WIP: Parse further VP8 header: SegmentHeader, FilterHeader, implement BitReader for VP8 (unfinished)

src/ImageSharp/Formats/WebP/BitReaderBase.cs

@@ -19,19 +19,6 @@ namespace SixLabors.ImageSharp.Formats.WebP
         /// </summary>
         protected byte[] Data { get; private set; }
 
-        /// <summary>
-        /// Reads a single bit from the stream.
-        /// </summary>
-        /// <returns>True if the bit read was 1, false otherwise.</returns>
-        public abstract bool ReadBit();
-
-        /// <summary>
-        /// Reads a unsigned short value from the inputStream. The bits of each byte are read in least-significant-bit-first order.
-        /// </summary>
-        /// <param name="nBits">The number of bits to read (should not exceed 16).</param>
-        /// <returns>A ushort value.</returns>
-        public abstract uint ReadValue(int nBits);
-
         /// <summary>
         /// Copies the raw encoded image data from the stream into a byte array.
         /// </summary>

src/ImageSharp/Formats/WebP/Vp8BitReader.cs

@@ -2,6 +2,7 @@
 // Licensed under the Apache License, Version 2.0.
 
 using System;
+using System.Buffers.Binary;
 using System.IO;
 
 using SixLabors.Memory;
@@ -13,15 +14,17 @@ namespace SixLabors.ImageSharp.Formats.WebP
     /// </summary>
     internal class Vp8BitReader : BitReaderBase
     {
+        private const int BitsCount = 56;
+
         /// <summary>
         /// Current value.
         /// </summary>
-        private long value;
+        private ulong value;
 
         /// <summary>
         /// Current range minus 1. In [127, 254] interval.
         /// </summary>
-        private int range;
+        private uint range;
 
         /// <summary>
         /// Number of valid bits left.
@@ -36,18 +39,23 @@ namespace SixLabors.ImageSharp.Formats.WebP
         /// <summary>
         /// End of read buffer.
         /// </summary>
-        private byte bufEnd;
+        // private byte bufEnd;
 
         /// <summary>
         /// Max packed-read position on buffer.
         /// </summary>
-        private byte bufMax;
+        // private byte bufMax;
 
         /// <summary>
         /// True if input is exhausted.
         /// </summary>
         private bool eof;
 
+        /// <summary>
+        /// Byte position in buffer.
+        /// </summary>
+        private long pos;
+
         /// <summary>
         /// Initializes a new instance of the <see cref="Vp8BitReader"/> class.
         /// </summary>
@@ -57,27 +65,126 @@ namespace SixLabors.ImageSharp.Formats.WebP
         public Vp8BitReader(Stream inputStream, uint imageDataSize, MemoryAllocator memoryAllocator)
         {
             this.ReadImageDataFromStream(inputStream, (int)imageDataSize, memoryAllocator);
+
+            this.range = 255 - 1;
+            this.value = 0;
+            this.bits = -8; // to load the very first 8bits;
+            this.eof = false;
+            this.pos = 0;
+
+            this.LoadNewBytes();
         }
 
-        /// <inheritdoc/>
-        public override bool ReadBit()
+        public int GetBit(int prob)
         {
-            throw new NotImplementedException();
+            Guard.MustBeGreaterThan(prob, 0, nameof(prob));
+
+            uint range = this.range;
+            if (this.bits < 0)
+            {
+                this.LoadNewBytes();
+            }
+
+            int pos = this.bits;
+            uint split = (uint)((range * prob) >> 8);
+            bool bit = this.value > split;
+            if (bit)
+            {
+                range -= split;
+                this.value -= (ulong)(split + 1) << pos;
+            }
+            else
+            {
+                range = split + 1;
+            }
+
+            int shift = 7 ^ this.BitsLog2Floor(range);
+            range <<= shift;
+            this.bits -= shift;
+
+            this.range = range - 1;
+
+            return bit ? 1 : 0;
+        }
+
+        public bool ReadBool()
+        {
+            return this.ReadValue(1) is 1;
         }
 
-        /// <inheritdoc/>
-        public override uint ReadValue(int nBits)
+        public uint ReadValue(int nBits)
         {
             Guard.MustBeGreaterThan(nBits, 0, nameof(nBits));
 
-            throw new NotImplementedException();
+            uint v = 0;
+            while (this.bits-- > 0)
+            {
+                v |= (uint)this.GetBit(0x80) << this.bits;
+            }
+
+            return v;
         }
 
         public int ReadSignedValue(int nBits)
         {
             Guard.MustBeGreaterThan(nBits, 0, nameof(nBits));
 
