RFR: 8359601: Fix window button states of an extended stage [v6]

[Cormac Redmond]

On Sat, 21 Jun 2025 23:37:13 GMT, Michael Strauß <mstrauss at openjdk.org> wrote:

>> The window button states (disabled/hidden) of extended stages with a `HeaderButtonOverlay` or custom header buttons are inconsistent with what we would expect from the OS (Windows and Linux). To figure out what we would expect, I started with gathering some data. The following table shows the button states of system-decorated windows on various platforms:
>> 
>> #### Windows 11
>> 
>> | Window attributes | Iconify | Maximize | Close |
>> |---|---|---|---|
>> | resizable, not modal | visible | visible | visible |
>> | not resizable, not modal | visible | visible, disabled | visible |
>> | resizable, modal | visible, disabled | visible | visible |
>> | not resizable, modal | hidden | hidden | visible, utility-style |
>> 
>> #### Ubuntu 24 / Fedora 41 (GNOME)
>> 
>> | Window attributes | Iconify | Maximize | Close |
>> |---|---|---|---|
>> | resizable, not modal | visible | visible | visible |
>> | not resizable, not modal | visible | hidden | visible |
>> | resizable, modal | visible, _not working_ | visible, _not working_ | visible |
>> | not resizable, modal | visible, _not working_ | hidden | visible |
>> 
>> #### Kubuntu 24 (KDE)
>> 
>> | Window attributes | Iconify | Maximize | Close |
>> |---|---|---|---|
>> | resizable, not modal | visible | visible | visible |
>> | not resizable, not modal | visible | hidden | visible |
>> | resizable, modal | visible, _not working_ | visible | visible |
>> | not resizable, modal | visible, _not working_ | hidden | visible |
>> 
>> ## Observations
>> 
>> 1. On Windows, buttons are generally disabled when their operation is not possible with the given window attributes.
>>    * Exception: modal/non-resizable windows look like utility windows (iconify and maximize are hidden)
>> 2. On GNOME and KDE, buttons are generally hidden when their operation is not possible.
>>    * Exception: iconify and maximize on modal windows is not hidden, but seems to simply not do anything (bug?)
>> 
>> ## Permitted window button operations
>> 
>> Given the gathered observations and some simple logic, this is the table of operations that are permitted for all combinations of modal and resizable window attributes:
>> 
>> | Window attributes | Iconify | Maximize | Close |
>> |---|---|---|---|
>> | resizable, not modal | yes | yes | yes |
>> | not resizable, not modal | yes | no | yes |
>> | resizable, modal | no | yes | yes |
>> | not resizable, modal | no | no | yes |
>> 
>> ## Fixes
>> 
>> This PR includes the following changes:
>> 1. Unused code relating to window modality is removed...
>
> Michael Strauß has updated the pull request incrementally with one additional commit since the last revision:
> 
>   fix resizable state of macOS window

I have found another bug/issue, which is again related to wrapping a root node in a StackPane (something that is common in, for example, ControlsFx). Although the observed behaviour is probably strictly logically correct, I think this should be prevented (e.g, HeaderBar has/gets special meaning/treatment).


public class DisappearingHeaderBarNodesBug extends Application {

    @Override
    public void start(Stage primaryStage) {
        BorderPane root = new BorderPane();
        Button button = new Button("Click for "bug()"!");
        button.setOnAction(_ -> bug(root));
        root.setCenter(new VBox(new Label("Something above"), button, new Label("Something below")));
        root.setTop(getHeaderBar());

        primaryStage.initStyle(StageStyle.EXTENDED);
        primaryStage.setScene(new Scene(root, 300, 200));
        primaryStage.show();
    }

    // Wrapping the root node in a stackpane is common
    private void bug(Pane root) {
        StackPane stackPane = new StackPane();
        root.getScene().setRoot(stackPane);
        stackPane.getChildren().addFirst(root);
    }

    private HeaderBar getHeaderBar() {
        HeaderBar headerBar = new HeaderBar();
        headerBar.setCenter(new Label("!!! HeaderBar !!!"));
        headerBar.setLeading(new Label("L"));
        return headerBar;
    }

    public static void main(String[] args) {
        launch(args);
    }
}


As you can see, after you click the button, and resize, the HeaderBar can disappear completely:

https://github.com/user-attachments/assets/93a320a5-0010-4941-a2a4-9e0e65cbd57d

-------------

PR Comment: https://git.openjdk.org/jfx/pull/1831#issuecomment-2999295206