Fixing most of things of review

Also I fixed a little bug with PreviouslySeenPixels array

It's weird, but I don't see any problems with encoding and the tests are ok, I wrote the memory stream to files and they look the same, but the hashes and bytes aren't the same

This is very weird

src/ImageSharp/Formats/Qoi/QoiChunkEnum.cs → src/ImageSharp/Formats/Qoi/QoiChunk.cs

@@ -7,7 +7,7 @@ namespace SixLabors.ImageSharp.Formats.Qoi;
 /// Enum that contains the operations that encoder and decoder must process, written
 /// in binary to be easier to compare them in the reference
 /// </summary>
-public enum QoiChunkEnum
+internal enum QoiChunk
 {
     /// <summary>
     /// Indicates that the operation is QOI_OP_RGB where the RGB values are written

src/ImageSharp/Formats/Qoi/QoiDecoderCore.cs

@@ -160,10 +160,10 @@ internal class QoiDecoderCore : IImageDecoderInternals
                 byte[] pixelBytes;
                 Rgba32 readPixel;
                 TPixel pixel = default;
-                switch ((QoiChunkEnum)operationByte)
+                switch ((QoiChunk)operationByte)
                 {
                     // Reading one pixel with previous alpha intact
-                    case QoiChunkEnum.QoiOpRgb:
+                    case QoiChunk.QoiOpRgb:
                         pixelBytes = new byte[3];
                         if (stream.Read(pixelBytes) < 3)
                         {
@@ -177,7 +177,7 @@ internal class QoiDecoderCore : IImageDecoderInternals
                         break;
 
                     // Reading one pixel with new alpha
-                    case QoiChunkEnum.QoiOpRgba:
+                    case QoiChunk.QoiOpRgba:
                         pixelBytes = new byte[4];
                         if (stream.Read(pixelBytes) < 4)
                         {
@@ -191,16 +191,16 @@ internal class QoiDecoderCore : IImageDecoderInternals
                         break;
 
                     default:
-                        switch ((QoiChunkEnum)(operationByte & 0b11000000))
+                        switch ((QoiChunk)(operationByte & 0b11000000))
                         {
                             // Getting one pixel from previously seen pixels
-                            case QoiChunkEnum.QoiOpIndex:
+                            case QoiChunk.QoiOpIndex:
                                 readPixel = previouslySeenPixels[operationByte];
                                 pixel.FromRgba32(readPixel);
                                 break;
 
                             // Get one pixel from the difference (-2..1) of the previous pixel
-                            case QoiChunkEnum.QoiOpDiff:
+                            case QoiChunk.QoiOpDiff:
                                 byte redDifference = (byte)((operationByte & 0b00110000) >> 4),
                                     greenDifference = (byte)((operationByte & 0b00001100) >> 2),
                                     blueDifference = (byte)(operationByte & 0b00000011);
@@ -217,7 +217,7 @@ internal class QoiDecoderCore : IImageDecoderInternals
 
                             // Get green difference in 6 bits and red and blue differences
                             // depending on the green one
-                            case QoiChunkEnum.QoiOpLuma:
+                            case QoiChunk.QoiOpLuma:
                                 byte diffGreen = (byte)(operationByte & 0b00111111),
                                     currentGreen = (byte)((previousPixel.G + (diffGreen - 32)) % 256),
                                     nextByte = (byte)stream.ReadByte(),
@@ -232,7 +232,7 @@ internal class QoiDecoderCore : IImageDecoderInternals
                                 break;
 
                             // Repeating the previous pixel 1..63 times
-                            case QoiChunkEnum.QoiOpRun:
+                            case QoiChunk.QoiOpRun:
                                 byte repetitions = (byte)(operationByte & 0b00111111);
                                 if (repetitions is 62 or 63)
                                 {

src/ImageSharp/Formats/Qoi/QoiEncoder.cs

@@ -1,6 +1,8 @@
 // Copyright (c) Six Labors.
 // Licensed under the Six Labors Split License.
 
