Is there a way in Java to be able to click through a JFrame?

Question

I'm trying to make an overlay for a HTML-based game running in a browser window and created an JFrame which is opaque. I'd like to be able to still play the game whilst having the overlay above the window. I tried some solutions that I've found but those didn't work for me.

I've thought of catching the click-event on my JFrame and "simulating" the click on the game window. But sadly I don't have an idea how thats possible.

My current code is using the JNA libarys to access the position and scale of the window (in my test code Task-Manager). I'm fine with using another libary or something like that, if it's even possible.

Thats my code so far:

import com.sun.jna.platform.DesktopWindow;
import com.sun.jna.platform.WindowUtils;

import javax.swing.*;
import java.awt.*;

public class Test {
    public static void main(String[] args) throws InterruptedException {
        JFrame frame = new JFrame("title");
        frame.setUndecorated(true);
        frame.setBackground(new Color(255, 69, 0, 100));
        frame.setAlwaysOnTop(true);
        frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);

        Rectangle rect = null;

        while (true) {
            for (DesktopWindow desktopWindow : WindowUtils.getAllWindows(true)) {
                if (desktopWindow.getTitle().contains("Task-Manager")) {
                    rect = desktopWindow.getLocAndSize();
                    frame.setSize(rect.width - 16, rect.height - 8);
                    frame.setLocation(rect.x + 8, rect.y);
                    frame.setVisible(true);
                    Thread.sleep(10);
                }
            }
        }
    }
}

Answer 1

A JFrame is a heavyweight component. There is a window in the host OS GUI system to go with it. The host OS GUI directs mouse events to the window. Perhaps using a lightweight component for your overlay and then disabling mouse events on it would be a better solution.

Your idea of catching the click event and "simulating it" on you game window should be fairly easy. If your JFrame event processing code has a reference to your game engine, it can determine the relative position of the windows and tell your game engine the corresponding point at which it should act as if it received a click. I.e. just call the same method of your game engine for click events that it received normally and also for the simulated ones.

An ugly hack (there is noticeable flicker) would be to hide the window and send the click through with the Robot class... like this:

import java.awt.AWTException;
import java.awt.Color;
import java.awt.Frame;
import java.awt.Graphics;
import java.awt.Point;
import java.awt.Robot;
import java.awt.event.InputEvent;
import java.awt.event.MouseEvent;
import java.awt.event.MouseListener;
import java.awt.event.MouseMotionListener;
import javax.swing.SwingUtilities;

public class ClickThrough  extends Frame implements MouseListener, MouseMotionListener {

    private final Robot robot;
    private Color bgColor = new Color(0x80808080, true);
    private Point dragPoint;

    public ClickThrough() throws AWTException {
        setAlwaysOnTop(true);
        robot = new Robot();
    }

    public static void main(String[] args) throws AWTException {
        ClickThrough w = new ClickThrough();
        w.setUndecorated(true);
        w.setSize(200, 100);
        w.setOpacity(0.7f);
        w.addMouseListener(w);
        w.addMouseMotionListener(w);
        w.setVisible(true);
    }

    @Override
    public void paint(Graphics g) {
        int w = getWidth();
        int h = getHeight();
        g.setColor(Color.GRAY);
        g.fillRect(0, 0, w, 16);
        g.setColor(bgColor);
        g.fillRect(0, 16, w, h-16);
        g.setColor(Color.BLACK);
        g.drawString("Go ahead, click on me...", 20, 50);
    }

    private void makeHole(MouseEvent e) {
        // Tried making a shape with a hole where the mouse was clicked,... didn't work (macOS).
        //setShape(windowWithHoleShape);
        setVisible(false);
    }

    private void repairHole(MouseEvent e) {
        //setShape(windowShape);
        setVisible(true);
    }

    @Override
    public void mousePressed(MouseEvent e) {
        Point p = e.getPoint();
        // give it a draggable area at the top
        if (p.y < 16) {
            dragPoint = p;
            return;
        }
        dragPoint = null;
        SwingUtilities.convertPointToScreen(p,this);
        makeHole(e);
        robot.mouseMove(p.x, p.y);
        robot.mousePress(InputEvent.getMaskForButton(e.getButton()));
        repairHole(e);
    }

    @Override public void mouseReleased(MouseEvent e) { }
    @Override public void mouseClicked(MouseEvent e) { }
    @Override public void mouseEntered(MouseEvent e) { }
    @Override public void mouseExited(MouseEvent e) { }

    @Override
    public void mouseDragged(MouseEvent e) {
        if (dragPoint != null) {
            Point p = e.getPoint();
            SwingUtilities.convertPointToScreen(p, this);
            p.translate(-dragPoint.x, -dragPoint.y);
            setLocation(p);
        }
    }

    @Override
    public void mouseMoved(MouseEvent e) { }
}

I tried to see if I could cut a hole in the window by setting the window Shape, but at least on macOS the hole does not allow the mouse events through.

I should also point out that if you switch your GUI framework to JAvaFX, then you have the option of running your HTML-based game UI in a JavaFX WebView, so you can integrate your game and overlay into a single coherent application. You could specifically make your overlay "mouse transparent". IMO that would be a much better approach than hacking around with the mouse events.