Asp.net 生成验证码

生成验证码一般来说大体有这么几步：

1、生成验证码字符串，一般由四个或更多随机字符拼凑而成；

2、填充图片背景，并绘制图片的背景噪音线；

3、将验证码绘制到图片中；

4、绘制前景噪点；

5、返回图片流，释放资源

 

public class CreateCodeImageUtil
    {
        public void CreateImage()
        {
            //声明code字体大小
            int fontsize = ;

            //获取code的值
            string code = GetCode();

            //声明一个图片实例
            Bitmap image = new Bitmap(code.Length * fontsize, );

            //声明画图类的实例
            Graphics g = Graphics.FromImage(image);
            g.Clear(Color.FromArgb(, , ));

            //任取四点，画四条贝塞尔样条作为背景噪音线
            Random random = new Random();
            Color color = Color.FromArgb(, , );
            Brush brush = new SolidBrush(color);
            Pen pen = new Pen(brush, );
            for (int i = ; i < ; i++)
            {
                Point p1 = new Point(random.Next(image.Width), random.Next(image.Height));
                Point p2 = new Point(random.Next(image.Width), random.Next(image.Height));
                Point p3 = new Point(random.Next(image.Width), random.Next(image.Height));
                Point p4 = new Point(random.Next(image.Width), random.Next(image.Height));

                g.DrawBezier(pen, p1, p2, p3, p4);
                //g.DrawLine(pen, p3, p4);
            }

            //绘制code
            int angle = random.Next(, );
            Font font = new Font("Arial", fontsize, (FontStyle.Bold | FontStyle.Italic));
            //线性渐变
            LinearGradientBrush textbrush = new LinearGradientBrush
            (new Rectangle(, , image.Width - , image.Height - ),
                Color.DimGray,
                Color.Purple,
                angle);
            g.DrawString(code, font, textbrush, , );

            //设置前景噪点
            for (int i = ; i < ; i++)
            {
                int x = random.Next(image.Width);
                int y = random.Next(image.Height);
                image.SetPixel(x, y, Color.FromArgb(, , ));
            }

            //将图片返回到输出流
            MemoryStream ms = new System.IO.MemoryStream();
            image.Save(ms, System.Drawing.Imaging.ImageFormat.Gif);
            HttpContext.Current.Response.ClearContent();
            HttpContext.Current.Response.ContentType = "image/Gif";
            HttpContext.Current.Response.BinaryWrite(ms.ToArray());

            //释放绘图资源
            g.Dispose();
            image.Dispose();
        }

        public string GetCode()
        {
            try
            {
                Random random = new Random();

                string code = "";
                int num = random.Next(, );
                for (int i = ; i < num; i++)
                {
                    char chr = (char)('' + (char)(random.Next() % ));
                    code += chr;
                }
                for (int i = ; i <  - num; i++)
                {
                    char chr = (char)('A' + (char)(random.Next() % ));
                    code += chr;
                }

                return code;
            }
            catch
            {
                return "";
            }
        }
    }