Animated webp encoder

src/ImageSharp/Common/Helpers/RiffHelper.cs

@@ -0,0 +1,124 @@
+// Copyright (c) Six Labors.
+// Licensed under the Six Labors Split License.
+
+using System.Buffers.Binary;
+using System.Text;
+
+namespace SixLabors.ImageSharp.Common.Helpers;
+
+internal static class RiffHelper
+{
+    /// <summary>
+    /// The header bytes identifying RIFF file.
+    /// </summary>
+    private const uint RiffFourCc = 0x52_49_46_46;
+
+    public static void WriteRiffFile(Stream stream, string formType, Action<Stream> func) =>
+        WriteChunk(stream, RiffFourCc, s =>
+        {
+            s.Write(Encoding.ASCII.GetBytes(formType));
+            func(s);
+        });
+
+    public static void WriteChunk(Stream stream, uint fourCc, Action<Stream> func)
+    {
+        Span<byte> buffer = stackalloc byte[4];
+
+        // write the fourCC
+        BinaryPrimitives.WriteUInt32BigEndian(buffer, fourCc);
+        stream.Write(buffer);
+
+        long sizePosition = stream.Position;
+        stream.Position += 4;
+
+        func(stream);
+
+        long position = stream.Position;
+
+        uint dataSize = (uint)(position - sizePosition - 4);
+
+        // padding
+        if (dataSize % 2 == 1)
+        {
+            stream.WriteByte(0);
+            position++;
+        }
+
+        BinaryPrimitives.WriteUInt32LittleEndian(buffer, dataSize);
+        stream.Position = sizePosition;
+        stream.Write(buffer);
+        stream.Position = position;
+    }
+
+    public static void WriteChunk(Stream stream, uint fourCc, ReadOnlySpan<byte> data)
+    {
+        Span<byte> buffer = stackalloc byte[4];
+
+        // write the fourCC
+        BinaryPrimitives.WriteUInt32BigEndian(buffer, fourCc);
+        stream.Write(buffer);
+        uint size = (uint)data.Length;
+        BinaryPrimitives.WriteUInt32LittleEndian(buffer, size);
+        stream.Write(buffer);
+        stream.Write(data);
+
+        // padding
+        if (size % 2 is 1)
+        {
+            stream.WriteByte(0);
+        }
+    }
+
+    public static unsafe void WriteChunk<TStruct>(Stream stream, uint fourCc, in TStruct chunk)
+        where TStruct : unmanaged
+    {
+        fixed (TStruct* ptr = &chunk)
+        {
+            WriteChunk(stream, fourCc, new Span<byte>(ptr, sizeof(TStruct)));
+        }
+    }
+
+    public static long BeginWriteChunk(Stream stream, uint fourCc)
+    {
+        Span<byte> buffer = stackalloc byte[4];
+
+        // write the fourCC
+        BinaryPrimitives.WriteUInt32BigEndian(buffer, fourCc);
+        stream.Write(buffer);
+
+        long sizePosition = stream.Position;
+        stream.Position += 4;
+
+        return sizePosition;
+    }
+
+    public static void EndWriteChunk(Stream stream, long sizePosition)
+    {
+        Span<byte> buffer = stackalloc byte[4];
+
+        long position = stream.Position;
+
+        uint dataSize = (uint)(position - sizePosition - 4);
+
+        // padding
+        if (dataSize % 2 is 1)
+        {
+            stream.WriteByte(0);
+            position++;
+        }
+
+        BinaryPrimitives.WriteUInt32LittleEndian(buffer, dataSize);
+        stream.Position = sizePosition;
+        stream.Write(buffer);
+        stream.Position = position;
+    }
+
+    public static long BeginWriteRiffFile(Stream stream, string formType)
+    {
+        long sizePosition = BeginWriteChunk(stream, RiffFourCc);
+        stream.Write(Encoding.ASCII.GetBytes(formType));
+        return sizePosition;
+    }
+
+    public static void EndWriteRiffFile(Stream stream, long sizePosition) => EndWriteChunk(stream, sizePosition);
+}

src/ImageSharp/Formats/Webp/AlphaDecoder.cs

@@ -59,7 +59,7 @@ public AlphaDecoder(int width, int height, IMemoryOwner<byte> data, byte alphaCh
 
         if (this.Compressed)
         {
-            Vp8LBitReader bitReader = new(data);
+            Vp8LBitReader bitReader = new Vp8LBitReader(data);
             this.LosslessDecoder = new WebpLosslessDecoder(bitReader, memoryAllocator, configuration);
             this.LosslessDecoder.DecodeImageStream(this.Vp8LDec, width, height, true);
 

