Remove some low hanging allocations

src/ImageSharp/Formats/WebP/BitReader/Vp8BitReader.cs

@@ -91,6 +91,7 @@ namespace SixLabors.ImageSharp.Formats.Experimental.WebP.BitReader
 
         public uint Remaining { get; set; }
 
+        [MethodImpl(InliningOptions.ShortMethod)]
         public int GetBit(int prob)
         {
             uint range = this.range;
@@ -184,6 +185,7 @@ namespace SixLabors.ImageSharp.Formats.Experimental.WebP.BitReader
             this.LoadNewBytes();
         }
 
+        [MethodImpl(InliningOptions.ColdPath)]
         private void LoadNewBytes()
         {
             if (this.pos < this.bufferMax)

src/ImageSharp/Formats/WebP/Lossless/WebPLosslessDecoder.cs

@@ -381,9 +381,12 @@ namespace SixLabors.ImageSharp.Formats.Experimental.WebP.Lossless
                 int huffmanXSize = LosslessUtils.SubSampleSize(xSize, huffmanPrecision);
                 int huffmanYSize = LosslessUtils.SubSampleSize(ySize, huffmanPrecision);
                 int huffmanPixels = huffmanXSize * huffmanYSize;
+
                 IMemoryOwner<uint> huffmanImage = this.DecodeImageStream(decoder, huffmanXSize, huffmanYSize, false);
                 Span<uint> huffmanImageSpan = huffmanImage.GetSpan();
                 decoder.Metadata.HuffmanSubSampleBits = huffmanPrecision;
+
+                // TODO: Isn't huffmanPixels the length of the span?
                 for (int i = 0; i < huffmanPixels; ++i)
                 {
                     // The huffman data is stored in red and green bytes.
@@ -440,6 +443,7 @@ namespace SixLabors.ImageSharp.Formats.Experimental.WebP.Lossless
                         WebPThrowHelper.ThrowImageFormatException("Huffman table size is zero");
                     }
 
+                    // TODO: Avoid allocation.
                     hTreeGroup.HTrees.Add(huffmanTable.ToArray());
 
                     HuffmanCode huffTableZero = huffmanTable[0];
@@ -472,10 +476,10 @@ namespace SixLabors.ImageSharp.Formats.Experimental.WebP.Lossless
                 hTreeGroup.IsTrivialCode = false;
                 if (isTrivialLiteral)
                 {
-                    uint red = hTreeGroup.HTrees[HuffIndex.Red].First().Value;
-                    uint blue = hTreeGroup.HTrees[HuffIndex.Blue].First().Value;
-                    uint green = hTreeGroup.HTrees[HuffIndex.Green].First().Value;
-                    uint alpha = hTreeGroup.HTrees[HuffIndex.Alpha].First().Value;
+                    uint red = hTreeGroup.HTrees[HuffIndex.Red][0].Value;
+                    uint blue = hTreeGroup.HTrees[HuffIndex.Blue][0].Value;
+                    uint green = hTreeGroup.HTrees[HuffIndex.Green][0].Value;
+                    uint alpha = hTreeGroup.HTrees[HuffIndex.Alpha][0].Value;
                     hTreeGroup.LiteralArb = (alpha << 24) | (red << 16) | blue;
                     if (totalSize == 0 && green < WebPConstants.NumLiteralCodes)
                     {
@@ -542,7 +546,7 @@ namespace SixLabors.ImageSharp.Formats.Experimental.WebP.Lossless
                     codeLengthCodeLengths[CodeLengthCodeOrder[i]] = (int)this.bitReader.ReadValue(3);
                 }
 
-                this.ReadHuffmanCodeLengths(table.ToArray(), codeLengthCodeLengths, alphabetSize, codeLengths);
+                this.ReadHuffmanCodeLengths(table, codeLengthCodeLengths, alphabetSize, codeLengths);
             }
 
             int size = HuffmanUtils.BuildHuffmanTable(table, HuffmanUtils.HuffmanTableBits, codeLengths, alphabetSize);
@@ -550,7 +554,7 @@ namespace SixLabors.ImageSharp.Formats.Experimental.WebP.Lossless
             return size;
         }
 
