How to convert GUI component's graphics to int[]or byte[]?


Has anyone ran into the problem of trying to get a GUI component's graphics converted into an array of ints (or, even better, bytes)?

I've tried doing this by having the component paint() its graphics on a java.awt.image.BufferedImage and then using a java.awt.image.PixelGrabber' s getPixels() to extract the array.
For some reason, no matter what the component GUI looks like, I get an array full of -16777216's.

Here's an SSCCE demonstrating what I'm trying to do:

<SSCCE>

import java.awt.image.PixelGrabber;
import java.awt.Frame;
import java.awt.Button;
import java.awt.Panel;
import java.awt.event.ActionEvent;
import java.awt.event.ActionListener;
import java.awt.BorderLayout;
import java.awt.image.BufferedImage;
import java.awt.Graphics;
import java.awt.Color;
import java.awt.event.WindowEvent;
import java.awt.event.WindowListener;

/**
 * <p>Title: PixelGrabbing Demo</p>
 * <p>Description: Simple test construct to attempt grabbing graphics
* pixels from a GUI component</p>
 * @author Aki Laukkanen
 * @version 0.0
 */

public class PixelGrabbingDemo {
  /**
   * Initial width of application GUI
   * */
  private static final int INIT_WIDTH = 90;

  /**
   * Initial height of application GUI
   * */
  private static final int INIT_HEIGHT = 120;

  private Frame appFrame;
  private TestGraphicPanel testPanel;
  private Button testButton;
  private PixelGrabber testGrabber;
  private int[] grabbedPixels;

  public PixelGrabbingDemo() {}

  /**
   * Test harness
   * @param args not used
   * */

  public static void main(String[] args) {
    PixelGrabbingDemo theDemo = new PixelGrabbingDemo();
    theDemo.initGUI();
  }

  /**
   * Populate appFrame and set it visible.
   * */

  private void initGUI() {
    appFrame = new Frame("Pixel Grabbing Test");
    testButton = new Button("Press to test");
    testButton.addActionListener(new TestButtonListener());
    testPanel = new TestGraphicPanel();
    appFrame.setLayout(new BorderLayout());
    appFrame.addWindowListener(new TestFrameListener());
    appFrame.add(testPanel, BorderLayout.CENTER);
    appFrame.add(testButton, BorderLayout.SOUTH);
    appFrame.pack();
    appFrame.setSize(INIT_WIDTH, INIT_HEIGHT);
    testPanel.setVisible(true);
    testPanel.setIgnoreRepaint(false);
    testPanel.repaint();
    appFrame.validate();
    appFrame.setVisible(true);
  }

  private class TestButtonListener implements ActionListener {
    /**
     * Simplified response to button click, validity checks etc.
* omitted.
     *
     * @param e ActionEvent detected
     */
    public void actionPerformed(ActionEvent e) {

try {
boolean grabbingSucceeded;
BufferedImage imageOfPanel = new BufferedImage(testPanel.getWidth(),testPanel.getHeight(),BufferedImage.TYPE_INT_RGB);

Graphics imageGraphics = imageOfPanel.getGraphics();
testPanel.paint(imageGraphics);
testGrabber = new PixelGrabber(imageOfPanel,0,0,testPanel.getWidth(),testPanel.getHeight(),true);

        try {
          grabbingSucceeded = testGrabber.grabPixels();
        }
        catch (InterruptedException ex) {
          ex.printStackTrace();
          grabbingSucceeded = false;
        }

        if (grabbingSucceeded) {
          System.out.println("Pixels grabbed successfully.");
          grabbedPixels = (int[]) testGrabber.getPixels();

          //Print out int value of each pixel on each row.
          int pixel = 0;
          for (int i = 0; i < testGrabber.getHeight(); i++) {
            for (int j = 0; j < testGrabber.getWidth(); j++) {
           System.out.print(Integer.toString(grabbedPixels[pixel])+',');
            }
            System.out.print('\n');
          }
        }
        else {
          System.out.println("Grabbing failed.");
          System.exit(1);
        }
      }
      catch (Exception exc) {
        exc.printStackTrace();
      }
    }
  }

  class TestFrameListener implements WindowListener {
    /**
     * Used to detect when user closes the test window.
     * */
    //Obligatory WindowListener boilerplate
    public void windowDeactivated(WindowEvent e) {}
    public void windowDeiconified(WindowEvent e) {}
    public void windowIconified(WindowEvent e) {}
    public void windowOpened(WindowEvent e) {}
    public void windowActivated(WindowEvent e) {}
    public void windowClosed(WindowEvent e) {}
    //React to window closing
    public void windowClosing(WindowEvent e) {
      System.exit( -1);
    }
  }

  class TestGraphicPanel extends Panel {

    /**
     * Paints alternating black and white quadrants
     * @param g Graphics configuration to paint on
     * */

    public void paint(Graphics g) {
      g.setColor(Color.white);
      g.fillRect(0,0,getWidth(),getHeight());
      g.setColor(Color.black);
      g.fillRect(0,0,(getWidth()/2),(getHeight()/2));
      g.fillRect((getWidth()/2),(getHeight()/2),getWidth(),getHeight());
    }
  }

}

</SSCCE>

--
-Aki "Sus" Laukkanen
.