RFR: 8359601: Fix window button states of an extended stage [v2]

[Cormac Redmond]

On Tue, 17 Jun 2025 00:23:48 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:
> 
>   Handle non-modal owned window correctly

Another suspected issue (not really related to this PR), close request handlers are not called when using EXTENDED. E.g.:


        stage.setOnCloseRequest(event -> {
            System.out.println("Never called...");;
        });


Same for dialogs...

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PR Comment: https://git.openjdk.org/jfx/pull/1831#issuecomment-2978564173