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

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Merged
ashtonav merged 4 commits into from
Sep 21, 2025
Merged

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

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368f9d7
fix(high-memory-usage): reuse SKTypeface to avoid high memory usage
ashtonav Sep 20, 2025
4fb1b00
improve from Sonarqube feedback
ashtonav Sep 21, 2025
eb2b40b
add comments about thread safety
ashtonav Sep 21, 2025
2cc2218
improve comments
ashtonav Sep 21, 2025
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10 changes: 8 additions & 2 deletions src/Captcha.Core/Constants.cs
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Original file line number Diff line number Diff line change
Expand Up @@ -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"));
}
26 changes: 5 additions & 21 deletions src/Captcha.Core/Services/CaptchaImageService.cs
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Expand Up @@ -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));
Expand Down Expand Up @@ -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);

Expand Down Expand Up @@ -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>
Expand Down
6 changes: 0 additions & 6 deletions tests/Captcha.UnitTests/ConstantsTests.cs
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Expand Up @@ -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")));

Expand Down
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