Create an image from a non-visible AWT Component?

I'm trying to create an image (screen-shot) of a non-visible AWT component. I can't use the Robot classes' screen capture functionality because the component is not visible on the screen. Trying to use the following code:

BufferedImage image = new BufferedImage(width, height, BufferedImage.TYPE_INT_RGB);
Graphics2D g = image.createGraphics();
component.paintAll(g);

Works sometimes, but does not work if the component contains things such as a text box or button, or some sort of OpenGL / 3D component (these things are left out of the image!). How can I take a proper s开发者_JAVA百科creenshot of the whole thing?

(disclamer: woops.. this doesn't seem to work for AWT )-:

I can't believe no one has suggested SwingUtilities.paintComponent or CellRendererPane.paintComponent which are made for this very purpose. From the documentation of the former:

Paints a component to the specified Graphics. This method is primarily useful to render Components that don't exist as part of the visible containment hierarchy, but are used for rendering.

Here is an example method that paints a non-visible component onto an image:

import java.awt.*;
import java.awt.image.BufferedImage;

import javax.swing.*;

public class ComponentPainter {

    public static BufferedImage paintComponent(Component c) {

        // Set it to it's preferred size. (optional)
        c.setSize(c.getPreferredSize());
        layoutComponent(c);

        BufferedImage img = new BufferedImage(c.getWidth(), c.getHeight(),
                BufferedImage.TYPE_INT_RGB);

        CellRendererPane crp = new CellRendererPane();
        crp.add(c);
        crp.paintComponent(img.createGraphics(), c, crp, c.getBounds());    
        return img;
    }

    // from the example of user489041
    public static void layoutComponent(Component c) {
        synchronized (c.getTreeLock()) {
            c.doLayout();
            if (c instanceof Container)
                for (Component child : ((Container) c).getComponents())
                    layoutComponent(child);
        }
    }
}

Here is a snippet of code that tests the above class:

JPanel p = new JPanel();
p.add(new JButton("Button 1"));
p.add(new JButton("Button 2"));
p.add(new JCheckBox("A checkbox"));

JPanel inner = new JPanel();
inner.setBorder(BorderFactory.createTitledBorder("A border"));
inner.add(new JLabel("Some label"));
p.add(inner);

BufferedImage img = ComponentPainter.paintComponent(p);

ImageIO.write(img, "png", new File("test.png"));

And here is the resulting image:

Component has a method paintAll(Graphics) (as you already have found). That method will paint itself on the passed graphics. But we have to pre-configure the graphics before we call the paint method. That's what I found about the AWT Component rendering at java.sun.com:

When AWT invokes this method, the Graphics object parameter is pre-configured with the appropriate state for drawing on this particular component:

• The Graphics object's color is set to the component's foreground property.
• The Graphics object's font is set to the component's font property.
• The Graphics object's translation is set such that the coordinate (0,0) represents the upper left corner of the component.
• The Graphics object's clip rectangle is set to the area of the component that is in need of repainting.

So, this is our resulting method:

public static BufferedImage componentToImage(Component component, Rectangle region)
{
    BufferedImage img = new BufferedImage(component.getWidth(), component.getHeight(), BufferedImage.TYPE_INT_ARGB_PRE);
    Graphics g = img.getGraphics();
    g.setColor(component.getForeground());
    g.setFont(component.getFont());
    component.paintAll(g);
    g.dispose();
    if (region == null)
    {
        return img;
    }
    return img.getSubimage(region.x, region.y, region.width, region.height);
}

This is also the better way instead of using Robot for the visible components.

EDIT:

A long time ago I used the code I posted here above, and it worked, but now not. So I searched further. I have a tested, working way. It is dirty, but works. The Idea of it is making a JDialog, put it somewhere out of the Screen bounds, set it visible, and then draw it on the graphics.

Here is the code:

public static BufferedImage componentToImageWithSwing(Component component, Rectangle region) {
    BufferedImage img = new BufferedImage(component.getWidth(), component.getHeight(), BufferedImage.TYPE_INT_RGB);
    Graphics g = img.createGraphics();

    // Real render
    if (component.getPreferredSize().height == 0 && component.getPreferredSize().width == 0)
    {
        component.setPreferredSize(component.getSize());
    }

    JDialog f = new JDialog();
    JPanel p = new JPanel();
    p.add(component);
    f.add(p);
    f.pack();
    f.setLocation(-f.getWidth() - 10, -f.getHeight() -10);
    f.setVisible(true);
    p.paintAll(g);
    f.dispose();
    // ---

    g.dispose();
    if (region == null) {
        return img;
    }
    return img.getSubimage(region.x, region.y, region.width, region.height);
}

So, this will work also on Windows and Mac. The other answer was to draw it on a virtual screen. But this doesn't need it.

Excellent question, I've thought about this myself from time to time!

