java - Some part of the image disappears when I scroll up and down on a jscrollpane

Question

Hi guys I have a problem with Images drawn in a JPanel.There is no problem when the images are drawn to the panel. The Problemm occurn when I scroll up or down the image. The part of the image that was not seen in the viewport is painted white when return to that part again.

I added a BufferedImage in a JPanel. I can also resize the image using AffineTransform. The problem is when I added a JScollPane to my image, whenever I scroll up or down the scrollpane some part of the image disappears ..

I also tried using drawRenderedImage it did solve the problem about the scroll but it messed up other functions.

this is the best concise code I can make;

package convert;

import java.awt.*;
import java.awt.event.*;
import java.awt.geom.*;
import java.awt.image.BufferedImage;
import java.io.*;
import java.net.*;
import java.util.ArrayList;
import javax.imageio.ImageIO;
import javax.swing.*;
import javax.swing.event.*;

public class ZoomTest {

    public static void main(String[] args) {
        ImagePanel panel = new ImagePanel();

        JFrame f = new JFrame();
        f.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);

        f.getContentPane().add(new JScrollPane(panel));
        f.setSize(1200, 1200);
        f.setLocationRelativeTo(null);
        f.setVisible(true);
    }
}

class ImagePanel extends JPanel {

    BufferedImage image;
    double scale;

    public ImagePanel() {
        loadImage();
        scale = .38;
        addMouseWheelListener(new MouseWheelListener() {

            @Override
            public void mouseWheelMoved(MouseWheelEvent e) {
                int rotation = e.getWheelRotation();
                if (rotation < 0) {
                    scale -= .05;
                } else {
                    scale += .05;
                }
                if (scale < 0) {
                    scale = 0;
                }

                revalidate();
                repaint();

            }
        });

    }

    @Override
    protected void paintComponent(Graphics g) {
        super.paintComponent(g);
        Graphics2D g2 = (Graphics2D) g;

        double x = (getWidth() - scale * image.getWidth()) / 2;
        double y = (getHeight() - scale * image.getHeight()) / 2;

        AffineTransform at = new AffineTransform();
        at.translate(x, y);

        at.scale(scale, scale);
        g2.setTransform(at);

        g2.drawImage(image, 0, 0, null);

    }

    public Dimension getPreferredSize() {
        int w = (int) (scale * image.getWidth());
        int h = (int) (scale * image.getHeight());
        return new Dimension(w, h);
    }

    private void loadImage() {
        String fileName = "c:\users\john ebarita\downloads\lorem-ipsum-1.jpg";
        try {
            image = ImageIO.read(new File(fileName));
        } catch (Exception e) {
            e.printStackTrace();
        }
    }
}

Answer 1

Take a look at Graphics2D#drawImage(Image, AffineTransform, ImageObserver). May be it helps.

package convert;

import java.awt.*;
import java.awt.event.*;
import java.awt.geom.*;
import java.awt.image.BufferedImage;
import java.io.*;
import java.net.*;
import java.util.ArrayList;
import javax.imageio.ImageIO;
import javax.swing.*;
import javax.swing.event.*;

public class ZoomTest2 {
  public static void main(String[] args) {
    ImagePanel panel = new ImagePanel();
    JFrame f = new JFrame();
    f.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
    f.getContentPane().add(new JScrollPane(panel));
    f.setSize(1200, 1200);
    f.setLocationRelativeTo(null);
    f.setVisible(true);
  }
}

class ImagePanel extends JPanel {
  BufferedImage image;
  double scale;

  public ImagePanel() {
    loadImage();
    scale = .38;
    addMouseWheelListener(new MouseWheelListener() {
      @Override
      public void mouseWheelMoved(MouseWheelEvent e) {
        int rotation = e.getWheelRotation();
        if (rotation < 0) {
          scale -= .05;
        } else {
          scale += .05;
        }
        if (scale < 0) {
          scale = 0;
        }
        revalidate();
        repaint();
      }
    });
  }

  @Override
  protected void paintComponent(Graphics g) {
    super.paintComponent(g);
    Graphics2D g2 = (Graphics2D) g.create();

    double x = (getWidth() - scale * image.getWidth()) / 2;
    double y = (getHeight() - scale * image.getHeight()) / 2;
    AffineTransform at = new AffineTransform();
    at.translate(x, y);
    at.scale(scale, scale);

    // g2.setTransform(at);
    // g2.drawImage(image, 0, 0, this);
    g2.drawImage(image, at, this);

    // or:
    // AffineTransform atf = g2.getTransform();
    // atf.concatenate(at);
    // g2.setTransform(atf);
    // g2.drawImage(image, 0, 0, this);

    g2.dispose();
  }

  public Dimension getPreferredSize() {
    int w = (int)(scale * image.getWidth());
    int h = (int)(scale * image.getHeight());
    return new Dimension(w, h);
  }

  private void loadImage() {
    String fileName = "aaa.png";
    try {
      image = ImageIO.read(new File(fileName));
    } catch (Exception e) {
      e.printStackTrace();
    }
  }
}