windows.ui.composition compatible with acrylic blur setting.

src/Windows/Avalonia.Win32/Composition/CompositionEglGlPlatformSurface.cs

@@ -6,7 +6,7 @@ using Windows.UI.Composition.Interop;
 
 namespace Avalonia.Win32
 {
-    public class CompositionEglGlPlatformSurface : EglGlPlatformSurfaceBase
+    internal class CompositionEglGlPlatformSurface : EglGlPlatformSurfaceBase
     {
         private readonly EglDisplay _display;
         private readonly EglContext _context;
@@ -21,9 +21,11 @@ namespace Avalonia.Win32
             _info = info;
         }
 
-        public void AttachToCompositionTree(IntPtr hwnd)
+        public IBlurHost AttachToCompositionTree(IntPtr hwnd)
         {
-            _surfaceInterop = CompositionHost.Instance.InitialiseWindowCompositionTree(hwnd, out _surface);
+            _surfaceInterop = CompositionHost.Instance.InitialiseWindowCompositionTree(hwnd, out _surface, out var blurHost);
+
+            return blurHost;
         }
 
         public override IGlPlatformSurfaceRenderTarget CreateGlRenderTarget()

src/Windows/Avalonia.Win32/Composition/CompositionHost.cs

@@ -7,6 +7,26 @@ using WinRT;
 
 namespace Avalonia.Win32
 {
+    internal interface IBlurHost
+    {
+        void SetBlur(bool enabled);
+    }
+
+    internal class CompositionBlurHost : IBlurHost
+    {
+        Windows.UI.Composition.Visual _blurVisual;
+
+        public CompositionBlurHost(Windows.UI.Composition.Visual blurVisual)
+        {
+            _blurVisual = blurVisual;
+        }
+
+        public void SetBlur(bool enabled)
+        {
+            _blurVisual.IsVisible = enabled;
+        }
+    }
+
     class CompositionHost
     {
         internal enum DISPATCHERQUEUE_THREAD_APARTMENTTYPE
@@ -61,7 +81,7 @@ namespace Avalonia.Win32
             _graphicsDevice = interop.CreateGraphicsDevice(display.GetDirect3DDevice());
         }
 
-        public ICompositionDrawingSurfaceInterop InitialiseWindowCompositionTree(IntPtr hwnd, out Windows.UI.Composition.Visual surfaceVisual)
+        public ICompositionDrawingSurfaceInterop InitialiseWindowCompositionTree(IntPtr hwnd, out Windows.UI.Composition.Visual surfaceVisual, out IBlurHost blurHost)
         {
             var target = CreateDesktopWindowTarget(hwnd);
 
@@ -84,6 +104,8 @@ namespace Avalonia.Win32
 
             var blur = CreateBlur();
 
+            blurHost = new CompositionBlurHost(blur);
+
             container.Children.InsertAtTop(blur);
 
             var visuals = target.Root.As<ContainerVisual>().Children;

src/Windows/Avalonia.Win32/WindowImpl.cs

@@ -47,6 +47,7 @@ namespace Avalonia.Win32
         private Thickness _offScreenMargin;
         private double _extendTitleBarHint = -1;
         private bool _isUsingComposition;
+        private IBlurHost _blurHost;
 
 #if USE_MANAGED_DRAG
         private readonly ManagedWindowResizeDragHelper _managedDrag;
@@ -114,7 +115,7 @@ namespace Avalonia.Win32
                 if (_isUsingComposition)
                 {
                     var cgl = new CompositionEglGlPlatformSurface(Win32GlManager.EglFeature.DeferredContext, this);
-                    cgl.AttachToCompositionTree(_hwnd);
+                    _blurHost = cgl.AttachToCompositionTree(_hwnd);
 
                     _gl = cgl;
 