-        private void ReadHuffmanCodeLengths(HuffmanCode[] table, int[] codeLengthCodeLengths, int numSymbols, int[] codeLengths)
+        private void ReadHuffmanCodeLengths(Span<HuffmanCode> table, int[] codeLengthCodeLengths, int numSymbols, int[] codeLengths)
         {
             int maxSymbol;
             int symbol = 0;
@@ -580,7 +584,7 @@ namespace SixLabors.ImageSharp.Formats.Experimental.WebP.Lossless
 
                 this.bitReader.FillBitWindow();
                 ulong prefetchBits = this.bitReader.PrefetchBits();
-                ulong idx = prefetchBits & 127;
+                int idx = (int)(prefetchBits & 127);
                 HuffmanCode huffmanCode = table[idx];
                 this.bitReader.AdvanceBitPosition(huffmanCode.BitsUsed);
                 uint codeLen = huffmanCode.Value;
@@ -625,6 +629,7 @@ namespace SixLabors.ImageSharp.Formats.Experimental.WebP.Lossless
             var transform = new Vp8LTransform(transformType, xSize, ySize);
 
             // Each transform is allowed to be used only once.
+            // TODO: No Linq, avoid 'transform' closure allocation.
             if (decoder.Transforms.Any(t => t.TransformType == transform.TransformType))
             {
                 WebPThrowHelper.ThrowImageFormatException("Each transform can only be present once");

src/ImageSharp/Formats/WebP/Lossy/LossyUtils.cs

@@ -492,7 +492,7 @@ namespace SixLabors.ImageSharp.Formats.Experimental.WebP.Lossy
 
         public static void TransformOne(Span<short> src, Span<byte> dst)
         {
-            var tmp = new int[4 * 4];
+            Span<int> tmp = stackalloc int[4 * 4];
             int tmpOffset = 0;
             for (int srcOffset = 0; srcOffset < 4; srcOffset++)
             {

src/ImageSharp/Formats/WebP/Lossy/WebPLossyDecoder.cs

@@ -55,14 +55,14 @@ namespace SixLabors.ImageSharp.Formats.Experimental.WebP.Lossy
             sbyte colorSpace = (sbyte)this.bitReader.ReadValue(1);
             sbyte clampType = (sbyte)this.bitReader.ReadValue(1);
             var pictureHeader = new Vp8PictureHeader()
-                                   {
-                                       Width = (uint)width,
-                                       Height = (uint)height,
-                                       XScale = info.XScale,
-                                       YScale = info.YScale,
-                                       ColorSpace = colorSpace,
-                                       ClampType = clampType
-                                   };
+            {
+                Width = (uint)width,
+                Height = (uint)height,
+                XScale = info.XScale,
+                YScale = info.YScale,
+                ColorSpace = colorSpace,
+                ClampType = clampType
+            };
 
             // Paragraph 9.3: Parse the segment header.
             var proba = new Vp8Proba();
@@ -135,10 +135,12 @@ namespace SixLabors.ImageSharp.Formats.Experimental.WebP.Lossy
             Span<byte> alphaSpan = alpha.Memory.Span;
             for (int y = 0; y < height; y++)
             {
+                // TODO: Can we use span.Length here?
                 int yMulWidth = y * width;
                 Span<TPixel> pixelRow = pixels.GetRowSpan(y);
                 for (int x = 0; x < width; x++)
                 {
+                    // TODO: Could use cast to Bgr24/Bgra32 then set alpha.
                     int offset = yMulWidth + x;
                     int idxBgr = offset * 3;
                     byte b = pixelData[idxBgr];
@@ -165,9 +167,10 @@ namespace SixLabors.ImageSharp.Formats.Experimental.WebP.Lossy
                     this.ParseIntraMode(dec, mbX);
                 }
 
-                for (; dec.MbX < dec.MbWidth; ++dec.MbX)
+                while (dec.MbX < dec.MbWidth)
                 {
                     this.DecodeMacroBlock(dec, bitreader);
+                    ++dec.MbX;
                 }
 
                 // Prepare for next scanline.

src/ImageSharp/Formats/WebP/WebPCommonUtils.cs

@@ -2,6 +2,7 @@
 // Licensed under the Apache License, Version 2.0.
 
