private void DrawStaticGraph(DrawingContext drawingContext)
{
    // PathGeometry is a nice alternative to drawingContext.DrawLine(...) as it 

    // allows the points to be rendered as an image that can be further manipulated

    PathGeometry geometry = new PathGeometry();

    // Add all points to the geometry

    foreach (Points pointXY in _points)
    {
        PathFigure figure = new PathFigure();
        figure.StartPoint = pointXY.FromPoint;
        figure.Segments.Add(new LineSegment(pointXY.ToPoint, true));
        geometry.Figures.Add(figure);
    }

    // Add the first point to close the gap from the graph's end point to graph's start point 

    PathFigure lastFigure = new PathFigure();
    lastFigure.StartPoint = _points[_points.Count - 1].FromPoint;
    lastFigure.Segments.Add(new LineSegment(_firstPoint, true));
    geometry.Figures.Add(lastFigure);

    // Create a new drawing and drawing group in order to apply a custom drawing effect

    GeometryDrawing drawing = new GeometryDrawing(this.Pen.Brush, this.Pen, geometry);
    DrawingGroup drawingGroup = new DrawingGroup();
    drawingGroup.Children.Add(drawing);

    ...
}