      if(rect != null)
         return true;
      return false;
    public void translate(double x, double y)
        this.XOffset += x;
        this.YOffset += y;
        //System.out.println("XOffset: " + XOffset + " YOffset: " + YOffset);
    public void mouseDragged(MouseEvent e)
       if(listener != null)
         //System.out.println("MyGlassPane.mouseDragged");
         listener.mouseDragged(e);
    public void mouseMoved(MouseEvent e)
       if(listener != null)
         //System.out.println("MyGlassPane.mouseMoved");
         listener.mouseMoved(e);
    public void mouseClicked(MouseEvent e) {
     public void mouseEntered(MouseEvent e) {
     public void mouseExited(MouseEvent e) {
     public void mousePressed(MouseEvent e)
       Object o = e.getSource();
       if(o instanceof JLabel)
         JLabel label = (JLabel)o;
         rect = label.getBounds();
         System.out.println("rect.getX(): " + rect.getX() + " rect.getY(): " + rect.getY() + " rect.getWidth(): " + rect.getWidth() + " rect.getHeight(): " + rect.getHeight());
     public void mouseReleased(MouseEvent e)
        if(listener != null)
          System.out.println("MyGlassPane.mouseReleased");
          listener.mouseReleased(e);
          shouldDrawRect = false;
          repaint();
          setVisible(false);
    protected void paintComponent(Graphics g)
        super.paintComponent(g);
        if(shouldDrawRect && rect != null)
           //We're dealing with a component
           g.setColor(Color.BLACK);
           double xValue = 0.0;
           double yValue = 0.0;
           //Solve for xValue first
           if(XOffset > 0.0)
             xValue = rect.getX() + XOffset;
           else
             xValue = rect.getX() - (XOffset * -1);
           //Solve for yValue next
           if(YOffset > 0.0 )
             yValue = rect.getY() + YOffset;
           else
             yValue = rect.getY() - (YOffset * -1);
           int x = new Double(xValue).intValue();
           int y = new Double(yValue).intValue();
           int width = new Double(rect.getWidth()).intValue();
           int height = new Double(rect.getHeight()).intValue();
           //System.out.println("xValue: " + xValue + " yValue: " + yValue + " XOffset: " + XOffset + " YOffset: " + YOffset);
           g.drawRect(x, y, width, height);
     * Listen for all events that our check box is likely to be
     * interested in.  Redispatch them to the check box.
   class CBListener extends MouseInputAdapter
     MyGlassPane glassPane;
     Container WhiteBoard;
     private Point theLastDraggingPosition;
    public CBListener(MyGlassPane glassPane, Container whiteboard)
       this.glassPane = glassPane;
       this.WhiteBoard = whiteboard;
     public void mouseMoved(MouseEvent e) {
       //System.out.println("CBListener.mouseMoved");
       redispatchMouseEvent(e, false);
     public void mouseDragged(MouseEvent e) {
       //System.out.println("CBListener.mouseDragged");
       redispatchMouseEvent(e, true);
     public void mouseClicked(MouseEvent e) {
       redispatchMouseEvent(e, false);
     public void mouseEntered(MouseEvent e) {
     public void mouseExited(MouseEvent e) {
     public void mousePressed(MouseEvent e) {
       redispatchMouseEvent(e, false);
     public void mouseReleased(MouseEvent e) {
       redispatchMouseEvent(e, false);
     //A basic implementation of redispatching events.
     private void redispatchMouseEvent(MouseEvent e, boolean repaint)
        Point glassPanePoint = e.getPoint();
        if(glassPane.areBoundsSet())
          int deltaX = 0;
          int deltaY = 0;
          if(theLastDraggingPosition != null)
            deltaX = glassPanePoint.x - theLastDraggingPosition.x;
            deltaY = glassPanePoint.y - theLastDraggingPosition.y;
          glassPane.translate(deltaX,deltaY);
          theLastDraggingPosition = glassPanePoint;
        //Update the glass pane if requested.
        if (repaint)
          glassPane.setVisible(true);
          glassPane.setDrawRect(true);
          glassPane.repaint();           
}Edited by: ashiers on Oct 8, 2007 10:05 AM

Answer 1

OK. For those who may be interested, the subject of the Glass Pane has been of great interest on this forum. Therefore, I've re-written this sample project so that others can see what I've done to demonstrate how one performs a "Paint Drag Preview" for a WhiteBoard by using a JPanel as a Glass Pane to draw a rectangular representation of an object being dragged to a new location. Keep in mind this example doesn't actually relocate the component. You will have to implement that logic on your own. I would recommend using an XYLayout Manager for the WhiteBoard. Hope this is helpful for someone else as it has been instructional for me.
