Java2D question.: How can you superimpose an image on another?

[Darrin Smith]

I have an application where I scale a thumbnail image to fit inside a preset area that displays it. The image gets stretched to fill up that area, so I would like to place it on a black image to act as a background that has the correct size. That way, the component won't stretch the image since the newly build one will fit exactly.

So, how do you superimpose one image (my thumbnail) over top of another one (the black image)?

THANKS!

[Ko Wey]

Have you tried something like this:


BufferedImage bufferedImage =
new BufferedImage(component.getWidth(),
component.getHeight(),
BufferedImage.TYPE_INT_RGB);
Graphics2D g2D = (Graphics2D)bufferedImage.getGraphics();
g2D.drawImage(thumbnail,0,0,null);


and then in the component's paintComponent()method

public void paintComponent(Graphics g){
if (bufferedImage!=null)
g.drawImage(bufferedImage,0,0,this);
}

the thumbnail will not be enlarged, I think.

[Craig Wood]

You can override the 'getPreferredSize' method in the component that draws the scaled–to–fill image. Add this component to a container with GridBagLayout and set its background to black. The container will expand to fill its parent and show the image component centered within the black field. If you put the container inside a JScrollPane the scrollpane will set its scrollbars with the information it gets (Swing takes care of this) when it calls 'getPreferredSize.'

[Jeff Albertson]

One way, as mentioned, is to use a BufferedImage. Another is to
have a component that paints one image on top of the other:

 import java.awt.*;
import java.awt.geom.*;
import java.awt.image.*;
import java.io.*;
import java.net.*;
import javax.imageio.*;
import javax.swing.*;
import javax.swing.event.*;
 
public class CompositeTest extends JComponent {
    private BufferedImage backImage, frontImage;
    private float alpha = 1;
 
    public CompositeTest() throws IOException {
        backImage = ImageIO.read(new URL("http://today.java.net/jag/bio/JagHeadshot-small.jpg"));
        frontImage = ImageIO.read(new URL("http://today.java.net/jag/Image54-small.jpeg"));
    }
 
    public Dimension getPreferredSize() {
        return new Dimension(backImage.getWidth(), backImage.getHeight());
    }
 
    public void setAlpha(float alpha) {
        this.alpha = alpha;
        repaint();
    }
 
    protected void paintComponent(Graphics g) {
        super.paintComponent(g);
        Graphics2D g2 = (Graphics2D) g;
        int x = (getWidth() - backImage.getWidth())/2;
        int y = (getHeight()- backImage.getHeight())/2;
        g2.drawRenderedImage(backImage, AffineTransform.getTranslateInstance(x, y));
        Composite old = g2.getComposite();
        g2.setComposite(AlphaComposite.getInstance(AlphaComposite.SRC_OVER, alpha));
        x = (getWidth() - frontImage.getWidth())/2;
        y = (getHeight()- frontImage.getHeight())/2;
        g2.drawRenderedImage(frontImage, AffineTransform.getTranslateInstance(x, y));
        g2.setComposite(old);
    }
 
    public static void main(String[] args) throws IOException {
        final CompositeTest app = new CompositeTest();
        JSlider slider = new JSlider();
        slider.addChangeListener(new ChangeListener(){
            public void stateChanged(ChangeEvent e) {
                JSlider source = (JSlider) e.getSource();
                app.setAlpha(source.getValue()/100f);
            }
        });
        slider.setValue(100);
        JFrame f = new JFrame("CompositeTest");
        f.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
        Container cp = f.getContentPane();
        cp.add(app);
        cp.add(slider, BorderLayout.SOUTH);
        f.pack();
        f.setLocationRelativeTo(null);
        f.setVisible(true);
    }
}