First attempt parsing minimal image info, infoIdentify works at least for reading the image dimensions so far

src/ImageSharp/Configuration.cs

@@ -8,6 +8,7 @@ using SixLabors.ImageSharp.Formats.Bmp;
 using SixLabors.ImageSharp.Formats.Gif;
 using SixLabors.ImageSharp.Formats.Jpeg;
 using SixLabors.ImageSharp.Formats.Png;
+using SixLabors.ImageSharp.Formats.WebP;
 using SixLabors.ImageSharp.IO;
 using SixLabors.ImageSharp.Processing;
 using SixLabors.Memory;
@@ -158,7 +159,8 @@ namespace SixLabors.ImageSharp
                 new PngConfigurationModule(),
                 new JpegConfigurationModule(),
                 new GifConfigurationModule(),
-                new BmpConfigurationModule());
+                new BmpConfigurationModule(),
+                new WebPConfigurationModule());
         }
     }
-}
+}

src/ImageSharp/Formats/WebP/ExtendedDecoder.cs

@@ -1,14 +0,0 @@
-// Copyright (c) Six Labors and contributors.
-// Licensed under the Apache License, Version 2.0.
-
-using System;
-using System.IO;
-
-namespace SixLabors.ImageSharp.Formats.WebP
-{
-    class ExtendedDecoderCore : WebPDecoderCoreBase
-    {
-        public override Image<TPixel> Decode<TPixel>(Stream stream)
-            => throw new NotImplementedException();
-    }
-}

src/ImageSharp/Formats/WebP/IWebPDecoderOptions.cs

@@ -0,0 +1,16 @@
+// Copyright (c) Six Labors and contributors.
+// Licensed under the Apache License, Version 2.0.
+
+namespace SixLabors.ImageSharp.Formats.WebP
+{
+    /// <summary>
+    /// Image decoder for generating an image out of a webp stream.
+    /// </summary>
+    internal interface IWebPDecoderOptions
+    {
+        /// <summary>
+        /// Gets a value indicating whether the metadata should be ignored when the image is being decoded.
+        /// </summary>
+        bool IgnoreMetadata { get; }
+    }
+}

src/ImageSharp/Formats/WebP/Readme.md

@@ -1,4 +1,8 @@
-= WebP Format
+# WebP Format
+
 Reference implementation, specification and stuff like that:
-https://developers.google.com/speed/webp
 
+- [google webp introduction](https://developers.google.com/speed/webp)
+- [WebP Spec 0.2](https://chromium.googlesource.com/webm/libwebp/+/v0.2.0/doc/webp-container-spec.txt)
+- [WebP VP8 chunk Spec](http://tools.ietf.org/html/rfc6386)
+- [WebP filefront](https://wiki.fileformat.com/image/webp/)

src/ImageSharp/Formats/WebP/SimpleLosslessDecoder.cs

@@ -1,14 +0,0 @@
-// Copyright (c) Six Labors and contributors.
-// Licensed under the Apache License, Version 2.0.
-
-using System;
-using System.IO;
-
-namespace SixLabors.ImageSharp.Formats.WebP
-{
-    class SimpleLosslessDecoder : WebPDecoderCoreBase
-    {
-        public override Image<TPixel> Decode<TPixel>(Stream stream)
-            => throw new NotImplementedException();
-    }
-}

src/ImageSharp/Formats/WebP/SimpleLossyDecoder.cs

@@ -1,14 +0,0 @@
-// Copyright (c) Six Labors and contributors.
-// Licensed under the Apache License, Version 2.0.
-
-using System;
-using System.IO;
-
-namespace SixLabors.ImageSharp.Formats.WebP
-{
-    class SimpleLossyDecoder : WebPDecoderCoreBase
-    {
-        public override Image<TPixel> Decode<TPixel>(Stream stream)
-            => throw new NotImplementedException();
-    }
-}

