Add support for decoding webp images with animations

src/ImageSharp/Formats/Gif/GifDecoderCore.cs

@@ -94,7 +94,7 @@ public GifDecoderCore(Configuration configuration, IGifDecoderOptions options)
         /// <summary>
         /// Gets the dimensions of the image.
         /// </summary>
-        public Size Dimensions => new Size(this.imageDescriptor.Width, this.imageDescriptor.Height);
+        public Size Dimensions => new(this.imageDescriptor.Width, this.imageDescriptor.Height);
 
         private MemoryAllocator MemoryAllocator => this.Configuration.MemoryAllocator;
 

src/ImageSharp/Formats/Gif/GifFormat.cs

@@ -1,4 +1,4 @@
-// Copyright (c) Six Labors.
+// Copyright (c) Six Labors.
 // Licensed under the Apache License, Version 2.0.
 
 using System.Collections.Generic;
@@ -17,7 +17,7 @@ private GifFormat()
         /// <summary>
         /// Gets the current instance.
         /// </summary>
-        public static GifFormat Instance { get; } = new GifFormat();
+        public static GifFormat Instance { get; } = new();
 
         /// <inheritdoc/>
         public string Name => "GIF";
@@ -32,9 +32,9 @@ private GifFormat()
         public IEnumerable<string> FileExtensions => GifConstants.FileExtensions;
 
         /// <inheritdoc/>
-        public GifMetadata CreateDefaultFormatMetadata() => new GifMetadata();
+        public GifMetadata CreateDefaultFormatMetadata() => new();
 
         /// <inheritdoc/>
-        public GifFrameMetadata CreateDefaultFormatFrameMetadata() => new GifFrameMetadata();
+        public GifFrameMetadata CreateDefaultFormatFrameMetadata() => new();
     }
 }

src/ImageSharp/Formats/Webp/AnimationBlendingMethod.cs

@@ -0,0 +1,23 @@
+// Copyright (c) Six Labors.
+// Licensed under the Apache License, Version 2.0.
+
+namespace SixLabors.ImageSharp.Formats.Webp
+{
+    /// <summary>
+    /// Indicates how transparent pixels of the current frame are to be blended with corresponding pixels of the previous canvas.
+    /// </summary>
+    internal enum AnimationBlendingMethod
+    {
+        /// <summary>
+        /// Use alpha blending. After disposing of the previous frame, render the current frame on the canvas using alpha-blending.
+        /// If the current frame does not have an alpha channel, assume alpha value of 255, effectively replacing the rectangle.
+        /// </summary>
+        AlphaBlending = 0,
+
+        /// <summary>
+        /// Do not blend. After disposing of the previous frame,
+        /// render the current frame on the canvas by overwriting the rectangle covered by the current frame.
+        /// </summary>
+        DoNotBlend = 1
+    }
+}

src/ImageSharp/Formats/Webp/AnimationDisposalMethod.cs

@@ -0,0 +1,21 @@
+// Copyright (c) Six Labors.
+// Licensed under the Apache License, Version 2.0.
+
+namespace SixLabors.ImageSharp.Formats.Webp
+{
+    /// <summary>
+    /// Indicates how the current frame is to be treated after it has been displayed (before rendering the next frame) on the canvas.
+    /// </summary>
+    internal enum AnimationDisposalMethod
+    {
+        /// <summary>
+        /// Do not dispose. Leave the canvas as is.
+        /// </summary>
+        DoNotDispose = 0,
+
+        /// <summary>
+        /// Dispose to background color. Fill the rectangle on the canvas covered by the current frame with background color specified in the ANIM chunk.
+        /// </summary>
+        Dispose = 1
+    }
+}

src/ImageSharp/Formats/Webp/AnimationFrameData.cs

@@ -0,0 +1,49 @@
+// Copyright (c) Six Labors.
+// Licensed under the Apache License, Version 2.0.
+
+namespace SixLabors.ImageSharp.Formats.Webp
+{
+    internal struct AnimationFrameData
+    {
+        /// <summary>
+        /// The animation chunk size.
+        /// </summary>
+        public uint DataSize;
+
+        /// <summary>
+        /// The X coordinate of the upper left corner of the frame is Frame X * 2.
+        /// </summary>
+        public uint X;
+
+        /// <summary>
+        /// The Y coordinate of the upper left corner of the frame is Frame Y * 2.
+        /// </summary>
+        public uint Y;
+
+        /// <summary>
+        /// The width of the frame.
+        /// </summary>
+        public uint Width;
+
+        /// <summary>
+        /// The height of the frame.
+        /// </summary>
+        public uint Height;
+
+        /// <summary>
+        /// The time to wait before displaying the next frame, in 1 millisecond units.
+        /// Note the interpretation of frame duration of 0 (and often smaller then 10) is implementation defined.
+        /// </summary>
+        public uint Duration;
+
+        /// <summary>
+        /// Indicates how transparent pixels of the current frame are to be blended with corresponding pixels of the previous canvas.
+        /// </summary>
+        public AnimationBlendingMethod BlendingMethod;
+
+        /// <summary>
+        /// Indicates how the current frame is to be treated after it has been displayed (before rendering the next frame) on the canvas.
+        /// </summary>
+        public AnimationDisposalMethod DisposalMethod;
+    }
+}

src/ImageSharp/Formats/Webp/IWebpDecoderOptions.cs

@@ -1,6 +1,8 @@
 // Copyright (c) Six Labors.
 // Licensed under the Apache License, Version 2.0.
 
+using SixLabors.ImageSharp.Metadata;
+
 namespace SixLabors.ImageSharp.Formats.Webp
 {
     /// <summary>
@@ -12,5 +14,10 @@ internal interface IWebpDecoderOptions
         /// Gets a value indicating whether the metadata should be ignored when the image is being decoded.
         /// </summary>
         bool IgnoreMetadata { get; }
+
+        /// <summary>
+        /// Gets the decoding mode for multi-frame images.
+        /// </summary>
+        FrameDecodingMode DecodingMode { get; }
     }
 }

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

@@ -87,7 +87,7 @@ public WebpLosslessDecoder(Vp8LBitReader bitReader, MemoryAllocator memoryAlloca
         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 @@ public WebpLossyDecoder(Vp8BitReader bitReader, MemoryAllocator memoryAllocator,
             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 @@ public void Decode<TPixel>(Buffer2D<TPixel> pixels, int width, int height, WebpI
                     using (var alphaDecoder = new AlphaDecoder(
                         width,
                         height,
-                        info.Features.AlphaData,
+                        alphaData,
                         info.Features.AlphaChunkHeader,
                         this.memoryAllocator,
                         this.configuration))

src/ImageSharp/Formats/Webp/MetadataExtensions.cs

@@ -17,5 +17,12 @@ public static partial class MetadataExtensions
         /// <param name="metadata">The metadata this method extends.</param>
         /// <returns>The <see cref="WebpMetadata"/>.</returns>
         public static WebpMetadata GetWebpMetadata(this ImageMetadata metadata) => metadata.GetFormatMetadata(WebpFormat.Instance);
+
+        /// <summary>
+        /// Gets the webp format specific metadata for the image frame.
+        /// </summary>
+        /// <param name="metadata">The metadata this method extends.</param>
+        /// <returns>The <see cref="WebpFrameMetadata"/>.</returns>
+        public static WebpFrameMetadata GetWebpMetadata(this ImageFrameMetadata metadata) => metadata.GetFormatMetadata(WebpFormat.Instance);
     }
 }