8362091: Window title bar should reflect scene color scheme

[mstr2]

Currently, the color scheme of a system-decorated stage is as follows:

• On Windows, the title bar is always light (even if the OS color scheme is dark).
• On macOS and Linux, the title bar is light or dark depending on the OS color scheme.

The expected behavior is that the title bar matches the color scheme of the Scene.
If an application doesn't specify a color scheme, the title bar color should match the OS color scheme.

This PR fixes the behavior for Windows and macOS, but not for Linux (there's no good way to do that).
Depending on how you look at it, this is either a bug fix or an enhancement.

/reviewers 2

---

Progress

• Change must not contain extraneous whitespace
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Issue

• JDK-8362091: Window title bar should reflect scene color scheme (Enhancement - P4)

Reviewing

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Update a local copy of the PR:
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$ git pull https://git.openjdk.org/jfx.git pull/1845/head

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$ git pr checkout 1845

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[bridgekeeper]

👋 Welcome back mstrauss! A progress list of the required criteria for merging this PR into master will be added to the body of your pull request. There are additional pull request commands available for use with this pull request.

[openjdk]

❗ This change is not yet ready to be integrated.
See the Progress checklist in the description for automated requirements.

[openjdk]

@mstr2
The total number of required reviews for this PR (including the jcheck configuration and the last /reviewers command) is now set to 2 (with at least 1 Reviewer, 1 Author).

[mlbridge]

Webrevs

• 01: Full (0942504f)
• 00: Full (8fa90944)

[Maran23]

This implementation looks correct. For comparison, I checked out the implementation in Godot.

Version check: https://github.com/godotengine/godot/blob/master/platform/windows/display_server_windows.cpp#L6853
Set the attribute: https://github.com/godotengine/godot/blob/master/platform/windows/display_server_windows.cpp#L4708

Note that the build numbers differ a little bit from here. But checking your linked commit, your numbers seem to be the right one! Will do some testing later (on Windows 11).

[bundgaard]

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[mstr2]

Is the extra code (beside looking at the version) so that I can toggle the darkbar from Java?

We have two places in JavaFX that are relevant to dark mode:

1. Platform.Preferences.colorScheme, which tells you the color scheme of the operating system (i.e. what you select in PC settings)
2. Scene.Preferences.colorScheme, which defaults to the OS color scheme, but is overridable for each scene.

This PR proposes to match the OS-provided title bar color to the value of Scene.Preferences.colorScheme, which allows developers to choose how their application should be presented:

• If you don't override the scene color scheme, the window title bar will match the OS by default (light or dark).
• However, if your application uses a fixed light or dark theme (i.e. it doesn't adapt its control theme colors to dark mode), then overriding the scene color scheme ensures consistent presentation independent of OS settings.