Transparent system color in gradient (WPF) - wpf

Question

How to achieve such effect in XAML:
<LinearGradientBrush x:Key="BrightSeparatorGradient" StartPoint="0.0, 0.5" EndPoint="1.0, 0.5">
<GradientStop Offset="0.0" Color="{StaticResource {x:Static SystemColors.ControlLightColorKey}}" /> <!-- But fully transparent -->
<GradientStop Offset="0.5" Color="{StaticResource {x:Static SystemColors.ControlLightColorKey}}" />
<GradientStop Offset="1.0" Color="{StaticResource {x:Static SystemColors.ControlLightColorKey}}" /> <!-- But fully transparent -->
</LinearGradientBrush>
I've tried to create two brushes with appropriate color and Opacity set, respectively, to 0.0 and 1.0, but the compiler refused to take Brush as a Color (what is quite logic, on a second thought :)).
Best regards -- Spook.

Answer 1

I would create a MarkupExtension that takes a Color and returns the Color with the specified opacity:
public class OpacityExtension : MarkupExtension
{
private readonly Color color;
public byte Opacity { get; set; } // defaults to 0, so you don't have
// to set it for the color to be transparent
public OpacityExtension(Color color)
{
this.color = color;
}
public override object ProvideValue(IServiceProvider serviceProvider)
{
return Color.FromArgb(Opacity, color.R, color.G, color.B);
}
}
And then you use it like so:
<LinearGradientBrush x:Key="BrightSeparatorGradient" StartPoint="0.0, 0.5" EndPoint="1.0, 0.5">
<GradientStop Offset="0" Color="{lcl:Opacity {StaticResource {x:Static SystemColors.ControlLightColorKey}}}" />
<GradientStop Offset=".5" Color="{StaticResource {x:Static SystemColors.ControlLightColorKey}}" />
<GradientStop Offset="1" Color="{lcl:Opacity {StaticResource {x:Static SystemColors.ControlLightColorKey}}}" />
</LinearGradientBrush>

Answer 2

Spook,
Why the following doesn't work for you?
<LinearGradientBrush x:Key="BrightSeparatorGradient" StartPoint="0.0, 0.5" EndPoint="1.0, 0.5">
<GradientStop Offset="0.0" Color="Transparent" />
<GradientStop Offset="0.5" Color="{StaticResource {x:Static SystemColors.ControlLightColorKey}}" />
<GradientStop Offset="1.0" Color="Transparent" />
</LinearGradientBrush>