fix(high-memory-usage): reuse SKTypeface to avoid high memory usage (#20 #21)

Author: ashtonav

src/Captcha.Core/Constants.cs

@@ -10,11 +10,17 @@ public static class Constants
     public const int DefaultCaptchaHeight = 100;
     public const float DefaultFrequency = 100F;
     public const int FrequencyScalingFactor = 40000; // on a 400 x 100 image
-    public const string DefaultCaptchaFontName = "Captcha.Core.Resources.Fonts.Caveat-SemiBold.ttf";
-    public const string DefaultCaptchaFallbackFontName = "Captcha.Core.Resources.Fonts.Unifont.ttf";
     public static readonly SKColor DefaultPrimaryColor = SKColor.Parse("FFD3D3D3");
     public static readonly SKColor DefaultSecondaryColor = SKColor.Parse("FFFFFFFF");
     public const string CaptchaContentType = "image/jpeg";
     public const float WarpCaptchaTextFrequency = 4F;
     public const int CaptchaNoise = 50;
+
+    // According to https://learn.microsoft.com/en-us/dotnet/api/skiasharp.sktypeface, this should be thread-safe
+    public static SKTypeface MainFontTypeface { get; } =
+        SKTypeface.FromStream(typeof(Constants).Assembly.GetManifestResourceStream("Captcha.Core.Resources.Fonts.Caveat-SemiBold.ttf"));
+
+    // According to https://learn.microsoft.com/en-us/dotnet/api/skiasharp.sktypeface, this should be thread-safe
+    public static SKTypeface FallbackFontTypeface { get; } =
+        SKTypeface.FromStream(typeof(Constants).Assembly.GetManifestResourceStream("Captcha.Core.Resources.Fonts.Unifont.ttf"));
 }

src/Captcha.Core/Services/CaptchaImageService.cs

@@ -6,22 +6,6 @@ namespace Captcha.Core.Services;
 
 public class CaptchaImageService : ICaptchaImageService
 {
-    private readonly SKTypeface _mainFontTypeface;
-    private readonly SKTypeface _fallbackFontTypeface;
-
-    public CaptchaImageService()
-    {
-        var assembly = typeof(CaptchaImageService).Assembly;
-
-        _mainFontTypeface = SKTypeface.FromStream(
-            assembly.GetManifestResourceStream(Constants.DefaultCaptchaFontName)
-        );
-
-        _fallbackFontTypeface = SKTypeface.FromStream(
-            assembly.GetManifestResourceStream(Constants.DefaultCaptchaFallbackFontName)
-        );
-    }
-
     public SKBitmap CreateCaptchaImage(CaptchaConfigurationData config)
     {
         var bitmap = new SKBitmap(new SKImageInfo(config.Width, config.Height));
@@ -89,7 +73,7 @@ private static void DrawWarpedText(CaptchaConfigurationData config, SKFont font,
         graphics.DrawPath(path, fillPaint);
     }
 
-    private SKFont GetFontThatFitsRectangle(CaptchaConfigurationData config, SKRect rectangle)
+    private static SKFont GetFontThatFitsRectangle(CaptchaConfigurationData config, SKRect rectangle)
     {
         var typeface = GetTypefaceThatCanRenderText(config.Text);
 
@@ -123,16 +107,16 @@ private static void FillInTheBackground(CaptchaConfigurationData config, SKRect
         graphics.DrawRect(rectangle, paint);
     }
 
-    private SKTypeface GetTypefaceThatCanRenderText(string text)
+    private static SKTypeface GetTypefaceThatCanRenderText(string text)
     {
-        using var mainFont = new SKFont(_mainFontTypeface);
+        using var mainFont = new SKFont(Constants.MainFontTypeface);
 
         if (mainFont.ContainsGlyphs(text))
         {
-            return _mainFontTypeface;
+            return Constants.MainFontTypeface;
         }
 
-        return _fallbackFontTypeface;
+        return Constants.FallbackFontTypeface;
     }
 
     /// <summary>

tests/Captcha.UnitTests/ConstantsTests.cs

@@ -22,12 +22,6 @@ public class ConstantsTests
     [Test]
     public void DefaultFrequencyShouldBe100() => Assert.That(Constants.DefaultFrequency, Is.EqualTo(100F));
 
-    [Test]
-    public void DefaultCaptchaFontNameShouldBeCaveat() => Assert.That(Constants.DefaultCaptchaFontName, Is.EqualTo("Captcha.Core.Resources.Fonts.Caveat-SemiBold.ttf"));
-
-    [Test]
-    public void FallbackCaptchaFontNameShouldBeUnifont() => Assert.That(Constants.DefaultCaptchaFallbackFontName, Is.EqualTo("Captcha.Core.Resources.Fonts.Unifont.ttf"));
-
     [Test]
     public void DefaultPrimaryColorShouldBeDarkGray() => Assert.That(Constants.DefaultPrimaryColor, Is.EqualTo(SKColor.Parse("FFD3D3D3")));