Drive Win32 composition effects from RenderTargetSceneInfo on the render thread

api/Avalonia.nupkg.xml

@@ -43,6 +43,12 @@
     <Left>baseline/Avalonia/lib/net10.0/Avalonia.Base.dll</Left>
     <Right>current/Avalonia/lib/net10.0/Avalonia.Base.dll</Right>
   </Suppression>
+  <Suppression>
+    <DiagnosticId>CP0002</DiagnosticId>
+    <Target>M:Avalonia.Platform.IRenderTarget.RenderTargetSceneInfo.#ctor(Avalonia.PixelSize,System.Double,Avalonia.Size,Avalonia.Rendering.Composition.CompositionTransparencyLevel)</Target>
+    <Left>baseline/Avalonia/lib/net10.0/Avalonia.Base.dll</Left>
+    <Right>current/Avalonia/lib/net10.0/Avalonia.Base.dll</Right>
+  </Suppression>
   <Suppression>
     <DiagnosticId>CP0002</DiagnosticId>
     <Target>M:Avalonia.Platform.IRenderTarget.RenderTargetSceneInfo.#ctor(Avalonia.PixelSize,System.Double,Avalonia.Size)</Target>
@@ -55,6 +61,12 @@
     <Left>baseline/Avalonia/lib/net10.0/Avalonia.Base.dll</Left>
     <Right>current/Avalonia/lib/net10.0/Avalonia.Base.dll</Right>
   </Suppression>
+  <Suppression>
+    <DiagnosticId>CP0002</DiagnosticId>
+    <Target>M:Avalonia.Platform.IRenderTarget.RenderTargetSceneInfo.Deconstruct(Avalonia.PixelSize@,System.Double@,Avalonia.Size@,Avalonia.Rendering.Composition.CompositionTransparencyLevel@)</Target>
+    <Left>baseline/Avalonia/lib/net10.0/Avalonia.Base.dll</Left>
+    <Right>current/Avalonia/lib/net10.0/Avalonia.Base.dll</Right>
+  </Suppression>
   <Suppression>
     <DiagnosticId>CP0002</DiagnosticId>
     <Target>M:Avalonia.Platform.IRenderTarget.RenderTargetSceneInfo.Deconstruct(Avalonia.PixelSize@,System.Double@,Avalonia.Size@)</Target>
@@ -127,6 +139,12 @@
     <Left>baseline/Avalonia/lib/net8.0/Avalonia.Base.dll</Left>
     <Right>current/Avalonia/lib/net8.0/Avalonia.Base.dll</Right>
   </Suppression>
+  <Suppression>
+    <DiagnosticId>CP0002</DiagnosticId>
+    <Target>M:Avalonia.Platform.IRenderTarget.RenderTargetSceneInfo.#ctor(Avalonia.PixelSize,System.Double,Avalonia.Size,Avalonia.Rendering.Composition.CompositionTransparencyLevel)</Target>
+    <Left>baseline/Avalonia/lib/net8.0/Avalonia.Base.dll</Left>
+    <Right>current/Avalonia/lib/net8.0/Avalonia.Base.dll</Right>
+  </Suppression>
   <Suppression>
     <DiagnosticId>CP0002</DiagnosticId>
     <Target>M:Avalonia.Platform.IRenderTarget.RenderTargetSceneInfo.#ctor(Avalonia.PixelSize,System.Double,Avalonia.Size)</Target>
@@ -139,6 +157,12 @@
     <Left>baseline/Avalonia/lib/net8.0/Avalonia.Base.dll</Left>
     <Right>current/Avalonia/lib/net8.0/Avalonia.Base.dll</Right>
   </Suppression>
+  <Suppression>
+    <DiagnosticId>CP0002</DiagnosticId>
+    <Target>M:Avalonia.Platform.IRenderTarget.RenderTargetSceneInfo.Deconstruct(Avalonia.PixelSize@,System.Double@,Avalonia.Size@,Avalonia.Rendering.Composition.CompositionTransparencyLevel@)</Target>
+    <Left>baseline/Avalonia/lib/net8.0/Avalonia.Base.dll</Left>
+    <Right>current/Avalonia/lib/net8.0/Avalonia.Base.dll</Right>
+  </Suppression>
   <Suppression>
     <DiagnosticId>CP0002</DiagnosticId>
     <Target>M:Avalonia.Platform.IRenderTarget.RenderTargetSceneInfo.Deconstruct(Avalonia.PixelSize@,System.Double@,Avalonia.Size@)</Target>

src/Avalonia.Base/Platform/IRenderTarget.cs

@@ -33,7 +33,10 @@ public interface IRenderTarget : IDisposable
         /// </summary>
         PlatformRenderTargetState PlatformRenderTargetState => PlatformRenderTargetState.Ready;
 
