QRAPI/API/Wood.Util/CaptchaHelper.cs

using SixLabors.Fonts;
using SixLabors.ImageSharp;
using SixLabors.ImageSharp.Drawing;
using SixLabors.ImageSharp.Drawing.Processing;
using SixLabors.ImageSharp.Formats.Gif;
using SixLabors.ImageSharp.Formats.Png;
using SixLabors.ImageSharp.PixelFormats;
using SixLabors.ImageSharp.Processing;
using System;
using System.IO;
using System.Numerics;

namespace Wood.Util
{
    public class CaptchaHelper
    {
        #region 得到验证码
        /// <summary>
        /// Tuple第一个值是表达式，第二个值是表达式结果
        /// </summary>
        /// <returns></returns>
        public static Tuple<string, int> GetCaptchaCode()
        {
            int value = 0;
            char[] operators = { '+', '-', '*' };
            string randomCode = string.Empty;
            Random random = new Random();

            int first = random.Next() % 10;
            int second = random.Next() % 10;
            char operatorChar = operators[random.Next(0, operators.Length)];
            switch (operatorChar)
            {
                case '+': value = first + second; break;
                case '-':
                    // 第1个数要大于第二个数
                    if (first < second)
                    {
                        int temp = first;
                        first = second;
                        second = temp;
                    }
                    value = first - second;
                    break;
                case '*': value = first * second; break;
            }

            char code = (char)('0' + (char)first);
            randomCode += code;
            randomCode += operatorChar;
            code = (char)('0' + (char)second);
            randomCode += code;
            randomCode += "=?";
            return new Tuple<string, int>(randomCode, value);
        }
        #endregion

        #region 生成验证码图片
        /// <summary>
        /// 生成验证码图片
        /// </summary>
        /// <param name="randomCode">验证码字符串</param>
        /// <returns>包含验证码图片的字节数组</returns>
        public static byte[] CreateCaptchaImage(string randomCode)
        {
            const int randAngle = 45; // 随机转动角度
            FontFamily fontFamily = SystemFonts.Collection.Get("Verdana");
            var font = fontFamily.CreateFont(36, FontStyle.Regular | FontStyle.Bold);

            // 计算文本的尺寸
            var textSize = TextMeasurer.MeasureSize(randomCode, new TextOptions(font));

            int mapWidth = (int)(textSize.Width + 10);
            int mapHeight = (int)(textSize.Height + 10);
            int singleCodeWidth = mapWidth / randomCode.Length;
            int paddingTop = 3;

            var aliceBlue = new Rgba32(240, 248, 255);

            using var image = new Image<Rgba32>(mapWidth, mapHeight, aliceBlue);

            var random = new Random();

            // 绘制干扰曲线
            for (int i = 0; i < 2; i++)
            {
                PointF p1 = new(0, random.Next(mapHeight));
                PointF p2 = new(random.Next(mapWidth), random.Next(mapHeight));
                PointF p3 = new(random.Next(mapWidth), random.Next(mapHeight));
                PointF p4 = new(mapWidth, random.Next(mapHeight));

                var path = new PathBuilder();
                path.AddCubicBezier(p1, p2, p3, p4);

                image.Mutate(x => x.Draw(Color.Gray, 1f, path.Build()));
            }

            // 定义颜色和字体
            Color[] colors = {
                Color.Black, Color.Red, Color.DarkBlue, Color.Green,
                Color.Orange, Color.Brown, Color.DarkCyan, Color.Purple
            };

            float x = 3; // 起始位置

            foreach (char t in randomCode)
            {
                int cIndex = random.Next(colors.Length);
                var color = colors[cIndex];
                // 加减乘运算符不进行旋转
                if (t == '+' || t == '-' || t == '*' || t == '=')
                {
                    // 加减乘运算符不进行旋转
                    image.Mutate(ctx => ctx.DrawText(t.ToString(), font, color, new PointF(x, paddingTop)));
                }
                else
                {
                    float angle = random.Next(-randAngle, randAngle + 1); // 确保包括正负randAngle

                    // 创建一个变换矩阵用于旋转文本
                    var transform = Matrix3x2.CreateRotation((float)Math.PI * angle / 180, new PointF(x + singleCodeWidth / 2, paddingTop + textSize.Height / 2));

                    // 设置绘图选项并应用变换矩阵
                    var drawingOptions = new DrawingOptions
                    {
                        Transform = transform,
                        GraphicsOptions = new GraphicsOptions()
                        {
                            Antialias = true,
                            ColorBlendingMode = PixelColorBlendingMode.Normal
                        }
                    };

                    // 绘制变换后的文本
                    image.Mutate(ctx =>
                        ctx.DrawText(drawingOptions, t.ToString(), font, color, new PointF(x, paddingTop))
                    );
                }

                x += singleCodeWidth; // 移动到下一个字符的位置
            }

            // 将图像保存为 GIF 格式并返回字节数组
            using var ms = new MemoryStream();
            image.Save(ms, new PngEncoder());
            return ms.ToArray();
        }
        #endregion
    }
}