How to get from a Shape object to a GeometryDrawing (WPF)

From:

=?Utf-8?B?U2ViYXN0aWFuIERhc2Vy?= <SebastianDaser@discussions.microsoft.com>

Newsgroups:

microsoft.public.dotnet.framework

Date:

Thu, 6 Aug 2009 07:48:01 -0700

Message-ID:

<2963B1B5-BC23-4FB3-8AE8-2489C6EA119C@microsoft.com>

Hi all,

I am trying to develop a WPF application which should show a Polygon Shape
inside an Image control. At a later point the Points of the Polygon should be
calculated by the application, so I need to create the objects in code.

I have tried the following:
public partial class ImageControl : Image
{
    public ImageControl()
    {
        InitializeComponent();

        DrawingGroup group = new DrawingGroup();

        Polygon polygon = new Polygon();
        polygon.Stretch = Stretch.Fill;
        polygon.Fill = Brushes.LightGreen;
        polygon.Stroke = Brushes.Black;
        polygon.Points.Add(new Point(0, 0));
        polygon.Points.Add(new Point(0, 0.5));
        polygon.Points.Add(new Point(0.7, 0.7));
        polygon.Points.Add(new Point(0.5, 0));

        Geometry polygonGeometry = polygon.RenderedGeometry;

        group.Children.Add(new GeometryDrawing(Brushes.Blue, null,
polygonGeometry));

        DrawingImage image = new DrawingImage(group);

        this.Source = image;
    }
}

However this does not work. When replacing the line
  Geometry polygonGeometry = polygon.RenderedGeometry;
with something like
  Geometry polygonGeometry = Geometry.Parse("M100,125 L300, 330 L700, 260
L430, 10");
a Polygon is drawn, so I guess the RenderGeometry method does not produce
the desired result.

How can I convert a Shape like Polygon to an object of type Geometry or
GeometryDrawing?

Thanks and kind regards
Sebastian