+            int value = (int)this.ReadValue(nBits);
+            return this.ReadValue(1) != 0 ? -value : value;
+        }
+
+        private void LoadNewBytes()
+        {
+            if (this.pos < this.Data.Length)
+            {
+                ulong bits;
+                ulong inBits = BinaryPrimitives.ReadUInt64LittleEndian(this.Data.AsSpan().Slice((int)this.pos, 8));
+                this.pos += BitsCount >> 3;
+                this.buf = this.Data[BitsCount >> 3];
+                bits = this.ByteSwap64(inBits);
+                bits >>= 64 - BitsCount;
+                this.value = bits | (this.value << BitsCount);
+                this.bits += BitsCount;
+            }
+            else
+            {
+                this.LoadFinalBytes();
+            }
+        }
+
+        private void LoadFinalBytes()
+        {
+            // Only read 8bits at a time.
+            if (this.pos < this.Data.Length)
+            {
+                this.bits += 8;
+                this.value = this.Data[this.pos++] | (this.value << 8);
+            }
+            else if (!this.eof)
+            {
+                this.value <<= 8;
+                this.bits += 8;
+                this.eof = true;
+            }
+            else
+            {
+                this.bits = 0;  // This is to avoid undefined behaviour with shifts.
+            }
+        }
+
+        private ulong ByteSwap64(ulong x)
+        {
+            x = ((x & 0xffffffff00000000ul) >> 32) | ((x & 0x00000000fffffffful) << 32);
+            x = ((x & 0xffff0000ffff0000ul) >> 16) | ((x & 0x0000ffff0000fffful) << 16);
+            x = ((x & 0xff00ff00ff00ff00ul) >> 8) | ((x & 0x00ff00ff00ff00fful) << 8);
+            return x;
+        }
+
+        private int BitsLog2Floor(uint n)
+        {
+            long firstSetBit;
             throw new NotImplementedException();
+            // BitScanReverse(firstSetBit, n);
         }
     }
 }

src/ImageSharp/Formats/WebP/Vp8FilterHeader.cs

@@ -0,0 +1,35 @@
+// Copyright (c) Six Labors and contributors.
+// Licensed under the Apache License, Version 2.0.
+
+namespace SixLabors.ImageSharp.Formats.WebP
+{
+    internal class Vp8FilterHeader
+    {
+        private const int NumRefLfDeltas = 4;
+
+        private const int NumModeLfDeltas = 4;
+
+        public Vp8FilterHeader()
+        {
+            this.RefLfDelta = new int[NumRefLfDeltas];
+            this.ModeLfDelta = new int[NumModeLfDeltas];
+        }
+
+        /// <summary>
+        /// Gets or sets the loop filter.
+        /// </summary>
+        public LoopFilter LoopFilter { get; set; }
+
+        // [0..63]
+        public int Level { get; set; }
+
+        // [0..7]
+        public int Sharpness { get; set; }
+
+        public bool UseLfDelta { get; set; }
+
+        public int[] RefLfDelta { get; private set; }
+
+        public int[] ModeLfDelta { get; private set; }
+    }
+}

src/ImageSharp/Formats/WebP/Vp8LBitReader.cs

@@ -95,8 +95,12 @@ namespace SixLabors.ImageSharp.Formats.WebP
             this.pos = length;
         }
 
-        /// <inheritdoc/>
-        public override uint ReadValue(int nBits)
+        /// <summary>
+        /// Reads a unsigned short value from the buffer. The bits of each byte are read in least-significant-bit-first order.
+        /// </summary>
+        /// <param name="nBits">The number of bits to read (should not exceed 16).</param>
+        /// <returns>A ushort value.</returns>
+        public uint ReadValue(int nBits)
         {
             Guard.MustBeGreaterThan(nBits, 0, nameof(nBits));
 
@@ -113,23 +117,37 @@ namespace SixLabors.ImageSharp.Formats.WebP
             return 0;
         }
 
-        /// <inheritdoc/>
-        public override bool ReadBit()
+        /// <summary>
+        /// Reads a single bit from the stream.
+        /// </summary>
+        /// <returns>True if the bit read was 1, false otherwise.</returns>
+        public bool ReadBit()
         {
             uint bit = this.ReadValue(1);
             return bit != 0;
         }
 
