Use proper preferences directories on desktop

Issue details

Currently, by default, libGDX Preferences are saved to ~/.prefs on Linux, which is nonstandard. The XDG Base Directory specification suggests that, to determine where to write configuration files to, programs should:

• First try the environment variable $XDG_CONFIG_HOME.
• If the environment variable is unset, default to $HOME/.config.

This standard serves to make the home directory cleaner, and normalize the way different programs save their configurations.

If this is adopted in libGDX, it would likely be necessary to check the (then legacy) ~/.prefs path in addition to the above two paths, as to not break existing configurations.

This is somewhat similar to #6367, but not the same as this pertains to preferences rather than local storage.

Please select the affected platforms

• Android
• iOS
• HTML/GWT
• Windows
• Linux
• MacOS

Thanks!

[lyze237]

While at it, it’d also be cool to save prefs in %appdata% on windows and in ~/Library/Preferences on macos. As those are also more recommended to save program preferences in.

[crykn]

I agree with @lyze237. The backend/platform can already be queried by calling Gdx.app.getType() and the OS can be determined via UIUtils, so there is no need for this class.

@tommyettinger: If it’s in the LWJGL3 backend, it can only be used from that backend, which requires a lot more work to actually use in the core part of an app.

Why would the core part of the app need to know where the preferences are saved on desktop? I think this is an implementation detail of Lwjgl3Preferences (as well as Lwjgl2Preferences and HeadlessPreferences) and doesn’t belong in core.

Also the Android and iOS stuff is unnecessary as those backends don’t save their preferences in certain directories, but rather use some platform specific stuff, and in addition, I don’t think System.getProperty("os.name") works on GWT.

@tommyettinger: Also, Lyze you’re saying two opposite things – there are already checks for the platform in core, but these checks don’t belong in core…?

I think what Lyze meant is that there are already checks in core (i.e., Gdx.app.getType(), UIUtils) and that is all well, but the additional methods (getUserDataDirectory, getUserConfigDirectory) don’t belong in core.