WPF: How to draw this polygon?

Question

I want to draw the following red polygon:

The problem is if I use somethign like this:

Polygon poly = new Polygon();
poly.StrokeThickness = 2;
poly.Stroke = Brushes.Black;
PointCollection points = new PointCollection();

for (int i = 0; i < this.NumberOfMetrics; i++)
{
   points.Add(new Point(MAX_VALUE - this.Metrics[n, i] * Math.Cos(DegreeToRadian(i * (360 / (this.NumberOfMetrics)))), MAX_Y_GUI - this.Metrics[n, i] * Math.Sin(DegreeToRadian(i * (360 / (this.NumberOfMetrics))))));
}       
poly.Points = points;

Then the polygon is always "filled" and in the example above the red and green polygon is drawn.

I already tried to add the 4 "inner" points to the PointCollection, but then nothing is drawn. So how can I achieve that?

I tried the solution proposed by David:

for (int n = 0; n < this.NumberOfRevisions; n++)
            {
                Path path = new Path();

                CombinedGeometry geometry = new CombinedGeometry();
                geometry.GeometryCombineMode = GeometryCombineMode.Union;

                Polygon poly = new Polygon();
                PointCollection points = new PointCollection();

                for (int i = 0; i < this.NumberOfMetrics; i++)
                {
                    points.Add(new Point(MAX_VALUE - this.Metrics[n, i] * Math.Cos(DegreeToRadian(i * (360 / (this.NumberOfMetrics)))), MAX_Y_GUI - this.Metrics[n, i] * Math.Sin(DegreeToRadian(i * (360 / (this.NumberOfMetrics))))));
                }

                poly.Points = points;

                geometry.Geometry1 = poly.RenderedGeometry;


                geometry.Geometry2 = poly.RenderedGeometry;


                path.Data = geometry;

                polygons.Add(poly);

                paths.Add(path);
            }

This is just a test but I thougth so I should get the same result as before, but it isn't drawn anything. Is there something wrong with my code?

Answer 1

If you want to have 2 independent shapes, with the possibility of the green one to be transparent as you stated in your comment, the best way to do is to use a combined geometry:

http://msdn.microsoft.com/en-en/library/ms653071%28v=VS.85%29.aspx

with the help of this, you can first create the green geometry, then the red by subtracting the green (or a copy of it) from the red one to create the hole.

So basically:

1. red shape, PLAIN
2. green shape on top of it, PLAIN
3. Subtract green shape or copy of it from red shape >> hole in red shape

this way you get the effect you want

easier done in Xaml, a bit more complicated in C# but still doable.

Edit: set the Combined Geometry as a Path's Data:

Path myPath = new Path();
CombinedGeometry myCombinedGeometry = new CombinedGeometry()

// here you set the combinedGeometry's geometries to create the shape you want

myPath.Data = myCombinedGeometry;

myGrid.Children.Add(myPath);

by the way, the PATH will be the place where you set the Fill / Stroke attribute for the colors, not the inside geometries. (see the examples in xaml in the link above, you basically just have to translate the code into C#)

Edit2:

don't forget to set a Fill on the Path:

for (int n = 0; n < this.NumberOfRevisions; n++)
{
    CombinedGeometry geometry = new CombinedGeometry() { GeometryCombineMode = GeometryCombineMode.Union };

    PointCollection points = new PointCollection();

    for (int i = 0; i < this.NumberOfMetrics; i++)
    {
        points.Add(new Point(MAX_VALUE - this.Metrics[n, i] * Math.Cos(DegreeToRadian(i * (360 / (this.NumberOfMetrics)))), MAX_Y_GUI - this.Metrics[n, i] * Math.Sin(DegreeToRadian(i * (360 / (this.NumberOfMetrics))))));
    }

    Polygon poly = new Polygon();
    poly.Points = points;

    geometry.Geometry1 = poly.RenderedGeometry;
    geometry.Geometry2 = poly.RenderedGeometry;

    polygons.Add(poly);

    paths.Add(path = new Path() { Data = geometry, Fill = Brushes.Red, Stroke = Brushes.Transparent });
}