vs2010 c# graphics绘制坐标系

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在txt文件里写入坐标，绘制图形，例如x1,y1,x2,y2,x3,y3。
鼠标位于坐标系内，显示2条红色十字线，和坐标值，离开坐标系，2者消失。
源码：

using System;
using System.Collections;
using System.Collections.Generic;
using System.ComponentModel;
using System.Data;
using System.IO;
using System.Drawing;
using System.Linq;
using System.Text;
using System.Windows.Forms;
using System.Runtime.InteropServices;
namespace TEST
{

    public partial class Form1 : Form
    {
        public Form1()
        {
            InitializeComponent();
        }
        string resultFile;
        private Point mouseOffset;
        bool flag=false;
        ToolTip tooltip = new ToolTip();
        int[] bufx=new int[1024];
        int[] bufy = new int[1024];
        int drawflag=0;
        int readlen = 0;
         // x1,y1为鼠标移动的坐标，画十字线用，xbuf,ybuf绘制点坐标数组
         void draw(int x1,int y1,int[] xbuf,int[] ybuf)
        {

            //定义画布大小
            int height = 350, width = 800;
            //创建位图
            System.Drawing.Bitmap image = new System.Drawing.Bitmap(width, height);
            //创建Graphics类对象
            Graphics g = Graphics.FromImage(image);
            //清空图片背景色
            g.Clear(Color.White);
            Font font = new System.Drawing.Font("Arial", 9, FontStyle.Regular);
            Font font1 = new System.Drawing.Font("宋体", 20, FontStyle.Regular);
            Font font2 = new System.Drawing.Font("Arial", 8, FontStyle.Regular);

            System.Drawing.Drawing2D.LinearGradientBrush brush = new System.Drawing.Drawing2D.LinearGradientBrush(new Rectangle(0, 0, image.Width, image.Height), Color.Blue, Color.Blue, 1.2f, true);
            g.FillRectangle(Brushes.SeaGreen, 0, 0, width, height);
            Brush brush1 = new SolidBrush(Color.Blue);
            Brush brush2 = new SolidBrush(Color.SaddleBrown);

            //画图片的边框线
            g.DrawRectangle(new Pen(Color.Black), 40, 40, 720, 270);
            g.DrawRectangle(new Pen(Color.Black), 40, 35, 720, 275);
            System.Drawing.Pen mypen = new Pen(brush, 1);
            System.Drawing.Pen mypen2 = new Pen(Color.Red, 2);
            System.Drawing.Pen mypen3 = new Pen(Color.Yellow,1);
            //绘制线条
            //绘制纵向线条

            int x = 80;
            for (int i = 0; i < 17; i++)
            {
                g.DrawLine(mypen, x, 40, x, 310);
                x = x + 40;
            }
            //Pen mypen1 = new Pen(Color.Blue, 2);
            //g.DrawLine(mypen1, x - 480, 80, x - 480, 340);
            //绘制横向线条

            int y = 70;
            for (int i = 0; i < 8; i++)
            {
                g.DrawLine(mypen, 40, y, 760, y);
                y = y + 30;
            }

            //x轴上对应的标记
            String[] n = { " 10", " 20", " 30", " 40", " 50", " 60", " 70",
               " 80", " 90", " 100", "110", "120", "130", "140", "150", "160", "170"};
            x = 70;
            for (int i = 0; i < 17; i++)
            {
                g.DrawString(n[i].ToString(), font, Brushes.Red, x, 315); //设置文字内容及输出位置

                x = x + 40;
            }

            //y轴上对应的标记
            String[] m = {"40", "35", "30", "25", "20", "15", "10",

         " 5"};
            y = 60;
            for (int i = 0; i < 8; i++)
            {
                g.DrawString(m[i].ToString(), font, Brushes.Red, 16, y); //设置文字内容及输出位置
                y = y + 30;
            }

            if (drawflag == 1)
            {
                for (int i = 0; i 2; i++)
                {

                    g.DrawEllipse(mypen2, xbuf[i] - 2, ybuf[i] - 2, 4, 4);
                    if (i < readlen / 2 - 1)
                        g.DrawLine(mypen3,xbuf[i], ybuf[i] ,xbuf[i + 1],ybuf[i+1]);
                }