Alan
//place in a seperate file
import javax.swing.*;
import java.awt.*;
import java.awt.event.*;
import java.awt.geom.*;
import javax.swing.event.*;
import javax.swing.border.*;
public class LabelComponent extends JLabel
  private JPanel parent;
  private boolean selected = true; 
  public LabelComponent()
    super();
  public LabelComponent(String text, JPanel parent)
    super(text);
    this.parent = parent;
    // Enable the events that you want to process.
    enableEvents(AWTEvent.MOUSE_MOTION_EVENT_MASK);
    enableEvents(AWTEvent.MOUSE_EVENT_MASK);
    //create a border for this object
    setBorder(new LineBorder(Color.blue, 2));
  public LabelComponent(JPanel parent)
    this.parent = parent;
    // Enable the events that you want to process.
    enableEvents(AWTEvent.MOUSE_MOTION_EVENT_MASK);
    enableEvents(AWTEvent.MOUSE_EVENT_MASK);
    //create a border for this object
    setBorder(new LineBorder(Color.blue, 2));
  public JPanel getParent()
    return parent;
  private void changeBorderColor(Color color)
    setBorder(new LineBorder(color, 2));
  public void processMouseEvent(MouseEvent evt)
    //In order so that coordinates appear properly on JCanvas ruler
    //as if TextComponent was any other Shape object, we're going
    //to adjust the values for X & Y of the MouseEvent before
    //passing it on.
    Rectangle rect = getBounds();
    Double xOffset = new Double(rect.getX());
    Double yOffset = new Double(rect.getY());
    evt.translatePoint(xOffset.intValue(), yOffset.intValue());
    if(selected)
      parent.dispatchEvent(evt);      
    else
      super.processMouseEvent(evt);
  public void processMouseMotionEvent(MouseEvent evt)
    //In order so that coordinates appear properly on JCanvas ruler
    //as if TextComponent was any other Shape object, we're going
    //to adjust the values for X & Y of the MouseEvent before
    //passing it on.
    Rectangle rect = getBounds();
    Double xOffset = new Double(rect.getX());
    Double yOffset = new Double(rect.getY());
    evt.translatePoint(xOffset.intValue(), yOffset.intValue());
    if(selected)
      parent.dispatchEvent(evt);      
    else
      super.processMouseEvent(evt);
  public Cursor getCursor() {
        if(selected)
           return new Cursor(Cursor.MOVE_CURSOR);
         else
            return new Cursor(Cursor.TEXT_CURSOR);
  public void setSelected(boolean value)
    System.out.println("TextComponent.setSelected() == " + value);
    if(value)
      changeBorderColor(Color.blue);
    else
      changeBorderColor(Color.black);
    selected = value;   
  public boolean isSelected()
    return selected;
//place in a seperate file
import java.awt.*;
import java.awt.event.*;
import javax.swing.*;
import javax.swing.event.*;
import javax.swing.border.*;
public class OverlayTest extends JFrame
  JPanel whiteboard = new JPanel();
  MyGlassPane glass = new MyGlassPane(whiteboard);
  public static void main(String[] args)
    OverlayTest ot = new OverlayTest();
    ot.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
    ot.init();
  public void init()
    setSize(400, 400);
    Container contentPane = getContentPane();
    contentPane.setLayout(new BorderLayout());
    whiteboard.setLayout(new FlowLayout());
    whiteboard.setBackground(Color.yellow);
    JPanel buttonPanel1 = new JPanel();
    JPanel buttonPanel2 = new JPanel();
    buttonPanel1.add(new JButton("Foo"));
    buttonPanel1.add(new JButton("Bar"));
    buttonPanel2.add(new JButton("Foo"));
    buttonPanel2.add(new JButton("Bar"));
    glass.setLayout(null);   
    LabelComponent label = new LabelComponent("MyComponent", whiteboard);
    whiteboard.add(label);
    whiteboard.addMouseListener(new MouseAdapter()
            public void mousePressed(MouseEvent e)
              glass.mousePressed(e);
            public void mouseReleased(MouseEvent e)
              glass.mouseReleased(e);
    whiteboard.addMouseMotionListener(new MouseMotionAdapter()
            public void mouseDragged(MouseEvent e)
              //System.out.println("whiteboard.mouseDragged");
              glass.mouseDragged(e);
            public void mouseMoved(MouseEvent e)
              //System.out.println("whiteboard.mouseMoved");
              glass.mouseMoved(e);
    contentPane.add(whiteboard, BorderLayout.CENTER);
    contentPane.add(buttonPanel1, BorderLayout.WEST);
    contentPane.add(buttonPanel2, BorderLayout.NORTH);
    setGlassPane(glass);
    setVisible(true);
  class MyGlassPane extends JComponent implements MouseListener, MouseMotionListener
    boolean shouldDrawRect = false;
    Rectangle rect = null;   
    int XOffset = 0;
    int YOffset = 0;
    CBListener listener = null;
    Container whiteboard = null;
    public MyGlassPane(Container whiteboard)
        this.whiteboard = whiteboard;
        listener = new CBListener(this, whiteboard);
        addMouseListener(listener);
        addMouseMotionListener(listener);
