Polygon lasso drawing

[Yang Li]

I am trying to use Java to implement a feature that is very like to polygon lasso tool in any image processing software, like FireWords, PhotoShop.

Basically, when a user clicks the polygon lasso icon I provided, he is ready to start to draw a polygon lasso. When he clicks anywhere in a drawing area, a dot will show up there; clicks again, a new dot will apprear. There is a solid or arrow between two dots. The last dot must overlap the first dot and it represents the drawing is finished and a polygon will appear; all points are decided by my clicks.

There are several constraints:

1. A user can only click selected times, i.e.: he can only click 5 times. Clicks beyond 5 times will not be accepted (no dot appeared)

2. A user must click selected times, i.e.: he must click 5 times. If he just clicks twice and decides to terminate the drawing, all dots and connected lines will disappear

3. The last dot and the first dot must be overlapped. Please note: As long as two points are very close, say, 2 px, we still say they are overlapped.

4. If the last dot and the first dot does not overlapped, I may choose to accept or not accept the drawing. If I do not accept it, all dots and connected lines will disappear

Any suggestion and/or sample code?

Thank you for your time.

[Craig Wood]

import java.awt.*;
import java.awt.event.*;
import java.awt.geom.*;
import java.util.ArrayList;
import java.util.List;
import javax.swing.*;
 
public class Lasso extends JPanel {
    List<Point> points = new ArrayList<Point>();
 
    protected void paintComponent(Graphics g) {
        super.paintComponent(g);
        Graphics2D g2 = (Graphics2D)g;
        g2.setRenderingHint(RenderingHints.KEY_ANTIALIASING,
                            RenderingHints.VALUE_ANTIALIAS_ON);
        g2.setPaint(Color.blue);
        for(int j = 0; j < points.size()-1; j++) {
            Point p = points.get(j);
            Point next = points.get(j+1);
            g2.draw(new Line2D.Double(p, next));
        }
        g2.setPaint(Color.red);
        for(int j = 0; j < points.size(); j++) {
            Point p = points.get(j);
            g2.fill(new Ellipse2D.Double(p.x-2, p.y-2, 4, 4));
        }
    }
 
    public Dimension getPreferredSize() {
        return new Dimension(400,400);
    }
 
    public static void main(String[] args) {
        Lasso lasso = new Lasso();
        lasso.addMouseListener(lasso.ml);
        JFrame f = new JFrame();
        f.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
        f.getContentPane().add(lasso);
        f.pack();
        f.setLocationRelativeTo(null);
        f.setVisible(true);
    }
 
    private MouseListener ml = new MouseAdapter() {
        int size = 5;
        int PROXIMAL = 5;
 
        public void mousePressed(MouseEvent e) {
            Point p = e.getPoint();
            if(points.size() == size-1) {
                if(points.get(0).distance(p) <= PROXIMAL) {
                    points.add((Point)points.get(0).clone());
                } else {
                    int retVal = JOptionPane.showConfirmDialog(null,
                                      "Do you want to keep this?", "Confirm",
                                       JOptionPane.YES_NO_OPTION);
                    if(retVal == JOptionPane.YES_OPTION) {
                        points.add((Point)points.get(0).clone());
                    } else {
                        points.clear();
                    }
                }
            } else if(points.size() < size) {
                points.add(p);
            } else if(e.getClickCount() == 2) {
                points.clear();
            }
            repaint();
        }
    };
}