RFR: 8313424: JavaFX controls in the title bar [v3]

[Michael Strauß]

On Mon, 21 Oct 2024 20:59:00 GMT, Andy Goryachev <angorya at openjdk.org> wrote:

> I suggest we convert this PR to Draft and first discuss this in the mailing list.

This has already been [discussed](https://mail.openjdk.org/pipermail/openjfx-dev/2021-July/031428.html) at various points in time, and was always received positively. The [previous](https://github.com/openjdk/jfx/pull/594) implementation is one of the most-upvoted feature proposals since OpenJFX moved to GitHub.

> There are so many issues with the proposal that need to be ironed first: CSS support, height limitation (what happens when the app or CSS places too large of the component?), user-defined color/accents/transparency on Windows, to name just a few.

What about these things? I don't understand the question, but let me try to give some answers nontheless:
1. CSS support: `HeaderBar` is a normal part of the scene graph, so it fully supports CSS styling.
2. Height limitation: the height of `HeaderBar` is user-configurable, just like any layout container. It can be as large as you want.
3. User-defined color/accents/transparency: Again, since `HeaderBar` is a part of the scene graph, all rules are the same.

> This change also may add a significant maintenance burden to the platform, for what I feel is a very small payout.

Popular demand says otherwise.

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PR Comment: https://git.openjdk.org/jfx/pull/1605#issuecomment-2427858907