Add decoding animated lossy webp

src/ImageSharp/Formats/Webp/Lossless/WebpLosslessDecoder.cs

@@ -87,7 +87,7 @@ namespace SixLabors.ImageSharp.Formats.Webp.Lossless
         private static ReadOnlySpan<byte> LiteralMap => new byte[] { 0, 1, 1, 1, 0 };
 
         /// <summary>
-        /// Decodes the image from the stream using the bitreader.
+        /// Decodes the lossless webp image from the stream.
         /// </summary>
         /// <typeparam name="TPixel">The pixel format.</typeparam>
         /// <param name="pixels">The pixel buffer to store the decoded data.</param>

src/ImageSharp/Formats/Webp/Lossy/WebpLossyDecoder.cs

@@ -57,7 +57,16 @@ namespace SixLabors.ImageSharp.Formats.Webp.Lossy
             this.configuration = configuration;
         }
 
-        public void Decode<TPixel>(Buffer2D<TPixel> pixels, int width, int height, WebpImageInfo info)
+        /// <summary>
+        /// Decodes the lossless webp image from the stream.
+        /// </summary>
+        /// <typeparam name="TPixel">The pixel format.</typeparam>
+        /// <param name="pixels">The pixel buffer to store the decoded data.</param>
+        /// <param name="width">The width of the image.</param>
+        /// <param name="height">The height of the image.</param>
+        /// <param name="info">Information about the image.</param>
+        /// <param name="alphaData">The ALPH chunk data.</param>
+        public void Decode<TPixel>(Buffer2D<TPixel> pixels, int width, int height, WebpImageInfo info, IMemoryOwner<byte> alphaData)
             where TPixel : unmanaged, IPixel<TPixel>
         {
             // Paragraph 9.2: color space and clamp type follow.
@@ -105,7 +114,7 @@ namespace SixLabors.ImageSharp.Formats.Webp.Lossy
                     using (var alphaDecoder = new AlphaDecoder(
                         width,
                         height,
-                        info.Features.AlphaData,
+                        alphaData,
                         info.Features.AlphaChunkHeader,
                         this.memoryAllocator,
                         this.configuration))

src/ImageSharp/Formats/Webp/WebpAnimationDecoder.cs

@@ -2,6 +2,7 @@
 // Licensed under the Apache License, Version 2.0.
 
 using System;
+using System.Buffers;
 using SixLabors.ImageSharp.Formats.Webp.Lossless;
 using SixLabors.ImageSharp.Formats.Webp.Lossy;
 using SixLabors.ImageSharp.IO;
@@ -14,7 +15,7 @@ namespace SixLabors.ImageSharp.Formats.Webp
     /// <summary>
     /// Decoder for animated webp images.
     /// </summary>
-    internal class WebpAnimationDecoder
+    internal class WebpAnimationDecoder : IDisposable
     {
         /// <summary>
         /// Reusable buffer.
@@ -47,6 +48,11 @@ namespace SixLabors.ImageSharp.Formats.Webp
             this.configuration = configuration;
         }
 
+        /// <summary>
+        /// Gets or sets the alpha data, if an ALPH chunk is present.
+        /// </summary>
+        public IMemoryOwner<byte> AlphaData { get; set; }
+
         /// <summary>
         /// Decodes the animated webp image from the specified stream.
         /// </summary>
@@ -108,12 +114,12 @@ namespace SixLabors.ImageSharp.Formats.Webp
             long streamStartPosition = stream.Position;
 
             WebpChunkType chunkType = WebpChunkParsingUtils.ReadChunkType(stream, this.buffer);
+            bool hasAlpha = false;
+            byte alphaChunkHeader = 0;
             if (chunkType is WebpChunkType.Alpha)
             {
-                // TODO: ignore alpha for now.
-                stream.Skip(4);
-                uint alphaChunkSize = WebpChunkParsingUtils.ReadChunkSize(stream, this.buffer);
-                stream.Skip((int)alphaChunkSize);
+                alphaChunkHeader = this.ReadAlphaData(stream);
+                hasAlpha = true;
                 chunkType = WebpChunkParsingUtils.ReadChunkType(stream, this.buffer);
             }
 
