RFR: 8301302: Platform preferences API [v2]

[Michael Strauß]

On Tue, 31 Jan 2023 20:00:00 GMT, Andy Goryachev <angorya at openjdk.org> wrote:

> In the context of adding theme support in javafx, I think this PR is a step in the right direction. I also like a small set of platform-independent properties like fg and bg colors. I wonder if the same approach can be extended for other aspects of platform L&F, like fonts, spacing, and may be other aspects (like, hiding scrollbars setting on Mac?)

That could indeed be a useful enhancement.

> 1. Appearance enum seems unnecessary - there might be more choices in a specific platform (Mac Ventura has three: dark/light/auto).  Perhaps using fg/bg color intensity is sufficient to find out whether the overall theme is "dark" or "light".

While dark/light mode can indeed be detected just by comparing foreground and background color, the reason for the `Appearance` enumeration and the `Preferences.appearance` property is to support dark window frames. In [this gist](https://gist.github.com/mstr2/9f46f92c98d3c86aa6a0b4224a9a6548) (see "Stage appearance"), I've described how the stage appearance and platform appearance APIs interact.

> 2. ObservableMap.  Similarly to Node.getProperties(), I wonder if there might be a better way to observe the changes.  May be a different metaphor (subscription?), like adding a value change listener to a specific key.  We do need a set of keys (perhaps that can be an ObservableSet).  Having said that, ObservableMap is good enough solution, and forgive me for stating the obvious, it should not initialize anything if the platform properties have not been requested by the application code.

The use of `ObservableMap` is debatable.
I think that always initializing platform properties makes it easier to reason about the code. Saving the allocation of just a single map with 20-or-so key-value pairs is not a convincing reason to complicate the implementation, especially since most of the platform preferences implementation lives in the Glass toolkit, and not in the user-facing framework.

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PR: https://git.openjdk.org/jfx/pull/1014