fix blur coordinate error

QuickLook/Controls/GlassLayer/ElementCoordinateConverter.cs

@@ -0,0 +1,47 @@
+// Copyright © 2017 Paddy Xu
+// 
+// This file is part of QuickLook program.
+// 
+// This program is free software: you can redistribute it and/or modify
+// it under the terms of the GNU General Public License as published by
+// the Free Software Foundation, either version 3 of the License, or
+// (at your option) any later version.
+// 
+// This program is distributed in the hope that it will be useful,
+// but WITHOUT ANY WARRANTY; without even the implied warranty of
+// MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+// GNU General Public License for more details.
+// 
+// You should have received a copy of the GNU General Public License
+// along with this program.  If not, see <http://www.gnu.org/licenses/>.
+
+using System;
+using System.Globalization;
+using System.Windows;
+using System.Windows.Data;
+
+namespace QuickLook.Controls.GlassLayer
+{
+    public sealed class ElementCoordinateConverter : DependencyObject, IValueConverter
+    {
+        public object Convert(object value, Type targetType, object parameter, CultureInfo culture)
+        {
+            var glass = (GlassLayer) value;
+
+            if (glass?.BlurredElement == null)
+                return null;
+
+            var target = glass.BlurredElement;
+
+            var trans = glass.TransformToVisual(target);
+            var p = trans.Transform(new Point(0, 0));
+
+            return new Rect {X = p.X, Y = p.Y, Width = glass.ActualWidth, Height = glass.ActualHeight};
+        }
+
+        public object ConvertBack(object value, Type targetType, object parameter, CultureInfo culture)
+        {
+            throw new NotImplementedException();
+        }
+    }
+}

QuickLook/Controls/GlassLayer/GlassLayer.xaml

@@ -7,6 +7,9 @@
              mc:Ignorable="d"
              x:Name="glassLayer"
              d:DesignHeight="300" d:DesignWidth="300">
+    <UserControl.Resources>
+        <local:ElementCoordinateConverter x:Key="ElementCoordinateConverter" />
+    </UserControl.Resources>
     <Grid>
         <Rectangle Panel.ZIndex="100" Visibility="{Binding ElementName=glassLayer, Path=NoiseVisibility}">
             <Rectangle.Fill>
@@ -29,9 +32,10 @@
                                               Shader="pack://application:,,,/QuickLook;component/Controls/GlassLayer/GaussianBlur.ps" />
                 </Grid.Effect>
                 <Grid.Background>
-                    <VisualBrush Visual="{Binding ElementName=glassLayer, Path=BlurredElement}" AlignmentX="Left"
-                                 AlignmentY="Top"
-                                 Stretch="None" />
+                    <VisualBrush x:Name="brush" Visual="{Binding ElementName=glassLayer, Path=BlurredElement}"
+                                 Viewbox="{Binding ElementName=glassLayer, Converter={StaticResource ElementCoordinateConverter}}"
+                                 ViewboxUnits="Absolute"
+                                 AlignmentX="Left" AlignmentY="Top" Stretch="None" />
                 </Grid.Background>
                 <StackPanel />
             </Grid>

QuickLook/Controls/GlassLayer/GlassLayer.xaml.cs

@@ -17,6 +17,7 @@
 
 using System.Windows;
 using System.Windows.Controls;
+using System.Windows.Data;
 using System.Windows.Media;
 using QuickLook.Helpers;
 
@@ -35,6 +36,11 @@ namespace QuickLook.Controls.GlassLayer
             noiseBrush.Viewport = new Rect(new Size(
                 noiseBrush.ImageSource.Width / scale.Horizontal,
                 noiseBrush.ImageSource.Height / scale.Vertical));
+
+            LayoutUpdated += (sender, e) =>
+            {
+                BindingOperations.GetBindingExpressionBase(brush, TileBrush.ViewboxProperty)?.UpdateTarget();
+            };
         }
 
         #region public Visual BlurredElement

QuickLook/QuickLook.csproj

@@ -111,6 +111,7 @@
     </Compile>
     <Compile Include="Controls\BusyDecorator\ISpinable.cs" />
     <Compile Include="Controls\BusyDecorator\SpinIcon.cs" />
+    <Compile Include="Controls\GlassLayer\ElementCoordinateConverter.cs" />
     <Compile Include="Controls\GlassLayer\GaussianBlurEffect.cs" />
     <Compile Include="Controls\GlassLayer\GlassLayer.xaml.cs">
       <DependentUpon>GlassLayer.xaml</DependentUpon>