Make scan order read only

src/ImageSharp/Formats/Heif/Av1/Pipeline/Quantification/Av1InverseQuantizer.cs

@@ -85,7 +85,7 @@ internal class Av1InverseQuantizer
     {
         Guard.NotNull(this.deQuantsDeltaQ);
         Av1ScanOrder scanOrder = Av1ScanOrderConstants.GetScanOrder(transformSize, transformType);
-        short[] scanIndices = scanOrder.Scan;
+        ReadOnlySpan<short> scanIndices = scanOrder.Scan;
         int maxValue = (1 << (7 + this.sequenceHeader.ColorConfig.BitDepth.GetBitCount())) - 1;
         int minValue = -(1 << (7 + this.sequenceHeader.ColorConfig.BitDepth.GetBitCount()));
         Av1TransformSize qmTransformSize = transformSize.GetAdjusted();

src/ImageSharp/Formats/Heif/Av1/Tiling/Av1SymbolDecoder.cs

@@ -217,7 +217,7 @@ internal ref struct Av1SymbolDecoder
         return r.ReadSymbol(this.chromeForLumaAlpha[context]);
     }
 
-    public void ReadCoefficientsEndOfBlock(Av1TransformClass transformClass, int endOfBlock, int height, Span<short> scan, int bwl, Span<int> levels, Av1TransformSize transformSizeContext, Av1PlaneType planeType)
+    public void ReadCoefficientsEndOfBlock(Av1TransformClass transformClass, int endOfBlock, int height, ReadOnlySpan<short> scan, int bwl, Span<int> levels, Av1TransformSize transformSizeContext, Av1PlaneType planeType)
     {
         int i = endOfBlock - 1;
         int pos = scan[i];
@@ -240,7 +240,7 @@ internal ref struct Av1SymbolDecoder
         levels[GetPaddedIndex(pos, bwl)] = level;
     }
 
-    public void ReadCoefficientsReverse2d(Av1TransformSize transformSize, int startSi, int endSi, Span<short> scan, int bwl, Span<int> levels, Av1TransformSize transformSizeContext, Av1PlaneType planeType)
+    public void ReadCoefficientsReverse2d(Av1TransformSize transformSize, int startSi, int endSi, ReadOnlySpan<short> scan, int bwl, Span<int> levels, Av1TransformSize transformSizeContext, Av1PlaneType planeType)
     {
         for (int c = endSi; c >= startSi; --c)
         {
@@ -265,7 +265,7 @@ internal ref struct Av1SymbolDecoder
         }
     }
 
-    public void ReadCoefficientsReverse(Av1TransformSize transformSize, Av1TransformClass transformClass, int startSi, int endSi, Span<short> scan, int bwl, Span<int> levels, Av1TransformSize transformSizeContext, Av1PlaneType planeType)
+    public void ReadCoefficientsReverse(Av1TransformSize transformSize, Av1TransformClass transformClass, int startSi, int endSi, ReadOnlySpan<short> scan, int bwl, Span<int> levels, Av1TransformSize transformSizeContext, Av1PlaneType planeType)
     {
         for (int c = endSi; c >= startSi; --c)
         {
@@ -290,7 +290,7 @@ internal ref struct Av1SymbolDecoder
         }
     }
 
-    public int ReadCoefficientsDc(Span<int> coefficientBuffer, int endOfBlock, Span<short> scan, int bwl, Span<int> levels, int dcSignContext, Av1PlaneType planeType)
+    public int ReadCoefficientsDc(Span<int> coefficientBuffer, int endOfBlock, ReadOnlySpan<short> scan, int bwl, Span<int> levels, int dcSignContext, Av1PlaneType planeType)
     {
         int maxScanLine = 0;
         int culLevel = 0;

src/ImageSharp/Formats/Heif/Av1/Tiling/Av1TileReader.cs

@@ -591,7 +591,7 @@ internal class Av1TileReader : IAv1TileReader
         transformInfo.Type = this.ComputeTransformType(planeType, partitionInfo, transformSize, transformInfo);
         Av1TransformClass transformClass = transformInfo.Type.ToClass();
         Av1ScanOrder scanOrder = Av1ScanOrderConstants.GetScanOrder(transformSize, transformInfo.Type);
-        Span<short> scan = scanOrder.Scan;
+        ReadOnlySpan<short> scan = scanOrder.Scan;
 
         endOfBlockPoint = reader.ReadEndOfBlockFlag(planeType, transformClass, transformSize);
         int endOfBlockShift = EndOfBlockOffsetBits[endOfBlockPoint];

src/ImageSharp/Formats/Heif/Av1/Transform/Av1ScanOrder.cs

@@ -5,23 +5,27 @@ namespace SixLabors.ImageSharp.Formats.Heif.Av1.Transform;
 
 internal readonly struct Av1ScanOrder
 {
+    private readonly short[] scan;
+    private readonly short[] inverseScan;
+    private readonly short[] neighbors;
+
     public Av1ScanOrder(short[] scan)
     {
-        this.Scan = scan;
-        this.InverseScan = [];
-        this.Neighbors = [];
+        this.scan = scan;
+        this.inverseScan = [];
+        this.neighbors = [];
     }
 
     public Av1ScanOrder(short[] scan, short[] inverseScan, short[] neighbors)
     {
-        this.Scan = scan;
-        this.InverseScan = inverseScan;
-        this.Neighbors = neighbors;
+        this.scan = scan;
+        this.inverseScan = inverseScan;
+        this.neighbors = neighbors;
     }
 
-    public short[] Scan { get; }
+    public ReadOnlySpan<short> Scan => this.scan;
 
-    public short[] InverseScan { get; }
+    public ReadOnlySpan<short> InverseScan => this.inverseScan;
 
-    public short[] Neighbors { get; }
+    public ReadOnlySpan<short> Neighbors => this.neighbors;
 }