Remove JTextPane's white background without setOpaque() over a translucent JFrame

问题

I have a Java code where I implemented a translucent JPanel with an image drawn on it with Graphics 2D. This image is a PNG that includes a white rectangle, 80% opaque, all over the JFrame. Now I need to add a JTextPane to display datas (I set it to use a custom font from the app package BTW), but I can't manage to make it translucent : its white background is opaque (even with the textPane.setOpaque(false); setting) and makes the transparency of my JFrame a bit useless... Wich is not cool.

So I am looking for a way to remove this white background that freaks me out.

I rolled many Google searches but everything I found was a boolean to set the opacity of the JTextPane. I also found that with the Graphics 2D I could create a custom JTextPane and Override its background, but It didn't work... I HAVE already tried all of this.

public class MyWindow extends JFrame {

    private static class MyTextPane extends JTextPane {
         public MyTextPane() {
            super();

            setText("Hello World");
            setOpaque(false);
            setBackground(new Color(0,0,0,0));
         }

         @Override
         protected void paintComponent(Graphics g) {
            g.setColor(new Color(0, 0, 0, 0));
            g.fillRect(0, 0, getWidth(), getHeight());

            super.paintComponent(g);
         }
    }

    public static void main(String[] args) {

         MyTextPane textPane = new MyTextPane();

         JPanel panel = new JPanel() {

             private static final long serialVersionUID = 1L;

             @Override
                         protected void paintComponent(Graphics g) {
                              try {
                Image img = ImageIO.read(new File("images/bg.png"));
                g.drawImage(img, 0, 0, this.getWidth(), this.getHeight(), this);
                              } catch (IOException e) {
                e.printStackTrace();
              }

                              if (g instanceof Graphics2D) {
                                final int R = 240;
                                final int G = 240;
                                final int B = 240;

                Paint p =
                    new GradientPaint(0.0f, 0.0f, new Color(R, G, B, 0),
                        0.0f, getHeight(), new Color(R, G, B, 0), true);
                Graphics2D g2d = (Graphics2D)g;
                g2d.setPaint(p);
                g2d.fillRect(0, 0, getWidth(), getHeight());
            }
        }
    };
    panel.add(textPane);
    setContentPane(panel);

    }

(Made the JFrame translucent with the explanations of Oracle, right here HERE) Thanks!

回答1:

This is how I might approach this kind of idea...

public class OverlayTextArea {

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

    public OverlayTextArea() {
        EventQueue.invokeLater(new Runnable() {
            @Override
            public void run() {
                try {
                    UIManager.setLookAndFeel(UIManager.getSystemLookAndFeelClassName());
                } catch (Exception ex) {
                }

                JFrame frame = new JFrame("Testing");
                frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
                frame.setContentPane(new ImagePane());
                frame.setLayout(new BorderLayout());
                frame.add(new TransparentTextArea());
                frame.pack();
                frame.setLocationRelativeTo(null);
                frame.setVisible(true);
            }
        });
    }

    public class TransparentTextArea extends JTextArea {

        public TransparentTextArea() {
            setOpaque(false);
            setBorder(new CompoundBorder(new EmptyBorder(10, 10, 10, 10), new LineBorder(Color.LIGHT_GRAY)));
        }

        @Override
        protected void paintComponent(Graphics g) {
            g.setColor(new Color(255, 255, 255, 128));
            Insets insets = getInsets();
            int x = insets.left;
            int y = insets.top;
            int width = getWidth() - (insets.left + insets.right);
            int height = getHeight() - (insets.top + insets.bottom);
            g.fillRect(x, y, width, height);
            super.paintComponent(g);
        }

    }

    public class ImagePane extends JPanel {

        private BufferedImage background;

        public ImagePane() {
            try {
                background = ImageIO.read(new File("/path/to/background.img"));
            } catch (IOException ex) {
                ex.printStackTrace();
            }
        }

        @Override
        public Dimension getPreferredSize() {
            return background == null ? super.getPreferredSize() : new Dimension(background.getWidth(), background.getHeight());
        }

        @Override
        protected void paintComponent(Graphics g) {
            super.paintComponent(g);
            if (background != null) {
                int x = (getWidth() - background.getWidth()) / 2;
                int y = (getHeight() - background.getHeight()) / 2;
                g.drawImage(background, x, y, this);
            }
        }

    }

}

Feedback

You really should call super.paintComponent, failing to do so can lead it some serious trouble, especially when you're dealing with transparent components.
Don't perform any long running tasks within the paintXxx methods, like loading images. These methods are intended to return quickly and may be called multiple times within succession...

回答2:

to make it work with Nimbus L&F:

jta.setOpaque(false);
jta.setBorder(BorderFactory.createEmptyBorder());
jta.setBackground(new Color(0,0,0,0));

来源：https://stackoverflow.com/questions/14177340/remove-jtextpanes-white-background-without-setopaque-over-a-translucent-jfram

标签

java

swing

transparency

jtextpane