Add patch dictionary stage

src/ImageSharp/Formats/Jxl/Processing/Decoder/JxlPatchDictionary.cs

@@ -53,7 +53,7 @@ internal sealed class JxlPatchDictionary
         this.blendingsStride = (int)(numExtraChannels + 1);
 
         List<byte> contextMap = [];
-        var code = new JxlAnsCode();
+        JxlAnsCode code = new();
 
         var status = DecodeHistograms(
             memoryManager,

src/ImageSharp/Formats/Jxl/Processing/RenderPipeline/PatchDictionaryStage.cs

@@ -0,0 +1,40 @@
+// Copyright (c) Six Labors.
+// Licensed under the Six Labors Split License.
+
+using System.Drawing;
+using SixLabors.ImageSharp.Formats.Jxl.IO.Metadata;
+using SixLabors.ImageSharp.Formats.Jxl.Processing.Decoder;
+using SixLabors.ImageSharp.Memory;
+
+namespace SixLabors.ImageSharp.Formats.Jxl.Processing.RenderPipeline;
+
+internal sealed class PatchDictionaryStage(Configuration configuration, JxlPatchDictionary patches, List<JxlExtraChannelInfo> extraChannelInfos)
+    : RenderPipelineStageBase(configuration)
+{
+    /// <inheritdoc />
+    public override string Name => "Patches";
+
+    /// <inheritdoc />
+    public override void ProcessRow(Buffer2D<Memory<float>> inputRows, Buffer2D<Memory<float>> outputRows, int xExtraLeft, int xExtraRight, int width, int xPos, int yPos)
+    {
+        int channels = 3 + extraChannelInfos.Count;
+
+        Span<Memory<float>> rowPtrs = new Memory<float>[channels];
+
+        for (int i = 0; i < channels; i++)
+        {
+            rowPtrs[i] = this.GetInputRowMemory(inputRows, i, 0, xExtraLeft);
+        }
+
+        return patches.AddOneRow(rowPtrs, yPos, xPos - xExtraLeft, width + xExtraLeft + xExtraRight, extraChannelInfos);
+    }
+
+    /// <inheritdoc />
+    public override RenderPipelineChannelMode GetChannelMode(int channel)
+    {
+        int numChannels = 3 + extraChannelInfos.Count;
+        return channel < numChannels
+            ? RenderPipelineChannelMode.InPlace
+            : RenderPipelineChannelMode.Ignored;
+    }
+}

src/ImageSharp/Formats/Jxl/Processing/RenderPipeline/RenderPipelineStageBase.cs

@@ -71,9 +71,15 @@ internal abstract class RenderPipelineStageBase(Configuration configuration) : I
     public Span<float> GetInputRow(Buffer2D<Memory<float>> inputRows, int c, int offset)
         => inputRows[c, this.Settings.BorderY + offset].Span[RenderPipelineXOffset..];
 
+    public Span<float> GetInputRow(Buffer2D<Memory<float>> inputRows, int c, int offset, int xExtraLeft)
+        => inputRows[c, this.Settings.BorderY + offset].Span[(RenderPipelineXOffset - xExtraLeft)..];
+
     public Memory<float> GetInputRowMemory(Buffer2D<Memory<float>> inputRows, int c, int offset)
         => inputRows[c, this.Settings.BorderY + offset][RenderPipelineXOffset..];
 
+    public Memory<float> GetInputRowMemory(Buffer2D<Memory<float>> inputRows, int c, int offset, int xExtraLeft)
+        => inputRows[c, this.Settings.BorderY + offset][(RenderPipelineXOffset - xExtraLeft)..];
+
     public static Span<float> GetOutputRow(Buffer2D<Memory<float>> outputRows, int c, int offset)
         => outputRows[c, offset].Span[RenderPipelineXOffset..];