-        public record struct RenderTargetSceneInfo(PixelSize Size, double Scaling, Size LogicalSize, CompositionTransparencyLevel TransparencyLevel)
+        // TopLevelSpecificSceneInfo is an opaque immutable object provided by the platform's
+        // ITopLevelImpl.TopLevelSpecificSceneInfo.
+        public record struct RenderTargetSceneInfo(PixelSize Size, double Scaling, Size LogicalSize,
+            CompositionTransparencyLevel TransparencyLevel, object? TopLevelSpecificSceneInfo = null)
         {
             public RenderTargetSceneInfo(PixelSize size, double scaling, CompositionTransparencyLevel transparencyLevel) : this(size, scaling, size.ToSize(scaling), transparencyLevel)
             {

src/Avalonia.Base/Rendering/Composition/Server/ServerCompositionTarget.cs

@@ -205,7 +205,9 @@ public void Render()
             try
             {
                 renderTargetContext =
-                    _renderTarget.CreateDrawingContext(new(PixelSize, Scaling, Size, TransparencyLevel), out properties);
+                    _renderTarget.CreateDrawingContext(
+                        new(PixelSize, Scaling, Size, TransparencyLevel, TopLevelSpecificSceneInfo),
+                        out properties);
             }
             catch (RenderTargetNotReadyException)
             {

src/Avalonia.Base/composition-schema.xml

@@ -11,6 +11,7 @@
     <Manual Name="Avalonia.Media.IImmutableBrush" Passthrough="true"/>
     <Manual Name="Avalonia.Media.IImmutableEffect" Passthrough="true"/>
     <Manual Name="Avalonia.Media.Immutable.ImmutableDashStyle" Passthrough="true"/>
+    <Manual Name="object" Passthrough="true"/>
     <Manual Name="CompositionSurface" />
     <Manual Name="CompositionDrawingSurface" />
     <Object Name="CompositionVisual" Abstract="true">
@@ -60,6 +61,7 @@
         <Property Name="Scaling" Type="double"/>
         <Property Name="Size" Type="Size" />
         <Property Name="TransparencyLevel" Type="CompositionTransparencyLevel" />
+        <Property Name="TopLevelSpecificSceneInfo" Type="object?" />
     </Object>
     <KeyFrameAnimation Name="Scalar" Type="float"/>
     <KeyFrameAnimation Name="Double" Type="double"/>

src/Avalonia.Controls/Platform/ITopLevelImpl.cs

@@ -76,6 +76,18 @@ public interface ITopLevelImpl : IOptionalFeatureProvider, IDisposable
         /// </summary>
         Action<WindowTransparencyLevel>? TransparencyLevelChanged { get; set; }
 
+        /// <summary>
+        /// Gets an opaque platform-specific object with extra information about the scene,
+        /// to be passed to the platform render target with each frame.
+        /// The object must be immutable; implementations must publish a new instance on change.
+        /// </summary>
+        object? TopLevelSpecificSceneInfo => null;
+
+        /// <summary>
+        /// Gets or sets a method called when <see cref="TopLevelSpecificSceneInfo"/> changes.
+        /// </summary>
+        Action<object?>? TopLevelSpecificSceneInfoChanged { get => null; set { } }
+
         /// <summary>
         /// Gets the compositor that's compatible with the toplevel
         /// </summary>

src/Avalonia.Controls/TopLevel.cs

@@ -223,6 +223,7 @@ internal TopLevel(ITopLevelImpl impl, IAvaloniaDependencyResolver? dependencyRes
 
             _source.Renderer.CompositionTarget.TransparencyLevel =
                 ToCompositionTransparencyLevel(_actualTransparencyLevel);
+            _source.Renderer.CompositionTarget.TopLevelSpecificSceneInfo = impl.TopLevelSpecificSceneInfo;
 
 
             _accessKeyHandler = TryGetService<IAccessKeyHandler>(dependencyResolver);
@@ -240,6 +241,7 @@ internal TopLevel(ITopLevelImpl impl, IAvaloniaDependencyResolver? dependencyRes
             impl.Resized = HandleResized;
             impl.ScalingChanged += HandleScalingChanged;
             impl.TransparencyLevelChanged = HandleTransparencyLevelChanged;
+            impl.TopLevelSpecificSceneInfoChanged = HandleTopLevelSpecificSceneInfoChanged;
 
