Question

I want to draw the lines between 2 JScrollPanes (first scroll pane on the left side, second on the right). These JScrollPanes contain images. I want to draw lines between these 2 images (use some layers, use some trick etc.). I tried do it different ways, but i failed. Is it possible? (if not, i will have to make 2 images in one JScrollPane and it won’t be nice).

EDIT

I want to draw between 2 images – throught components – get some points from images and draw lines between them. I apologize for poorly formulated question.

Answer 1

In order to accomplish this, I believe you’ll need to make use of the Glass Pane. The Glass Pane sits on top of everything in the JRootPane and fills the entire view. This particular position allows two distinct capabilities:

• Intercepting mouse and keyboard events
• Drawing over the entire user interface

I believe your question is addressed by the second capability. The following is an example implementation, which you can later tailor to meet your own needs. Note that I’ve left out a lot of detail with regard to Glass Pane that you’ll need to research on your own.

CODE

import java.awt.Color;
import java.awt.Graphics;
import java.awt.Graphics2D;
import java.awt.Point;
import java.awt.RenderingHints;
import java.awt.event.ComponentAdapter;
import java.awt.event.ComponentEvent;
import java.awt.event.KeyAdapter;
import java.awt.event.MouseAdapter;
import java.awt.event.MouseEvent;
import java.awt.event.MouseMotionAdapter;
import java.awt.image.BufferedImage;
import java.io.File;
import java.io.IOException;

import javax.imageio.ImageIO;
import javax.swing.ImageIcon;
import javax.swing.JComponent;
import javax.swing.JFrame;
import javax.swing.JLabel;
import javax.swing.JPanel;
import javax.swing.SwingUtilities;

public class GlassPaneDemo {
        private static BufferedImage bi;

        public static void main(String[] args){
            try {
                loadImages();

                SwingUtilities.invokeLater(new Runnable(){
                    @Override
                    public void run() {
                        createAndShowGUI();             
                    }
                });
            } catch (IOException e) {
                // handle exception
            }
        }

        private static void loadImages() throws IOException{
            bi = ImageIO.read(new File("src/resources/person.png"));
        }

        private static void createAndShowGUI(){
            final JFrame frame = new JFrame();
            frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
            frame.setResizable(false);
            frame.setGlassPane(new CustomGlassPane());
            frame.getContentPane().add(getButtonPanel());
            frame.pack();
            frame.setLocationRelativeTo(null);
            frame.getGlassPane().setVisible(true);
            frame.setVisible(true);
        }

        private static final JPanel getButtonPanel(){
            @SuppressWarnings("serial")
            final JPanel panel = new JPanel(){
                @Override
                protected void paintComponent(Graphics g){
                    Graphics gCopy = g.create();

                    gCopy.setColor(Color.BLUE.darker());
                    gCopy.fillRect(0, 0, getWidth(), getHeight());

                    gCopy.dispose();
                }
            };

            final JLabel labelOne = new JLabel();
            labelOne.setIcon(new ImageIcon(bi));
            final JLabel labelTwo = new JLabel();
            labelTwo.setIcon(new ImageIcon(bi));
            panel.add(labelOne);
            panel.add(labelTwo);

            return panel;
        }

        @SuppressWarnings("serial")
        private static class CustomGlassPane extends JComponent{
            private Point p1;
            private Point p2;
            private boolean lineDrawn;

            public CustomGlassPane(){
                addMouseListener(new MouseAdapter(){
                    @Override
                    public void mouseClicked(MouseEvent e){
                        if(p1 == null || lineDrawn){
                            if(lineDrawn){
                                p1 = null;
                                p2 = null;
                                lineDrawn = false;
                            }
                            p1 = e.getPoint();
                        }else{
                            p2 = e.getPoint();
                            repaint(); // not optimal
                            lineDrawn = true;
                        }
                    }
                });

                // Block all other input events
                addMouseMotionListener(new MouseMotionAdapter(){});
                addKeyListener(new KeyAdapter(){});
                addComponentListener(new ComponentAdapter(){
                    @Override
                    public void componentShown(ComponentEvent e){
                        requestFocusInWindow();
                    }
                });
                setFocusTraversalKeysEnabled(false);
            }

            @Override
            protected void paintComponent(Graphics g){
                if(p1 != null && p2 != null){
                    Graphics2D g2 = (Graphics2D) g.create();

                    g2.setRenderingHint(
                            RenderingHints.KEY_ANTIALIASING, 
                            RenderingHints.VALUE_ANTIALIAS_ON);
                    g2.setColor(Color.RED);
                    g2.drawLine((int)p1.getX(), (int)p1.getY(), (int)p2.getX(), (int)p2.getY());

                    g2.dispose();
                }
            }
        }
  }

OUTPUT

EXPLANATION

In this example, I clicked two arbitrary points within each JLabel, and then drew a connecting line.