Implement spline abstractions

Implementation of spline.h

src/ImageSharp/Formats/Jxl/Metadata/InlineArrays.cs → src/ImageSharp/Formats/Jxl/InlineArrays.cs

@@ -5,7 +5,7 @@ using System.Runtime.CompilerServices;
 
 #pragma warning disable SA1649 // File name should match first type name
 
-namespace SixLabors.ImageSharp.Formats.Jxl.Metadata;
+namespace SixLabors.ImageSharp.Formats.Jxl;
 
 [InlineArray(3)]
 internal struct InlineArray3<T>

src/ImageSharp/Formats/Jxl/Splines/JxlQuantizedSpline.cs

@@ -0,0 +1,26 @@
+// Copyright (c) Six Labors.
+// Licensed under the Six Labors Split License.
+
+namespace SixLabors.ImageSharp.Formats.Jxl.Splines;
+
+internal sealed class JxlQuantizedSpline
+{
+    public JxlQuantizedSpline()
+    {
+        for (int i = 0; i < 3; i++)
+        {
+            this.ColorDct[i] = new int[32];
+        }
+    }
+
+    public Dictionary<long, long> ControlPoints { get; set; } = [];
+
+    // NOTE: Do not use Configuration.MemoryAllocator.Allocate2D. This is
+    // a 3x32 array, and renting memory introduces too much overhead for
+    // 384 bytes of memory.
+    // Additionally, prefer jagged arrays instead of multidimensional arrays
+    // for performance.
+    public int[][] ColorDct { get; set; } = new int[3][];
+
+    public int[] SigmaDct { get; set; } = new int[32];
+}

src/ImageSharp/Formats/Jxl/Splines/JxlSpline.cs

@@ -0,0 +1,13 @@
+// Copyright (c) Six Labors.
+// Licensed under the Six Labors Split License.
+
+namespace SixLabors.ImageSharp.Formats.Jxl.Splines;
+
+internal sealed class JxlSpline
+{
+    public List<PointF> ControlPoints { get; set; } = [];
+
+    public JxlDct32[] ColorDct { get; set; } = [];
+
+    public JxlDct32 SigmaDct { get; set; }
+}

src/ImageSharp/Formats/Jxl/Splines/JxlSplineDataView.cs

@@ -0,0 +1,13 @@
+// Copyright (c) Six Labors.
+// Licensed under the Six Labors Split License.
+
+namespace SixLabors.ImageSharp.Formats.Jxl.Splines;
+
+internal sealed class JxlSplineDataView
+{
+    public List<JxlQuantizedSpline> Splines { get; set; } = [];
+
+    public List<PointF> StartingPoints { get; set; } = [];
+
+    public bool HasAny => this.Splines.Count > 0;
+}

src/ImageSharp/Formats/Jxl/Splines/JxlSplineEntropyContext.cs

@@ -0,0 +1,15 @@
+// Copyright (c) Six Labors.
+// Licensed under the Six Labors Split License.
+
+namespace SixLabors.ImageSharp.Formats.Jxl.Splines;
+
+internal enum JxlSplineEntropyContext
+{
+    QuantizationAdjustment,
+    StartingPosition,
+    NumSplines,
+    NumControlPoints,
+    ControlPoints,
+    Dct,
+    NumSplineContexts
+}

src/ImageSharp/Formats/Jxl/Splines/JxlSplineSegment.cs

@@ -0,0 +1,17 @@
+// Copyright (c) Six Labors.
+// Licensed under the Six Labors Split License.
+
+namespace SixLabors.ImageSharp.Formats.Jxl.Splines;
+
+internal struct JxlSplineSegment
+{
+    public PointF Center { get; set; }
+
+    public float MaximumDistance { get; set; }
+
+    public float InverseSigma { get; set; }
+
+    public float SigmaOver4TimesIntensity { get; set; }
+
+    public InlineArray3<float> Color { get; set; }
+}

src/ImageSharp/Formats/Jxl/Splines/JxlSplineSegmentSpan.cs

@@ -0,0 +1,11 @@
+// Copyright (c) Six Labors.
+// Licensed under the Six Labors Split License.
+
+namespace SixLabors.ImageSharp.Formats.Jxl.Splines;
+
+internal struct JxlSplineSegmentSpan(int startInclusive, int endInclusive)
+{
+    public int StartInclusive { get; set; } = startInclusive;
+
+    public int EndInclusive { get; set; } = endInclusive;
+}