C#中橡皮筋问题

想做一个类似于以下代码生成的一个橡皮筋，但是不知道怎么改，求高手指教。把箭头放到起点处。谢谢！
using System;
using System.Collections.Generic;
using System.ComponentModel;
using System.Data;
using System.Drawing;
using System.Text;
using System.Windows.Forms;
using System.Drawing.Drawing2D;//包含这个高级二维图形命名空间namespace ReverseLines
{
    public partial class Form1 : Form
    {
        public Form1()
        {
            InitializeComponent();            //激活双缓冲技术
            SetStyle(ControlStyles.UserPaint, true);
            SetStyle(ControlStyles.AllPaintingInWmPaint, true);
            SetStyle(ControlStyles.DoubleBuffer, true);
        }        private Point[][] tranGroup = new Point[1000][];//变换组
        private int tranNumb = 0;//变换序号
        private int pushNumb = 0;//左键按下情况：0为开始画变换，1为结束
        private Point curP;//存储变换时鼠标的当前点
        private Point startP, oldP;//变换的起点和鼠标移动时的当前点
        private Graphics g0,g3;//窗口绘图面和采用双缓冲时的临时绘图面
        private Point endPoint;//存储右键按下时放弃绘制相连变换的鼠标点
        private Color clr,clr1;//获取窗体背景色和反转背景色
        private Pen p;//重画变换时所用的笔
        private Bitmap bitmap = null;//双缓冲时用的位图        private void Form1_Paint(object sender, PaintEventArgs e)
        {
            g0 = e.Graphics;            bitmap = new Bitmap(ClientSize.Width, ClientSize.Height);//创建临时位图
            g3 = Graphics.FromImage(bitmap);//从位图创建绘图面
            g3.Clear(this.BackColor);//清除背景色
            g3.SmoothingMode = SmoothingMode.AntiAlias;//设置抗锯齿平滑模式            //在临时位图上重画变换，抗锯齿，带线冒
            for (int i = 0; i < tranNumb; i++)
            {
                g3.DrawLine(p, tranGroup[i][0], tranGroup[i][1]);
            }            //把临时位图拷贝到窗体绘图面
            g0.DrawImage(bitmap, 0, 0);
        }        private void Form1_Load(object sender, EventArgs e)
        {
            clr = this.BackColor;//获取窗体背景色           
            clr1 = Color.FromArgb(clr.A, 255 - clr.R, 255 - clr.G, 255 - clr.B);//反转背景色
            p = new Pen(clr1, 1);//定义鼠标左键按下并移动时绘制变换所用的笔            //自定义线冒
            AdjustableArrowCap cap = new AdjustableArrowCap(3, 3);
            cap.WidthScale = 3;
            cap.BaseCap = LineCap.Square;
            cap.Height = 3;
            p.CustomEndCap = cap;            //循环绘制变换组中的变换
            for (int i = 0; i < 1000; i++)
            {
                tranGroup[i] = new Point[2];
            }
        }        private void Form1_MouseDown(object sender, MouseEventArgs e)
        {
            Graphics g2 = CreateGraphics();            //判断变换数
            if (tranNumb >= 999)
            {
                pushNumb = 0;
                Capture = false;
                return;
            }            //左键按下
            if (e.Button == MouseButtons.Left)
            {
                if (pushNumb == 0)//判断是否是折线的开始
                {
                    if (endPoint.X != e.X || endPoint.Y != e.Y)
                    {
                        pushNumb++;                        startP.X = e.X;
                        startP.Y = e.Y;
                        oldP.X = e.X;
                        oldP.Y = e.Y;                        Capture = true;//捕获鼠标
                    }                }
                else if (pushNumb == 1)//如果不是一段新的折线的开始
                {
                    ControlPaint.DrawReversibleLine(PointToScreen(startP), PointToScreen(new Point(e.X, e.Y)), clr);
                    ControlPaint.DrawReversibleLine(PointToScreen(startP), PointToScreen(new Point(e.X, e.Y)), clr);
                                                           //把变换存入变换组中
                    curP.X = e.X;
                    curP.Y = e.Y;
                    tranGroup[tranNumb][0] = startP;
                    tranGroup[tranNumb][1] = curP;
                    tranNumb++;
                    startP.X = e.X;
                    startP.Y = e.Y;                    //存储一段折线的最后一个点的坐标
                    endPoint.X = e.X;
                    endPoint.Y = e.Y;
                }              
            }            //右键按下
            if (e.Button == MouseButtons.Right)
            {
                //变换数超过变换组最大限度
                if (pushNumb == 0)
                    return;                //变换数没有超过变换组最大限度
                pushNumb = 0;//一段折线结束
                Capture = false;//释放鼠标                //绘制最后一个变换
                ControlPaint.DrawReversibleLine(PointToScreen(startP), PointToScreen(new Point(e.X, e.Y)), clr);
            }            //失效重画，为抗锯齿
            Invalidate();
            g2.Dispose();
        }        private void Form1_MouseMove(object sender, MouseEventArgs e)
        {
            Graphics g1 = CreateGraphics();            //左键按下并移动鼠标
            if (pushNumb == 1)
            {
                if (oldP.X != e.X || oldP.Y != e.Y)
                {
                    //在屏幕上指定的起始点和结束点内绘制具有指定背景色的可逆线
                    //再次绘制同一条线会逆转该方法的结果。使用该方法绘制线类似于反转屏幕的一个区域，
                    //不过它提供了更好的性能适用于更广泛的颜色。                    ControlPaint.DrawReversibleLine(PointToScreen(startP), PointToScreen(oldP), clr);
                    ControlPaint.DrawReversibleLine(PointToScreen(startP), PointToScreen(new Point(e.X, e.Y)), clr);
                   
                    //存储一个变换的终点，作为下一变换的起点
                    oldP.X = e.X;
                    oldP.Y = e.Y;
                }            }
            g1.Dispose();
        } 
       //释放资源
        private void Form1_FormClosed(object sender, FormClosedEventArgs e)
        {
            g3.Dispose();
            bitmap.Dispose();
            g0.Dispose();
        }
    }
}