Question

Can JPanels background be set to transparent?

My frame is has two JPanels:

• Image Panel and
• Feature Panel.

Feature Panel is overlapping Image Panel.
The Image Panel is working as a background and it loads image from a remote URL.

On Feature Panel I want to draw shapes. Now Image Panel cannot be seen due to Feature Panel’s background color.

I need to make Feature Panel background transparent while still drawing its shapes and I want Image Panel to be visible (since it is doing tiling and cache function of images).

I’m using two JPanel‘s, because I need to seperate the image and shape drawing .

Is there a way the overlapping Jpanel have a transparent background?

Answer 1

Alternatively, consider The Glass Pane, discussed in the article How to Use Root Panes. You could draw your “Feature” content in the glass pane’s paintComponent() method.

Addendum: Working with the GlassPaneDemo, I added an image:

//Set up the content pane, where the "main GUI" lives.
frame.add(changeButton, BorderLayout.SOUTH);
frame.add(new JLabel(new ImageIcon("img.jpg")), BorderLayout.CENTER);

and altered the glass pane’s paintComponent() method:

protected void paintComponent(Graphics g) {
    if (point != null) {
        Graphics2D g2d = (Graphics2D) g;
        g2d.setRenderingHint(
            RenderingHints.KEY_ANTIALIASING,
            RenderingHints.VALUE_ANTIALIAS_ON);
        g2d.setComposite(AlphaComposite.getInstance(
            AlphaComposite.SRC_OVER, 0.3f));
        g2d.setColor(Color.yellow);
        g2d.fillOval(point.x, point.y, 120, 60);
    }
}

As noted here, Swing components must honor the opaque property; in this variation, the ImageIcon completely fills the BorderLayout.CENTER of the frame’s default layout.