As you already have written, that rending heavy weight components such as 3D and AWT onto an image is a big problem. These components are (almost) directly transferred to the graphic card so they cannot be re-rendered to an image using the normal paintComponent stuff, you need help from the operative system or doing your own rendering of these components.

1. Making your own to image renderer

For each component that does not have a to image rendering method you need to create your own. For example using jogl you can take a off-screen screenshot using this method (SO post).

2. Rendering onto a virtual screen

Prerequisites:

1. Can you start the program/component in a headless environment?
2. Are you using Linux?

Then you can use Xvfb to render the whole program onto a virtual screen and then taking a screenshot from that virtual screen like this:

Xvfb :1 &
DISPLAY=:1 java YourMainClass
xwd -display :1 -root -out image.xwd

Maybe you need to tweek Xvfb a little bit by passing the size of the program you want to render to it (-screen 0 1024x768x24).

The Screen Image class shows how this can be done for Swing components. I've never tried it with AWT components, buy I could guess the concept would be the same.

How about something like this. The JFrame that holds all of the components is not visible.

import java.awt.Color;
import java.awt.Component;
import java.awt.Container;
import java.awt.Dimension;
import java.awt.Graphics2D;
import java.awt.Rectangle;
import java.awt.image.BufferedImage;
import java.io.File;
import java.io.IOException;
import java.util.Arrays;
import java.util.List;
import java.util.logging.Level;
import java.util.logging.Logger;
import javax.imageio.ImageIO;
import javax.swing.JButton;
import javax.swing.JComponent;
import javax.swing.JFrame;
import javax.swing.JPanel;
import javax.swing.JTextArea;


/**
 * Captures an invisible awt component
 * @author dvargo
 */
public class ScreenCapture
{

private static List<String> types = Arrays.asList( ImageIO.getWriterFileSuffixes() );

/**
 * Build GUI
 * @param args
 */
public static void main(String [] args)
{
    JFrame invisibleFrame = new JFrame();
    invisibleFrame.setSize(300, 300);
    JPanel colorPanel = new JPanel();
    colorPanel.setBackground(Color.red);
    colorPanel.setSize(invisibleFrame.getSize());
    JTextArea textBox = new JTextArea("Here is some text");
    colorPanel.add(textBox);
    invisibleFrame.add(colorPanel);
    JButton theButton = new JButton("Click Me");
    colorPanel.add(theButton);

    theButton.setVisible(true);
    textBox.setVisible(true);
    colorPanel.setVisible(true);

    //take screen shot
    try 
    {
        BufferedImage screenShot = createImage((JComponent) colorPanel, new Rectangle(invisibleFrame.getBounds()));
        writeImage(screenShot, "filePath");
    } 
    catch (IOException ex)
    {
        Logger.getLogger(ScreenCapture.class.getName()).log(Level.SEVERE, null, ex);
    }

}


/**
 *  Create a BufferedImage for Swing components.
 *  All or part of the component can be captured to an image.
 *
 *  @param  component component to create image from
 *  @param  region The region of the component to be captured to an image
 *  @return image the image for the given region
 */
public static BufferedImage createImage(Component component, Rectangle region) {
    //  Make sure the component has a size and has been layed out.
    //  (necessary check for components not added to a realized frame)

    if (!component.isDisplayable()) {
        Dimension d = component.getSize();

        if (d.width == 0 || d.height == 0) {
            d = component.getPreferredSize();
            component.setSize(d);
        }

        layoutComponent(component);
    }

    BufferedImage image = new BufferedImage(region.width, region.height, BufferedImage.TYPE_INT_RGB);
    Graphics2D g2d = image.createGraphics();

    //  Paint a background for non-opaque components,
    //  otherwise the background will be black

    if (!component.isOpaque()) {
        g2d.setColor(component.getBackground());
        g2d.fillRect(region.x, region.y, region.width, region.height);
    }

    g2d.translate(-region.x, -region.y);
    component.paint(g2d);
    g2d.dispose();
    return image;
}

public static void layoutComponent(Component component) {
    synchronized (component.getTreeLock()) {
        component.doLayout();

        if (component instanceof Container) {
            for (Component child : ((Container) component).getComponents()) {
                layoutComponent(child);
            }
        }
    }
}

/**
 *  Write a BufferedImage to a File.
 *
 *  @param   image image to be written
 *  @param   fileName name of file to be created
 *  @exception IOException if an error occurs during writing
*/
public static void writeImage(BufferedImage image, String fileName)
    throws IOException
{
    if (fileName == null) return;

    int offset = fileName.lastIndexOf( "." );

    if (offset == -1)
    {
        String message = "file suffix was not specified";
        throw new IOException( message );
    }

    String type = fileName.substring(offset + 1);

    if (types.contains(type))
    {
        ImageIO.write(image, type, new File( fileName ));
    }
    else
    {
        String message = "unknown writer file suffix (" + type + ")";
        throw new IOException( message );
    }
}