src/ImageSharp/Formats/WebP/WebPConstants.cs

@@ -16,5 +16,70 @@ namespace SixLabors.ImageSharp.Formats.WebP
         /// The list of mimetypes that equate to a jpeg.
         /// </summary>
         public static readonly IEnumerable<string> MimeTypes = new[] { "image/webp", };
+
+        /// <summary>
+        /// The header bytes identifying RIFF file.
+        /// </summary>
+        public static readonly byte[] FourCcBytes =
+        {
+            0x52, // R
+            0x49, // I
+            0x46, // F
+            0x46 // F
+        };
+
+        /// <summary>
+        /// The header bytes identifying a WebP.
+        /// </summary>
+        public static readonly byte[] WebPHeader =
+        {
+            0x57, // W
+            0x45, // E
+            0x42, // B
+            0x50 // P
+        };
+
+        /// <summary>
+        /// Header signaling the use of VP8 video format.
+        /// </summary>
+        public static readonly byte[] Vp8Header =
+        {
+            0x56, // V
+            0x50, // P
+            0x38, // 8
+            0x20, // Space
+        };
+
+        /// <summary>
+        /// Header for a extended-VP8 chunk.
+        /// </summary>
+        public static readonly byte[] Vp8XHeader =
+        {
+            0x56, // V
+            0x50, // P
+            0x38, // 8
+            0x88, // X
+        };
+
+        public static readonly byte LossLessFlag = 0x4C; // L
+
+        /// <summary>
+        /// VP8 header, signaling the use of VP8L lossless format.
+        /// </summary>
+        public static readonly byte[] Vp8LHeader =
+        {
+            0x56, // V
+            0x50, // P
+            0x38, // 8
+            LossLessFlag // L
+        };
+
+        public static readonly byte[] AlphaHeader =
+        {
+            0x41, // A
+            0x4C, // L
+            0x50, // P
+            0x48, // H
+        };
     }
 }

src/ImageSharp/Formats/WebP/WebPDecoder.cs

@@ -9,20 +9,31 @@ namespace SixLabors.ImageSharp.Formats.WebP
     /// <summary>
     /// Image decoder for generating an image out of a webp stream.
     /// </summary>
-    public sealed class WebPDecoder : IImageDecoder
+    public sealed class WebPDecoder : IImageDecoder, IWebPDecoderOptions, IImageInfoDetector
     {
+        /// <summary>
+        /// Gets or sets a value indicating whether the metadata should be ignored when the image is being decoded.
+        /// </summary>
+        public bool IgnoreMetadata { get; set; }
+
         /// <inheritdoc/>
         public Image<TPixel> Decode<TPixel>(Configuration configuration, Stream stream)
             where TPixel : struct, IPixel<TPixel>
         {
-            // TODO: [brianpopow] parse chunks and decide which decoder (subclass of WebPDecoderCoreBase) to use
-            throw new System.NotImplementedException();
+            Guard.NotNull(stream, nameof(stream));
+
+            return new WebPDecoderCore(configuration, this).Decode<TPixel>(stream);
         }
 
         /// <inheritdoc/>
-        public Image Decode(Configuration configuration, Stream stream)
+        public IImageInfo Identify(Configuration configuration, Stream stream)
         {
-            throw new System.NotImplementedException();
+            Guard.NotNull(stream, nameof(stream));
+
+            return new WebPDecoderCore(configuration, this).Identify(stream);
         }
+
+        /// <inheritdoc />
+        public Image Decode(Configuration configuration, Stream stream) => this.Decode<Rgba32>(configuration, stream);
     }
 }

