private void SetProgressBarIndicatorLength()
{
    double minimum = base.Minimum;
    double maximum = base.Maximum;
    double num3 = base.Value;
    if ((this.ElementTrack != null) && (this.ElementIndicator != null))
    {
        FrameworkElement parent = VisualTreeHelper.GetParent(this.ElementIndicator) as FrameworkElement;
        if (parent != null)
        {
            double num4 = this.ElementIndicator.Margin.Left + this.ElementIndicator.Margin.Right;
            Border border = parent as Border;
            if (border != null)
            {
                num4 += border.Padding.Left + border.Padding.Right;
            }
            else
            {
                Control control = parent as Control;
                if (control != null)
                {
                    num4 += control.Padding.Left + control.Padding.Right;
                }
            }
            double num5 = (this.IsIndeterminate || (maximum == minimum)) ? 1.0 : ((num3 - minimum) / (maximum - minimum));
            double num6 = Math.Max((double) 0.0, (double) (parent.ActualWidth - num4));
            this.ElementIndicator.Width = num5 * num6;
        }
    }
}

<ControlTemplate TargetType="ProgressBar">
  <Grid x:Name="LayoutRoot">
    <!-- attach the view model -->
    <local:CircularProgressBarViewModel.Attach>
      <local:CircularProgressBarViewModel/>
    </local:CircularProgressBarViewModel.Attach>
 
    <!-- the rest of the template now has CircularProgressBarViewModel as the DataContext -->
  </Grid>
</ControlTemplate>

/// <summary>
/// Change handler for the Attach property
/// </summary>
private static void OnAttachChanged(DependencyObject d, DependencyPropertyChangedEventArgs e)
{
  // set the view model as the DataContext for the rest of the template
  FrameworkElement targetElement = d as FrameworkElement;
  CircularProgressBarViewModel viewModel = e.NewValue as CircularProgressBarViewModel;
  targetElement.DataContext = viewModel;
 
  // handle the loaded event
  targetElement.Loaded += new RoutedEventHandler(Element_Loaded);
}
 
/// <summary>
/// Handle the Loaded event of the element to which this view model is attached
/// in order to enable the attached
/// view model to bind to properties of the parent element
/// </summary>
static void Element_Loaded(object sender, RoutedEventArgs e)
{
  FrameworkElement targetElement = sender as FrameworkElement;
  CircularProgressBarViewModel attachedModel = GetAttach(targetElement);
 
  // find the ProgressBar and associated it with the view model
  var progressBar = targetElement.Ancestors<ProgressBar>().Single() as ProgressBar;
  attachedModel.SetProgressBar(progressBar);
}

/// <summary>
/// Add handlers for the updates on various properties of the ProgressBar
/// </summary>
private void SetProgressBar(ProgressBar progressBar)
{
  _progressBar = progressBar;
  _progressBar.SizeChanged += (s, e) => ComputeViewModelProperties();
  RegisterForNotification("Value", progressBar, (d,e) => ComputeViewModelProperties());
  RegisterForNotification("Maximum", progressBar, (d, e) => ComputeViewModelProperties());
  RegisterForNotification("Minimum", progressBar, (d, e) => ComputeViewModelProperties());
 
  ComputeViewModelProperties();
}
 
 
/// Add a handler for a DP change
/// see: http://amazedsaint.blogspot.com/2009/12/silverlight-listening-to-dependency.html
private void RegisterForNotification(string propertyName, FrameworkElement element, PropertyChangedCallback callback)
{
 
  //Bind to a dependency property  
  Binding b = new Binding(propertyName) { Source = element };
  var prop = System.Windows.DependencyProperty.RegisterAttached(
      "ListenAttached" + propertyName,
      typeof(object),
      typeof(UserControl),
      new PropertyMetadata(callback));
 
  element.SetBinding(prop, b);
}

/// <summary>
/// Re-computes the various properties that the elements in the template bind to.
/// </summary>
protected virtual void ComputeViewModelProperties()
{
  if (_progressBar == null)
    return;
 
