Non-opaque JButton background in non top level window becomes opaque?

Question

Before you read, here are some clarifications on what the question is about:

1. The SSCCE is designed for Java 7. It would be possible to use sun.*.AWTUtilities to adapt it to Java 6, but it does not matter to me how it works on Java 6.
2. The faulting line is [...]new JDialog(someWindow). Ghosting can be fixed in the SSCCE by simply changing that line to [...]new JDialog().

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Why don't top level windows exhibit ghosting?

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Expected behavior: final JDialog d = new JDialog() (see SSCCE)

As you can see, the right window has a semitransparent background (as expected).

Actual behavior: final JDialog d = new JDialog(f) (see SSCCE)

In this case, the right window has an opaque background. As a matter of fact, it takes 3-4 repaints due to any reason (easiest to reproduce is repaint on rollover) for the background to become completely opaque.

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SSCCE:

import java.awt.Color;
import java.awt.Font;
import java.awt.Graphics;

import javax.swing.JButton;
import javax.swing.JComponent;
import javax.swing.JDialog;
import javax.swing.JFrame;
import javax.swing.SwingUtilities;
import javax.swing.UIManager;
import javax.swing.plaf.synth.ColorType;
import javax.swing.plaf.synth.Region;
import javax.swing.plaf.synth.SynthConstants;
import javax.swing.plaf.synth.SynthContext;
import javax.swing.plaf.synth.SynthLookAndFeel;
import javax.swing.plaf.synth.SynthPainter;
import javax.swing.plaf.synth.SynthStyle;
import javax.swing.plaf.synth.SynthStyleFactory;

public class SynthSSCCE
{
        public static void main(String[] args) throws Exception
        {
                final SynthLookAndFeel laf = new SynthLookAndFeel();
                UIManager.setLookAndFeel(laf);
                SynthLookAndFeel.setStyleFactory(new StyleFactory());

                SwingUtilities.invokeLater(new Runnable()
                {
                        @Override
                        public void run()
                        {
                                final JFrame f = new JFrame();
                                {
                                        f.add(new JButton("Works properly"));
                                        f.setUndecorated(true);
                                        f.setBackground(new Color(0, true));
                                        f.setSize(300, 300);
                                        f.setLocation(0, 0);
                                        f.setVisible(true);
                                }
                                {
                                        final JDialog d = new JDialog(f);
                                        final JButton btn = new JButton("WTF?");
                                        // uncomment and notice that this has no effect
                                        // btn.setContentAreaFilled(false);
                                        d.add(btn);
                                        d.setUndecorated(true);
                                        d.setBackground(new Color(0, true));
                                        d.setSize(300, 300);
                                        d.setLocation(320, 0);
                                        d.setVisible(true);
                                }
                        }
                });
        }

        static class StyleFactory extends SynthStyleFactory
        {
                private final SynthStyle style = new Style();

                @Override
                public SynthStyle getStyle(JComponent c, Region id)
                {
                        return style;
                }
        }

        static class Style extends SynthStyle
        {
                private final SynthPainter painter = new Painter();

                @Override
                protected Color getColorForState(SynthContext context, ColorType type)
                {
                        if (context.getRegion() == Region.BUTTON && type == ColorType.FOREGROUND)
                                return Color.GREEN;

                        return null;
                }

                @Override
                protected Font getFontForState(SynthContext context)
                {
                        return Font.decode("Monospaced-BOLD-30");
                }

                @Override
                public SynthPainter getPainter(SynthContext context)
                {
                        return painter;
                }

                @Override
                public boolean isOpaque(SynthContext context)
                {
                        return false;
                }
        }

        static class Painter extends SynthPainter
        {
                @Override
                public void paintPanelBackground(SynthContext context, Graphics g, int x, int y, int w, int h)
                {
                        final Graphics g2 = g.create();
                        try
                        {
                                g2.setColor(new Color(255, 255, 255, 128));

                                g2.fillRect(x, y, w, h);
                        }
                        finally
                        {
                                g2.dispose();
                        }
                }

                @Override
                public void paintButtonBackground(SynthContext context, Graphics g, int x, int y, int w, int h)
                {
                        final Graphics g2 = g.create();
                        try
                        {
                                if ((context.getComponentState() & SynthConstants.MOUSE_OVER) == SynthConstants.MOUSE_OVER)
                                        g2.setColor(new Color(255, 0, 0, 255));
                                else
                                        g2.setColor(new Color(0xAA, 0xAA, 0xAA, 255));
                                g2.fillRoundRect(x, y, w, h, w / 2, h / 2);
                        }
                        finally
                        {
                                g2.dispose();
                        }
                }
        }
}

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And these are my questions...

1. What is going on? As in, why this exhibits behavior of a custom-painted non-opaque component that forgets to call super?
2. Why doesn't it happen to TL windows?
3. What is the easiest way to fix it, aside from not using non-TL windows?

Answer 1

it takes 3-4 repaints due to any reason (easiest to reproduce is repaint on rollover) for the background to become completely opaque.

Check out Backgrounds With Transparency which should give you some insight into the problem.

I've never played with Synth so I don't know if the same solution will work or not.

Answer 2

Why don't top level windows exhibit ghosting?

According to Oracle (Java Tutorials):

Each top-level container has a content pane that, generally speaking, contains (directly or indirectly) the visible components in that top-level container's GUI.

http://docs.oracle.com/javase/tutorial/uiswing/components/toplevel.html

The glass pane is often used to intercept input events occuring over the top-level container, and can also be used to paint over multiple components. It doesnt allow transparency.

Hence how you used

final Graphics g2 = g.create();

If you have the javax.swing.JComponent.paintComponent overrided in a method opposed to creating the graphics object yourself it should mitigate the transparency by super.g();

Fix this by creating a separate method listed above for graphics