@@ -123,6 +129,8 @@ namespace SixLabors.ImageSharp.Formats.Webp
             {
                 case WebpChunkType.Vp8:
                     webpInfo = WebpChunkParsingUtils.ReadVp8Header(this.memoryAllocator, stream, this.buffer, features);
+                    features.Alpha = hasAlpha;
+                    features.AlphaChunkHeader = alphaChunkHeader;
                     break;
                 case WebpChunkType.Vp8L:
                     webpInfo = WebpChunkParsingUtils.ReadVp8LHeader(this.memoryAllocator, stream, this.buffer, features);
@@ -171,6 +179,25 @@ namespace SixLabors.ImageSharp.Formats.Webp
             return (uint)(stream.Position - streamStartPosition);
         }
 
+        /// <summary>
+        /// Reads the ALPH chunk data.
+        /// </summary>
+        /// <param name="stream">The stream to read from.</param>
+        private byte ReadAlphaData(BufferedReadStream stream)
+        {
+            this.AlphaData?.Dispose();
+
+            uint alphaChunkSize = WebpChunkParsingUtils.ReadChunkSize(stream, this.buffer);
+            int alphaDataSize = (int)(alphaChunkSize - 1);
+            this.AlphaData = this.memoryAllocator.Allocate<byte>(alphaDataSize);
+
+            byte alphaChunkHeader = (byte)stream.ReadByte();
+            Span<byte> alphaData = this.AlphaData.GetSpan();
+            stream.Read(alphaData, 0, alphaDataSize);
+
+            return alphaChunkHeader;
+        }
+
         /// <summary>
         /// Decodes the either lossy or lossless webp image data.
         /// </summary>
@@ -191,7 +218,7 @@ namespace SixLabors.ImageSharp.Formats.Webp
             else
             {
                 var lossyDecoder = new WebpLossyDecoder(webpInfo.Vp8BitReader, this.memoryAllocator, this.configuration);
-                lossyDecoder.Decode(pixelBufferDecoded, (int)webpInfo.Width, (int)webpInfo.Height, webpInfo);
+                lossyDecoder.Decode(pixelBufferDecoded, (int)webpInfo.Width, (int)webpInfo.Height, webpInfo, this.AlphaData);
             }
 
             return decodedImage;
@@ -326,5 +353,8 @@ namespace SixLabors.ImageSharp.Formats.Webp
 
             return data;
         }
+
+        /// <inheritdoc/>
+        public void Dispose() => this.AlphaData?.Dispose();
     }
 }

src/ImageSharp/Formats/Webp/WebpChunkParsingUtils.cs

@@ -25,7 +25,7 @@ namespace SixLabors.ImageSharp.Formats.Webp
             stream.Read(buffer, 0, 4);
             uint dataSize = BinaryPrimitives.ReadUInt32LittleEndian(buffer);
 
-            // remaining counts the available image data payload.
+            // Remaining counts the available image data payload.
             uint remaining = dataSize;
 
             // Paragraph 9.1 https://tools.ietf.org/html/rfc6386#page-30

src/ImageSharp/Formats/Webp/WebpDecoder.cs

@@ -26,7 +26,7 @@ namespace SixLabors.ImageSharp.Formats.Webp
         {
             Guard.NotNull(stream, nameof(stream));
 
-            var decoder = new WebpDecoderCore(configuration, this);
+            using var decoder = new WebpDecoderCore(configuration, this);
 
             try
             {
@@ -57,7 +57,7 @@ namespace SixLabors.ImageSharp.Formats.Webp
         {
             Guard.NotNull(stream, nameof(stream));
 
-            var decoder = new WebpDecoderCore(configuration, this);
+            using var decoder = new WebpDecoderCore(configuration, this);
 
             try
             {

src/ImageSharp/Formats/Webp/WebpDecoderCore.cs

@@ -1,6 +1,8 @@
 // Copyright (c) Six Labors.
 // Licensed under the Apache License, Version 2.0.
 