-        public void AdvanceBitPosition(int bitPosition)
+        /// <summary>
+        /// For jumping over a number of bits in the bit stream when accessed with PrefetchBits and FillBitWindow.
+        /// </summary>
+        /// <param name="numberOfBits">The number of bits to advance the position.</param>
+        public void AdvanceBitPosition(int numberOfBits)
         {
-            this.bitPos += bitPosition;
+            this.bitPos += numberOfBits;
         }
 
+        /// <summary>
+        /// Return the pre-fetched bits, so they can be looked up.
+        /// </summary>
+        /// <returns>Prefetched bits.</returns>
         public ulong PrefetchBits()
         {
             return this.value >> (this.bitPos & (Vp8LLbits - 1));
         }
 
+        /// <summary>
+        /// Advances the read buffer by 4 bytes to make room for reading next 32 bits.
+        /// </summary>
         public void FillBitWindow()
         {
             if (this.bitPos >= Vp8LWbits)
@@ -138,6 +156,10 @@ namespace SixLabors.ImageSharp.Formats.WebP
             }
         }
 
+        /// <summary>
+        /// Returns true if there was an attempt at reading bit past the end of the buffer.
+        /// </summary>
+        /// <returns>True, if end of buffer was reached.</returns>
         public bool IsEndOfStream()
         {
             return this.eos || ((this.pos == this.len) && (this.bitPos > Vp8LLbits));

src/ImageSharp/Formats/WebP/Vp8PictureHeader.cs

@@ -26,12 +26,16 @@ namespace SixLabors.ImageSharp.Formats.WebP
         public sbyte YScale { get; set; }
 
         /// <summary>
-        /// Gets or sets the colorspace. 0 = YCbCr.
+        /// Gets or sets the colorspace.
+        /// 0 - YUV color space similar to the YCrCb color space defined in.
+        /// 1 - Reserved for future use.
         /// </summary>
         public sbyte ColorSpace { get; set; }
 
         /// <summary>
         /// Gets or sets the clamp type.
+        /// 0 - Decoders are required to clamp the reconstructed pixel values to between 0 and 255 (inclusive).
+        /// 1 - Reconstructed pixel values are guaranteed to be between 0 and 255; no clamping is necessary.
         /// </summary>
         public sbyte ClampType { get; set; }
     }

src/ImageSharp/Formats/WebP/Vp8SegmentHeader.cs

@@ -8,6 +8,14 @@ namespace SixLabors.ImageSharp.Formats.WebP
     /// </summary>
     internal class Vp8SegmentHeader
     {
+        private const int NumMbSegments = 4;
+
+        public Vp8SegmentHeader()
+        {
+            this.Quantizer = new byte[NumMbSegments];
+            this.FilterStrength = new byte[NumMbSegments];
+        }
+
         public bool UseSegment { get; set; }
 
         /// <summary>
@@ -16,18 +24,19 @@ namespace SixLabors.ImageSharp.Formats.WebP
         public bool UpdateMap { get; set; }
 
         /// <summary>
-        /// Gets or sets the absolute or delta values for quantizer and filter.
+        /// Gets or sets a value indicating whether to use delta values for quantizer and filter.
+        /// If this value is false, absolute values are used.
         /// </summary>
-        public int AbsoluteOrDelta { get; set; }
+        public bool Delta { get; set; }
 
         /// <summary>
-        /// Gets or sets quantization changes.
+        /// Gets quantization changes.
         /// </summary>
-        public byte[] Quantizer { get; set; }
+        public byte[] Quantizer { get; private set; }
 
         /// <summary>
-        /// Gets or sets the filter strength for segments.
+        /// Gets the filter strength for segments.
         /// </summary>
-        public byte[] FilterStrength { get; set; }
+        public byte[] FilterStrength { get; private set; }
     }
 }

src/ImageSharp/Formats/WebP/WebPDecoderCore.cs

@@ -85,7 +85,7 @@ namespace SixLabors.ImageSharp.Formats.WebP
                 WebPThrowHelper.ThrowNotSupportedException("Animations are not supported");
             }
 
-            var image = new Image<TPixel>(this.configuration, imageInfo.Width, imageInfo.Height, this.Metadata);
+            var image = new Image<TPixel>(this.configuration, (int)imageInfo.Width, (int)imageInfo.Height, this.Metadata);
             Buffer2D<TPixel> pixels = image.GetRootFramePixelBuffer();
             if (imageInfo.IsLossLess)
             {
@@ -118,7 +118,7 @@ namespace SixLabors.ImageSharp.Formats.WebP
             this.ReadImageHeader();
             WebPImageInfo imageInfo = this.ReadVp8Info();
 
