Capture (trap) the mouse cursor in a window in Java

Question

Hi all, I am looking for a way to capture or trap the mouse in a window after it has entered that window much like a mouse is trapped in a virtual machine window until a user presses CTRL+ALT+DEL or release the mouse in some other manner. How do I make this happen in Java? Going full screen is not an option.

EDIT:

Here is some SSCCE for ya. This code will trap your mouse in the window. To get out you just have to within the generated frame and move directly to the close button. If you will notice when your mouse tries to leave it automatically goes back to (0,0). What I need to know is how do I get it to go back to the coordinates where it exited from. I tried getX() and getY() in place of (0,0) but the robot does not return the mouse there (I think the response time is to slow). I also have had the robot move the mouse back to crosshair.x and crosshair.y but this (as well as the others) still allows the mouse to escape if the user clicks at the right moment. Any thoughts?

Main Class:

import java.awt.AWTException;
import java.awt.Color;
import java.awt.Cursor;
import java.awt.event.MouseEvent;
import java.awt.event.MouseListener;
import java.awt.event.MouseMotionListener;
import java.awt.Graphics;
import java.awt.Image;
import java.awt.image.BufferStrategy;
import java.awt.image.MemoryImageSource;
import java.awt.Point;
import java.awt.Robot;
import java.awt.Toolkit;
import javax.swing.JFrame;

public class Game extends JFrame implements MouseMotionListener, MouseListener{

    private int windowWidth = 640;
    private int windowHeight = 480;
        private Crosshair crosshair;

    public static void main(String[] args) {
        new Game();
    }

    public Game() {
        this.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
        this.setSize(windowWidth, windowHeight);
        this.setResizable(false);
        this.setLocation(0,0);
        this.setVisible(true);

        this.createBufferStrategy(2);
                addMouseMotionListener(this);
                addMouseListener(this);
        initGame();

        while(true) {
            long start = System.currentTimeMillis();
            gameLoop();
            while(System.currentTimeMillis()-start < 5) {
                            //empty while loop
            }
        }
    }

    private void initGame() {
            hideCursor();
            crosshair = new Crosshair (windowWidth/2, windowHeight/2);
    }

        private void gameLoop() {
            //game logic
            drawFrame();
        }

        private void drawFrame() {

            BufferStrategy bf = this.getBufferStrategy();
            Graphics g = (Graphics)bf.getDrawGraphics();
            try {
                g = bf.getDrawGraphics();
                Color darkBlue = new Color(0x010040);
                g.setColor(darkBlue);
                g.fillRect(0, 0, windowWidth, windowHeight);
                drawCrossHair(g);
            } finally {
                g.dispose();
            }
            bf.show();
            Toolkit.getDefaultToolkit().sync();
        }

        private void drawCrossHair(Graphics g){
            Color yellow = new Color (0xEDFF62);
            g.setColor(yellow);
            g.drawOval(crosshair.x, crosshair.y, 40, 40);

            g.fillArc(crosshair.x + 10, crosshair.y + 21 , 20, 20, -45, -90);
            g.fillArc(crosshair.x - 1, crosshair.y + 10, 20, 20, -135, -90);
            g.fillArc(crosshair.x + 10, crosshair.y - 1, 20, 20, -225, -90);
            g.fillArc(crosshair.x + 21, crosshair.y + 10, 20, 20, -315, -90);
        }

        @Override
        public void mouseDragged(MouseEvent e) {
        //empty method
        }

        @Override
        public void mouseMoved(MouseEvent e) {
        crosshair.x = e.getX();
        crosshair.y = e.getY();
        }

        private void hideCursor() {
            int[] pixels = new int[16 * 16];
            Image image = Toolkit.getDefaultToolkit().createImage(new MemoryImageSource(16, 16, pixels, 0, 16));
            Cursor transparentCursor = Toolkit.getDefaultToolkit().createCustomCursor(image, new Point(0, 0), "invisiblecursor");
            getContentPane().setCursor(transparentCursor);
    }

        public void mouseExited(MouseEvent e) {
            System.out.println("Event: " + e);
            try {
                Robot robot = new Robot();
                robot.mouseMove(0, 0);// When I use (getX(),getY()) instead of (0,0) the robot will not move the mouse at all even though getX() and getY() are the coordinates I want the mouse to be moved to.  Also the mouse can still escape, even when crosshair.x and crosshair.y are used as the coordinates.  It seems that robot is too slow.
            }
            catch (AWTException ex) {
                ex.printStackTrace();
            }
        }

        public void mouseEntered(MouseEvent e){
        }

        public void mousePressed(MouseEvent e) {
        }

        public void mouseReleased(MouseEvent e) {
        }

        public void mouseClicked(MouseEvent e) {
        }
}

Another Class:

public class Crosshair{
        public int x;
    public int y;
    public Crosshair(int x, int y) {
        this.x = x;
        this.y = y;
        }
}

Answer 1

I guess you could use a Global Event Listener to listen for mouse entered events for the frame. Then on a mouse exited event I suppose you could use the Robot to reset the location of the mouse once it leaves the frame.