src/ImageSharp/Formats/WebP/WebPDecoderCore.cs

@@ -0,0 +1,187 @@
+// Copyright (c) Six Labors and contributors.
+// Licensed under the Apache License, Version 2.0.
+
+using System;
+using System.Buffers.Binary;
+using System.IO;
+
+using SixLabors.ImageSharp.Memory;
+using SixLabors.ImageSharp.Metadata;
+using SixLabors.ImageSharp.PixelFormats;
+using SixLabors.Memory;
+
+namespace SixLabors.ImageSharp.Formats.WebP
+{
+    /// <summary>
+    /// Performs the bitmap decoding operation.
+    /// </summary>
+    internal sealed class WebPDecoderCore
+    {
+        /// <summary>
+        /// Reusable buffer.
+        /// </summary>
+        private readonly byte[] buffer = new byte[4];
+
+        /// <summary>
+        /// The global configuration.
+        /// </summary>
+        private readonly Configuration configuration;
+
+        /// <summary>
+        /// Used for allocating memory during processing operations.
+        /// </summary>
+        private readonly MemoryAllocator memoryAllocator;
+
+        /// <summary>
+        /// The bitmap decoder options.
+        /// </summary>
+        private readonly IWebPDecoderOptions options;
+
+        /// <summary>
+        /// The stream to decode from.
+        /// </summary>
+        private Stream currentStream;
+
+        /// <summary>
+        /// The metadata.
+        /// </summary>
+        private ImageMetadata metadata;
+
+        /// <summary>
+        /// Initializes a new instance of the <see cref="WebPDecoderCore"/> class.
+        /// </summary>
+        /// <param name="configuration">The configuration.</param>
+        /// <param name="options">The options.</param>
+        public WebPDecoderCore(Configuration configuration, IWebPDecoderOptions options)
+        {
+            this.configuration = configuration;
+            this.memoryAllocator = configuration.MemoryAllocator;
+            this.options = options;
+        }
+
+        public Image<TPixel> Decode<TPixel>(Stream stream)
+            where TPixel : struct, IPixel<TPixel>
+        {
+            var metadata = new ImageMetadata();
+            WebPMetadata webpMetadata = metadata.GetFormatMetadata(WebPFormat.Instance);
+            this.currentStream = stream;
+
+            uint chunkSize = this.ReadImageHeader();
+            WebPImageInfo imageInfo = this.ReadVp8Info();
+            // TODO: there can be optional chunks after that, like EXIF.
+
+            var image = new Image<TPixel>(this.configuration, imageInfo.Width, imageInfo.Height, this.metadata);
+            Buffer2D<TPixel> pixels = image.GetRootFramePixelBuffer();
+            if (imageInfo.IsLooseLess)
+            {
+                ReadSimpleLossless(pixels, image.Width, image.Height);
+            }
+            else
+            {
+                ReadSimpleLossy(pixels, image.Width, image.Height);
+            }
+
+            return image;
+        }
+
+        /// <summary>
+        /// Reads the raw image information from the specified stream.
+        /// </summary>
+        /// <param name="stream">The <see cref="Stream"/> containing image data.</param>
+        public IImageInfo Identify(Stream stream)
+        {
+            var metadata = new ImageMetadata();
+            WebPMetadata webpMetadata = metadata.GetFormatMetadata(WebPFormat.Instance);
+            this.currentStream = stream;
+
+            this.ReadImageHeader();
+            WebPImageInfo imageInfo = this.ReadVp8Info();