+using System;
+using System.Buffers;
 using System.Buffers.Binary;
 using System.IO;
 using System.Threading;
@@ -19,7 +21,7 @@ namespace SixLabors.ImageSharp.Formats.Webp
     /// <summary>
     /// Performs the webp decoding operation.
     /// </summary>
-    internal sealed class WebpDecoderCore : IImageDecoderInternals
+    internal sealed class WebpDecoderCore : IImageDecoderInternals, IDisposable
     {
         /// <summary>
         /// Reusable buffer.
@@ -76,6 +78,11 @@ namespace SixLabors.ImageSharp.Formats.Webp
         /// </summary>
         public Size Dimensions => new((int)this.webImageInfo.Width, (int)this.webImageInfo.Height);
 
+        /// <summary>
+        /// Gets or sets the alpha data, if an ALPH chunk is present.
+        /// </summary>
+        public IMemoryOwner<byte> AlphaData { get; set; }
+
         /// <inheritdoc />
         public Image<TPixel> Decode<TPixel>(BufferedReadStream stream, CancellationToken cancellationToken)
             where TPixel : unmanaged, IPixel<TPixel>
@@ -89,7 +96,7 @@ namespace SixLabors.ImageSharp.Formats.Webp
             {
                 if (this.webImageInfo.Features is { Animation: true })
                 {
-                    var animationDecoder = new WebpAnimationDecoder(this.memoryAllocator, this.Configuration);
+                    using var animationDecoder = new WebpAnimationDecoder(this.memoryAllocator, this.Configuration);
                     return animationDecoder.Decode<TPixel>(stream, this.webImageInfo.Features, this.webImageInfo.Width, this.webImageInfo.Height, fileSize);
                 }
 
@@ -104,7 +111,7 @@ namespace SixLabors.ImageSharp.Formats.Webp
                 else
                 {
                     var lossyDecoder = new WebpLossyDecoder(this.webImageInfo.Vp8BitReader, this.memoryAllocator, this.Configuration);
-                    lossyDecoder.Decode(pixels, image.Width, image.Height, this.webImageInfo);
+                    lossyDecoder.Decode(pixels, image.Width, image.Height, this.webImageInfo, this.AlphaData);
                 }
 
                 // There can be optional chunks after the image data, like EXIF and XMP.
@@ -120,7 +127,7 @@ namespace SixLabors.ImageSharp.Formats.Webp
             this.currentStream = stream;
 
             this.ReadImageHeader();
-            using (this.webImageInfo = this.ReadVp8Info())
+            using (this.webImageInfo = this.ReadVp8Info(true))
             {
                 return new ImageInfo(new PixelTypeInfo((int)this.webImageInfo.BitsPerPixel), (int)this.webImageInfo.Width, (int)this.webImageInfo.Height, this.Metadata);
             }
@@ -149,8 +156,9 @@ namespace SixLabors.ImageSharp.Formats.Webp
         /// <summary>
         /// Reads information present in the image header, about the image content and how to decode the image.
         /// </summary>
+        /// <param name="ignoreAlpha">For identify, the alpha data should not be read.</param>
         /// <returns>Information about the webp image.</returns>
-        private WebpImageInfo ReadVp8Info()
+        private WebpImageInfo ReadVp8Info(bool ignoreAlpha = false)
         {
             this.Metadata = new ImageMetadata();
             this.webpMetadata = this.Metadata.GetFormatMetadata(WebpFormat.Instance);
@@ -183,7 +191,7 @@ namespace SixLabors.ImageSharp.Formats.Webp
                         }
                         else if (WebpChunkParsingUtils.IsOptionalVp8XChunk(chunkType))
                         {
-                            bool isAnimationChunk = this.ParseOptionalExtendedChunks(chunkType, features);
+                            bool isAnimationChunk = this.ParseOptionalExtendedChunks(chunkType, features, ignoreAlpha);
                             if (isAnimationChunk)
                             {
                                 return webpInfos;
@@ -207,8 +215,9 @@ namespace SixLabors.ImageSharp.Formats.Webp
         /// </summary>
         /// <param name="chunkType">The chunk type.</param>
         /// <param name="features">The webp image features.</param>
+        /// <param name="ignoreAlpha">For identify, the alpha data should not be read.</param>
         /// <returns>true, if animation chunk was found.</returns>
-        private bool ParseOptionalExtendedChunks(WebpChunkType chunkType, WebpFeatures features)
+        private bool ParseOptionalExtendedChunks(WebpChunkType chunkType, WebpFeatures features, bool ignoreAlpha)
         {
             int bytesRead;
             switch (chunkType)
@@ -293,10 +302,16 @@ namespace SixLabors.ImageSharp.Formats.Webp
 
