ASP.NET WebService的图片验证码服务

/// <summary>
/// 生成图片验证码
/// </summary>
/// <param name="nLen">验证码的长度</param>
/// <param name="strKey">输出参数，验证码的内容</param>
/// <returns>图片字节流</returns>
[WebMethod]
public byte[] GenerateVerifyImage(int nLen,ref string strKey)
{
   int nBmpWidth = 13*nLen+5;
   int nBmpHeight = 25;
   System.Drawing.Bitmap bmp = new System.Drawing.Bitmap(nBmpWidth,nBmpHeight);

   // 1. 生成随机背景颜色
   int nRed,nGreen,nBlue; // 背景的三元色
   System.Random rd = new Random((int)System.DateTime.Now.Ticks);
   nRed = rd.Next(255)%128+128;
   nGreen = rd.Next(255)%128+128;
   nBlue = rd.Next(255)%128+128;

   // 2. 填充位图背景
   System.Drawing.Graphics graph = System.Drawing.Graphics.FromImage(bmp);
   graph.FillRectangle(new SolidBrush(System.Drawing.Color.FromArgb(nRed,nGreen,nBlue))
    ,0
    ,0
    ,nBmpWidth
    ,nBmpHeight);

   // 3. 绘制干扰线条，采用比背景略深一些的颜色

int nLines = 3;
   System.Drawing.Pen pen = new System.Drawing.Pen(System.Drawing.Color.FromArgb(nRed-17,nGreen-17,nBlue-17),2);
   for(int a =0;a< nLines;a++)

   {
    int x1 = rd.Next() % nBmpWidth;
    int y1 = rd.Next() % nBmpHeight;
    int x2 = rd.Next() % nBmpWidth;
    int y2 = rd.Next() % nBmpHeight;
    graph.DrawLine(pen,x1,y1,x2,y2);
   }

   // 采用的字符集，可以随即拓展，并可以控制字符出现的几率
   string strCode = "ABCDEFGHIJKLMNOPQRSTUVWXYZ";

   // 4. 循环取得字符，并绘制
   string strResult = "";
   for(int i=0;i<nLen;i++)
   {
    int x = (i*13 + rd.Next(3));
    int y = rd.Next(4) + 1;

    // 确定字体
    System.Drawing.Font font = new System.Drawing.Font("Courier New",
     12 + rd.Next()%4,
     System.Drawing.FontStyle.Bold);
    char c = strCode[rd.Next(strCode.Length)]; // 随机获取字符
    strResult += c.ToString();

    // 绘制字符
    graph.DrawString(c.ToString(),
     font,
     new SolidBrush(System.Drawing.Color.FromArgb(nRed-60+y*3,nGreen-60+y*3,nBlue-40+y*3)),
     x,
     y);
   }

   // 5. 输出字节流
   System.IO.MemoryStream bstream = new System.IO.MemoryStream();
   bmp.Save(bstream,System.Drawing.Imaging.ImageFormat.Jpeg);
   bmp.Dispose();
   graph.Dispose();

   strKey = strResult;

byte[] byteReturn = bstream.ToArray();
   bstream.Close();

   return byteReturn;
}

　　2. 测试WebMethod，添加一个WebForm，引用上述WebService，引用名为imagesvr。在Page_Load中添加代码：

   ...
   imagesvr.MyService imgsvr = new imagesvr.MyService();
   string strKey = "";
   byte[] data = imgsvr.GenerateVerifyImage(5,ref strKey);

   Response.OutputStream.Write(data,0,data.Length);
   ...

　　3. 运行。每次refresh这个WebForm时，就会显示一个新生成的图片验证码，而函数的输出参数strKey保存的就是这个验证码的实际内容，可以保存在Session中，作为验证使用。

　　

　　滤镜效果主要采用波形（wave）算法，通过对X轴Y轴的正弦波形处理，产生叠加效果。算法主要描述如下：

private const double PI = 3.1415926535897932384626433832795;
private const double PI2 = 6.283185307179586476925286766559;

/// <summary>
/// 正弦曲线Wave扭曲图片
/// </summary>
/// <param name="srcBmp"></param>
/// <param name="bXDir"></param>
/// <param name="nMultValue">波形的幅度倍数</param>
/// <param name="dPhase">波形的起始相位，取值区间[0-2*PI)</param>
/// <returns></returns>
public System.Drawing.Bitmap TwistImage(Bitmap srcBmp,bool bXDir,double dMultValue,double dPhase)
{
   System.Drawing.Bitmap destBmp = new Bitmap(srcBmp.Width,srcBmp.Height);

   // 将位图背景填充为白色
   System.Drawing.Graphics graph = System.Drawing.Graphics.FromImage(destBmp);
   graph.FillRectangle(new SolidBrush(System.Drawing.Color.White),0,0,destBmp.Width,destBmp.Height);

graph.Dispose();

   double dBaseAxisLen = bXDir ? (double)destBmp.Height : (double)destBmp.Width;

   for(int i=0;i<destBmp.Width;i++)
   {
    for(int j=0;j<destBmp.Height;j++)
    {
     double dx = 0;
     dx = bXDir ? (PI2*(double)j)/dBaseAxisLen : (PI2*(double)i)/dBaseAxisLen;
     dx += dPhase;
     double dy = Math.Sin(dx);

     // 取得当前点的颜色

     int nOldX = 0,nOldY = 0;
     nOldX = bXDir ? i + (int)(dy*dMultValue) : i;
     nOldY = bXDir ? j : j + (int)(dy*dMultValue);

     System.Drawing.Color color = srcBmp.GetPixel(i,j);
     if(nOldX >= 0 && nOldX < destBmp.Width
      && nOldY >=0 && nOldY < destBmp.Height)
     {
      destBmp.SetPixel(nOldX,nOldY,color);
     }
    }
   }

   return destBmp;
}