Re: Translucent volatile image appears opaque

From:
Knute Johnson <nospam@rabbitbrush.frazmtn.com>
Newsgroups:
comp.lang.java.gui
Date:
Fri, 16 Jul 2010 08:49:26 -0700
Message-ID:
<dc%%n.10095$Zp1.6880@newsfe15.iad>
On 7/16/2010 3:30 AM, Qu0ll wrote:

I create a TRANSLUCENT volatile image, render some stuff in it and then
draw the image on to the screen. I expected that the rendering in the
image would be "overlaid" over the existing screen graphics and that the
regions of the image that I didn't render to would be transparent and
not obscure any graphics on the screen.

But that is not the case. Instead I see an opaque black background which
obliterates anything already on the screen. The graphics I rendered in
the image are appearing but the image itself does not appear to be
translucent.

So, is this the expected behaviour? Does a translucent volatile image
start off life with an opaque black background? If so, how do I get it
to be translucent?


If I had to guess, I would say that your image isn't really translucent.

Compile and run this little SSCCE. Then change the image type to RGB
instead of ARGB and run it again.

import java.awt.*;
import java.awt.event.*;
import java.awt.image.*;
import javax.swing.*;

public class test extends JPanel {
     private BufferedImage bi;

     public test() {
         setPreferredSize(new Dimension(400,300));
         setBackground(Color.BLUE);
         bi = new BufferedImage(400,300,BufferedImage.TYPE_INT_ARGB);
         if (bi.getTransparency() == BufferedImage.TRANSLUCENT)
             System.out.println("TRANSPARENT");
         System.out.println(bi.getRGB(0,0));
         Graphics2D g = bi.createGraphics();
         g.setColor(Color.WHITE);
         g.drawString("Hello World",5,20);
     }

     public void paintComponent(Graphics g) {
         super.paintComponent(g);
         g.drawImage(bi,0,0,null);
     }

     public static void main(String[] args) {
         EventQueue.invokeLater(new Runnable() {
             public void run() {
                 JFrame f = new JFrame();
                 f.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
                 test t = new test();
                 f.add(t);
                 f.pack();
                 f.setVisible(true);
             }
         });
     }
}

--

Knute Johnson
email s/nospam/knute2010/

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