RFR: 8313424: JavaFX controls in the title bar [v65]

[Markus Mack]

On Thu, 24 Apr 2025 14:36:35 GMT, Michael Strauß <mstrauss at openjdk.org> wrote:

>> modules/javafx.graphics/src/main/java/javafx/stage/StageStyle.java line 117:
>> 
>>> 115:      * <h4>Custom header buttons</h4>
>>> 116:      * If more control over the header buttons is desired, applications can opt out of the default header buttons
>>> 117:      * by setting {@link HeaderBar#setPrefButtonHeight(Stage, double)} to zero and providing custom header buttons
>> 
>> Setting height to zero to disable something is unfortunately often misused without actually disabling anything. Even though implemented correctly here, I'd prefer a more semantic way of doing this, e.g. by adding a "showHeaderButtons" property.
>
> I agree when it actually makes a semantic difference. For example, there's a difference between setting `Node.opacity` to zero, and setting `Node.visible` to `false`. In the first case, the node will still receive events, while in the second case it won't. But what's the semantic difference between non-existing header buttons, and header buttons with zero height?
> 
> One argument against setting `prefButtonHeight` to zero could be that it special-cases one specific value (or two, because there's also the special value `USE_DEFAULT_SIZE`). In general, the property only describes a _preferred_ height, which the toolkit is free to honor (in any way it sees fit) or to ignore entirely. However, the two special values 0 and `USE_DEFAULT_SIZE` are specified to be honored by all toolkits in all cases.

Typically it's issues related to keyboard navigation that forget to handle the zero-size case. But I agree it's ok to leave it as it is because it's documented in a way that can be trusted.

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PR Review Comment: https://git.openjdk.org/jfx/pull/1605#discussion_r2058660143