Webp improvements

src/ImageSharp/Formats/Webp/EntropyIx.cs

@@ -6,7 +6,7 @@ namespace SixLabors.ImageSharp.Formats.Webp
     /// <summary>
     /// These five modes are evaluated and their respective entropy is computed.
     /// </summary>
-    internal enum EntropyIx
+    internal enum EntropyIx : byte
     {
         Direct = 0,
 

src/ImageSharp/Formats/Webp/HistoIx.cs

@@ -3,7 +3,7 @@
 
 namespace SixLabors.ImageSharp.Formats.Webp
 {
-    internal enum HistoIx
+    internal enum HistoIx : byte
     {
         HistoAlpha = 0,
 

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

@@ -2,11 +2,13 @@
 // Licensed under the Apache License, Version 2.0.
 
 using System;
+using System.Buffers;
 using System.Collections.Generic;
+using SixLabors.ImageSharp.Memory;
 
 namespace SixLabors.ImageSharp.Formats.Webp.Lossless
 {
-    internal class BackwardReferenceEncoder
+    internal static class BackwardReferenceEncoder
     {
         /// <summary>
         /// Maximum bit length.
@@ -41,6 +43,7 @@ public static Vp8LBackwardRefs GetBackwardReferences(
             int quality,
             int lz77TypesToTry,
             ref int cacheBits,
+            MemoryAllocator memoryAllocator,
             Vp8LHashChain hashChain,
             Vp8LBackwardRefs best,
             Vp8LBackwardRefs worst)
@@ -69,7 +72,7 @@ public static Vp8LBackwardRefs GetBackwardReferences(
                         BackwardReferencesLz77(width, height, bgra, 0, hashChain, worst);
                         break;
                     case Vp8LLz77Type.Lz77Box:
-                        hashChainBox = new Vp8LHashChain(width * height);
+                        hashChainBox = new Vp8LHashChain(memoryAllocator, width * height);
                         BackwardReferencesLz77Box(width, height, bgra, 0, hashChain, hashChainBox, worst);
                         break;
                 }
@@ -100,7 +103,7 @@ public static Vp8LBackwardRefs GetBackwardReferences(
             if ((lz77TypeBest == (int)Vp8LLz77Type.Lz77Standard || lz77TypeBest == (int)Vp8LLz77Type.Lz77Box) && quality >= 25)
             {
                 Vp8LHashChain hashChainTmp = lz77TypeBest == (int)Vp8LLz77Type.Lz77Standard ? hashChain : hashChainBox;
-                BackwardReferencesTraceBackwards(width, height, bgra, cacheBits, hashChainTmp, best, worst);
+                BackwardReferencesTraceBackwards(width, height, memoryAllocator, bgra, cacheBits, hashChainTmp, best, worst);
                 var histo = new Vp8LHistogram(worst, cacheBits);
                 double bitCostTrace = histo.EstimateBits(stats, bitsEntropy);
                 if (bitCostTrace < bitCostBest)
@@ -111,6 +114,8 @@ public static Vp8LBackwardRefs GetBackwardReferences(
 
             BackwardReferences2DLocality(width, best);
 
+            hashChainBox?.Dispose();
+
             return best;
         }
 
@@ -234,29 +239,32 @@ private static int CalculateBestCacheSize(ReadOnlySpan<uint> bgra, int quality,
         private static void BackwardReferencesTraceBackwards(
             int xSize,
             int ySize,
+            MemoryAllocator memoryAllocator,
             ReadOnlySpan<uint> bgra,
             int cacheBits,
             Vp8LHashChain hashChain,
             Vp8LBackwardRefs refsSrc,
             Vp8LBackwardRefs refsDst)
         {
             int distArraySize = xSize * ySize;
-            ushort[] distArray = new ushort[distArraySize];
+            using IMemoryOwner<ushort> distArrayBuffer = memoryAllocator.Allocate<ushort>(distArraySize);
+            Span<ushort> distArray = distArrayBuffer.GetSpan();
 