+using System.Text;
+
 namespace SixLabors.ImageSharp.Formats.Qoi;
 
 /// <summary>
@@ -8,10 +10,24 @@ namespace SixLabors.ImageSharp.Formats.Qoi;
 /// </summary>
 public class QoiEncoder : ImageEncoder
 {
+    /// <summary>
+    /// Gets the color channels on the image that can be
+    /// RGB or RGBA. This is purely informative. It doesn't
+    /// change the way data chunks are encoded.
+    /// </summary>
+    public QoiChannels? Channels { get; init; }
+
+    /// <summary>
+    /// Gets the color space of the image that can be sRGB with
+    /// linear alpha or all channels linear. This is purely
+    /// informative. It doesn't change the way data chunks are encoded.
+    /// </summary>
+    public QoiColorSpace? ColorSpace { get; init; }
+
     /// <inheritdoc />
     protected override void Encode<TPixel>(Image<TPixel> image, Stream stream, CancellationToken cancellationToken)
     {
-        QoiEncoderCore encoder = new();
+        QoiEncoderCore encoder = new(this);
         encoder.Encode(image, stream, cancellationToken);
     }
 }

src/ImageSharp/Formats/Qoi/QoiEncoderCore.cs

@@ -12,12 +12,11 @@ namespace SixLabors.ImageSharp.Formats.Qoi;
 /// </summary>
 public class QoiEncoderCore : IImageEncoderInternals
 {
+    private readonly QoiEncoder encoder;
     /// <summary>
     /// Initializes a new instance of the <see cref="QoiEncoderCore"/> class.
     /// </summary>
-    public QoiEncoderCore()
+    public QoiEncoderCore(QoiEncoder encoder) => this.encoder = encoder;
-    {
-    }
 
     /// <inheritdoc />
     public void Encode<TPixel>(Image<TPixel> image, Stream stream, CancellationToken cancellationToken)
@@ -26,23 +25,21 @@ public class QoiEncoderCore : IImageEncoderInternals
         Guard.NotNull(image, nameof(image));
         Guard.NotNull(stream, nameof(stream));
 
-        WriteHeader(image, stream);
+        this.WriteHeader(image, stream);
         WritePixels(image, stream);
         WriteEndOfStream(stream);
         stream.Flush();
     }
 
-    private static void WriteHeader(Image image, Stream stream)
+    private void WriteHeader(Image image, Stream stream)
     {
         // Get metadata
         Span<byte> width = stackalloc byte[4];
         Span<byte> height = stackalloc byte[4];
         BinaryPrimitives.WriteUInt32BigEndian(width, (uint)image.Width);
         BinaryPrimitives.WriteUInt32BigEndian(height, (uint)image.Height);
-        QoiChannels qoiChannels = image.PixelType.BitsPerPixel == 24 ? QoiChannels.Rgb : QoiChannels.Rgba;
+        QoiChannels qoiChannels = this.encoder.Channels ?? QoiChannels.Rgba;
-
+        QoiColorSpace qoiColorSpace = this.encoder.ColorSpace ?? QoiColorSpace.SrgbWithLinearAlpha;
-        // I need to check this, how do I check it with the pixel type or metadata of the original image?
-        const QoiColorSpace qoiColorSpace = QoiColorSpace.SrgbWithLinearAlpha;
 
         // Write header to the stream
         stream.Write(QoiConstants.Magic);
@@ -58,11 +55,9 @@ public class QoiEncoderCore : IImageEncoderInternals
         // Start image encoding
         Rgba32[] previouslySeenPixels = new Rgba32[64];
         Rgba32 previousPixel = new(0, 0, 0, 255);
-        int pixelArrayPosition = GetArrayPosition(previousPixel);
-        previouslySeenPixels[pixelArrayPosition] = previousPixel;
-
-        Buffer2D<TPixel> pixels = image.Frames[0].PixelBuffer;
         Rgba32 currentRgba32 = default;
+        Buffer2D<TPixel> pixels = image.Frames[0].PixelBuffer;
+
         for (int i = 0; i < pixels.Height; i++)
         {
             for (int j = 0; j < pixels.Width && i < pixels.Height; j++)
@@ -105,7 +100,7 @@ public class QoiEncoderCore : IImageEncoderInternals
                     while (currentRgba32.Equals(previousPixel) && repetitions < 62);
 
                     j--;
-                    stream.WriteByte((byte)((byte)QoiChunkEnum.QoiOpRun | (repetitions - 1)));
+                    stream.WriteByte((byte)((byte)QoiChunk.QoiOpRun | (repetitions - 1)));
 
                     /* If it's a QOI_OP_RUN, we don't overwrite the previous pixel since
                      * it will be taken and compared on the next iteration
@@ -115,7 +110,7 @@ public class QoiEncoderCore : IImageEncoderInternals
 
