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 * FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public License

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import com.sun.awt.AWTUtilities;

import javax.swing.*;

import java.awt.*;

import java.awt.image.BufferedImage;

public class bug6683775 {

    static final int LOC = 100,

            SIZE = 200;

    public static void main(String[] args) throws Exception {

        GraphicsConfiguration gc = getGC();

       if (!AWTUtilities.isTranslucencySupported(

               AWTUtilities.Translucency.PERPIXEL_TRANSLUCENT)

                || gc == null) {

            return;

        }

        Robot robot = new Robot();

        final JFrame testFrame = new JFrame(gc);

        SwingUtilities.invokeAndWait(() -> {

            JFrame backgroundFrame = new JFrame("Background frame");

            backgroundFrame.setUndecorated(true);

            JPanel panel = new JPanel();

            panel.setBackground(Color.RED);

            backgroundFrame.add(panel);

            backgroundFrame.setBounds(LOC, LOC, SIZE, SIZE);

            backgroundFrame.setVisible(true);

            testFrame.setUndecorated(true);

            JPanel p = new JPanel();

            p.setOpaque(false);

            testFrame.add(p);

            AWTUtilities.setWindowOpaque(testFrame, false);

            testFrame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);

            testFrame.setBounds(LOC, LOC, SIZE, SIZE);

            testFrame.setVisible(true);

        });

        robot.waitForIdle();

        Thread.sleep(1500);

        //robot.getPixelColor() didn't work right for some reason

        BufferedImage capture =

                robot.createScreenCapture(new Rectangle(LOC, LOC, SIZE, SIZE));

        int redRGB = Color.RED.getRGB();

        if (redRGB != capture.getRGB(SIZE/2, SIZE/2)) {

            throw new RuntimeException("Transparent frame is not transparent!");

        }

    }

    private static GraphicsConfiguration getGC() {

        GraphicsConfiguration transparencyCapableGC =

                GraphicsEnvironment.getLocalGraphicsEnvironment()

                        .getDefaultScreenDevice().getDefaultConfiguration();

        if (!AWTUtilities.isTranslucencyCapable(transparencyCapableGC)) {

            transparencyCapableGC = null;

            GraphicsEnvironment env =

                    GraphicsEnvironment.getLocalGraphicsEnvironment();

            GraphicsDevice[] devices = env.getScreenDevices();

            for (int i = 0; i < devices.length && transparencyCapableGC == null; i++) {

                GraphicsConfiguration[] configs = devices[i].getConfigurations();

                for (int j = 0; j < configs.length && transparencyCapableGC == null; j++) {

                    if (AWTUtilities.isTranslucencyCapable(configs[j])) {

                        transparencyCapableGC = configs[j];

                    }

                }

            }

        }

        return transparencyCapableGC;

    }

}