-            BackwardReferencesHashChainDistanceOnly(xSize, ySize, bgra, cacheBits, hashChain, refsSrc, distArray);
+            BackwardReferencesHashChainDistanceOnly(xSize, ySize, memoryAllocator, bgra, cacheBits, hashChain, refsSrc, distArrayBuffer);
             int chosenPathSize = TraceBackwards(distArray, distArraySize);
-            Span<ushort> chosenPath = distArray.AsSpan(distArraySize - chosenPathSize);
+            Span<ushort> chosenPath = distArray.Slice(distArraySize - chosenPathSize);
             BackwardReferencesHashChainFollowChosenPath(bgra, cacheBits, chosenPath, chosenPathSize, hashChain, refsDst);
         }
 
         private static void BackwardReferencesHashChainDistanceOnly(
             int xSize,
             int ySize,
+            MemoryAllocator memoryAllocator,
             ReadOnlySpan<uint> bgra,
             int cacheBits,
             Vp8LHashChain hashChain,
             Vp8LBackwardRefs refs,
-            ushort[] distArray)
+            IMemoryOwner<ushort> distArrayBuffer)
         {
             int pixCount = xSize * ySize;
             bool useColorCache = cacheBits > 0;
@@ -275,22 +283,24 @@ private static void BackwardReferencesHashChainDistanceOnly(
             }
 
             costModel.Build(xSize, cacheBits, refs);
-            var costManager = new CostManager(distArray, pixCount, costModel);
+            using var costManager = new CostManager(memoryAllocator, distArrayBuffer, pixCount, costModel);
+            Span<float> costManagerCosts = costManager.Costs.GetSpan();
+            Span<ushort> distArray = distArrayBuffer.GetSpan();
 
             // We loop one pixel at a time, but store all currently best points to non-processed locations from this point.
             distArray[0] = 0;
 
             // Add first pixel as literal.
-            AddSingleLiteralWithCostModel(bgra, colorCache, costModel, 0, useColorCache, 0.0f, costManager.Costs, distArray);
+            AddSingleLiteralWithCostModel(bgra, colorCache, costModel, 0, useColorCache, 0.0f, costManagerCosts, distArray);
 
             for (int i = 1; i < pixCount; i++)
             {
-                float prevCost = costManager.Costs[i - 1];
+                float prevCost = costManagerCosts[i - 1];
                 int offset = hashChain.FindOffset(i);
                 int len = hashChain.FindLength(i);
 
                 // Try adding the pixel as a literal.
-                AddSingleLiteralWithCostModel(bgra, colorCache, costModel, i, useColorCache, prevCost, costManager.Costs, distArray);
+                AddSingleLiteralWithCostModel(bgra, colorCache, costModel, i, useColorCache, prevCost, costManagerCosts, distArray);
 
                 // If we are dealing with a non-literal.
                 if (len >= 2)
@@ -334,7 +344,7 @@ private static void BackwardReferencesHashChainDistanceOnly(
                             costManager.UpdateCostAtIndex(j - 1, false);
                             costManager.UpdateCostAtIndex(j, false);
 
-                            costManager.PushInterval(costManager.Costs[j - 1] + offsetCost, j, lenJ);
+                            costManager.PushInterval(costManagerCosts[j - 1] + offsetCost, j, lenJ);
                             reach = j + lenJ - 1;
                         }
                     }
@@ -346,7 +356,7 @@ private static void BackwardReferencesHashChainDistanceOnly(
             }
         }
 
-        private static int TraceBackwards(ushort[] distArray, int distArraySize)
+        private static int TraceBackwards(Span<ushort> distArray, int distArraySize)
         {
             int chosenPathSize = 0;
             int pathPos = distArraySize;
@@ -426,8 +436,8 @@ private static void AddSingleLiteralWithCostModel(
             int idx,
             bool useColorCache,
             float prevCost,
-            float[] cost,
-            ushort[] distArray)
+            Span<float> cost,
+            Span<ushort> distArray)
         {
             double costVal = prevCost;
             uint color = bgra[idx];
@@ -617,7 +627,8 @@ private static void BackwardReferencesLz77Box(int xSize, int ySize, ReadOnlySpan
                 }
             }
 
