// Fields
    private double mArrowAngle = 0.17453292519943295;
    private double mArrowLengh = 30.0;// Methods
    public override Geometry Create(double x1, double y1, double x2, double y2)
    {
        Point point = new Point(x1, y1);
        Point point2 = new Point(x2, y2);
        double num = Math.Atan((y2 - y1) / (x2 - x1));
        double d = num - this.ArrowAngle;
        double num3 = num + this.ArrowAngle;
        int num4 = (x2 > x1) ? -1 : 1;
        double x = x2 + ((num4 * this.ArrowLengh) * Math.Cos(d));
        double y = y2 + ((num4 * this.ArrowLengh) * Math.Sin(d));
        double num7 = x2 + ((num4 * this.ArrowLengh) * Math.Cos(num3));
        double num8 = y2 + ((num4 * this.ArrowLengh) * Math.Sin(num3));
        Point point3 = new Point(x, y);
        Point point4 = new Point(num7, num8);
        PathGeometry geometry = new PathGeometry();
        PathFigure figure = new PathFigure();
        figure.IsFilled = true;
        figure.StartPoint = point2;
        Point[] points = new Point[] { point, point2, point3, point4, point2 };//从point2到point 然后在倒回来到point2，然后画箭头。及从point2到point3到point4到point2.....
        PolyLineSegment segment = new PolyLineSegment(points, true);
        figure.Segments.Add(segment);
        geometry.Figures.Add(figure);
        geometry.Freeze();
        return geometry;
    }// Properties
    public double ArrowAngle
    {
        get
        {
            return this.mArrowAngle;
        }
        set
        {
            this.mArrowAngle = value;
        }
    }public double ArrowLengh
    {
        get
        {
            return this.mArrowLengh;
        }
        set
        {
            this.mArrowLengh = value;
        }
    }