             CreatePlatformImplBinding(TransparencyLevelHintProperty, hint => PlatformImpl.SetTransparencyLevelHint(hint ?? Array.Empty<WindowTransparencyLevel>()));
 
@@ -771,6 +773,11 @@ private void HandleTransparencyLevelChanged(WindowTransparencyLevel transparency
                 ToCompositionTransparencyLevel(transparencyLevel);
         }
 
+        private void HandleTopLevelSpecificSceneInfoChanged(object? sceneInfo)
+        {
+            Renderer.CompositionTarget.TopLevelSpecificSceneInfo = sceneInfo;
+        }
+
         protected override void OnApplyTemplate(TemplateAppliedEventArgs e)
         {
             base.OnApplyTemplate(e);

src/Windows/Avalonia.Win32/DComposition/DirectCompositedWindowSurface.cs

@@ -16,7 +16,6 @@ internal class DirectCompositedWindowSurface : IDirect3D11TexturePlatformSurface
     private readonly EglGlPlatformSurface.IEglWindowGlPlatformSurfaceInfo _info;
     private readonly DirectCompositionShared _shared;
     private DirectCompositedWindow? _window;
-    private BlurEffect _blurEffect;
 
     public DirectCompositedWindowSurface(DirectCompositionShared shared, EglGlPlatformSurface.IEglWindowGlPlatformSurfaceInfo info)
     {
@@ -32,7 +31,6 @@ IDirect3D11TextureRenderTarget IDirect3D11TexturePlatformSurface.CreateRenderTar
     public IDirect3D11TextureRenderTarget2 CreateRenderTarget(IPlatformGraphicsContext context, IntPtr d3dDevice)
     {
         _window ??= new DirectCompositedWindow(_info, _shared);
-        SetBlur(_blurEffect);
 
         return new DirectCompositedWindowRenderTarget(context, d3dDevice, _shared, _window);
     }
@@ -43,14 +41,8 @@ public void Dispose()
         _window = null;
     }
 
-    // TODO: we can implement BlurEffect.GaussianBlur in with IDCompositionDevice3.CreateGaussianBlurEffect. 
+    // TODO: we can implement BlurEffect.GaussianBlur in with IDCompositionDevice3.CreateGaussianBlurEffect.
     public bool IsBlurSupported(BlurEffect effect) => effect == BlurEffect.None;
-
-    public void SetBlur(BlurEffect enable)
-    {
-        _blurEffect = enable;
-        // _window?.SetBlur(enable);
-    }
 }
 
 internal class DirectCompositedWindowRenderTarget : IDirect3D11TextureRenderTarget, IDirect3D11TextureRenderTarget2

src/Windows/Avalonia.Win32/IBlurHost.cs

@@ -12,6 +12,4 @@ internal enum BlurEffect
 internal interface ICompositionEffectsSurface
 {
     bool IsBlurSupported(BlurEffect effect);
-
-    void SetBlur(BlurEffect enable);
 }

src/Windows/Avalonia.Win32/Win32TopLevelSceneInfo.cs

@@ -0,0 +1,10 @@
+using Avalonia.Platform;
+
+namespace Avalonia.Win32;
+
+/// <summary>
+/// An immutable bag with Win32-specific per-frame scene information, published via
+/// <see cref="ITopLevelImpl.TopLevelSpecificSceneInfo"/> and consumed by render targets
+/// on the render thread.
+/// </summary>
+internal sealed record Win32TopLevelSceneInfo(PlatformThemeVariant ThemeVariant);

src/Windows/Avalonia.Win32/WinRT/Composition/WinUiCompositedWindow.cs

@@ -1,8 +1,11 @@
 using System;
+using System.Diagnostics;
 using System.Numerics;
 using System.Threading;
 using Avalonia.OpenGL.Egl;
+using Avalonia.Platform;
 using Avalonia.Reactive;
+using Avalonia.Rendering.Composition;
 using MicroCom.Runtime;
 
 namespace Avalonia.Win32.WinRT.Composition;
@@ -17,6 +20,7 @@ internal class WinUiCompositedWindow : IDisposable
     private readonly IVisual _blur;
     private readonly IVisual _visual;
     private PixelSize _size;
+    private BlurEffect? _appliedBlurEffect;
     private readonly ICompositionSurfaceBrush _surfaceBrush;
     private readonly ICompositionTarget _target;
 
