add blur and avalonia surface visual ontop of blur.

samples/ControlCatalog/MainWindow.xaml

@@ -7,7 +7,8 @@
         xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
         xmlns:vm="clr-namespace:ControlCatalog.ViewModels"
         xmlns:v="clr-namespace:ControlCatalog.Views"
-        x:Class="ControlCatalog.MainWindow" WindowState="{Binding WindowState, Mode=TwoWay}" Background="{DynamicResource SystemControlPageBackgroundAltHighBrush}">
+        TransparencyLevelHint="Transparent"
+        x:Class="ControlCatalog.MainWindow" WindowState="{Binding WindowState, Mode=TwoWay}" Background="{x:Null}">
   <NativeMenu.Menu>
     <NativeMenu>
       <NativeMenuItem Header="File">

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

@@ -155,7 +155,7 @@ namespace Avalonia.Win32
 
             var gDevice = interop.CreateGraphicsDevice(display.GetDirect3DDevice());
 
-            var surface = gDevice.CreateDrawingSurface(new Windows.Foundation.Size(100, 100),
+            var surface = gDevice.CreateDrawingSurface(new Windows.Foundation.Size(0, 0),
                 Windows.Graphics.DirectX.DirectXPixelFormat.B8G8R8A8UIntNormalized,
                 Windows.Graphics.DirectX.DirectXAlphaMode.Premultiplied);
 
@@ -167,10 +167,13 @@ namespace Avalonia.Win32
 
             visual.RelativeSizeAdjustment = new System.Numerics.Vector2(1.0f, 1.0f);
             visual.Brush = brush;
+            //_target.Root = visual;
 
-            _target.Root = visual;
+            CreateBlur();
+
+            var visuals = _target.Root.As<ContainerVisual>().Children;
 
-            //CreateBlur();
+            visuals.InsertAtTop(visual);
 
             return surfaceInterop;
         }
@@ -196,7 +199,7 @@ namespace Avalonia.Win32
         void CreateCompositionRoot()
         {
             var root = _compositor.CreateContainerVisual();
-            root.RelativeSizeAdjustment = new System.Numerics.Vector2(1.0f, 1.0f);
+            root.RelativeSizeAdjustment = new System.Numerics.Vector2(1.0f, 1.0f);            
             //root.Offset = new System.Numerics.Vector3(0, 0, 0);
             _target.Root = root;
         }

src/Windows/Avalonia.Win32/Interop/UnmanagedMethods.cs

@@ -465,6 +465,7 @@ namespace Avalonia.Win32.Interop
             WS_VSCROLL = 0x200000,
             WS_EX_DLGMODALFRAME = 0x00000001,
             WS_EX_NOPARENTNOTIFY = 0x00000004,
+            WS_EX_NOREDIRECTIONBITMAP = 0x00200000,
             WS_EX_TOPMOST = 0x00000008,
             WS_EX_ACCEPTFILES = 0x00000010,
             WS_EX_TRANSPARENT = 0x00000020,

src/Windows/Avalonia.Win32/WindowImpl.cs

@@ -106,6 +106,10 @@ namespace Avalonia.Win32
             {
                 cgl.AttachToCompositionTree(_hwnd);
             }
+            else
+            {
+                CompositionHost.Instance.Initialize(_hwnd);
+            }
 
             Screen = new ScreenImpl();