Re-paint on translucent frame/panel/component.

Question

I'm trying to create a translucent window with Java on OSX and add a JLabel to it.

This JLabel changes its text every second....

However the component is not repainting well.

How can I solve this problem?

I've found the these articles, but I can't figure out how to solve it.

If possible, please paste the fixing source code, here's mine:

import javax.swing.JFrame;
import javax.swing.JPanel;
import javax.swing.JLabel;
import java.awt.Color;
import java.awt.Font;
import java.util.Timer;
import java.util.TimerTask;

public class Translucent {
    public static void main( String [] args ) {

        JFrame frame = new JFrame();

        frame.setBackground( new Color( 0.0f,0.0f,0.0f,0.3f));

        final JLabel label =  new JLabel("Hola");
        label.setFont( new Font( label.getFont().getFamily(), Font.PLAIN, 46 ) );
        label.setForeground( Color.white );

        frame.add( label );
        frame.pack();
        frame.setLocationRelativeTo( null );
        frame.setVisible( true );

        Timer timer = new Timer();
        timer.schedule( new TimerTask(){
            int i = 0;
            public void run() {
                label.setText("Hola "+ i++ );
            }
        }, 0, 1000 );


    }   
}

Answer 1

I've had some luck extending JLabel and implementing Icon to get a translucent component working the way I want. You can see the result of various rule combinations in this AlphaCompositeDemo. The example below is 100% white atop 50% black.

Addendum: Note how this example composites opaque text on a clear offscreen background over the translucent frame background.

Addendum: Here's a way to make the whole frame translucent. Unfortunately, it dims the content, too.

import java.awt.AlphaComposite;
import java.awt.Color;
import java.awt.Dimension;
import java.awt.EventQueue;
import java.awt.Font;
import java.awt.FontMetrics;
import java.awt.Graphics;
import java.awt.Graphics2D;
import java.awt.RenderingHints;
import java.awt.event.ActionEvent;
import java.awt.event.ActionListener;
import java.awt.image.BufferedImage;
import java.text.SimpleDateFormat;
import java.util.Date;
import javax.swing.JFrame;
import javax.swing.JPanel;
import javax.swing.Timer;

public class Translucent extends JPanel implements ActionListener {

    private static final int W = 300;
    private static final int H = 100;
    private static final Font font =
        new Font("Serif", Font.PLAIN, 48);
    private static final SimpleDateFormat df =
        new SimpleDateFormat("HH:mm:ss");
    private final Date now = new Date();
    private final Timer timer = new Timer(1000, this);
    private BufferedImage time;
    private Graphics2D timeG;

    public Translucent() {
        super(true);
        this.setPreferredSize(new Dimension(W, H));
        timer.start();
    }

    @Override
    protected void paintComponent(Graphics g) {
        Graphics2D g2d = (Graphics2D) g;
        g2d.setRenderingHint(
            RenderingHints.KEY_ANTIALIASING,
            RenderingHints.VALUE_ANTIALIAS_ON);
        int w = this.getWidth();
        int h = this.getHeight();
        g2d.setComposite(AlphaComposite.Clear);
        g2d.fillRect(0, 0, w, h);
        g2d.setComposite(AlphaComposite.Src);
        g2d.setPaint(g2d.getBackground());
        g2d.fillRect(0, 0, w, h);
        renderTime(g2d);
        int w2 = time.getWidth() / 2;
        int h2 = time.getHeight() / 2;
        g2d.setComposite(AlphaComposite.SrcOver);
        g2d.drawImage(time, w / 2 - w2, h / 2 - h2, null);
    }

    private void renderTime(Graphics2D g2d) {
        g2d.setFont(font);
        String s = df.format(now);
        FontMetrics fm = g2d.getFontMetrics();
        int w = fm.stringWidth(s);
        int h = fm.getHeight();
        if (time == null && timeG == null) {
            time = new BufferedImage(w, h, BufferedImage.TYPE_INT_ARGB);
            timeG = time.createGraphics();
            timeG.setRenderingHint(
                RenderingHints.KEY_ANTIALIASING,
                RenderingHints.VALUE_ANTIALIAS_ON);
            timeG.setFont(font);
        }
        timeG.setComposite(AlphaComposite.Clear);
        timeG.fillRect(0, 0, w, h);
        timeG.setComposite(AlphaComposite.Src);
        timeG.setPaint(Color.green);
        timeG.drawString(s, 0, fm.getAscent());
    }

    private static void create() {
        JFrame f = new JFrame();
        f.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
        f.setBackground(new Color(0f, 0f, 0f, 0.3f));
        f.setUndecorated(true);
        f.add(new Translucent());
        f.pack();
        f.setLocationRelativeTo(null);
        f.setVisible(true);
    }

    @Override
    public void actionPerformed(ActionEvent e) {
        now.setTime(System.currentTimeMillis());
        this.repaint();
    }

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