WP สอบถามเกี่ยวกับโค้ดเส้น ทำไงให้เส้นที่เราวาดมันใหญ่ขึ้นครับ

 public MainPage()
        {
            InitializeComponent();
            Touch.FrameReported += new TouchFrameEventHandler(Touch_FrameReported);
        }

        // preXArray and preYArray are used to store the start point 
        // for each touch point. currently silverlight support 4 muliti-touch
        // here declare as 10 points for further needs. 
        double[] preXArray = new double[10];
        double[] preYArray = new double[10];

        /// <summary>
        /// Every touch action will rise this event handler. 
        /// </summary>
        void Touch_FrameReported(object sender, TouchFrameEventArgs e)
        {
            int pointsNumber = e.GetTouchPoints(drawCanvas).Count;
            TouchPointCollection pointCollection = e.GetTouchPoints(drawCanvas);

            for (int i = 0; i < pointsNumber; i++)
            {
                if (pointCollection[i].Action == TouchAction.Down)
                {
                    preXArray[i] = pointCollection[i].Position.X;
                    preYArray[i] = pointCollection[i].Position.Y;
                }
                if (pointCollection[i].Action == TouchAction.Move)
                {
                    Line line = new Line();
                    line.X1 = preXArray[i];
                    line.Y1 = preYArray[i];
                    line.X2 = pointCollection[i].Position.X;
                    line.Y2 = pointCollection[i].Position.Y;

                    //pen = new Pen(Brushes.DeepSkyBlue, 4);
                    //e.Graphics.DrawLine(pen, 10, 120, 220, 120);
                    //pen.Dispose();
                    line.Stroke = new SolidColorBrush(Colors.Black);                 
                    line.Fill = new SolidColorBrush(Colors.Black);
                    drawCanvas.Children.Add(line);         
                    preXArray[i] = pointCollection[i].Position.X;
                    preYArray[i] = pointCollection[i].Position.Y;
                }
            }
        }