Strange behavior of DropShadowEffect
Yesterday, I spent the whole morning wrestling with WPF because an object I was re-implementing was appearing too blurry when compared to the existing native version. This was a basic label object, containing a picture and some text. Both the picture and the text were quite fuzzy, and don’t get me wrong, I am aware that WPF 3.5 SP1 still has issues with the text layout mechanism (the ideal layout compared to pixel-aligned layout). But this was much worse, as you can see in the screen grab:
You may notice that I am applying a drop shadow effect to the label, for some eye candy. And believe it or not, after a few hours of tweaking the XAML, and selectively disabling Visuals, I found the culprit to be the DropShadowEffect! As a designer, I would expect the DropShadowEffect to create a shadow behind my object, with the same shape as the object boundaries. Apparently this is not what the effect does, but rather overlays (or underlays?) a version of the source Visual, causing the blur effect. The solution to these types of problems is very simple: you just need to embed my Visual inside a Grid, so that you can add a Border with the same shape under my Visual. That Border will then have the effect applied to it, so basically I have moved any blurriness behind my label:
compared to 
You can easily test this behavior in Kaxaml, by entering the following XAML, and removing the Effect from the Border element:
<Border Background="Yellow" BorderBrush="Black" BorderThickness="1" Width="100" Height="26"> <Border.Effect> <DropShadowEffect/> </Border.Effect> <TextBlock Text="Label"/> </Border>
I would still like to understand the reason for this behavior of the DropShadowEffect, so if you have any explanation for it, do let me know.
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Not totally strange. When an effect is applied, your visual is rendered to an offscreen surface, and the shader is then applied to that texture.
One consequence of rendering to a texture is that ClearType is not applied and text falls back to anti-aliased mode (much thicker and blurry).
I had that problem myself and solved it just the same: overlay one visual with the drop shadow and another with the actual _crisp_ content.
Hopefully WPF 4 will make things better (I haven’t tested that yet, but you can selectively force ClearType where WPF would disable it by default – that is when rendering to an offscreen surface).
Hmm, I can understand there is a technical reason behind the behavior, but I think this is one of those cases which would warrant a change of behavior to avoid this trap. I don’t think anyone would want (or expect) this behavior by default.