Opacity Masks in WPF / Silverlight

Discovered the opacitymask property today! If you want to be able to apply a gradient brush to an object in one direction, but change the opacity in another (think blending out objects horizontally against a background with a gradient running vertically) then you can do it like this…

<Rectangle>
<Rectangle.OpacityMask>
<LinearGradientBrush EndPoint="0.0,0.5" StartPoint="1,0.5">
<GradientStop Color="#FF000000" Offset="0"/>
<GradientStop Color="#00FFFFFF" Offset="1"/>
</LinearGradientBrush>
</Rectangle.OpacityMask>
<Rectangle.Fill>
<LinearGradientBrush EndPoint="0.5,1" StartPoint="0.5,0">
<GradientStop Color="#FF03D3E0"/>
<GradientStop Color="#FF006A74" Offset="1"/>
</LinearGradientBrush>
</Rectangle.Fill>
</Rectangle>