ImageSharp/tests/ImageSharp.Tests/Processing/Processors/Dithering/DitherTests.cs

// Copyright (c) Six Labors.
// Licensed under the Six Labors Split License.

using SixLabors.ImageSharp.PixelFormats;
using SixLabors.ImageSharp.Processing;
using SixLabors.ImageSharp.Processing.Processors.Dithering;
using SixLabors.ImageSharp.Tests.TestUtilities.ImageComparison;

namespace SixLabors.ImageSharp.Tests.Processing.Processors.Dithering;

[Trait("Category", "Processors")]
public class DitherTests
{
    public const PixelTypes CommonNonDefaultPixelTypes =
        PixelTypes.Rgba32 | PixelTypes.Bgra32 | PixelTypes.Rgb24 | PixelTypes.RgbaVector;

    public static readonly string[] CommonTestImages = [TestImages.Png.CalliphoraPartial, TestImages.Png.Bike];

    public static readonly TheoryData<IDither, string> ErrorDiffusers
        = new()
        {
            { KnownDitherings.Atkinson, nameof(KnownDitherings.Atkinson) },
            { KnownDitherings.Burks, nameof(KnownDitherings.Burks) },
            { KnownDitherings.FloydSteinberg, nameof(KnownDitherings.FloydSteinberg) },
            { KnownDitherings.JarvisJudiceNinke, nameof(KnownDitherings.JarvisJudiceNinke) },
            { KnownDitherings.Sierra2, nameof(KnownDitherings.Sierra2) },
            { KnownDitherings.Sierra3, nameof(KnownDitherings.Sierra3) },
            { KnownDitherings.SierraLite, nameof(KnownDitherings.SierraLite) },
            { KnownDitherings.StevensonArce, nameof(KnownDitherings.StevensonArce) },
            { KnownDitherings.Stucki, nameof(KnownDitherings.Stucki) },
        };

    public static readonly TheoryData<IDither, string> OrderedDitherers
        = new()
        {
            { KnownDitherings.Bayer2x2, nameof(KnownDitherings.Bayer2x2) },
            { KnownDitherings.Bayer4x4, nameof(KnownDitherings.Bayer4x4) },
            { KnownDitherings.Bayer8x8, nameof(KnownDitherings.Bayer8x8) },
            { KnownDitherings.Bayer16x16, nameof(KnownDitherings.Bayer16x16) },
            { KnownDitherings.Ordered3x3, nameof(KnownDitherings.Ordered3x3) }
        };

    public static readonly TheoryData<IDither> DefaultInstanceDitherers
        = new()
        {
            default(ErrorDither),
            default(OrderedDither)
        };

    private static readonly ImageComparer ValidatorComparer = ImageComparer.TolerantPercentage(0.05f);

    private static IDither DefaultDitherer => KnownDitherings.Bayer4x4;

    private static IDither DefaultErrorDiffuser => KnownDitherings.Atkinson;

    /// <summary>
    /// The output is visually correct old 32bit runtime,
    /// but it is very different because of floating point inaccuracies.
    /// </summary>
    private static readonly bool SkipAllDitherTests =
        !TestEnvironment.Is64BitProcess && TestEnvironment.NetCoreVersion == null;

    [Theory]
    [WithFile(TestImages.Png.CalliphoraPartial, PixelTypes.Rgba32)]
    public void ApplyDiffusionFilterInBox<TPixel>(TestImageProvider<TPixel> provider)
        where TPixel : unmanaged, IPixel<TPixel>
    {
        if (SkipAllDitherTests)
        {
            return;
        }

        provider.RunRectangleConstrainedValidatingProcessorTest(
            (x, rect) => x.Dither(DefaultErrorDiffuser, rect),
            comparer: ValidatorComparer);
    }

