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;

}