RFR: 8369836: Update HeaderBar API [v16]

[Michael Strauß]

On Thu, 8 Jan 2026 19:38:42 GMT, Andy Goryachev <angorya at openjdk.org> wrote:

>> You _should_ see mouse events not related to the press-drag-release gesture.
>> 
>> However, I've changed a tiny detail: when you press the left mouse button on the title bar and then move the cursor, you'll get a small number of `MOUSE_DRAGGED` events until the cursor leaves the "dead zone" and the move-modal loop starts. Once the move-modal loop has started, you won't receive events related to the window drag gesture.
>> 
>> I think that the few drag events at the beginning of a PDR gesture are just noise, therefore I've changed it so that from the perspective of the application, a PDR gesture on the title bar only produces `MOUSE_PRESSED` followed by `MOUSE_RELEASED`, but no drag events in-between.
>
> Could it have any impact on DnD to/from the header bar?

I've tested this, and you can drop something _onto_ a header bar, but you can't do the oppsite and drag-and-drop the header bar itself. That seems obvious, as any attempt to press-and-drag the header bar will just move the window instead of starting a DnD operation.

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PR Review Comment: https://git.openjdk.org/jfx/pull/1936#discussion_r2673681732