src/ImageSharp/Formats/Webp/AlphaEncoder.cs

@@ -19,25 +19,25 @@ internal static class AlphaEncoder
     /// Data is either compressed as lossless webp image or uncompressed.
     /// </summary>
     /// <typeparam name="TPixel">The pixel format.</typeparam>
-    /// <param name="image">The <see cref="ImageFrame{TPixel}"/> to encode from.</param>
+    /// <param name="frame">The <see cref="ImageFrame{TPixel}"/> to encode from.</param>
     /// <param name="configuration">The global configuration.</param>
     /// <param name="memoryAllocator">The memory manager.</param>
     /// <param name="skipMetadata">Whether to skip metadata encoding.</param>
     /// <param name="compress">Indicates, if the data should be compressed with the lossless webp compression.</param>
     /// <param name="size">The size in bytes of the alpha data.</param>
     /// <returns>The encoded alpha data.</returns>
     public static IMemoryOwner<byte> EncodeAlpha<TPixel>(
-        Image<TPixel> image,
+        ImageFrame<TPixel> frame,
         Configuration configuration,
         MemoryAllocator memoryAllocator,
         bool skipMetadata,
         bool compress,
         out int size)
         where TPixel : unmanaged, IPixel<TPixel>
     {
-        int width = image.Width;
-        int height = image.Height;
-        IMemoryOwner<byte> alphaData = ExtractAlphaChannel(image, configuration, memoryAllocator);
+        int width = frame.Width;
+        int height = frame.Height;
+        IMemoryOwner<byte> alphaData = ExtractAlphaChannel(frame, configuration, memoryAllocator);
 
         if (compress)
         {
@@ -58,9 +58,9 @@ internal static class AlphaEncoder
             // The transparency information will be stored in the green channel of the ARGB quadruplet.
             // The green channel is allowed extra transformation steps in the specification -- unlike the other channels,
             // that can improve compression.
-            using Image<Rgba32> alphaAsImage = DispatchAlphaToGreen(image, alphaData.GetSpan());
+            using ImageFrame<Rgba32> alphaAsFrame = DispatchAlphaToGreen(frame, alphaData.GetSpan());
 
-            size = lossLessEncoder.EncodeAlphaImageData(alphaAsImage, alphaData);
+            size = lossLessEncoder.EncodeAlphaImageData(alphaAsFrame, alphaData);
 
             return alphaData;
         }
@@ -73,19 +73,19 @@ internal static class AlphaEncoder
     /// Store the transparency in the green channel.
     /// </summary>
     /// <typeparam name="TPixel">The pixel format.</typeparam>
-    /// <param name="image">The <see cref="ImageFrame{TPixel}"/> to encode from.</param>
+    /// <param name="frame">The <see cref="ImageFrame{TPixel}"/> to encode from.</param>
     /// <param name="alphaData">A byte sequence of length width * height, containing all the 8-bit transparency values in scan order.</param>
-    /// <returns>The transparency image.</returns>
-    private static Image<Rgba32> DispatchAlphaToGreen<TPixel>(Image<TPixel> image, Span<byte> alphaData)
+    /// <returns>The transparency frame.</returns>
+    private static ImageFrame<Rgba32> DispatchAlphaToGreen<TPixel>(ImageFrame<TPixel> frame, Span<byte> alphaData)
         where TPixel : unmanaged, IPixel<TPixel>
     {
-        int width = image.Width;
-        int height = image.Height;
-        Image<Rgba32> alphaAsImage = new(width, height);
+        int width = frame.Width;
+        int height = frame.Height;
+        ImageFrame<Rgba32> alphaAsFrame = new ImageFrame<Rgba32>(Configuration.Default, width, height);
 
         for (int y = 0; y < height; y++)
         {
-            Memory<Rgba32> rowBuffer = alphaAsImage.DangerousGetPixelRowMemory(y);
+            Memory<Rgba32> rowBuffer = alphaAsFrame.DangerousGetPixelRowMemory(y);
             Span<Rgba32> pixelRow = rowBuffer.Span;
             Span<byte> alphaRow = alphaData.Slice(y * width, width);
             for (int x = 0; x < width; x++)
@@ -95,23 +95,23 @@ private static Image<Rgba32> DispatchAlphaToGreen<TPixel>(Image<TPixel> image, S
             }
         }
 
-        return alphaAsImage;
+        return alphaAsFrame;
     }
 
     /// <summary>
     /// Extract the alpha data of the image.
     /// </summary>
     /// <typeparam name="TPixel">The pixel format.</typeparam>
-    /// <param name="image">The <see cref="ImageFrame{TPixel}"/> to encode from.</param>
+    /// <param name="frame">The <see cref="ImageFrame{TPixel}"/> to encode from.</param>
     /// <param name="configuration">The global configuration.</param>
     /// <param name="memoryAllocator">The memory manager.</param>
     /// <returns>A byte sequence of length width * height, containing all the 8-bit transparency values in scan order.</returns>
-    private static IMemoryOwner<byte> ExtractAlphaChannel<TPixel>(Image<TPixel> image, Configuration configuration, MemoryAllocator memoryAllocator)
+    private static IMemoryOwner<byte> ExtractAlphaChannel<TPixel>(ImageFrame<TPixel> frame, Configuration configuration, MemoryAllocator memoryAllocator)
         where TPixel : unmanaged, IPixel<TPixel>
     {
-        Buffer2D<TPixel> imageBuffer = image.Frames.RootFrame.PixelBuffer;
-        int height = image.Height;
-        int width = image.Width;
+        Buffer2D<TPixel> imageBuffer = frame.PixelBuffer;
+        int height = frame.Height;
+        int width = frame.Width;
         IMemoryOwner<byte> alphaDataBuffer = memoryAllocator.Allocate<byte>(width * height);
         Span<byte> alphaData = alphaDataBuffer.GetSpan();