-            return new ImageInfo(new PixelTypeInfo((int)imageInfo.BitsPerPixel), imageInfo.Width, imageInfo.Height, this.Metadata);
+            return new ImageInfo(new PixelTypeInfo((int)imageInfo.BitsPerPixel), (int)imageInfo.Width, (int)imageInfo.Height, this.Metadata);
         }
 
         /// <summary>
@@ -200,12 +200,12 @@ namespace SixLabors.ImageSharp.Formats.WebP
             // 3 bytes for the width.
             this.currentStream.Read(this.buffer, 0, 3);
             this.buffer[3] = 0;
-            int width = BinaryPrimitives.ReadInt32LittleEndian(this.buffer) + 1;
+            uint width = (uint)BinaryPrimitives.ReadInt32LittleEndian(this.buffer) + 1;
 
             // 3 bytes for the height.
             this.currentStream.Read(this.buffer, 0, 3);
             this.buffer[3] = 0;
-            int height = BinaryPrimitives.ReadInt32LittleEndian(this.buffer) + 1;
+            uint height = (uint)BinaryPrimitives.ReadInt32LittleEndian(this.buffer) + 1;
 
             // Optional chunks ICCP, ALPH and ANIM can follow here.
             WebPChunkType chunkType;
@@ -288,7 +288,7 @@ namespace SixLabors.ImageSharp.Formats.WebP
             this.currentStream.Read(this.buffer, 0, 4);
             uint dataSize = BinaryPrimitives.ReadUInt32LittleEndian(this.buffer);
 
-            // https://tools.ietf.org/html/rfc6386#page-30
+            // See paragraph 9.1 https://tools.ietf.org/html/rfc6386#page-30
             // Frame tag that contains four fields:
             // - A 1-bit frame type (0 for key frames, 1 for interframes).
             // - A 3-bit version number.
@@ -328,15 +328,103 @@ namespace SixLabors.ImageSharp.Formats.WebP
             }
 
             this.currentStream.Read(this.buffer, 0, 4);
-            int width = BinaryPrimitives.ReadInt16LittleEndian(this.buffer) & 0x3fff;
-            int height = BinaryPrimitives.ReadInt16LittleEndian(this.buffer.AsSpan(2)) & 0x3fff;
+            uint tmp = (uint)BinaryPrimitives.ReadInt16LittleEndian(this.buffer);
+            uint width = tmp & 0x3fff;
+            sbyte xScale = (sbyte)(tmp >> 6);
+            tmp = (uint)BinaryPrimitives.ReadInt16LittleEndian(this.buffer.AsSpan(2));
+            uint height = tmp & 0x3fff;
+            sbyte yScale = (sbyte)(tmp >> 6);
             if (width is 0 || height is 0)
             {
                 WebPThrowHelper.ThrowImageFormatException("width or height can not be zero");
             }
 
+            var vp8FrameHeader = new Vp8FrameHeader()
+                                 {
+                                     KeyFrame = true,
+                                     Profile = (sbyte)version,
+                                     PartitionLength = partitionLength
+                                 };
+
             var bitReader = new Vp8BitReader(this.currentStream, dataSize - 10, this.memoryAllocator);
 
