【C#】三维立体验证码 (3DCaptcha)

本技术来源：

3DCaptcha http://www-personal.umich.edu/~mressl/3dcaptcha/

下载地址 http://code.google.com/p/3dcaptcha/

官方LOGO

本例完全由此样例程序翻译而来,未作任何附加处理.

以下是C#对此算法的实现

/*
 * 3DCaptcha for .net
 * 
 * http://www-personal.umich.edu/~mressl/3dcaptcha/     (php)
 * http://code.google.com/p/3dcaptcha/                  (php)
 * 
 * Translate :  Aimeast
 * Blog      :  http://www.cnblogs.com/Aimeast/
 */

using System;
using System.Drawing;

namespace Captcha
{
    public static class Captcha
    {
        private static double[] addVector(double[] a, double[] b)
        {
            return new double[] { a[0] + b[0], a[1] + b[1], a[2] + b[2] };
        }

        private static double[] scalarProduct(double[] vector, double scalar)
        {
            return new double[] { vector[0] * scalar, vector[1] * scalar, vector[2] * scalar };
        }

        private static double dotProduct(double[] a, double[] b)
        {
            return a[0] * b[0] + a[1] * b[1] + a[2] * b[2];
        }

        private static double norm(double[] vector)
        {
            return Math.Sqrt(dotProduct(vector, vector));
        }

        private static double[] normalize(double[] vector)
        {
            return scalarProduct(vector, 1.0 / norm(vector));
        }

        // http://en.wikipedia.org/wiki/Cross_product
        private static double[] crossProduct(double[] a, double[] b)
        {
            return new double[] {
                (a[1] * b[2] - a[2] * b[1]),
                (a[2] * b[0] - a[0] * b[2]),
                (a[0] * b[1] - a[1] * b[0])
            };
        }

        private static double[] vectorProductIndexed(double[] v, double[] m, int i)
        {
            return new double[]{
                v[i + 0] * m[0] + v[i + 1] * m[4] + v[i + 2] * m[8] + v[i + 3] * m[12],
                v[i + 0] * m[1] + v[i + 1] * m[5] + v[i + 2] * m[9] + v[i + 3] * m[13],
                v[i + 0] * m[2] + v[i + 1] * m[6] + v[i + 2] * m[10]+ v[i + 3] * m[14],
                v[i + 0] * m[3] + v[i + 1] * m[7] + v[i + 2] * m[11]+ v[i + 3] * m[15]
            };
        }

        private static double[] vectorProduct(double[] v, double[] m)
        {
            return vectorProductIndexed(v, m, 0);
        }

        private static double[] matrixProduct(double[] a, double[] b)
        {
            double[] o1 = vectorProductIndexed(a, b, 0);
            double[] o2 = vectorProductIndexed(a, b, 4);
            double[] o3 = vectorProductIndexed(a, b, 8);
            double[] o4 = vectorProductIndexed(a, b, 12);

            return new double[]{
                o1[0], o1[1], o1[2], o1[3],
                o2[0], o2[1], o2[2], o2[3],
                o3[0], o3[1], o3[2], o3[3],
                o4[0], o4[1], o4[2], o4[3]
            };
        }

        // http://graphics.idav.ucdavis.edu/education/GraphicsNotes/Camera-Transform/Camera-Transform.html
        private static double[] cameraTransform(double[] C, double[] A)
        {
            double[] w = normalize(addVector(C, scalarProduct(A, -1)));
            double[] y = new double[] { 0, 1, 0 };
            double[] u = normalize(crossProduct(y, w));
            double[] v = crossProduct(w, u);
            double[] t = scalarProduct(C, -1);

            return new double[]{
                u[0], v[0], w[0], 0,
                u[1], v[1], w[1], 0,
                u[2], v[2], w[2], 0,
                dotProduct(u, t), dotProduct(v, t), dotProduct(w, t), 1
            };
        }

        // http://graphics.idav.ucdavis.edu/education/GraphicsNotes/Viewing-Transformation/Viewing-Transformation.html
        private static double[] viewingTransform(double fov, double n, double f)
        {
            fov *= (Math.PI / 180);
            double cot = 1.0 / Math.Tan(fov / 2);

            return new double[]{
                cot,	0,		0,		0,
                0,		cot,	0,		0, 
                0,		0,		(f + n) / (f - n),		-1,
                0,		0,		2 * f * n / (f - n),	0
            };
        }

        public static Image Generate(string captchaText)
        {
            Random rnd = new Random();

            // 3dcha parameters
            int fontsize = 24;
            Font font = new Font("Arial", fontsize);

            SizeF sizeF;
            using (Graphics g = Graphics.FromImage(new Bitmap(1, 1)))
            {
                sizeF = g.MeasureString(captchaText, font, 0, StringFormat.GenericDefault);
            }

            int image2d_x = (int)sizeF.Width;
            int image2d_y = (int)(fontsize * 1.3);

            double bevel = 4;

            // Create 2d image
            Bitmap image2d = new Bitmap(image2d_x, image2d_y);
            Color black = Color.Black;
            Color white = Color.White;

            // Paint 2d image
            using (Graphics g = Graphics.FromImage(image2d))
            {
                g.Clear(black);
                g.DrawString(captchaText, font, Brushes.White, 0, 0);
            }
            // Calculate projection matrix
            double[] T = cameraTransform(
                   new double[] { rnd.Next(-90, 90), -200, rnd.Next(150, 250) },
                   new double[] { 0, 0, 0 }
                );
            T = matrixProduct(
                    T,
                    viewingTransform(60, 300, 3000)
                );

            // Calculate coordinates
            double[][] coord = new double[image2d_x * image2d_y][];

            int count = 0;
            for (int y = 0; y < image2d_y; y += 2)
            {
                for (int x = 0; x < image2d_x; x++)
                {
                    // calculate x1, y1, x2, y2
                    int xc = x - image2d_x / 2;
                    int zc = y - image2d_y / 2;
                    double yc = -(double)(image2d.GetPixel(x, y).ToArgb() & 0xff) / 256 * bevel;
                    double[] xyz = new double[] { xc, yc, zc, 1 };
                    xyz = vectorProduct(xyz, T);

                    coord[count] = xyz;
                    count++;
                }
            }

            // Create 3d image
            int image3d_x = 256;
            //$image3d_y = $image3d_x / 1.618;
            int image3d_y = image3d_x * 9 / 16;
            Bitmap image3d = new Bitmap(image3d_x, image3d_y);
            Color fgcolor = Color.White;
            Color bgcolor = Color.Black;
            using (Graphics g = Graphics.FromImage(image3d))
            {
                g.Clear(bgcolor);
                count = 0;
                double scale = 1.75 - (double)image2d_x / 400;
                for (int y = 0; y < image2d_y; y += 2)
                {
                    for (int x = 0; x < image2d_x; x++)
                    {
                        if (x > 0)
                        {
                            double x0 = coord[count - 1][0] * scale + image3d_x / 2;
                            double y0 = coord[count - 1][1] * scale + image3d_y / 2;
                            double x1 = coord[count][0] * scale + image3d_x / 2;
                            double y1 = coord[count][1] * scale + image3d_y / 2;
                            g.DrawLine(new Pen(fgcolor), (float)x0, (float)y0, (float)x1, (float)y1);
                        }
                        count++;
                    }
                }
            }
            return image3d;
        }
    }
}

使用方法

this.BackgroundImage = Captcha.Generate("Code");

效果截图