@@ -80,18 +84,30 @@ public WinUiCompositedWindow(EglGlPlatformSurface.IEglWindowGlPlatformSurfaceInf
 
     public void SetSurface(ICompositionSurface surface) => _surfaceBrush.SetSurface(surface);
 
-    public void SetBlur(BlurEffect blurEffect)
+    // Called from the render thread with the transaction (SyncRoot) held, so effect changes
+    // are applied within the same composition batch as the frame they belong to.
+    public void ApplyEffects(CompositionTransparencyLevel transparencyLevel, PlatformThemeVariant themeVariant)
     {
-        lock (_shared.SyncRoot)
+        Debug.Assert(Monitor.IsEntered(_shared.SyncRoot));
+
+        var blurEffect = transparencyLevel switch
         {
-            _blur.SetIsVisible(blurEffect == BlurEffect.Acrylic
-                               || (blurEffect == BlurEffect.MicaLight && _micaLight == null) ||
-                               (blurEffect == BlurEffect.MicaDark && _micaDark == null) ?
-                1 :
-                0);
-            _micaLight?.SetIsVisible(blurEffect == BlurEffect.MicaLight ? 1 : 0);
-            _micaDark?.SetIsVisible(blurEffect == BlurEffect.MicaDark ? 1 : 0);
-        }
+            CompositionTransparencyLevel.AcrylicBlur => BlurEffect.Acrylic,
+            CompositionTransparencyLevel.Mica when themeVariant == PlatformThemeVariant.Dark => BlurEffect.MicaDark,
+            CompositionTransparencyLevel.Mica => BlurEffect.MicaLight,
+            _ => BlurEffect.None
+        };
+        if (_appliedBlurEffect == blurEffect)
+            return;
+
+        _blur.SetIsVisible(blurEffect == BlurEffect.Acrylic
+                           || (blurEffect == BlurEffect.MicaLight && _micaLight == null) ||
+                           (blurEffect == BlurEffect.MicaDark && _micaDark == null) ?
+            1 :
+            0);
+        _micaLight?.SetIsVisible(blurEffect == BlurEffect.MicaLight ? 1 : 0);
+        _micaDark?.SetIsVisible(blurEffect == BlurEffect.MicaDark ? 1 : 0);
+        _appliedBlurEffect = blurEffect;
     }
 
     public IDisposable BeginTransaction()
@@ -102,14 +118,13 @@ public IDisposable BeginTransaction()
 
     public void ResizeIfNeeded(PixelSize size)
     {
-        lock (_shared.SyncRoot)
+        Debug.Assert(Monitor.IsEntered(_shared.SyncRoot));
+
+        if (_size != size)
         {
-            if (_size != size)
-            {
-                _visual.SetSize(new Vector2(size.Width, size.Height));
-                _compositionRoundedRectangleGeometry?.SetSize(new Vector2(size.Width, size.Height));
-                _size = size;
-            }
+            _visual.SetSize(new Vector2(size.Width, size.Height));
+            _compositionRoundedRectangleGeometry?.SetSize(new Vector2(size.Width, size.Height));
+            _size = size;
         }
     }
 }

src/Windows/Avalonia.Win32/WinRT/Composition/WinUiCompositedWindowSurface.cs

@@ -14,7 +14,6 @@ internal class WinUiCompositedWindowSurface : IDirect3D11TexturePlatformSurface,
         private readonly WinUiCompositionShared _shared;
         private readonly EglGlPlatformSurface.IEglWindowGlPlatformSurfaceInfo _info;
         private WinUiCompositedWindow? _window;
-        private BlurEffect _blurEffect;
 
         public WinUiCompositedWindowSurface(WinUiCompositionShared shared, EglGlPlatformSurface.IEglWindowGlPlatformSurfaceInfo info)
         {
@@ -32,7 +31,6 @@ public IDirect3D11TextureRenderTarget2 CreateRenderTarget(IPlatformGraphicsConte
             var cornerRadius = AvaloniaLocator.Current.GetService<Win32PlatformOptions>()
                 ?.WinUICompositionBackdropCornerRadius;
             _window ??= new WinUiCompositedWindow(_info, _shared, cornerRadius);
-            _window.SetBlur(_blurEffect);
 