Answer 2

As camickr mentions, you can do this using the Robot. It's generally something that people would recommend against, but here's a pretty good Robot primer to get you started:

http://www.developer.com/java/other/article.php/2212401/Introduction-to-the-Java-Robot-Class-in-Java.htm

Answer 3

Well, I don't pretend to be a game developer but the code presented in the link is terrible (from what I can tell) for a simple "pong game". I copied the code and got it running so that the ball bounces around.

On my computer the CPU is 50% because of the infinite while loop that wastes CPU time to provide the animation for ball movement. The simple change to use a Thread that sleeps for 5ms rather than hog the CPU for 5ms, causes the CPU usage to drop down to about 18%.

I then changed the code to do the ball animation on a Swing panel. The code is easier to write and the CPU usage dropped to 1% and the ball animation was much faster.

Here is my final version. You should be able to swap back to using the buffered strategy by not adding the panel to the frame and then by invoking the drawFrame() method again.

import java.awt.Color;
import java.awt.Graphics;
import java.awt.Toolkit;
import java.awt.image.BufferStrategy;

import javax.swing.*;

public class Game3 extends JFrame {

    /**
     * @author Georgi Khomeriki
     */

    private Ball ball;

    // added this
    private JPanel gamePanel;

    private int windowWidth = 800;
    private int windowHeight = 600;


    public static void main(String[] args) {
        new Game3();
    }

    public Game3() {
        this.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
        this.setSize(windowWidth, windowHeight);
        this.setResizable(false);
        this.setLocation(100, 100);
        this.setVisible(true);

        this.createBufferStrategy(2);

        initGame3();
/*
        while(true) {
            long start = System.currentTimeMillis();
            gameLoop();
            while(System.currentTimeMillis()-start < 5) {
                 //do nothing
            }
        }
*/

        Thread thread = new Thread(new Runnable()
        {
            public void run()
            {
                while(true)
                {
                    gameLoop();
                    try { Thread.sleep(5); }
                    catch(Exception e) {}
                }
            }
        });
        thread.start();

    }

    private void initGame3() {
        // all you're game variables should be initialized here
        ball = new Ball(windowWidth/2, windowHeight/2, 5, 5);

        // added these lines

        gamePanel = new GamePanel();
        gamePanel.setBackground(Color.BLACK);
        add(gamePanel);
    }

    private void gameLoop() {
        // your game logic goes here

// move the ball
    ball.x = ball.x + ball.dx;
    ball.y = ball.y + ball.dy;

    // change the direction of the ball if it hits a wall
    if(ball.x <= 0 || ball.x >= windowWidth-40)
        ball.dx = -ball.dx;
    if(ball.y <= 0 || ball.y >= windowHeight-40)
        ball.dy = -ball.dy;


        // changed to following to use Swing instead of buffer strategy
//      drawFrame();
        gamePanel.repaint();
    }

    private void drawFrame() {
        // code for the drawing goes here
        BufferStrategy bf = this.getBufferStrategy();
        Graphics g = null;

        try {
            g = bf.getDrawGraphics();

            // clear the back buffer (just draw a big black rectangle over it)
            g.setColor(Color.BLACK);
            g.fillRect(0, 0, windowWidth, windowHeight);

drawBall(g);


        } finally {
            // It is best to dispose() a Graphics object when done with it.
            g.dispose();
        }

        // Shows the contents of the backbuffer on the screen.
        bf.show();

        //Tell the System to do the Drawing now, otherwise it can take a few extra ms until
        //Drawing is done which looks very jerky
        Toolkit.getDefaultToolkit().sync();
    }

    private void drawBall(Graphics g) {

        g.setColor(Color.GREEN);
        g.fillOval(ball.x, ball.y, 40, 40);
    }

    // added this

    class GamePanel extends JPanel
    {
        protected void paintComponent(Graphics g)
        {
            super.paintComponent(g);
            drawBall(g);
        }
    }


    class Ball {

        public int x;
        public int y;
        public int dx;
        public int dy;

        public Ball(int x, int y, int dx, int dy) {
            this.x = x;
            this.y = y;
            this.dx = dx;
            this.dy = dy;
        }
    }



}