                 case WebpChunkType.Alpha:
                     uint alphaChunkSize = WebpChunkParsingUtils.ReadChunkSize(this.currentStream, this.buffer);
+                    if (ignoreAlpha)
+                    {
+                        this.currentStream.Skip((int)alphaChunkSize);
+                    }
+
                     features.AlphaChunkHeader = (byte)this.currentStream.ReadByte();
                     int alphaDataSize = (int)(alphaChunkSize - 1);
-                    features.AlphaData = this.memoryAllocator.Allocate<byte>(alphaDataSize);
-                    this.currentStream.Read(features.AlphaData.Memory.Span, 0, alphaDataSize);
+                    this.AlphaData = this.memoryAllocator.Allocate<byte>(alphaDataSize);
+                    Span<byte> alphaData = this.AlphaData.GetSpan();
+                    this.currentStream.Read(alphaData, 0, alphaDataSize);
                     break;
                 default:
                     WebpThrowHelper.ThrowImageFormatException("Unexpected chunk followed VP8X header");
@@ -324,5 +339,8 @@ namespace SixLabors.ImageSharp.Formats.Webp
                 WebpChunkParsingUtils.ParseOptionalChunks(this.currentStream, chunkType, this.Metadata, this.IgnoreMetadata, this.buffer);
             }
         }
+
+        /// <inheritdoc/>
+        public void Dispose() => this.AlphaData?.Dispose();
     }
 }

src/ImageSharp/Formats/Webp/WebpFeatures.cs

@@ -1,15 +1,12 @@
 // Copyright (c) Six Labors.
 // Licensed under the Apache License, Version 2.0.
 
-using System;
-using System.Buffers;
-
 namespace SixLabors.ImageSharp.Formats.Webp
 {
     /// <summary>
     /// Image features of a VP8X image.
     /// </summary>
-    internal class WebpFeatures : IDisposable
+    internal class WebpFeatures
     {
         /// <summary>
         /// Gets or sets a value indicating whether this image has an ICC Profile.
@@ -21,11 +18,6 @@ namespace SixLabors.ImageSharp.Formats.Webp
         /// </summary>
         public bool Alpha { get; set; }
 
-        /// <summary>
-        /// Gets or sets the alpha data, if an ALPH chunk is present.
-        /// </summary>
-        public IMemoryOwner<byte> AlphaData { get; set; }
-
         /// <summary>
         /// Gets or sets the alpha chunk header.
         /// </summary>
@@ -56,8 +48,5 @@ namespace SixLabors.ImageSharp.Formats.Webp
         /// This color MAY be used to fill the unused space on the canvas around the frames, as well as the transparent pixels of the first frame..
         /// </summary>
         public Color? AnimationBackgroundColor { get; set; }
-
-        /// <inheritdoc/>
-        public void Dispose() => this.AlphaData?.Dispose();
     }
 }

src/ImageSharp/Formats/Webp/WebpImageInfo.cs

@@ -63,7 +63,6 @@ namespace SixLabors.ImageSharp.Formats.Webp
         {
             this.Vp8BitReader?.Dispose();
             this.Vp8LBitReader?.Dispose();
-            this.Features?.AlphaData?.Dispose();
         }
     }
 }