    [Theory]
    [WithFile(TestImages.Png.CalliphoraPartial, PixelTypes.Rgba32)]
    public void ApplyDitherFilterInBox<TPixel>(TestImageProvider<TPixel> provider)
        where TPixel : unmanaged, IPixel<TPixel>
    {
        if (SkipAllDitherTests)
        {
            return;
        }

        provider.RunRectangleConstrainedValidatingProcessorTest(
            (x, rect) => x.Dither(DefaultDitherer, rect),
            comparer: ValidatorComparer);
    }

    [Theory]
    [WithFile(TestImages.Png.Filter0, CommonNonDefaultPixelTypes)]
    public void DiffusionFilter_ShouldNotDependOnSinglePixelType<TPixel>(TestImageProvider<TPixel> provider)
        where TPixel : unmanaged, IPixel<TPixel>
    {
        if (SkipAllDitherTests)
        {
            return;
        }

        // Increased tolerance because of compatibility issues on .NET 4.6.2:
        ImageComparer comparer = ImageComparer.TolerantPercentage(1f);
        provider.RunValidatingProcessorTest(x => x.Dither(DefaultErrorDiffuser), comparer: comparer);
    }

    [Theory]
    [WithFileCollection(nameof(CommonTestImages), nameof(ErrorDiffusers), PixelTypes.Rgba32)]
    public void DiffusionFilter_WorksWithAllErrorDiffusers<TPixel>(
        TestImageProvider<TPixel> provider,
        IDither diffuser,
        string name)
        where TPixel : unmanaged, IPixel<TPixel>
    {
        if (SkipAllDitherTests)
        {
            return;
        }

        provider.RunValidatingProcessorTest(
            x => x.Dither(diffuser),
            testOutputDetails: name,
            comparer: ValidatorComparer,
            appendPixelTypeToFileName: false);
    }

    [Theory]
    [WithFile(TestImages.Png.Filter0, CommonNonDefaultPixelTypes)]
    public void DitherFilter_ShouldNotDependOnSinglePixelType<TPixel>(TestImageProvider<TPixel> provider)
        where TPixel : unmanaged, IPixel<TPixel>
    {
        if (SkipAllDitherTests)
        {
            return;
        }

        provider.RunValidatingProcessorTest(
            x => x.Dither(DefaultDitherer),
            comparer: ValidatorComparer);
    }

    [Theory]
    [WithFileCollection(nameof(CommonTestImages), nameof(OrderedDitherers), PixelTypes.Rgba32)]
    public void DitherFilter_WorksWithAllDitherers<TPixel>(
        TestImageProvider<TPixel> provider,
        IDither ditherer,
        string name)
        where TPixel : unmanaged, IPixel<TPixel>
    {
        if (SkipAllDitherTests)
        {
            return;
        }

        provider.RunValidatingProcessorTest(
            x => x.Dither(ditherer),
            testOutputDetails: name,
            comparer: ValidatorComparer,
            appendPixelTypeToFileName: false);
    }

    [Theory]
    [WithFile(TestImages.Png.Bike, PixelTypes.Rgba32, nameof(OrderedDither.Ordered3x3))]
    [WithFile(TestImages.Png.Bike, PixelTypes.Rgba32, nameof(ErrorDither.FloydSteinberg))]
    public void CommonDitherers_WorkWithDiscoBuffers<TPixel>(
        TestImageProvider<TPixel> provider,
        string name)
        where TPixel : unmanaged, IPixel<TPixel>
    {
        IDither dither = TestUtils.GetDither(name);
        if (SkipAllDitherTests)
        {
            return;
        }

        provider.RunBufferCapacityLimitProcessorTest(
            41,
            c => c.Dither(dither),
            name);
    }

    [Theory]
    [MemberData(nameof(DefaultInstanceDitherers))]
    public void ShouldThrowForDefaultDitherInstance(IDither dither)
    {
        void Command()
        {
            using Image<Rgba32> image = new(10, 10);
            image.Mutate(x => x.Dither(dither));
        }

        Assert.Throws<ImageProcessingException>(Command);
    }
}