Margus Martsepp (Stackoverflow:Wanting a type of grid for a pixel editor) 2

import java.awt.AWTException;
import java.awt.Dimension;
import java.awt.EventQueue;
import java.awt.Graphics;
import java.awt.MouseInfo;
import java.awt.Point;
import java.awt.Rectangle;
import java.awt.Robot;
import java.awt.event.MouseEvent;
import java.awt.event.MouseMotionListener;
import java.awt.image.BufferedImage;
import javax.swing.JFrame;
import javax.swing.JPanel;

/** @see http://stackoverflow.com/questions/3742731 */
public class Zoom extends JPanel implements MouseMotionListener {

    private static final int SIZE = 12;
    private static final int S2 = SIZE / 2;
    private static final int SCALE = 48;
    private BufferedImage img;
    private Robot robot;

    public Zoom() {
        super(true);
        this.setPreferredSize(new Dimension(SIZE * SCALE, SIZE * SCALE));
        img = new BufferedImage(SIZE, SIZE, BufferedImage.TYPE_INT_RGB);
        try {
            robot = new Robot();
        } catch (AWTException e) {
            e.printStackTrace(System.err);
        }
    }

    boolean ifdone = true;

    @Override
    protected void paintComponent(Graphics g) {
        if (ifdone) {
            ifdone = false;
            g.drawImage(img, 0, 0, getWidth(), getHeight(), null);
            ifdone = true;
        }
    }

    @Override
    public void mouseMoved(MouseEvent e) {
        Point p = e.getPoint();
        int x = p.x * SIZE / getWidth();
        int y = p.y * SIZE / getHeight();
        int c = img.getRGB(x, y);
        this.setToolTipText(x + "," + y + ": " + String.format("%08X", c));
    }

    @Override
    public void mouseDragged(MouseEvent e) {
        final Point p = MouseInfo.getPointerInfo().getLocation();
        Rectangle rect = new Rectangle(p.x - S2, p.y - S2, SIZE, SIZE);
        img = robot.createScreenCapture(rect);
        repaint();
    }

    private static void create() {
        JFrame f = new JFrame("Click & drag to zoom.");
        f.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
        Zoom zoom = new Zoom();
        f.add(zoom);
        f.pack();
        f.setVisible(true);
        Ticker t = new Ticker(zoom);
        zoom.addMouseMotionListener(zoom);
        t.start();
    }

    private static class Ticker extends Thread {
        private final Robot robot;
        public boolean update = true;
        private final Zoom view;

        public Ticker(Zoom zoomPanel) {
            view = zoomPanel;
            try {
                robot = new Robot();
            } catch (AWTException e) {
                throw new RuntimeException(e);
            }
        }

        public void done() {
            update = false;
        }

        public void run() {
            while (update) {
                final Point p = MouseInfo.getPointerInfo().getLocation();
                Rectangle rect = new Rectangle(p.x - S2, p.y - S2, SIZE, SIZE);
                view.img = robot.createScreenCapture(rect);
                view.repaint();
            }
        }
    }

    public static void main(String[] args) {
        EventQueue.invokeLater(new Runnable() {
            @Override
            public void run() {
                create();
            }
        });
    }
}