Drawing Line

int x1, y1 = 0;
        bool c = false;
        private void Form1_MouseDown(object sender, MouseEventArgs e)
        {
                x1 = e.X;
                y1 = e.Y;
                c = true;
                al.Add(new Point(e.X, e.Y));
        }
        System.Collections.ArrayList al = new System.Collections.ArrayList();
        private void Form1_MouseMove(object sender, MouseEventArgs e)
        {
            if (c == true)
            {
                System.Drawing.Drawing2D.LinearGradientBrush brush1= new
                System.Drawing.Drawing2D.LinearGradientBrush(
                new Rectangle(0, 0, 2, 2), Color.YellowGreen, Color.Green,
                System.Drawing.Drawing2D.LinearGradientMode.BackwardDiagonal);
                Bitmap b = new Bitmap(Width, Height);
                Graphics g = Graphics.FromImage(b);
                g.SmoothingMode = System.Drawing.Drawing2D.SmoothingMode.AntiAlias;
                al.Add(new Point(e.X, e.Y));
                Point[] p = new Point[al.Count];
                al.CopyTo(p);
                g.DrawLines(new Pen(brush1,5), p);
                this.BackgroundImage = b;
            }
        }

        private void Form1_MouseUp(object sender, MouseEventArgs e)
        {
            c = false;
        }