RFR: 8301302: Platform preferences API [v2]

[Michael Strauß]

On Tue, 31 Jan 2023 23:07:12 GMT, Andy Goryachev <angorya at openjdk.org> wrote:

> I think that, by default, the FX frame decorations should pick up the platform theme (dark, light, accent color, etc.). It should be possible to override this behavior somehow - possibly by setting the base/accent color - but using an enum for this purpose feels unnecessary.

I think it shouldn't do that automatically, because the default themes do not support a dark mode out of the box. _No_ theme will support multiple appearances without being specifically designed to do so.

If a theme supports multiple appearances, the "just use the platform appearance" behavior only requires a single line of code, which also takes care of macOS's "auto" appearance:


    var stage = new Stage();
    stage.appearanceProperty().bind(Platform.getPreferences().appearanceProperty());


By the way, `Stage.appearance` doesn't really have anything to do with `StyleTheme`. A style theme is the proposed collection of stylesheets that define the look of a JavaFX application, while the stage appearance _only_ determines the appearance of native window decorations.

On Windows, the dark appearance adds the `DWMA_USE_IMMERSIVE_DARK_MODE` flag to the native window (see [Support Dark and Light themes in Win32 apps](https://learn.microsoft.com/en-us/windows/apps/desktop/modernize/apply-windows-themes)), on macOS it chooses the "DarkAqua" appearance instead of the "Aqua" appearance (see [Choosing a Specific Appearance for Your macOS App](https://developer.apple.com/documentation/appkit/nsappearancecustomization/choosing_a_specific_appearance_for_your_macos_app)). There is no middle ground, it's either dark or it's not. Therefore I think the enumeration is a useful representation of this distinction.

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