protected override void OnRender(System.Windows.Media.DrawingContext drawingContext)
{
base.OnRender(drawingContext);
var root = Window.GetWindow(this);
var adornerLayer = AdornerLayer.GetAdornerLayer(AdornedElement);
var presentationSource = PresentationSource.FromVisual(adornerLayer);
Matrix transformToDevice = presentationSource.CompositionTarget.TransformToDevice;
var sizeInPixels = transformToDevice.Transform((Vector)adornerLayer.RenderSize);
RenderTargetBitmap rtb = new RenderTargetBitmap((int)(sizeInPixels.X), (int)(sizeInPixels.Y), 96, 96, PixelFormats.Default);
var oldEffect = root.Effect;
var oldVisibility = AdornedElement.Visibility;
root.Effect = new BlurEffect();
AdornedElement.SetCurrentValue(FrameworkElement.VisibilityProperty, Visibility.Hidden);
rtb.Render(root);
AdornedElement.SetCurrentValue(FrameworkElement.VisibilityProperty, oldVisibility);
root.Effect = oldEffect;
drawingContext.DrawImage(rtb, adornerLayer.TransformToVisual(AdornedElement).TransformBounds(new Rect(adornerLayer.RenderSize)));
drawingContext.DrawRectangle(new SolidColorBrush(Color.FromArgb(22, 0, 0, 0)), null, adornerLayer.TransformToVisual(AdornedElement).TransformBounds(new Rect(adornerLayer.RenderSize)));
drawingContext.DrawRectangle(new VisualBrush(AdornedElement)
{
AlignmentX = AlignmentX.Left, TileMode = TileMode.None, Stretch = Stretch.None
},
null,
AdornedElement.RenderTransform.TransformBounds(new Rect(AdornedElement.RenderSize)));
}