            }
            if (flag == true)
            {
                g.DrawLine(mypen2, x1, 41, x1, 310);
                g.DrawLine(mypen2, 41, y1, 760, y1);
            } 

            g.Dispose();
            this.pictureBox1.Image = image;

        }

        private void Form1_Load(object sender, EventArgs e)
        {
           label1.Visible = false;
           label1.Parent = pictureBox1;

           draw(1, 1, bufx, bufy);
        }

        private void Form1_FormClosed(object sender, FormClosedEventArgs e)
        {

        }

        private void 关于ToolStripMenuItem_Click(object sender, EventArgs e)
        {
            Form2 f=new Form2();
            f.Show();
        }
        private void pictureBox1_MouseMove(object sender, MouseEventArgs e)
        {

            int ex = e.X;
            int ey = e.Y;

           mouseOffset.X= (e.X-40)/4;
           mouseOffset.Y=(310- e.Y)/6;
            if ((ex > 40 && ex < 760) && (ey > 40 && ey < 310))
            {
                flag = true;
                label1.BackColor = Color.FromArgb(80, Color.White);

                label1.Visible = true;
                label1.Text = ("坐标值：" + "\n" + "x=" + mouseOffset.X + "\n" + "y=" + mouseOffset.Y);
                label1.Location = new Point(ex+20, ey+10);

               // this.Cursor = Cursors.Cross;  
                //tooltip.Show("x=" + e.X + ";y=" + e.Y, this, new Point(MousePosition.X, MousePosition.Y));
            }
            else
            {
                flag = false;
                label1.Visible = false;
               // this.Cursor = Cursors.Arrow;
            }
            draw(ex, ey, bufx, bufy);
        }

        private void buttonFile_Click(object sender, EventArgs e)
        {
            OpenFileDialog OpenFile = new OpenFileDialog();
            // OpenFile.InitialDirectory = "E:\\1work\\FILE";//初始目录
            OpenFile.Filter = "All files(*.*)|*.*|txt files(*.txt)|*.txt";//文本筛选
            OpenFile.FilterIndex = 1;//文本筛选器索引，选择第一项就是1
            OpenFile.RestoreDirectory = true;
            if (OpenFile.ShowDialog() == DialogResult.OK)
                resultFile = OpenFile.FileName;
            textBoxFile.Text = resultFile;
        }

        private void buttonDraw_Click(object sender, EventArgs e)
        {
            if (resultFile == null)
            {
                MessageBox.Show("请选取要绘图的文件！", "错误",
                          MessageBoxButtons.OK, MessageBoxIcon.Exclamation);
                return;
            }
            else
            {
                StreamReader fileRead = new StreamReader(File.Open(textBoxFile.Text, FileMode.Open), System.Text.Encoding.Default);
                string txtLine = fileRead.ReadLine();
                readlen = 0;
                while (true)
                {
                    txtLine = fileRead.ReadLine();
                    if (txtLine == null)
                        break;

                        if (txtLine.Length >= 3)
                        {
                            String[] date = txtLine.Split(',');
                            int len = date.Length;
                            //label2.Text =Convert.ToString(date[11]);
                            int j = 0;
                            for (int i = 0; i < len / 2; i++)
                            {//x:70 ,4*  x=70+4*d;
                                //y:310,*6  y=310-6*d

                                bufx[readlen/2 + i] = Convert.ToInt32(date[j]) * 4 + 40;
                                bufy[readlen/2 + i] = 310 - Convert.ToInt32(date[j + 1]) * 6;
                                j += 2;

                            }
                            readlen += len;
                      }

                }

                fileRead.Close();

                drawflag = 1;
                draw(1, 1, bufx, bufy);
                label2.Text = Convert.ToString("输出点个数："+readlen/2);
            }

        }

        private void buttonClear_Click(object sender, EventArgs e)
        {

            drawflag = 0;
            draw(1, 1, bufx, bufy);
            label2.Text = Convert.ToString("输出点个数：");
        }

    }
}