@@ -341,54 +342,63 @@ namespace Avalonia.Win32
 
         private WindowTransparencyLevel Win10EnableBlur(WindowTransparencyLevel transparencyLevel)
         {
-            bool canUseAcrylic = Win32Platform.WindowsVersion.Major > 10 || Win32Platform.WindowsVersion.Build >= 19628;
-
-            var accent = new AccentPolicy();
-            var accentStructSize = Marshal.SizeOf(accent);
-
-            if (transparencyLevel == WindowTransparencyLevel.AcrylicBlur && !canUseAcrylic)
+            if (_isUsingComposition)
             {
-                transparencyLevel = WindowTransparencyLevel.Blur;
-            }
+                _blurHost?.SetBlur(transparencyLevel >= WindowTransparencyLevel.Blur);
 
-            switch (transparencyLevel)
+                return transparencyLevel;
+            }
+            else
             {
-                default:
-                case WindowTransparencyLevel.None:
-                    accent.AccentState = AccentState.ACCENT_DISABLED;
-                    break;
+                bool canUseAcrylic = Win32Platform.WindowsVersion.Major > 10 || Win32Platform.WindowsVersion.Build >= 19628;
 
-                case WindowTransparencyLevel.Transparent:
-                    accent.AccentState = AccentState.ACCENT_ENABLE_TRANSPARENTGRADIENT;
-                    break;
+                var accent = new AccentPolicy();
+                var accentStructSize = Marshal.SizeOf(accent);
 
-                case WindowTransparencyLevel.Blur:
-                    accent.AccentState = AccentState.ACCENT_ENABLE_BLURBEHIND;
-                    break;
+                if (transparencyLevel == WindowTransparencyLevel.AcrylicBlur && !canUseAcrylic)
+                {
+                    transparencyLevel = WindowTransparencyLevel.Blur;
+                }
 
-                case WindowTransparencyLevel.AcrylicBlur:
-                case (WindowTransparencyLevel.AcrylicBlur + 1): // hack-force acrylic.
-                    accent.AccentState = AccentState.ACCENT_ENABLE_ACRYLIC;
-                    transparencyLevel = WindowTransparencyLevel.AcrylicBlur;
-                    break;
-            }
+                switch (transparencyLevel)
+                {
+                    default:
+                    case WindowTransparencyLevel.None:
+                        accent.AccentState = AccentState.ACCENT_DISABLED;
+                        break;
+
+                    case WindowTransparencyLevel.Transparent:
+                        accent.AccentState = AccentState.ACCENT_ENABLE_TRANSPARENTGRADIENT;
+                        break;
+
+                    case WindowTransparencyLevel.Blur:
+                        accent.AccentState = AccentState.ACCENT_ENABLE_BLURBEHIND;
+                        break;
+
+                    case WindowTransparencyLevel.AcrylicBlur:
+                    case (WindowTransparencyLevel.AcrylicBlur + 1): // hack-force acrylic.
+                        accent.AccentState = AccentState.ACCENT_ENABLE_ACRYLIC;
+                        transparencyLevel = WindowTransparencyLevel.AcrylicBlur;
+                        break;
+                }
 
-            accent.AccentFlags = 2;
-            accent.GradientColor = 0x01000000;
+                accent.AccentFlags = 2;
+                accent.GradientColor = 0x01000000;
 
-            var accentPtr = Marshal.AllocHGlobal(accentStructSize);
-            Marshal.StructureToPtr(accent, accentPtr, false);
+                var accentPtr = Marshal.AllocHGlobal(accentStructSize);
+                Marshal.StructureToPtr(accent, accentPtr, false);
 
-            var data = new WindowCompositionAttributeData();
-            data.Attribute = WindowCompositionAttribute.WCA_ACCENT_POLICY;
-            data.SizeOfData = accentStructSize;
-            data.Data = accentPtr;
+                var data = new WindowCompositionAttributeData();
+                data.Attribute = WindowCompositionAttribute.WCA_ACCENT_POLICY;
+                data.SizeOfData = accentStructSize;
+                data.Data = accentPtr;
 
-            SetWindowCompositionAttribute(_hwnd, ref data);
+                SetWindowCompositionAttribute(_hwnd, ref data);
 
-            Marshal.FreeHGlobal(accentPtr);
+                Marshal.FreeHGlobal(accentPtr);
 
-            return transparencyLevel;
+                return transparencyLevel;
+            }
         }
 
         public IEnumerable<object> Surfaces => new object[] { Handle, _gl, _framebuffer };