-            hashChain.OffsetLength[0] = 0;
+            Span<uint> hashChainOffsetLength = hashChain.OffsetLength.GetSpan();
+            hashChainOffsetLength[0] = 0;
             for (i = 1; i < pixelCount; i++)
             {
                 int ind;
@@ -695,19 +706,19 @@ private static void BackwardReferencesLz77Box(int xSize, int ySize, ReadOnlySpan
 
                 if (bestLength <= MinLength)
                 {
-                    hashChain.OffsetLength[i] = 0;
+                    hashChainOffsetLength[i] = 0;
                     bestOffsetPrev = 0;
                     bestLengthPrev = 0;
                 }
                 else
                 {
-                    hashChain.OffsetLength[i] = (uint)((bestOffset << MaxLengthBits) | bestLength);
+                    hashChainOffsetLength[i] = (uint)((bestOffset << MaxLengthBits) | bestLength);
                     bestOffsetPrev = bestOffset;
                     bestLengthPrev = bestLength;
                 }
             }
 
-            hashChain.OffsetLength[0] = 0;
+            hashChainOffsetLength[0] = 0;
             BackwardReferencesLz77(xSize, ySize, bgra, cacheBits, hashChain, refs);
         }
 

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

@@ -1,7 +1,10 @@
 // Copyright (c) Six Labors.
 // Licensed under the Apache License, Version 2.0.
 
+using System;
+using System.Buffers;
 using System.Collections.Generic;
+using SixLabors.ImageSharp.Memory;
 
 namespace SixLabors.ImageSharp.Formats.Webp.Lossless
 {
@@ -10,20 +13,29 @@ namespace SixLabors.ImageSharp.Formats.Webp.Lossless
     /// It caches the different CostCacheInterval, caches the different
     /// GetLengthCost(costModel, k) in costCache and the CostInterval's.
     /// </summary>
-    internal class CostManager
+    internal sealed class CostManager : IDisposable
     {
         private CostInterval head;
 
-        public CostManager(ushort[] distArray, int pixCount, CostModel costModel)
+        private const int FreeIntervalsStartCount = 25;
+
+        private readonly Stack<CostInterval> freeIntervals = new(FreeIntervalsStartCount);
+
+        public CostManager(MemoryAllocator memoryAllocator, IMemoryOwner<ushort> distArray, int pixCount, CostModel costModel)
         {
             int costCacheSize = pixCount > BackwardReferenceEncoder.MaxLength ? BackwardReferenceEncoder.MaxLength : pixCount;
 
             this.CacheIntervals = new List<CostCacheInterval>();
             this.CostCache = new List<double>();
-            this.Costs = new float[pixCount];
+            this.Costs = memoryAllocator.Allocate<float>(pixCount);
             this.DistArray = distArray;
             this.Count = 0;
 
+            for (int i = 0; i < FreeIntervalsStartCount; i++)
+            {
+                this.freeIntervals.Push(new CostInterval());
+            }
+
             // Fill in the cost cache.
             this.CacheIntervalsSize++;
             this.CostCache.Add(costModel.GetLengthCost(0));
@@ -64,10 +76,7 @@ public CostManager(ushort[] distArray, int pixCount, CostModel costModel)
             }
 
             // Set the initial costs high for every pixel as we will keep the minimum.
-            for (int i = 0; i < pixCount; i++)
-            {
-                this.Costs[i] = 1e38f;
-            }
+            this.Costs.GetSpan().Fill(1e38f);
         }
 
         /// <summary>
@@ -82,9 +91,9 @@ public CostManager(ushort[] distArray, int pixCount, CostModel costModel)
 
         public int CacheIntervalsSize { get; }
 
-        public float[] Costs { get; }
+        public IMemoryOwner<float> Costs { get; }
 
-        public ushort[] DistArray { get; }
+        public IMemoryOwner<ushort> DistArray { get; }
 
         public List<CostCacheInterval> CacheIntervals { get; }
 
@@ -128,17 +137,19 @@ public void PushInterval(double distanceCost, int position, int len)
             // interval logic, just serialize it right away. This constant is empirical.
             int skipDistance = 10;
 
+            Span<float> costs = this.Costs.GetSpan();
+            Span<ushort> distArray = this.DistArray.GetSpan();
             if (len < skipDistance)
             {
                 for (int j = position; j < position + len; j++)
                 {
                     int k = j - position;
                     float costTmp = (float)(distanceCost + this.CostCache[k]);
 
