import java.awt.*;
import java.awt.event.*;
import javax.swing.*;
import java.awt.image.*;
 
public class GridSnap extends JFrame {
    int vpw = 800;//viewport width
    int vph = 500;//viewport height
    int gw = 25;//grid width
    int gh = 25;//grid height
 
    BufferedImage buf;//double buffer
    JPanel vp;//viewport for display
    JLabel status;//status bar
    int npx, npy;//current snap coords
   
    BufferedImage img = null;{
        try {
            img = ImageIO.read(new File("BG1.jpg"));
        } catch (IOException e) {
    }
}
   
    public GridSnap() {
        super("Grid Snapping");
 
    status = new JLabel("Status bar");
 
    vp = new JPanel();
    vp.setPreferredSize(new Dimension(vpw, vph));
    vp.addMouseMotionListener(new MouseMotionAdapter(){
        public void mouseMoved(MouseEvent e) {//get the nearest snap point
            int x = e.getX(), y = e.getY();
            int mx = x % gw, my = y % gh;

            npx = x - mx;
           
            npy = y - my;
           
        //    if (mx<gw/2) npx = x - mx;
       //     else npx = x + (gw-mx);
 
        //    if (my<gh/2) npy = y - my;
        //    else npy = y + (gh-my);
 
            status.setText(npx+", "+npy);
            repaint();
        }
    });
    //buffer
    buf = new BufferedImage(vpw, vph, BufferedImage.TYPE_INT_RGB);
 
    add(vp);
    add(status, BorderLayout.SOUTH);
    setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
    pack();
    setVisible(true);
}
public void paint (Graphics notused) {
    Graphics2D g = (Graphics2D)buf.createGraphics();
   
    boolean Graphics.drawImage(Image img, 0, 0,ImageObserver observer);
 
    g.setColor(Color.DARK_GRAY);
    //grid vertical lines
    for (int i=gw;i<vpw;i+=gw) {
        g.drawLine(i, 0, i, vph);
        }
        //grid horizontal lines
        for (int j=gh;j<vph;j+=gh) {
            g.drawLine(0, j, vpw, j);
        }
        //show the snapped point
        g.setColor(Color.WHITE);
        if (npx>=0 && npy>=0 && npx<=vpw && npy<=vph) {
            g.drawRect(npx, npy, gw, gh);
        }
 
        vp.getGraphics().drawImage(buf, 0, 0, Color.BLACK, null);
   }
    public static void main(String args[]) {
        new GridSnap();
    }
}

boolean Graphics.drawImage(Image img, 0, 0,ImageObserver observer);

g.drawImage (img, 0, 0, null);

BufferedImage img;
    try {
        img = ImageIO.read (new File ("BG1.jpg"));
         catch (IOException e) {
    }
}

import javax.imageio;
import java.io.File;