+
+            // TODO: not sure yet where to get this info. Assuming 24 bits for now.
+            int bitsPerPixel = 24;
+            return new ImageInfo(new PixelTypeInfo(bitsPerPixel), imageInfo.Width, imageInfo.Height, this.metadata);
+        }
+
+        private uint ReadImageHeader()
+        {
+            // Skip FourCC header, we already know its a RIFF file at this point.
+            this.currentStream.Skip(4);
+
+            // Read Chunk size.
+            this.currentStream.Read(this.buffer, 0, 4);
+            uint chunkSize = BinaryPrimitives.ReadUInt32LittleEndian(this.buffer);
+
+            // Skip 'WEBP' from the header.
+            this.currentStream.Skip(4);
+
+            return chunkSize;
+        }
+
+        private WebPImageInfo ReadVp8Info()
+        {
+            // Read VP8 chunk header.
+            this.currentStream.Read(this.buffer, 0, 4);
+            if (this.buffer.AsSpan().SequenceEqual(WebPConstants.AlphaHeader))
+            {
+                WebPThrowHelper.ThrowImageFormatException("Alpha channel is not yet supported");
+            }
+
+            if (this.buffer.AsSpan().SequenceEqual(WebPConstants.Vp8XHeader))
+            {
+                WebPThrowHelper.ThrowImageFormatException("Vp8X is not yet supported");
+            }
+
+            if (!(this.buffer.AsSpan().SequenceEqual(WebPConstants.Vp8Header)
+                  || this.buffer.AsSpan().SequenceEqual(WebPConstants.Vp8LHeader)))
+            {
+                WebPThrowHelper.ThrowImageFormatException("Unrecognized VP8 header");
+            }
+
+            bool isLossLess = this.buffer[3] == WebPConstants.LossLessFlag;
+
+            // VP8 data size.
+            this.currentStream.Read(this.buffer, 0, 3);
+            this.buffer[3] = 0;
+            uint dataSize = BinaryPrimitives.ReadUInt32LittleEndian(this.buffer);
+
+            // https://tools.ietf.org/html/rfc6386#page-30
+            var imageInfo = new byte[11];
+            this.currentStream.Read(imageInfo, 0, imageInfo.Length);
+            int tmp = (imageInfo[2] << 16) | (imageInfo[1] << 8) | imageInfo[0];
+            int isKeyFrame = tmp & 0x1;
+            int version = (tmp >> 1) & 0x7;
+            int showFrame = (tmp >> 4) & 0x1;
+
+            // TODO: Get horizontal and vertical scale
+            int width = BinaryPrimitives.ReadInt16LittleEndian(imageInfo.AsSpan(7)) & 0x3fff;
+            int height = BinaryPrimitives.ReadInt16LittleEndian(imageInfo.AsSpan(9)) & 0x3fff;
+
+            return new WebPImageInfo()
+            {
+                Width = width,
+                Height = height,
+                IsLooseLess = isLossLess,
+                Version = version,
+                DataSize = dataSize
+            };
+        }
+
+        private void ReadSimpleLossy<TPixel>(Buffer2D<TPixel> pixels, int width, int height)
+            where TPixel : struct, IPixel<TPixel>
+        {
+            // TODO: implement decoding
+        }
+
+        private void ReadSimpleLossless<TPixel>(Buffer2D<TPixel> pixels, int width, int height)
+            where TPixel : struct, IPixel<TPixel>
+        {
+            // TODO: implement decoding
+        }
+
+        private void ReadExtended<TPixel>(Buffer2D<TPixel> pixels, int width, int height)
+            where TPixel : struct, IPixel<TPixel>
+        {
+            // TODO: implement decoding
+        }
+    }
+}