        setOpaque(false);
    public void setDrawRect(boolean value)
      shouldDrawRect = value;
    public boolean areBoundsSet()
      if(rect != null)
         return true;
      return false;
    public void translate(double x, double y)
        this.XOffset += x;
        this.YOffset += y;
        //System.out.println("XOffset: " + XOffset + " YOffset: " + YOffset);
    public void mouseDragged(MouseEvent e)
       if(listener != null)
         //System.out.println("MyGlassPane.mouseDragged");
         listener.mouseDragged(e);
    public void mouseMoved(MouseEvent e)
       if(listener != null)
         //System.out.println("MyGlassPane.mouseMoved");
         listener.mouseMoved(e);
    public void mouseClicked(MouseEvent e) {
     public void mouseEntered(MouseEvent e) {
     public void mouseExited(MouseEvent e) {
     public void mousePressed(MouseEvent e)
       Object o = e.getSource();
       if(o instanceof JLabel)
         JLabel label = (JLabel)o;
         rect = label.getBounds();
         System.out.println("rect.getX(): " + rect.getX() + " rect.getY(): " + rect.getY() + " rect.getWidth(): " + rect.getWidth() + " rect.getHeight(): " + rect.getHeight());
     public void mouseReleased(MouseEvent e)
        if(listener != null)
          System.out.println("MyGlassPane.mouseReleased");
          listener.mouseReleased(e);
          shouldDrawRect = false;
          repaint();
          setVisible(false);
    protected void paintComponent(Graphics g)
        super.paintComponent(g);
        if(shouldDrawRect && rect != null)
           //Get the bounds of the whiteboard so that the rectangle
           //is drawn over the same space and not somewhere else in the JFrame.
           Rectangle rectangle = whiteboard.getBounds();
           double wbX = rectangle.getX();
           double wbY = rectangle.getY();
           //System.out.println("wbX: " + wbX + " wbY: " + wbY);
           //We're dealing with a component
           g.setColor(Color.BLACK);
           double xValue = 0.0;
           double yValue = 0.0;
           //Solve for xValue first
           if(XOffset > 0.0)
             xValue = rect.getX() + XOffset;
           else
             xValue = rect.getX() - (XOffset * -1);
           //Solve for yValue next
           if(YOffset > 0.0 )
             yValue = rect.getY() + YOffset;
           else
             yValue = rect.getY() - (YOffset * -1);
           //Now adjust the xValue and yValue to provide
           //proper coordinates over the whiteboard.
           xValue = wbX + xValue;
           yValue = wbY + yValue;
           int x = new Double(xValue).intValue();
           int y = new Double(yValue).intValue();
           int width = new Double(rect.getWidth()).intValue();
           int height = new Double(rect.getHeight()).intValue();
           System.out.println("xValue: " + xValue + " yValue: " + yValue + " XOffset: " + XOffset + " YOffset: " + YOffset);
           //Prevent the rectangle from being drawn outside the bounds
           //of the whiteboard.
           if(xValue > wbX && yValue > wbY)
              g.drawRect(x, y, width, height);
     * Listen for all events that our check box is likely to be
     * interested in.  Redispatch them to the check box.
   class CBListener extends MouseInputAdapter
     MyGlassPane glassPane;
     Container WhiteBoard;
     private Point theLastDraggingPosition;
    public CBListener(MyGlassPane glassPane, Container whiteboard)
       this.glassPane = glassPane;
       this.WhiteBoard = whiteboard;
     public void mouseMoved(MouseEvent e) {
       //System.out.println("CBListener.mouseMoved");
       redispatchMouseEvent(e, false);
     public void mouseDragged(MouseEvent e) {
       //System.out.println("CBListener.mouseDragged");
       redispatchMouseEvent(e, true);
     public void mouseClicked(MouseEvent e) {
       redispatchMouseEvent(e, false);
     public void mouseEntered(MouseEvent e) {
     public void mouseExited(MouseEvent e) {
     public void mousePressed(MouseEvent e) {
       redispatchMouseEvent(e, false);
     public void mouseReleased(MouseEvent e) {
       redispatchMouseEvent(e, false);
     //A basic implementation of redispatching events.
     private void redispatchMouseEvent(MouseEvent e, boolean repaint)
        Point glassPanePoint = e.getPoint();
        if(glassPane.areBoundsSet())
          int deltaX = 0;
          int deltaY = 0;
          if(theLastDraggingPosition != null)
            deltaX = glassPanePoint.x - theLastDraggingPosition.x;
            deltaY = glassPanePoint.y - theLastDraggingPosition.y;
          glassPane.translate(deltaX,deltaY);
          theLastDraggingPosition = glassPanePoint;
        //Update the glass pane if requested.
        if (repaint)
          glassPane.setVisible(true);
          glassPane.setDrawRect(true);
          glassPane.repaint();           
}Edited by: ashiers on Oct 10, 2007 7:06 AM