  Angle = (_progressBar.Value - _progressBar.Minimum) * 360 / (_progressBar.Maximum - _progressBar.Minimum);
  CentreX = _progressBar.ActualWidth / 2;
  CentreY = _progressBar.ActualHeight / 2;
  Radius = Math.Min(CentreX, CentreY);
  Diameter = Radius * 2;
  InnerRadius = Radius * HoleSizeFactor;
  Percent = Angle / 360;
}

<Style TargetType="ProgressBar" x:Key="PieProgressBarStyle">
  <Setter Property="Template">
    <Setter.Value>
      <ControlTemplate TargetType="ProgressBar">
        <Grid x:Name="LayoutRoot">
          <!-- attach the view model -->
          <local:CircularProgressBarViewModel.Attach>
            <local:CircularProgressBarViewModel HoleSizeFactor="0.75"/>
          </local:CircularProgressBarViewModel.Attach>
 
          <!-- a circular outline -->
          <Ellipse Width="{Binding Diameter}" Height="{Binding Diameter}"
                    HorizontalAlignment="Center" VerticalAlignment="Center"
                    Stroke="LightGray" Fill="Transparent"
                    StrokeThickness="0.3">
          </Ellipse>
 
          <!-- a pie-piece that indicates the progress -->
          <local:PiePiece CentreX="{Binding CentreX}" CentreY="{Binding CentreY}"
                          RotationAngle="0" WedgeAngle="{Binding Angle}"
                          Radius="{Binding Radius}" Fill="LightBlue"/>
 
          <!-- progress as a percent -->
          <Grid util:GridUtils.RowDefinitions="*,3.5*,*"
                util:GridUtils.ColumnDefinitions="*,3.5*,*">
            <TextBlock Text="{Binding Percent, StringFormat=0%}"
                        Foreground="DarkBlue"
                        FontWeight="Bold" FontSize="20"
                        Grid.Row="1" Grid.Column="1"
                        VerticalAlignment="Center" HorizontalAlignment="Center"/>
          </Grid>
        </Grid>
      </ControlTemplate>
    </Setter.Value>
  </Setter>
</Style>

<Style TargetType="ProgressBar" x:Key="SegmentedProgressBarStyle">
  <Setter Property="Template">
    <Setter.Value>
      <ControlTemplate TargetType="ProgressBar">
        <Grid x:Name="LayoutRoot">
          <!-- attach the view model -->
          <local:CircularProgressBarViewModel.Attach>
            <local:SegmentedProgressBarViewModel HoleSizeFactor="0.7"/>
          </local:CircularProgressBarViewModel.Attach>
 
          <!-- render the segments -->
          <ItemsControl ItemsSource="{Binding Segments}">
            <ItemsControl.ItemsPanel>
              <ItemsPanelTemplate>
                <Grid/>
              </ItemsPanelTemplate>
            </ItemsControl.ItemsPanel>
            <ItemsControl.ItemTemplate>
              <DataTemplate>
                <Grid>
                  <!-- a grey segment -->
                  <local:PiePiece CentreX="{Binding Parent.CentreX}" CentreY="{Binding Parent.CentreY}"
                            RotationAngle="{Binding StartAngle}" WedgeAngle="{Binding WedgeAngle}"
                            Radius="{Binding Parent.Radius}" InnerRadius="{Binding Parent.InnerRadius}"
                            Fill="LightGray" Stroke="White" Opacity="0.5"/>
                  <!-- a blue segment, with an Opacity bound to the view model -->
                  <local:PiePiece CentreX="{Binding Parent.CentreX}" CentreY="{Binding Parent.CentreY}"
                            RotationAngle="{Binding StartAngle}" WedgeAngle="{Binding WedgeAngle}"
                            Radius="{Binding Parent.Radius}" InnerRadius="{Binding Parent.InnerRadius}"
                            Fill="DarkBlue" Stroke="White" Opacity="{Binding Opacity}"/>
                </Grid>
              </DataTemplate>
            </ItemsControl.ItemTemplate>                  
          </ItemsControl>
        </Grid>
      </ControlTemplate>
    </Setter.Value>
  </Setter>
</Style>