JWindow and JToolTip How to achieve backdrop transparent ?

[Link-Kou]

macOS： JWindow and JToolTip backdrop not transparent

[DevCharly]

Sorry, but I've no idea what you're doing... 😕

Is this even related to FlatLaf?
Tooltips are not rounded on macOS with FlatLaf.

[Link-Kou]

JDK version：JDK17
flatlaf version： 3.1.1
Yes, when I open the style, JWindow has an extra background color.

@DevCharly

[DevCharly]

What does it look like without FlatLaf?
E.g. with Metal or Aqua L&F.

[Link-Kou]

When there is no flatlaf, the background can be transparent normally

[DevCharly]

When there is no flatlaf, the background can be transparent normally

Do you have a screenshot?

[Link-Kou]

@DevCharly

[DevCharly]

Finally, I realized what you mean 😔 : a JWindow with transparent background is not shown transparent on macOS

Test case to reproduce:

import java.awt.Color;
import javax.swing.*;
import javax.swing.border.LineBorder;
import com.formdev.flatlaf.FlatLightLaf;

public class WindowTest
{
    public static void main( String[] args ) {
        SwingUtilities.invokeLater( () -> {
            FlatLightLaf.setup();

            JLabel label = new JLabel( "text" );
            label.setBorder( new LineBorder( Color.red ) );

            JWindow window = new JWindow();
            window.setBackground( new Color( 0, 0, 0, 0 ) );
            window.add( label );
            window.setBounds( 50, 50, 200, 200 );
            window.setVisible( true );
        } );
    }
}

On macOS this shows gray window with drop shadow:

On Windows it works and does not show window border or background:

The reason seems to be that FlatLaf sets background color for root pane here:

FlatLaf/flatlaf-core/src/main/java/com/formdev/flatlaf/ui/FlatRootPaneUI.java

Line 139 in bb636ba

c.setBackground( UIManager.getColor( "RootPane.background" ) );

To workaround this issue make the root pane also transparent:

_jWindow.getRootPane().setBackground(new Color(0, 0, 0, 0));

Anyway, I'll fix this issue soon...

[DevCharly]

fixed in latest 3.4-SNAPSHOT: https://github.com/JFormDesigner/FlatLaf#snapshots