如何將slider.value綁定到橢圓漸變起點

Question

如何使用滑塊調整顏色？

這樣

http://s2.ipicture.ru/uploads/20140220/4q71sUT5.jpg

http://s4.postimg.org/43lecgnjx/Bind.jpg

Answer 1

<StackPanel> 
    <Ellipse x:Name="ell" Width="50" Height="50"> 
     <Ellipse.Fill> 
      <LinearGradientBrush EndPoint="0.5,1" StartPoint="0.5,0"> 
       <GradientStop Color="Black" Offset="0"/> 
       <GradientStop x:Name="stopToBind" Color="#FFFF0808" Offset="1"/> 
      </LinearGradientBrush> 
     </Ellipse.Fill> 
    </Ellipse> 

    <Slider Value="{Binding ElementName=stopToBind, Path=Offset, Mode=TwoWay}"/> 
</StackPanel> 

UPDATE

不順利：

<StackPanel> 
    <Ellipse x:Name="ell" Width="50" Height="50"> 
     <Ellipse.Fill> 
      <LinearGradientBrush StartPoint="0,0" EndPoint="0,1"> 
       <GradientStop Color="Red" Offset="{Binding ElementName=sl, Path=Value, Mode=TwoWay}"/> 
       <GradientStop Color="Black" Offset="{Binding ElementName=sl, Path=Value, Mode=TwoWay}"/> 
      </LinearGradientBrush> 
     </Ellipse.Fill> 

    </Ellipse> 

    <Slider Value="0.5" x:Name="sl" Maximum="1" Minimum="0"/> 
</StackPanel>