 using System.Runtime.CompilerServices;
+using System.Runtime.InteropServices;
 
 namespace SixLabors.ImageSharp.Formats.Experimental.WebP
 {
@@ -23,7 +24,7 @@ namespace SixLabors.ImageSharp.Formats.Experimental.WebP
                 n >>= 8;
             }
 
-            return logValue + WebPLookupTables.LogTable8Bit[n];
+            return logValue + Unsafe.Add(ref MemoryMarshal.GetReference(WebPLookupTables.LogTable8Bit), (int)n);
         }
     }
 }

src/ImageSharp/Formats/WebP/WebPLookupTables.cs

@@ -6,6 +6,7 @@ using System.Collections.Generic;
 
 namespace SixLabors.ImageSharp.Formats.Experimental.WebP
 {
+#pragma warning disable SA1201 // Elements should appear in the correct order
     internal static class WebPLookupTables
     {
         public static readonly Dictionary<int, byte> Abs0;
@@ -418,7 +419,7 @@ namespace SixLabors.ImageSharp.Formats.Experimental.WebP
         };
 
         // 31 ^ clz(i)
-        public static readonly byte[] LogTable8Bit =
+        public static ReadOnlySpan<byte> LogTable8Bit => new byte[]
         {
             0, 0, 1, 1, 2, 2, 2, 2, 3, 3, 3, 3, 3, 3, 3, 3,
             4, 4, 4, 4, 4, 4, 4, 4, 4, 4, 4, 4, 4, 4, 4, 4,

tests/ImageSharp.Benchmarks/Codecs/DecodeWebp.cs

@@ -5,7 +5,7 @@ using System.IO;
 using BenchmarkDotNet.Attributes;
 
 using ImageMagick;
-
+using SixLabors.ImageSharp.Formats.Experimental.WebP;
 using SixLabors.ImageSharp.PixelFormats;
 using SixLabors.ImageSharp.Tests;
 
@@ -14,6 +14,8 @@ namespace SixLabors.ImageSharp.Benchmarks.Codecs
     [Config(typeof(Config.ShortClr))]
     public class DecodeWebp : BenchmarkBase
     {
+        private Configuration configuration;
+
         private byte[] webpLossyBytes;
 
         private byte[] webpLosslessBytes;
@@ -31,6 +33,9 @@ namespace SixLabors.ImageSharp.Benchmarks.Codecs
         [GlobalSetup]
         public void ReadImages()
         {
+            this.configuration = Configuration.CreateDefaultInstance();
+            new WebPConfigurationModule().Configure(this.configuration);
+
             this.webpLossyBytes ??= File.ReadAllBytes(this.TestImageLossyFullPath);
             this.webpLosslessBytes ??= File.ReadAllBytes(this.TestImageLosslessFullPath);
         }
@@ -47,7 +52,7 @@ namespace SixLabors.ImageSharp.Benchmarks.Codecs
         public int WebpLossy()
         {
             using var memoryStream = new MemoryStream(this.webpLossyBytes);
-            using var image = Image.Load<Rgba32>(memoryStream);
+            using var image = Image.Load<Rgba32>(this.configuration, memoryStream);
             return image.Height;
         }
 
@@ -63,7 +68,7 @@ namespace SixLabors.ImageSharp.Benchmarks.Codecs
         public int WebpLossless()
         {
             using var memoryStream = new MemoryStream(this.webpLosslessBytes);
-            using var image = Image.Load<Rgba32>(memoryStream);
+            using var image = Image.Load<Rgba32>(this.configuration, memoryStream);
             return image.Height;
         }
 

tests/ImageSharp.Tests/Formats/WebP/WebPDecoderTests.cs

@@ -332,5 +332,13 @@ namespace SixLabors.ImageSharp.Tests.Formats.WebP
                     }
                 });
         }
+
+        [Theory]
+        [WithFile(Lossless.Earth, PixelTypes.Rgba32)]
+        public void ProfileTestLossless<TPixel>(TestImageProvider<TPixel> provider)
+            where TPixel : unmanaged, IPixel<TPixel>
+        {
+            using Image<TPixel> image = provider.GetImage(WebpDecoder);
+        }
     }
 }