Java - set opacity in JPanel

问题

Let's say I want to make the opacity of a JPanel %20 viewable? I don't mean setOpaque (draw or not draw) or setVisible (show or hide)... I mean make it see-through JPanel.. you know?

Is this possible?

回答1:

panel.setBackground( new Color(r, g, b, a) );

You should also look at Backgrounds With Transparency to understand any painting problems you might have when you use this.

回答2:

Use the alpha attribute for the color.

For instance:

panel.setBackground(new Color(0,0,0,64));

Will create a black color, with 64 of alpha ( transparency )

Resulting in this:

Here's the code

package test;

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

public class See {
    public static void main( String [] args ){
        JFrame frame = new JFrame();
        frame.setBackground( Color.orange );


        frame.add( new JPanel(){{
                        add( new JLabel("Center"));
                        setBackground(new Color(0,0,0,64));
                    }} , BorderLayout.CENTER );
        frame.add( new JLabel("North"), BorderLayout.NORTH);
        frame.add( new JLabel("South"), BorderLayout.SOUTH);

        frame.pack();
        frame.setVisible( true );
    }
}

With out it it looks like this:

setBackground( new Color( 0,0,0 )  ); // or setBackground( Color.black );

回答3:

AWTUtilities.setWindowOpacity(aWindow, aFloat);

Where aWindow is the Swing component, and aFloat is the opacity.

回答4:

It doesn't work so well on windows 7.

panel.setBackground( new Color(r, g, b, a) );

the alpha channel just lightens the color.

when an element is updated on a color with an alpha channel, the computer gets confused and resets the background of the updated element without an alpha. I'm going to try

AWTUtilities.setWindowOpacity(aWindow, aFloat);

next.

回答5:

How about override the paintComponent method of the JPanel(in order to do this you have to sub class the JPanel itself and implement your own paintComponent method) inside the paintComponent you can retrieve a buffered image of the component, from there you can manipulate the alpha of the buffered image and paint it back to the JPanel. I have red this long time ago. Still looking for the code.

回答6:

If you have a custom panel and want the whole thing to be semi-transparent, I advise you to do override its method paintComponent like this :

@Override
    protected void paintComponent(Graphics graphics) {
        super.paintComponent(graphics);
        Graphics2D g2d = (Graphics2D) graphics;
        g2d.setComposite(AlphaComposite.getInstance(AlphaComposite.SRC_OVER, 0.5f));
    }

来源：https://stackoverflow.com/questions/3562225/java-set-opacity-in-jpanel

标签

java

jpanel

opacity