-                    if (this.Costs[j] > costTmp)
+                    if (costs[j] > costTmp)
                     {
-                        this.Costs[j] = costTmp;
-                        this.DistArray[j] = (ushort)(k + 1);
+                        costs[j] = costTmp;
+                        distArray[j] = (ushort)(k + 1);
                     }
                 }
 
@@ -201,10 +212,8 @@ public void PushInterval(double distanceCost, int position, int len)
                             this.InsertInterval(interval, interval.Cost, interval.Index, end, endOriginal);
                             break;
                         }
-                        else
-                        {
-                            interval.End = start;
-                        }
+
+                        interval.End = start;
                     }
                 }
 
@@ -226,6 +235,10 @@ private void PopInterval(CostInterval interval)
 
             this.ConnectIntervals(interval.Previous, interval.Next);
             this.Count--;
+
+            interval.Next = null;
+            interval.Previous = null;
+            this.freeIntervals.Push(interval);
         }
 
         private void InsertInterval(CostInterval intervalIn, float cost, int position, int start, int end)
@@ -236,13 +249,19 @@ private void InsertInterval(CostInterval intervalIn, float cost, int position, i
             }
 
             // TODO: should we use COST_CACHE_INTERVAL_SIZE_MAX?
-            var intervalNew = new CostInterval()
+            CostInterval intervalNew;
+            if (this.freeIntervals.Count > 0)
             {
-                Cost = cost,
-                Start = start,
-                End = end,
-                Index = position
-            };
+                intervalNew = this.freeIntervals.Pop();
+                intervalNew.Cost = cost;
+                intervalNew.Start = start;
+                intervalNew.End = end;
+                intervalNew.Index = position;
+            }
+            else
+            {
+                intervalNew = new CostInterval() { Cost = cost, Start = start, End = end, Index = position };
+            }
 
             this.PositionOrphanInterval(intervalNew, intervalIn);
             this.Count++;
@@ -297,12 +316,17 @@ private void ConnectIntervals(CostInterval prev, CostInterval next)
         /// </summary>
         private void UpdateCost(int i, int position, float cost)
         {
+            Span<float> costs = this.Costs.GetSpan();
+            Span<ushort> distArray = this.DistArray.GetSpan();
             int k = i - position;
-            if (this.Costs[i] > cost)
+            if (costs[i] > cost)
             {
-                this.Costs[i] = cost;
-                this.DistArray[i] = (ushort)(k + 1);
+                costs[i] = cost;
+                distArray[i] = (ushort)(k + 1);
             }
         }
+
+        /// <inheritdoc />
+        public void Dispose() => this.Costs.Dispose();
     }
 }

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

@@ -13,16 +13,16 @@ namespace SixLabors.ImageSharp.Formats.Webp.Lossless
     ///  - UsePackedTable: few enough literal symbols, so all the bit codes can fit into a small look-up table PackedTable[]
     /// The common literal base, if applicable, is stored in 'LiteralArb'.
     /// </summary>
-    internal class HTreeGroup
+    internal struct HTreeGroup
     {
         public HTreeGroup(uint packedTableSize)
         {
             this.HTrees = new List<HuffmanCode[]>(WebpConstants.HuffmanCodesPerMetaCode);
             this.PackedTable = new HuffmanCode[packedTableSize];
-            for (int i = 0; i < packedTableSize; i++)
-            {
-                this.PackedTable[i] = new HuffmanCode();
-            }
+            this.IsTrivialCode = false;
+            this.IsTrivialLiteral = false;
+            this.LiteralArb = 0;
+            this.UsePackedTable = false;
         }
 
         /// <summary>

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

@@ -9,7 +9,7 @@ namespace SixLabors.ImageSharp.Formats.Webp.Lossless
     /// A classic way to do entropy coding where a smaller number of bits are used for more frequent codes.
     /// </summary>
     [DebuggerDisplay("BitsUsed: {BitsUsed}, Value: {Value}")]
-    internal class HuffmanCode
+    internal struct HuffmanCode
     {
         /// <summary>
         /// Gets or sets the number of bits used for this symbol.