Scale jpanel background image

[Esseghier Abderrahmane]

Hello

Am new be in java and i wan to standarelize image as banner ,the image am using is big to get optimal quality,and i wan to create JPanel extended class to use it in the diffrent JFrames with this image in background.

so i must scale it i'v tried many examples but i down't know how exately i should use BufferedImage,and AffineTransform,and paintComponent.

can give an example please.

public class Banniere extends JPanel{
  protected static final double SCALE_FACTOR = 1.0;   
  private static final int TIMER_DELAY = 200;   
  private JScrollPane scrollpane;   
  private ImagePanel imagePanel;   
 
  public Banniere() {   
     BufferedImage img = null;   
     try {   
        img = ImageIO.read(new File("images/banniere.JPG"));   
     } catch (MalformedURLException e) {   
        e.printStackTrace();   
        System.exit(-1);   
     } catch (IOException e) {   
        e.printStackTrace();   
        System.exit(-1);   
     }   
 
     imagePanel = new ImagePanel(img);   
     scrollpane = new JScrollPane(imagePanel);   
 
     setLayout(new BorderLayout());   
     add(scrollpane, BorderLayout.CENTER);   
 
     new Timer(TIMER_DELAY, new ActionListener() {   
        double scale = 1.0;   
 
        public void actionPerformed(ActionEvent e) {   
           scale *= SCALE_FACTOR;   
           imagePanel.reScale(scale);   
           imagePanel.repaint();   
           //!! scrollpane.getViewport().revalidate();  // **** un-comment this line ****   
        }   
     }).start();   
  }   
 
}   
 
@SuppressWarnings("serial")   
class ImagePanel extends JPanel {   
  private BufferedImage image;   
  private AffineTransform at = new AffineTransform(); // identity transform   
  private int initWidth, initHeight;   
 
  public ImagePanel(BufferedImage image) {   
     this.image = image;   
     initWidth = image.getWidth();   
     initHeight = image.getHeight();   
     setPreferredSize(new Dimension(initWidth, initHeight));   
  }   
 
  public void reScale(double scale) {   
     at = AffineTransform.getScaleInstance(scale, scale);   
     int width = (int) (scale * initWidth);   
     int height = (int) (scale * initHeight);   
     setPreferredSize(new Dimension(width, height));   
     repaint();   
  }   
 
  @Override  
  protected void paintComponent(Graphics g) {   
     super.paintComponent(g);   
     Graphics2D g2 = (Graphics2D) g;   
     g2.transform(at);   
     if (image != null) {   
        g.drawImage(image, 0, 0, null);   
     }   
  }   

}

this one dosn't work

[Rob Camick]

If you want the image to fill the entire background then you can check out Background Panel for example code. This uses dynamic painting and does not keep the width/height aspect ratio.

[Darryl Burke]

... and if you're using the JPanel only to display an image (that is, you're not adding any other components to it) you can user a JLabel instead, with a StretchIcon or ShrinkIcon. You can find those classes on the site linked by Rob.