Tucaen Tucaen - 1 year ago 113
Java Question

JDialog with transparent background which blurs things underneath

I'm trying to make a transparent JDialog, which blures what´s underneath it (for better readability). Already found this link, but there the contents of the dialog are blurred. Also I found this, but there everything (things underneath and contents of the Dialog) is blured and it's flickering.

Here's a screenshot for better understanding:

enter image description here

The top is what I already have and the bottom what I want to achieve.

Answer Source

After some testing it appears to be pretty tricky to get something like what you want to achieve. I ended up using a JLayeredPane which contains one layer for the blurred background and one for the actual content.

I am not entirely happy with the result but I didn't find a better solution now. The problem is that Java does not provide a proper way to capture things behind the actual application which leads to the need of hiding the content before taking the screenshot. That also is the problem which causes the flickering you mentioned. To avoid this I do only reaint the background if the application gets resized or moved. There should be put some more effort into this once really used, e.g. if the app gets minimized. But since this example cannot be resized ord minimized it's not really important right now. The downside of this approach however is that it's completely ignoring whether or not the Background isn't static. If you use the application in front of a video for example, the current version does not change the background based on the videos current frame. This may be possible if you uncomment the Timer in my examples setVisible(...) but then we get the flickering back.

I'd suggest you to think about using JavaFx. Since CSS already provides a blur-functionality it may work for Fx as well. But since I didn't try that yet I cannot assure you it's working.

Long story short, here's the example. The blurring function is used from your link above.

import java.awt.AWTException;
import java.awt.BorderLayout;
import java.awt.Color;
import java.awt.Dimension;
import java.awt.Graphics;
import java.awt.Rectangle;
import java.awt.Robot;
import java.awt.event.ActionEvent;
import java.awt.event.ActionListener;
import java.awt.event.ComponentEvent;
import java.awt.event.ComponentListener;
import java.awt.image.BufferedImage;
import java.awt.image.BufferedImageOp;
import java.awt.image.ConvolveOp;
import java.awt.image.Kernel;

import javax.swing.JComponent;
import javax.swing.JFrame;
import javax.swing.JLabel;
import javax.swing.JLayeredPane;
import javax.swing.JPanel;
import javax.swing.SwingConstants;

public class BlurryFrame extends JFrame implements ActionListener, ComponentListener {

    public static void main(String... sss) {

        JLabel label1 = new JLabel("TestLabel 1");
        label1.setSize(500, 100);

        JLabel label2 = new JLabel("TestLabel 2");

        JPanel testPanel = new JPanel();
        testPanel.setLayout(new BorderLayout());
        testPanel.add(label1, BorderLayout.CENTER);
        testPanel.add(label2, BorderLayout.SOUTH);

        BlurryFrame frame = new BlurryFrame(800, 600, testPanel);
        frame.setBackground(new Color(0, 0, 0, 100));

    private final BackgroundPanel backgroundPane;
    private final JLayeredPane container;
    private final JPanel containerPane;
    private final Robot robot;

    // This rectangle is going to be your screenshots bounds to keep the image only as big as necessary
    private final Rectangle captureRect;

    // This is going to be the blurred screenshot
    private BufferedImage background;

    public BlurryFrame() {
        this(1280, 800);

    public BlurryFrame(int width, int height) {
        this(width, height, null);

    public BlurryFrame(int width, int height, JComponent component) {

        this.captureRect = new Rectangle();
        try {
            this.robot = new Robot();
        } catch (AWTException e) {
            throw new RuntimeException(e);

        this.backgroundPane = new BackgroundPanel();
        this.backgroundPane.setLayout(new BorderLayout());
        this.backgroundPane.setBounds(0, 0, width, height);

        this.containerPane = new JPanel();
        this.containerPane.setLayout(new BorderLayout());
        this.containerPane.add(component, BorderLayout.CENTER);
        this.containerPane.setBounds(0, 0, width, height);

        this.setSize(width, height);

        this.container = new JLayeredPane();
        this.container.setLayout(new BorderLayout());
        this.container.add(this.backgroundPane, 1);
        this.container.add(this.containerPane, 0);

        this.getContentPane().add(this.container, BorderLayout.CENTER);

    public void add(JComponent component) {
        this.containerPane.add(component, BorderLayout.CENTER);

    // This method does not really do much but ultimately triggers the screenshot by ending up in #componentHidden(...)
    private void capture() {

    public void setVisible(boolean visible) {


        // XXX uncomment this if you want to see the flickering
        // Timer timer = new Timer(60, this);
        // timer.start();

    public void setSize(int width, int height) {

        super.setSize(width, height);

        this.captureRect.setSize(width, height);
        this.backgroundPane.setBounds(0, 0, width, height);
        this.containerPane.setBounds(0, 0, width, height);

        if (this.isVisible())

    public void setSize(Dimension dimension) {


        this.backgroundPane.setBounds(0, 0, dimension.width, dimension.height);
        this.containerPane.setBounds(0, 0, dimension.width, dimension.height);

        if (this.isVisible())

    public void setPreferredSize(Dimension dimension) {


        this.backgroundPane.setBounds(0, 0, dimension.width, dimension.height);
        this.containerPane.setBounds(0, 0, dimension.width, dimension.height);

        if (this.isVisible())

    public void actionPerformed(ActionEvent e) {

    int i = 0;

    // This is where the magic happens. The capturing needs to be done here in order to assure the applications content has really been hidden
    public void componentHidden(ComponentEvent e) {

        int x = this.getLocationOnScreen().x;
        int y = this.getLocationOnScreen().y;

        this.captureRect.setLocation(x, y);

        this.background = this.robot.createScreenCapture(this.captureRect);

        //XXX uncomment this if you want to see what gets captured
        //      if (this.i < 1) {
        //          try {
        //              ImageIO.write(this.background, "png", new File(System.getProperty("user.home") + "\\test.png"));
        //          } catch (IOException ex) {
        //              ex.printStackTrace();
        //          }
        //          this.i++;
        //      }


    public void componentMoved(ComponentEvent e) {

    public void componentResized(ComponentEvent e) {

    private class BackgroundPanel extends JPanel {

        private final float[] matrix = {
                0.111f, 0.111f, 0.111f,
                0.111f, 0.111f, 0.111f,
                0.111f, 0.111f, 0.111f,

        public void paintComponent(Graphics g) {


            if (BlurryFrame.this.background != null) {

                BufferedImageOp op = new ConvolveOp(new Kernel(3, 3, this.matrix));
                BufferedImage blurryBack = op.filter(BlurryFrame.this.background, null);

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

    public void componentShown(ComponentEvent e) {
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