FreeDesktop/x11 implementation

src/Avalonia.FreeDesktop/DBusPlatformSettings.cs

@@ -0,0 +1,74 @@
+using System;
+using System.Threading.Tasks;
+using Avalonia.Logging;
+using Avalonia.Platform;
+
+namespace Avalonia.FreeDesktop;
+
+internal class DBusPlatformSettings : DefaultPlatformSettings
+{
+    private readonly IDBusSettings? _settings;
+    private PlatformColorValues? _lastColorValues;
+
+    public DBusPlatformSettings()
+    {
+        _settings = DBusHelper.TryInitialize()?
+            .CreateProxy<IDBusSettings>("org.freedesktop.portal.Desktop", "/org/freedesktop/portal/desktop");
+
+        if (_settings is not null)
+        {
+            _ = _settings.WatchSettingChangedAsync(SettingsChangedHandler);
+
+            _ = TryGetInitialValue();
+        }
+    }
+
+    public override PlatformColorValues GetColorValues()
+    {
+        return _lastColorValues ?? base.GetColorValues();
+    }
+
+    private async Task TryGetInitialValue()
+    {
+        var colorSchemeTask = _settings!.ReadAsync("org.freedesktop.appearance", "color-scheme");
+        if (colorSchemeTask.Status == TaskStatus.RanToCompletion)
+        {
+            _lastColorValues = GetColorValuesFromSetting(colorSchemeTask.Result);
+        }
+        else
+        {
+            try
+            {
+                var value = await colorSchemeTask;
+                _lastColorValues = GetColorValuesFromSetting(value);
+                OnColorValuesChanged(_lastColorValues.Value);
+            }
+            catch (Exception ex)
+            {
+                _lastColorValues = base.GetColorValues();
+                Logger.TryGet(LogEventLevel.Error, LogArea.FreeDesktopPlatform)?.Log(this, "Unable to get setting value", ex);
+            }
+        }
+    }
+    
+    private void SettingsChangedHandler((string @namespace, string key, object value) tuple)
+    {
+        if (tuple.@namespace == "org.freedesktop.appearance"
+            && tuple.key == "color-scheme")
+        {
+            /*
+            <member>0: No preference</member>
+            <member>1: Prefer dark appearance</member>
+            <member>2: Prefer light appearance</member>
+            */
+            _lastColorValues = GetColorValuesFromSetting(tuple.value);
+            OnColorValuesChanged(_lastColorValues.Value);
+        }
+    }
+    
+    private static PlatformColorValues GetColorValuesFromSetting(object value)
+    {
+        var isDark = value?.ToString() == "1";
+        return new PlatformColorValues(isDark ? PlatformThemeVariant.Dark : PlatformThemeVariant.Light);
+    }
+}

src/Avalonia.FreeDesktop/DBusSettings.cs

@@ -0,0 +1,16 @@
+using System;
+using System.Collections.Generic;
+using System.Threading.Tasks;
+using Tmds.DBus;
+
+namespace Avalonia.FreeDesktop;
+
+[DBusInterface("org.freedesktop.portal.Settings")]
+internal interface IDBusSettings : IDBusObject
+{
+    Task<(string @namespace, IDictionary<string, object>)> ReadAllAsync(string[] namespaces);
+
+    Task<object> ReadAsync(string @namespace, string key);
+
+    Task<IDisposable> WatchSettingChangedAsync(Action<(string @namespace, string key, object value)> handler, Action<Exception>? onError = null);
+}

src/Avalonia.X11/X11Platform.cs

@@ -80,7 +80,7 @@ namespace Avalonia.X11
                 .Bind<IKeyboardDevice>().ToFunc(() => KeyboardDevice)
                 .Bind<ICursorFactory>().ToConstant(new X11CursorFactory(Display))
                 .Bind<IClipboard>().ToConstant(new X11Clipboard(this))
-                .Bind<IPlatformSettings>().ToSingleton<DefaultPlatformSettings>()
+                .Bind<IPlatformSettings>().ToSingleton<DBusPlatformSettings>()
                 .Bind<IPlatformIconLoader>().ToConstant(new X11IconLoader())
                 .Bind<IMountedVolumeInfoProvider>().ToConstant(new LinuxMountedVolumeInfoProvider())
                 .Bind<IPlatformLifetimeEventsImpl>().ToConstant(new X11PlatformLifetimeEvents(this));

src/Avalonia.X11/X11Window.cs

@@ -1225,6 +1225,8 @@ namespace Avalonia.X11
         public WindowTransparencyLevel TransparencyLevel =>
             _transparencyHelper?.CurrentLevel ?? WindowTransparencyLevel.None;
 
+        public void SetFrameThemeVariant(PlatformThemeVariant themeVariant) { }
+
         public AcrylicPlatformCompensationLevels AcrylicCompensationLevels { get; } = new AcrylicPlatformCompensationLevels(1, 0.8, 0.8);
 
         public bool NeedsManagedDecorations => false;

src/Linux/Avalonia.LinuxFramebuffer/FramebufferToplevelImpl.cs

@@ -83,6 +83,8 @@ namespace Avalonia.LinuxFramebuffer
 
         public WindowTransparencyLevel TransparencyLevel { get; private set; }
 
+        public void SetFrameThemeVariant(PlatformThemeVariant themeVariant) { }
+
         public AcrylicPlatformCompensationLevels AcrylicCompensationLevels { get; } = new AcrylicPlatformCompensationLevels(1, 1, 1);
     }
 }