                 // else, we check if it exists in the previously seen pixels
                 // If so, we do a QOI_OP_INDEX
-                pixelArrayPosition = GetArrayPosition(currentRgba32);
+                int pixelArrayPosition = GetArrayPosition(currentRgba32);
                 if (previouslySeenPixels[pixelArrayPosition].Equals(currentPixel))
                 {
                     stream.WriteByte((byte)pixelArrayPosition);
@@ -140,7 +135,7 @@ public class QoiEncoderCore : IImageEncoderInternals
                         byte dr = (byte)(diffRed + 2),
                             dg = (byte)(diffGreen + 2),
                             db = (byte)(diffBlue + 2),
-                            valueToWrite = (byte)((byte)QoiChunkEnum.QoiOpDiff | (dr << 4) | (dg << 2) | db);
+                            valueToWrite = (byte)((byte)QoiChunk.QoiOpDiff | (dr << 4) | (dg << 2) | db);
                         stream.WriteByte(valueToWrite);
                     }
                     else
@@ -156,7 +151,7 @@ public class QoiEncoderCore : IImageEncoderInternals
                         {
                             byte dr_dg = (byte)(diffRedGreen + 8),
                                 db_dg = (byte)(diffBlueGreen + 8),
-                                byteToWrite1 = (byte)((byte)QoiChunkEnum.QoiOpLuma | (diffGreen + 32)),
+                                byteToWrite1 = (byte)((byte)QoiChunk.QoiOpLuma | (diffGreen + 32)),
                                 byteToWrite2 = (byte)((dr_dg << 4) | db_dg);
                             stream.WriteByte(byteToWrite1);
                             stream.WriteByte(byteToWrite2);
@@ -167,7 +162,7 @@ public class QoiEncoderCore : IImageEncoderInternals
                             // If so, we do a QOI_OP_RGB
                             if (currentRgba32.A == previousPixel.A)
                             {
-                                stream.WriteByte((byte)QoiChunkEnum.QoiOpRgb);
+                                stream.WriteByte((byte)QoiChunk.QoiOpRgb);
                                 stream.WriteByte(currentRgba32.R);
                                 stream.WriteByte(currentRgba32.G);
                                 stream.WriteByte(currentRgba32.B);
@@ -175,7 +170,7 @@ public class QoiEncoderCore : IImageEncoderInternals
                             else
                             {
                                 // else, we do a QOI_OP_RGBA
-                                stream.WriteByte((byte)QoiChunkEnum.QoiOpRgba);
+                                stream.WriteByte((byte)QoiChunk.QoiOpRgba);
                                 stream.WriteByte(currentRgba32.R);
                                 stream.WriteByte(currentRgba32.G);
                                 stream.WriteByte(currentRgba32.B);

src/ImageSharp/Formats/Qoi/QoiMetadata.cs

@@ -21,22 +21,10 @@ public class QoiMetadata : IDeepCloneable
     /// <param name="other">The metadata to create an instance from.</param>
     public QoiMetadata(QoiMetadata other)
     {
-        this.Width = other.Width;
-        this.Height = other.Height;
         this.Channels = other.Channels;
         this.ColorSpace = other.ColorSpace;
     }
 
-    /// <summary>
-    /// Gets or sets image width in pixels (BE)
-    /// </summary>
-    public uint Width { get; set; }
-
-    /// <summary>
-    /// Gets or sets image height in pixels (BE)
-    /// </summary>
-    public uint Height { get; set; }
-
     /// <summary>
     /// Gets or sets color channels of the image. 3 = RGB, 4 = RGBA.
     /// </summary>

tests/ImageSharp.Tests/Formats/Qoi/QoiEncoderTests.cs

@@ -4,6 +4,7 @@
 using SixLabors.ImageSharp.Formats.Qoi;
 using SixLabors.ImageSharp.PixelFormats;
 using SixLabors.ImageSharp.Tests.TestUtilities.ImageComparison;
+using SixLabors.ImageSharp.Tests.TestUtilities.ReferenceCodecs;
 
 namespace SixLabors.ImageSharp.Tests.Formats.Qoi;
 
@@ -24,12 +25,12 @@ public class QoiEncoderTests
     private static void Encode<TPixel>(TestImageProvider<TPixel> provider)
         where TPixel : unmanaged, IPixel<TPixel>
     {
-        using Image<TPixel> image = provider.GetImage();
+        using Image<TPixel> image = provider.GetImage(new MagickReferenceDecoder());
         using MemoryStream stream = new();
         QoiEncoder encoder = new();
         image.Save(stream, encoder);
         stream.Position = 0;
         using Image<TPixel> encodedImage = (Image<TPixel>)Image.Load(stream);
-        ImageComparingUtils.CompareWithReferenceDecoder(provider, encodedImage);
+        ImageComparer.Exact.CompareImages(image, encodedImage);
     }
 }