+            // Paragraph 9.2: color space and clamp type follow
+            sbyte colorSpace = (sbyte)bitReader.ReadValue(1);
+            sbyte clampType = (sbyte)bitReader.ReadValue(1);
+            var vp8PictureHeader = new Vp8PictureHeader()
+                                   {
+                                       Width = width,
+                                       Height = height,
+                                       XScale = xScale,
+                                       YScale = yScale,
+                                       ColorSpace = colorSpace,
+                                       ClampType = clampType
+                                   };
+
+            // Paragraph 9.3: Parse the segment header.
+            var vp8SegmentHeader = new Vp8SegmentHeader();
+            vp8SegmentHeader.UseSegment = bitReader.ReadBool();
+            if (vp8SegmentHeader.UseSegment)
+            {
+                vp8SegmentHeader.UpdateMap = bitReader.ReadBool();
+                bool updateData = bitReader.ReadBool();
+                if (updateData)
+                {
+                    vp8SegmentHeader.Delta = bitReader.ReadBool();
+                    for (int i = 0; i < vp8SegmentHeader.Quantizer.Length; i++)
+                    {
+                        bool hasValue = bitReader.ReadBool();
+                        uint quantizeValue = hasValue ? bitReader.ReadValue(7) : 0;
+                        vp8SegmentHeader.Quantizer[i] = (byte)quantizeValue;
+                    }
+
+                    for (int i = 0; i < vp8SegmentHeader.FilterStrength.Length; i++)
+                    {
+                        bool hasValue = bitReader.ReadBool();
+                        uint filterStrengthValue = hasValue ? bitReader.ReadValue(6) : 0;
+                        vp8SegmentHeader.FilterStrength[i] = (byte)filterStrengthValue;
+                    }
+
+                    if (vp8SegmentHeader.UpdateMap)
+                    {
+                        // TODO: Read VP8Proba
+                    }
+                }
+            }
+
+            // Paragraph 9.4: Parse the filter specs.
+            var vp8FilterHeader = new Vp8FilterHeader();
+            vp8FilterHeader.LoopFilter = bitReader.ReadBool() ? LoopFilter.Simple : LoopFilter.Normal;
+            vp8FilterHeader.Level = (int)bitReader.ReadValue(6);
+            vp8FilterHeader.Sharpness = (int)bitReader.ReadValue(3);
+            vp8FilterHeader.UseLfDelta = bitReader.ReadBool();
+            if (vp8FilterHeader.UseLfDelta)
+            {
+                // Update lf-delta?
+                if (bitReader.ReadBool())
+                {
+                    for (int i = 0; i < vp8FilterHeader.RefLfDelta.Length; i++)
+                    {
+                        bool hasValue = bitReader.ReadBool();
+                        if (hasValue)
+                        {
+                            vp8FilterHeader.RefLfDelta[i] = bitReader.ReadSignedValue(6);
+                        }
+                    }
+
+                    for (int i = 0; i < vp8FilterHeader.ModeLfDelta.Length; i++)
+                    {
+                        bool hasValue = bitReader.ReadBool();
+                        if (hasValue)
+                        {
+                            vp8FilterHeader.ModeLfDelta[i] = bitReader.ReadSignedValue(6);
+                        }
+                    }
+                }
+            }
+
+            // TODO: ParsePartitions
+
             return new WebPImageInfo()
                    {
                        Width = width,
@@ -345,6 +433,10 @@ namespace SixLabors.ImageSharp.Formats.WebP
                        IsLossLess = false,
                        Features = features,
                        Vp8Profile = (sbyte)version,
+                       Vp8FrameHeader = vp8FrameHeader,
+                       Vp8SegmentHeader = vp8SegmentHeader,
+                       Vp8FilterHeader = vp8FilterHeader,
+                       Vp8PictureHeader = vp8PictureHeader,
                        Vp8BitReader = bitReader
                    };
         }
@@ -392,8 +484,8 @@ namespace SixLabors.ImageSharp.Formats.WebP
 
             return new WebPImageInfo()
                    {
-                       Width = (int)width,
-                       Height = (int)height,
+                       Width = width,
+                       Height = height,
                        BitsPerPixel = WebPBitsPerPixel.Pixel32,
                        IsLossLess = true,
                        Features = features,

src/ImageSharp/Formats/WebP/WebPImageInfo.cs

@@ -8,12 +8,12 @@ namespace SixLabors.ImageSharp.Formats.WebP
         /// <summary>
         /// Gets or sets the bitmap width in pixels (signed integer).
         /// </summary>
-        public int Width { get; set; }
+        public uint Width { get; set; }
 
         /// <summary>
         /// Gets or sets the bitmap height in pixels (signed integer).
         /// </summary>
-        public int Height { get; set; }
+        public uint Height { get; set; }
 
         /// <summary>
         /// Gets or sets the bits per pixel.
@@ -36,7 +36,27 @@ namespace SixLabors.ImageSharp.Formats.WebP
         public int Vp8Profile { get; set; } = -1;
 
         /// <summary>
-        /// Gets or sets the Vp8L bitreader. Will be null, if its not lossless image.
+        /// Gets or sets the VP8 frame header.
+        /// </summary>
+        public Vp8FrameHeader Vp8FrameHeader { get; set; }
+
+        /// <summary>
+        /// Gets or sets the VP8 picture header.
+        /// </summary>
+        public Vp8PictureHeader Vp8PictureHeader { get; set; }
+
+        /// <summary>
+        /// Gets or sets the VP8 segment header.
+        /// </summary>
+        public Vp8SegmentHeader Vp8SegmentHeader { get; set; }
+
+        /// <summary>
+        /// Gets or sets the VP8 filter header.
+        /// </summary>
+        public Vp8FilterHeader Vp8FilterHeader { get; set; }
+
+        /// <summary>
+        /// Gets or sets the VP8L bitreader. Will be null, if its not lossless image.
         /// </summary>
         public Vp8LBitReader Vp8LBitReader { get; set; } = null;