using System;
using System.Drawing;
using System.IO;

public partial class _Default : System.Web.UI.Page
{
    Random ran = new Random();
    protected void Page_Load(object sender, EventArgs e)
    {
        string str = getRandomValidate(4);
        Session["check"] = str;
        //这一步是为了将验证码写入Session，进行验证，不能缺省，也可一使用cookie
        getImageValidate(str);
    }
    //得到随机字符串,长度自己定义
    private string getRandomValidate(int len)
    {
        int num;
        int tem;
        string rtuStr = "";
        for (int i = 0; i < len; i++)
        {
            num = ran.Next();
            /*
             * 这里可以选择生成字符和数字组合的验证码
             */
            tem = num % 10 + '0';//生成数字
           // tem = num % 26 + 'A';//生成字符
            rtuStr += Convert.ToChar(tem).ToString();
        }
        return rtuStr;
    }
    //生成图像
    private void getImageValidate(string strValue)
    {
        //string str = "OO00"; //前两个为字母O，后两个为数字0
        int width = Convert.ToInt32(strValue.Length * 33.5);    //计算图像宽度
        Bitmap img = new Bitmap(width, 50);
        Graphics gfc = Graphics.FromImage(img);           //产生Graphics对象，进行画图
        gfc.Clear(Color.White);
        drawLine(gfc, img);
        //写验证码，需要定义Font
        Font font = new Font("Consolas", 35, FontStyle.Bold);
        System.Drawing.Drawing2D.LinearGradientBrush brush =
            new System.Drawing.Drawing2D.LinearGradientBrush(new Rectangle(0, 0, img.Width, img.Height), Color.DarkOrchid, Color.Blue, 1.5f, true);
        gfc.DrawString(strValue, font, brush, 3, 2);
        drawPoint(img);
        gfc.DrawRectangle(new Pen(Color.White), 0, 0, img.Width - 1, img.Height - 1);
        //将图像添加到页面
        MemoryStream ms = new MemoryStream();
        img.Save(ms, System.Drawing.Imaging.ImageFormat.Gif);
        //更改Http头
        Response.ClearContent();
        Response.ContentType = "image/gif";
        Response.BinaryWrite(ms.ToArray());
        //Dispose
        gfc.Dispose();
        img.Dispose();
        Response.End();
    }
    private void drawLine(Graphics gfc, Bitmap img)
    {
        //选择画10条线,也可以增加，也可以不要线，只要随机杂点即可
        for (int i = 0; i < 10; i++)
        {
            int x1 = ran.Next(img.Width);
            int y1 = ran.Next(img.Height);
            int x2 = ran.Next(img.Width);
            int y2 = ran.Next(img.Height);
            gfc.DrawLine(new Pen(Color.Silver), x1, y1, x2, y2);      //注意画笔一定要浅颜色，否则验证码看不清楚
        }
    }
    private void drawPoint(Bitmap img)
    {
        /*
        //选择画100个点,可以根据实际情况改变
        for (int i = 0; i < 100; i++)
        {
            int x = ran.Next(img.Width);
            int y = ran.Next(img.Height);
            img.SetPixel(x,y,Color.FromArgb(ran.Next()));//杂点颜色随机
        }
         */
        int col = ran.Next();//在一次的图片中杂店颜色相同
        for (int i = 0; i < 100; i++)
        {
            int x = ran.Next(img.Width);
            int y = ran.Next(img.Height);
            img.SetPixel(x, y, Color.FromArgb(col));
        }
    }


}