             return new WinUiCompositedWindowRenderTarget(context, _window, d3dDevice, _shared.Compositor);
         }
@@ -51,12 +49,6 @@ public void Dispose()
             BlurEffect.MicaDark => Win32Platform.WindowsVersion >= WinUiCompositionShared.MinHostBackdropVersion,
             _ => false
         };
-
-        public void SetBlur(BlurEffect enable)
-        {
-            _blurEffect = enable;
-            _window?.SetBlur(enable);
-        }
     }
 
     internal class WinUiCompositedWindowRenderTarget : IDirect3D11TextureRenderTarget, IDirect3D11TextureRenderTarget2
@@ -171,6 +163,9 @@ public unsafe IDirect3D11TextureRenderTargetRenderSession BeginDraw(
                 var size = sceneInfo.Size;
                 var scale = sceneInfo.Scaling;
                 _window.ResizeIfNeeded(size);
+                _window.ApplyEffects(sceneInfo.TransparencyLevel,
+                    (sceneInfo.TopLevelSpecificSceneInfo as Win32TopLevelSceneInfo)?.ThemeVariant ??
+                    PlatformThemeVariant.Light);
                 _window.SetSurface(_surface);
 
                 void* pTexture;

src/Windows/Avalonia.Win32/WindowImpl.cs

@@ -118,6 +118,7 @@ internal partial class WindowImpl : IWindowImpl, EglGlPlatformSurface.IEglWindow
         private static POINTER_INFO[]? s_historyInfos;
         private static MOUSEMOVEPOINT[]? s_mouseHistoryInfos;
         private PlatformThemeVariant _currentThemeVariant;
+        private Win32TopLevelSceneInfo _sceneInfo = new(PlatformThemeVariant.Light);
 
         public WindowImpl()
         {
@@ -216,6 +217,10 @@ internal IInputRoot Owner
 
         public Action<WindowTransparencyLevel>? TransparencyLevelChanged { get; set; }
 
+        public object? TopLevelSpecificSceneInfo => _sceneInfo;
+
+        public Action<object?>? TopLevelSpecificSceneInfoChanged { get; set; }
+
         public Thickness BorderThickness
         {
             get
@@ -437,43 +442,29 @@ private bool IsSupported(WindowTransparencyLevel level)
             return false;
         }
 
+        // The composition effects themselves are applied by the render target on the render thread,
+        // based on the transparency level and theme variant it receives with RenderTargetSceneInfo.
+        // Here we only adjust the DWM window attributes that have to be set from the UI thread.
+
         private bool SetTransparencyTransparent()
         {
-            if (CompositionEffectsSurface is { } surface)
-            {
-                surface.SetBlur(BlurEffect.None);
+            if (CompositionEffectsSurface is not null)
                 return true;
-            }
-            else
-            {
-                return SetLegacyTransparency(true);
-            }
+
+            return SetLegacyTransparency(true);
         }
 
         private bool SetTransparencyAcrylicBlur()
         {
             SetUseHostBackdropBrush(true);
             SetLegacyTransparency(false);
-
-            CompositionEffectsSurface!.SetBlur(BlurEffect.Acrylic);
             return true;
         }
 
-        /// <summary>
-        /// Sets the transparency mica
-        /// </summary>
-        /// <exception cref="ArgumentOutOfRangeException"></exception>
         private bool SetTransparencyMica()
         {
             SetUseHostBackdropBrush(false);
             SetLegacyTransparency(false);
-
-            CompositionEffectsSurface!.SetBlur(_currentThemeVariant switch
-            {
-                PlatformThemeVariant.Light => BlurEffect.MicaLight,
-                PlatformThemeVariant.Dark => BlurEffect.MicaDark,
-                _ => throw new ArgumentOutOfRangeException()
-            });
             return true;
         }
 
@@ -951,6 +942,11 @@ private void EnsureTopmost()
         public unsafe void SetFrameThemeVariant(PlatformThemeVariant? themeVariant)
         {
             _currentThemeVariant = themeVariant ?? Win32Platform.Instance.PlatformSettings.GetColorValues().ThemeVariant;
+            if (_sceneInfo.ThemeVariant != _currentThemeVariant)
+            {
+                _sceneInfo = new Win32TopLevelSceneInfo(_currentThemeVariant);
+                TopLevelSpecificSceneInfoChanged?.Invoke(_sceneInfo);
+            }
             if (Win32Platform.WindowsVersion.Build >= 22000)
             {
                 var pvUseBackdropBrush = _currentThemeVariant == PlatformThemeVariant.Dark ? 1 : 0;