improved Captcha generator algorithm

bezzad · Jun 10, 2023 · 7c83e29 · 7c83e29
1 parent 7c9a3bb
commit 7c83e29
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Showing 5 changed files with 37 additions and 13 deletions.
diff --git a/src/Captcha.Net.Sample/Program.cs b/src/Captcha.Net.Sample/Program.cs
@@ -17,7 +17,7 @@
     Console.WriteLine();
     stopWatch.Stop();
     times.Add(stopWatch.ElapsedMilliseconds);
-    File.WriteAllBytes($"{currentDirectory.FullName}/captcha-{i}.png", result.CaptchaByteData);
+    File.WriteAllBytes($"{currentDirectory.FullName}/captcha-{i}.jpg", result.CaptchaByteData);
 }
 
 Console.WriteLine($"Duration:  Max({times.Max()}ms),  Min({times.Min()}ms),  Average({times.Average()}ms)");    

diff --git a/src/Captcha.Net.Test/IntegrationTests/CaptchaGeneratorTest.cs b/src/Captcha.Net.Test/IntegrationTests/CaptchaGeneratorTest.cs
@@ -29,6 +29,7 @@ public void GenerateCaptchaImageTest()
             // arrange
             ushort width = 100;
             ushort height = 50;
+            var jpegWhiteBalanceRatio = 0.99; // 99% like white color
             var code = "012340";
             var generator = new CaptchaGenerator();
             var backgroundHistogram = 0;
@@ -39,7 +40,7 @@ public void GenerateCaptchaImageTest()
             var pixels = image.GetPixelMemoryGroup().SelectMany(g => g.ToArray());
             foreach (var pixel in pixels)
             {
-                if (pixel == Color.White.ToPixel<Rgba32>())
+                if (pixel.Rgba >= Color.White.ToPixel<Rgba32>().Rgba * jpegWhiteBalanceRatio)
                     backgroundHistogram++;
             }
 

diff --git a/src/Captcha.Net/Captcha.cs b/src/Captcha.Net/Captcha.cs
@@ -4,22 +4,39 @@
 using SixLabors.ImageSharp.PixelFormats;
 using SixLabors.ImageSharp.Processing;
 using System;
+using System.Collections.Concurrent;
 using System.IO;
 using System.Numerics;
 
 namespace Captcha.Net
 {
     public class Captcha : ICaptchaModule
     {
-        protected readonly static Random Rand = new Random(DateTime.Now.GetHashCode());
+        protected static readonly Random Rand = new Random(DateTime.Now.GetHashCode());
+        protected static readonly ConcurrentDictionary<int, ushort> TextMeasures = new ConcurrentDictionary<int, ushort>();
+        protected static Font _font;
+        protected static AffineTransformBuilder RotationBuilder;
         protected readonly CaptchaOptions _options;
-        protected Font _font;
 
         public Captcha(CaptchaOptions options)
         {
             _options = options;
-            var fontName = _options.FontFamilies[Rand.Next(0, _options.FontFamilies.Length)];
-            _font = SystemFonts.CreateFont(fontName, _options.FontSize, _options.FontStyle);
+            if (_font == null)
+            {
+                try
+                {
+                    var fontName = _options.FontFamilies[0];
+                    _font = SystemFonts.CreateFont(fontName, _options.FontSize, _options.FontStyle);
+                }
+                catch
+                {
+                    if (_options.FontFamilies.Length > 1)
+                    {
+                        var fontName = _options.FontFamilies[1];
+                        _font = SystemFonts.CreateFont(fontName, _options.FontSize, _options.FontStyle);
+                    }
+                }
+            }
         }
 
         public byte[] Generate(string text)
@@ -28,7 +45,7 @@ public byte[] Generate(string text)
             imgText.Mutate(ctx => DrawText(ctx, _font, text));
 
             // add the dynamic image to original image
-            var size = (ushort)TextMeasurer.Measure(text, new TextOptions(_font)).Width;
+            var size = TextMeasures.GetOrAdd(text.Length, len => (ushort)TextMeasurer.Measure(text, new TextOptions(_font)).Width);
             using var img = new Image<Rgba32>(size + 15, _options.Height);
             img.Mutate(ctx => Draw(ctx, img.Width, img.Height, imgText));
 
@@ -51,8 +68,8 @@ protected void DrawText(IImageProcessingContext imgContext, Font font, string te
             }
 
             // add rotation
-            AffineTransformBuilder rotation = GetRotation();
-            imgContext.Transform(rotation);
+            RotationBuilder ??= GetRotation();
+            imgContext.Transform(RotationBuilder);
         }
 
         protected void Draw(IImageProcessingContext imgContext, int width, int height, Image<Rgba32> imgText)
@@ -94,7 +111,9 @@ protected AffineTransformBuilder GetRotation()
             var width = Rand.Next(Math.Min((ushort)10u, _options.Width), _options.Width);
             var height = Rand.Next(Math.Min((ushort)10u, _options.Height), _options.Height);
             var pointF = new PointF(width, height);
-            var rotationDegrees = Rand.Next(0, _options.MaxRotationDegrees);
+            var rotationDegrees = _options.RotationDegree.HasValue && _options.RotationDegree <= _options.MaxRotationDegrees 
+                ? _options.RotationDegree.Value 
+                : Rand.Next(0, _options.MaxRotationDegrees);
             var result = GetRotation(rotationDegrees, pointF);
             return result;
         }

diff --git a/src/Captcha.Net/CaptchaGenerator.cs b/src/Captcha.Net/CaptchaGenerator.cs
@@ -22,8 +22,11 @@ public CaptchaResult GenerateCaptchaImage(ushort width, ushort height, string ca
                     Width = width,
                     Height = height,
                     MaxRotationDegrees = 15,
+                    RotationDegree = 10,
+                    NoiseRate = 50,
+                    DrawLines = 4,
                     FontSize = GetFontSize(width, captchaCode.Length),
-                    EncoderType = EncoderTypes.Png
+                    EncoderType = EncoderTypes.Jpeg
                 }));
 
             var captchaCodeBytes = captcha.Generate(captchaCode);

diff --git a/src/Captcha.Net/CaptchaOptions.cs b/src/Captcha.Net/CaptchaOptions.cs
@@ -18,15 +18,16 @@ public class CaptchaOptions
         public float MaxLineThickness { get; set; } = 2.0f;
         public ushort Width { get; set; } = 180;
         public ushort Height { get; set; } = 50;
-        public ushort NoiseRate { get; set; } = 300;
+        public ushort NoiseRate { get; set; } = 100;
         public Color[] NoiseRateColor { get; set; } = new Color[] { Color.Gray };
         public byte FontSize { get; set; } = 29;
         public FontStyle FontStyle { get; set; } = FontStyle.Regular;
-        public EncoderTypes EncoderType { get; set; } = EncoderTypes.Png;
+        public EncoderTypes EncoderType { get; set; } = EncoderTypes.Jpeg;
         public IImageEncoder Encoder => Extensions.GetEncoder(EncoderType);
         public byte DrawLines { get; set; } = 5;
         public byte MaxRotationDegrees { get; set; } = 5;
         public Color[] BackgroundColor { get; set; } = new Color[] { Color.White };
+        public float? RotationDegree { get; set; } = 3;
 
         public CaptchaOptions()
         {