src/ImageSharp/Formats/WebP/WebPDecoderCoreBase.cs

@@ -1,18 +0,0 @@
-// Copyright (c) Six Labors and contributors.
-// Licensed under the Apache License, Version 2.0.
-
-using System.IO;
-
-using SixLabors.ImageSharp.PixelFormats;
-
-namespace SixLabors.ImageSharp.Formats.WebP
-{
-    /// <summary>
-    /// Base class for the WebP image decoders.
-    /// </summary>
-    public abstract class WebPDecoderCoreBase
-    {
-        public abstract Image<TPixel> Decode<TPixel>(Stream stream)
-            where TPixel : struct, IPixel<TPixel>;
-    }
-}

src/ImageSharp/Formats/WebP/WebPImageFormatDetector.cs

@@ -6,7 +6,7 @@ using System;
 namespace SixLabors.ImageSharp.Formats.WebP
 {
     /// <summary>
-    /// Detects WebP file headers
+    /// Detects WebP file headers.
     /// </summary>
     public sealed class WebPImageFormatDetector : IImageFormatDetector
     {
@@ -26,20 +26,24 @@ namespace SixLabors.ImageSharp.Formats.WebP
                    this.IsWebPFile(header);
         }
 
+        /// <summary>
+        /// Checks, if the header starts with a valid RIFF FourCC.
+        /// </summary>
+        /// <param name="header">The header bytes.</param>
+        /// <returns>True, if its a valid RIFF FourCC.</returns>
         private bool IsRiffContainer(ReadOnlySpan<byte> header)
         {
-            return header[0] == 0x52 && // R
-                   header[1] == 0x49 && // I
-                   header[2] == 0x46 && // F
-                   header[3] == 0x46; // F
+            return header.Slice(0, 4).SequenceEqual(WebPConstants.FourCcBytes);
         }
 
+        /// <summary>
+        /// Checks if 'WEBP' is present in the header.
+        /// </summary>
+        /// <param name="header">The header bytes.</param>
+        /// <returns>True, if its a webp file.</returns>
         private bool IsWebPFile(ReadOnlySpan<byte> header)
         {
-            return header[8] == 0x57 && // W
-                   header[9] == 0x45 && // E
-                   header[10] == 0x42 && // B
-                   header[11] == 0x50; // P
+            return header.Slice(8, 4).SequenceEqual(WebPConstants.WebPHeader);
         }
     }
 }

src/ImageSharp/Formats/WebP/WebPImageInfo.cs

@@ -0,0 +1,27 @@
+// Copyright (c) Six Labors and contributors.
+// Licensed under the Apache License, Version 2.0.
+
+namespace SixLabors.ImageSharp.Formats.WebP
+{
+    internal class WebPImageInfo
+    {
+        /// <summary>
+        /// Gets or sets the bitmap width in pixels (signed integer).
+        /// </summary>
+        public int Width { get; set; }
+
+        /// <summary>
+        /// Gets or sets the bitmap height in pixels (signed integer).
+        /// </summary>
+        public int Height { get; set; }
+
+        /// <summary>
+        /// Gets or sets whether this image uses a looseless compression.
+        /// </summary>
+        public bool IsLooseLess { get; set; }
+
+        public int Version { get; set; }
+
+        public uint DataSize { get; set; }
+    }
+}

src/ImageSharp/Formats/WebP/WebPThrowHelper.cs

@@ -0,0 +1,20 @@
+// Copyright (c) Six Labors and contributors.
+// Licensed under the Apache License, Version 2.0.
+
+using System.Runtime.CompilerServices;
+
+namespace SixLabors.ImageSharp.Formats.WebP
+{
+    internal static class WebPThrowHelper
+    {
+        /// <summary>
+        /// Cold path optimization for throwing <see cref="ImageFormatException"/>-s
+        /// </summary>
+        /// <param name="errorMessage">The error message for the exception.</param>
+        [MethodImpl(MethodImplOptions.NoInlining)]
+        public static void ThrowImageFormatException(string errorMessage)
+        {
+            throw new ImageFormatException(errorMessage);
+        }
+    }
+}

src/ImageSharp/Formats/WebP/WebpConfigurationModule.cs

@@ -0,0 +1,18 @@
+// Copyright (c) Six Labors and contributors.
+// Licensed under the Apache License, Version 2.0.
+
+namespace SixLabors.ImageSharp.Formats.WebP
+{
+    /// <summary>
+    /// Registers the image encoders, decoders and mime type detectors for the webp format.
+    /// </summary>
+    public sealed class WebPConfigurationModule : IConfigurationModule
+    {
+        /// <inheritdoc/>
+        public void Configure(Configuration configuration)
+        {
+            configuration.ImageFormatsManager.SetDecoder(WebPFormat.Instance, new WebPDecoder());
+            configuration.ImageFormatsManager.AddImageFormatDetector(new WebPImageFormatDetector());
+        }
+    }
+}