public class Pie : Shape {
    protected override System.Windows.Media.Geometry DefiningGeometry {
        get {
            StreamGeometry geometry = new StreamGeometry();
            geometry.FillRule = FillRule.EvenOdd;

            using (StreamGeometryContext context = geometry.Open()) {
                DrawGeometry(context);
            }

            geometry.Freeze();
            return geometry;
        }
    }

    private void DrawGeometry(StreamGeometryContext context) {
        var startPoint = new Point(CenterX, CenterY);
        var endPoint = GetEndPoint();
        context.BeginFigure(startPoint, true, true);
        context.LineTo(new Point(CenterX, CenterY - Radius), true, true);
        context.ArcTo(endPoint, new Size(Radius, Radius), 0, Angle > 180, SweepDirection.Clockwise, true, true);
    }

    private Point GetEndPoint() {
        Point result = new Point();
        double a = Angle / 180.0f * Math.PI;
        result.X = CenterX + Radius * Math.Sin(a);
        result.Y = CenterY - Radius * Math.Cos(a);
        return result;
    }

    protected override void OnRender(DrawingContext dc) {
        //dc.DrawRectangle(Brushes.Yellow, null, new Rect(RenderSize));
        base.OnRender(dc);
    }

    public double Radius {
        get { return (double)GetValue(RadiusProperty); }
        set { SetValue(RadiusProperty, value); }
    }

    public static readonly DependencyProperty RadiusProperty =
        DependencyProperty.Register("Radius", typeof(double), typeof(Pie), new FrameworkPropertyMetadata(0.0, FrameworkPropertyMetadataOptions.AffectsRender | FrameworkPropertyMetadataOptions.AffectsMeasure));


    public double Angle {
        get { return (double)GetValue(AngleProperty); }
        set { SetValue(AngleProperty, value); }
    }

    public static readonly DependencyProperty AngleProperty =
        DependencyProperty.Register("Angle", typeof(double), typeof(Pie), new FrameworkPropertyMetadata(0.0, FrameworkPropertyMetadataOptions.AffectsRender | FrameworkPropertyMetadataOptions.AffectsMeasure));

    public double CenterX {
        get { return (double)GetValue(CenterXProperty); }
        se