WPF ControlTemplate设置圆角按钮半径等于其宽度的一半

<Button Width="100" Height="50" Content="按钮"/>

<Button Width="100" Height="50" Content="按钮">
    <Button.Style>
        <Style TargetType="Button">
            <Setter Property="Template">
                <Setter.Value>
                    <ControlTemplate TargetType="Button">
                        <Border Background="LightBlue" BorderBrush="Gray" BorderThickness="2"
                                CornerRadius="{Binding Path=Width, RelativeSource={RelativeSource TemplatedParent}, Converter={StaticResource HalfValueConverter}}">
                            <ContentPresenter HorizontalAlignment="Center" VerticalAlignment="Center"/>
                        </Border>
                    </ControlTemplate>
                </Setter.Value>
            </Setter>
        </Style>
    </Button.Style>
</Button>

<Window.Resources>
    <local:HalfValueConverter x:Key="HalfValueConverter"/>
</Window.Resources>

public class HalfValueConverter : IValueConverter
{
    public object Convert(object value, Type targetType, object parameter, CultureInfo culture)
    {
        if (value is double)
        {
            return (double)value / 2;
        }
        return value;
    }

    public object ConvertBack(object value, Type targetType, object parameter, CultureInfo culture)
    {
        throw new NotImplementedException();
    }
}