WPF后台绘制折线，填充到一个GRID下

private void btnPreview_Click(object sender, RoutedEventArgs e)        {            GridImg.Children.Clear();            System.Drawing.Point p0 = new System.Drawing.Point(0, 0);            System.Drawing.Point p1 = new System.Drawing.Point(0, 0);            System.Drawing.Point p2 = new System.Drawing.Point(0, 0);            System.Drawing.Point p3 = new System.Drawing.Point(0, 0);            int x1 = Convert.ToInt32(txta1.Text);            int y1 = Convert.ToInt32(txtb1.Text);            int x2 = Convert.ToInt32(txta2.Text);            int y2 = Convert.ToInt32(txtb2.Text);            p0.X = 0; p0.Y = 255;            p1.X = x1; p1.Y = 255 - y1;            p2.X = x2; p2.Y = 255 - y2;            p3.X = 255; p3.Y = 0;            Line LX = new Line();//X轴            LX.X1 = 0; LX.X2 = 255; LX.Y1 = 255; LX.Y2 = 255;            LX.StrokeThickness = 1;            LX.Stroke = System.Windows.Media.Brushes.Black;            Line LY = new Line();//Y轴            LY.X1 = 0; LY.X2 = 0; LY.Y1 = 0; LY.Y2 = 255;            LY.StrokeThickness = 1;            LY.Stroke = System.Windows.Media.Brushes.Black;            Polyline PL = new Polyline();//绘制折线            PointCollection collection = new PointCollection();            collection.Add(new System.Windows.Point(p0.X, p0.Y));            collection.Add(new System.Windows.Point(p1.X, p1.Y));            collection.Add(new System.Windows.Point(p2.X, p2.Y));            collection.Add(new System.Windows.Point(p3.X, p3.Y));            PL.Points = collection;            PL.Stroke = new SolidColorBrush(Colors.Red);            PL.StrokeThickness = 1;            GridImg.Children.Add(LX);            GridImg.Children.Add(LY);            GridImg.Children.Add(PL);        }