Styjun

What I want to do:

I want to write a small application that can display an image. The user has to be able to zoom in and out of the image, move it around, and mark points on the image. Further down the line I want to analyze the points clicked, but I'm not there yet.

What I have so far:

In order to track down my problem I wrote a MVCE:

GUI class for handling the JFrame (and other UI elements later):

import javax.swing.*;
import java.net.MalformedURLException;
import java.net.URL;

public class MCVE_GUI 

 public static void main(String[] args) throws MalformedURLException 
 MCVE_ZoomPane zp = new MCVE_ZoomPane(new URL("https://fiji.sc/site/logo.png"));

 JFrame f = new JFrame("PictureMeasurement");
 f.setDefaultCloseOperation(WindowConstants.DISPOSE_ON_CLOSE);
 f.setContentPane(zp);
 f.pack();
 f.setLocationRelativeTo(null);
 f.revalidate();
 f.repaint();
 f.setVisible(true);
 

ZoomPanel for handling the image and zooming:

import javax.swing.*;
import java.awt.*;
import java.awt.event.*;
import java.net.URL;

class MCVE_ZoomPane extends JPanel implements MouseMotionListener 

 MCVE_ZoomPane(URL url)
 JLabel image = new JLabel();
 JScrollPane jsp = new JScrollPane(image);

 //image.setIcon(new ImageIcon(url)); // picture, no input
 //jsp.setPreferredSize(new Dimension(300,300)); //picture, no input
 jsp.setPreferredSize(image.getPreferredSize()); //depends on position of image.setIcon
 image.setIcon(new ImageIcon(url)); //no picture, input

 this.add(jsp);
 this.setPreferredSize(image.getPreferredSize());
 this.addMouseMotionListener(this);
 

 @Override
 public void paintComponent(Graphics g)
 super.paintComponent(g);
 

 public void mouseDragged(MouseEvent e) 
 System.out.format("Dragged X:%d Y:%dn",e.getX(), e.getY());
 

 public void mouseMoved(MouseEvent e) 

The problem:

Depending on where I put the image.setIcon(new ImageIcon(url)) I get either the image displayed or can listen to mouse clicks, but not both together. If I set the JScrollPane to a fixed preferred size without calling image.getPreferredSize() I always get a picture but no input.

Apparently I'm stupid. The JScrollPane/JLabel covered the JPanel which was the only component which had a MouseMotionListener. The solution is to add the single line of image.addMouseMotionListener(this);.

I thought about and tried different soltuions to this for at least three hours now. It's a hobby project, so no time constaints, but man do I feel stupid now.