Add method to get "base" system UI color and system theme change callback.

[bruvzg]

Implements DisplayServer.get_base_color to get default control background color (on macOS and Windows).
Implements DisplayServer.set_system_theme_change_callback to set theme change callback (all platforms, except web, tested on Windows 11, macOS 14.2.1, PopOS, Android 14 and iOS 17.2).

func _theme_upd():
	$ColorRectBack.color = DisplayServer.get_base_color()
	$ColorRectFront.color = DisplayServer.get_accent_color()

func _ready():
	DisplayServer.set_system_theme_change_callback(Callable(self, "_theme_upd"))
	_theme_upd()

Note: theme_change callback is triggered by any OS UI style related change, it's not necessarily mean that dark/light mode was switched or accent/base color changed.

[bruvzg]

Added theme change callback support for the rest of platforms (except web).

[Riteo]

@bruvzg

for Linux there's no standard "accent" color, maybe we can get something, but it will be at least DE specific.

There's an accent-color XDG Portal setting: https://flatpak.github.io/xdg-desktop-portal/docs/doc-org.freedesktop.portal.Settings.html

[bruvzg]

There's an accent-color XDG Portal setting: https://flatpak.github.io/xdg-desktop-portal/docs/doc-org.freedesktop.portal.Settings.html

This seems to be a new addition, so I'm not sure if any real DE support it, but since it's D-Bus we probably should try reading it anyway.

[m4gr3d]

Some minor feedback to address and the Android logic should be good to go!

[m4gr3d]

The Android section looks good!

[akien-mga]

Looks good to me!

I wonder if the "theme_change" methods/signals should be "system_theme_change" to make it clear that it's about the OS theme settings and not the Godot editor/project theme?

[bruvzg]

Renamed callback to system_theme_change and added in to Wayland DS.

[akien-mga]

Needs a rebase.

[Calinou]

Tested locally on Fedora 39 KDE X11, this returns a fully transparent color for both base and accent color (so nothing is visible):

extends Node2D

func _theme_upd():
	print("Updating theme")
	$ColorRectBack.color = DisplayServer.get_base_color()
	print($ColorRectBack.color)
	$ColorRectFront.color = DisplayServer.get_accent_color()
	print($ColorRectFront.color)

func _ready():
	DisplayServer.set_system_theme_change_callback(Callable(self, "_theme_upd"))
	_theme_upd()

I'm using the Breeze Dark theme. The theme switch callback works (it's called if I switch system themes), but colors are still fully transparent.

[bruvzg]

Tested locally on Fedora 39 KDE X11

Colors are supported only on macOS and Windows, there's no standard Linux API for this.

[akien-mga]

Thanks!