Support Netstandard 2.0 again

.github/workflows/dotnetcore.yml

@@ -16,7 +16,7 @@ jobs:
   build-and-test:
 
     name: build-and-test
-    runs-on: ubuntu-latest
+    runs-on: windows-latest
 
     steps:
     - uses: actions/checkout@v3

BCnEnc.Net/AssemblyInfo.cs

@@ -1,3 +1,4 @@
 using System.Runtime.CompilerServices;
 
 [assembly: InternalsVisibleTo("BCnEncTests")]
+[assembly: InternalsVisibleTo("BCnEncTests.Framework")]

BCnEnc.Net/BCnEncoder.csproj

@@ -1,7 +1,8 @@
 <Project Sdk="Microsoft.NET.Sdk">
 
   <PropertyGroup>
-    <TargetFramework>netstandard2.1</TargetFramework>
+	<TargetFrameworks>netstandard2.1;netstandard2.0</TargetFrameworks>
+	<LangVersion>8.0</LangVersion>
     <PublishRepositoryUrl>true</PublishRepositoryUrl>
     <IncludeSymbols>true</IncludeSymbols>
     <SymbolPackageFormat>snupkg</SymbolPackageFormat>
@@ -49,5 +50,12 @@ Supported formats are:
     <PackageReference Include="CommunityToolkit.HighPerformance" Version="8.4.0" />
     <PackageReference Include="Microsoft.SourceLink.GitHub" Version="8.0.0" PrivateAssets="All" />
   </ItemGroup>
+  <ItemGroup Condition="'$(TargetFramework)' == 'netstandard2.0'">
+	<PackageReference Include="PolySharp" Version="1.15.0">
+      <PrivateAssets>all</PrivateAssets>
+      <IncludeAssets>runtime; build; native; contentfiles; analyzers; buildtransitive</IncludeAssets>
+	</PackageReference>
+	<PackageReference Include="Microsoft.Bcl.Numerics" Version="10.0.3" />
+  </ItemGroup>
 
 </Project>

BCnEnc.Net/Decoder/BcDecoder.cs

@@ -166,7 +166,7 @@ public Task<Memory2D<ColorRgba32>> Decode2DAsync(Stream inputStream, Cancellatio
 		/// <returns>The awaitable operation to retrieve the decoded image.</returns>
 		public Task<Memory2D<ColorRgba32>[]> DecodeAllMipMaps2DAsync(Stream inputStream, CancellationToken token = default)
 		{
-			return Task.Run(() => DecodeFromStreamInternal2D(inputStream, false, token), token);
+			return Task.Run(() => DecodeFromStreamInternal2D(inputStream, true, token), token);
 		}
 
 		/// <summary>
@@ -675,7 +675,7 @@ public Task<Memory2D<ColorRgbFloat>> DecodeHdr2DAsync(Stream inputStream, Cancel
 		/// <returns>The awaitable operation to retrieve the decoded image.</returns>
 		public Task<Memory2D<ColorRgbFloat>[]> DecodeAllMipMapsHdr2DAsync(Stream inputStream, CancellationToken token = default)
 		{
-			return Task.Run(() => DecodeFromStreamInternalHdr2D(inputStream, false, token), token);
+			return Task.Run(() => DecodeFromStreamInternalHdr2D(inputStream, true, token), token);
 		}
 
 		/// <summary>

BCnEnc.Net/Encoder/Bptc/BptcEncodingHelpers.cs

@@ -5,6 +5,10 @@
 using System.Text;
 using BCnEncoder.Shared;
 
+#if NETSTANDARD2_0
+using MemoryMarshal = BCnEncoder.Shared.MemoryMarshalPolyfills;
+#endif
+
 namespace BCnEncoder.Encoder.Bptc
 {
 	internal static class BptcEncodingHelpers
@@ -20,7 +24,7 @@ public static int InterpolateInt(int e0, int e1, int index, int indexPrecision)
 			var aWeights2 = ColorInterpolationWeights2;
 			var aWeights3 = ColorInterpolationWeights3;
 			var aWeights4 = ColorInterpolationWeights4;
-			
+
 			if (indexPrecision == 2)
 				return (((64 - aWeights2[index]) * e0 + aWeights2[index] * e1 + 32) >> 6);
 			if (indexPrecision == 3)
@@ -50,22 +54,33 @@ public static int[] Rank2SubsetPartitions(ClusterIndices4X4 reducedIndicesBlock,
 		{
 			var output = Enumerable.Range(0, smallIndex ? 32 : 64).ToArray();
 
+			// Copy struct to array before the closure so that reducedIndicesBlock is not
+			// heap-captured. On .NET Framework, MemoryMarshalPolyfills.CreateSpan uses
+			// Unsafe.AsPointer, which is only GC-safe for stack-allocated structs.
+			#if NETSTANDARD2_0
+			var indices = new int[16];
+			reducedIndicesBlock.AsSpan.CopyTo(indices);
+			#endif
 
 			int CalculatePartitionError(int partitionIndex)
-			{ 
+			{
+				#if NETSTANDARD2_1
+				var indices = reducedIndicesBlock.AsSpan;
+				#endif
+
 				var error = 0;
 				ReadOnlySpan<int> partitionTable = Bc7Block.Subsets2PartitionTable[partitionIndex];
 				Span<int> subset0 = stackalloc int[numDistinctClusters];
 				Span<int> subset1 = stackalloc int[numDistinctClusters];
 				var max0Idx = 0;
 				var max1Idx = 0;
 
-				//Calculate largest cluster index for each subset 
+				//Calculate largest cluster index for each subset
 				for (var i = 0; i < 16; i++)
 				{
 					if (partitionTable[i] == 0)
 					{
-						var r = reducedIndicesBlock[i];
+						var r = indices[i];
 						subset0[r]++;
 						var count = subset0[r];
 						if (count > subset0[max0Idx])
@@ -75,7 +90,7 @@ int CalculatePartitionError(int partitionIndex)
 					}
 					else
 					{
-						var r = reducedIndicesBlock[i];
+						var r = indices[i];
 						subset1[r]++;
 						var count = subset1[r];
 						if (count > subset1[max1Idx])
@@ -90,11 +105,11 @@ int CalculatePartitionError(int partitionIndex)
 				{
 					if (partitionTable[i] == 0)
 					{
-						if (reducedIndicesBlock[i] != max0Idx) error++;
+						if (indices[i] != max0Idx) error++;
 					}
 					else
 					{
-						if (reducedIndicesBlock[i] != max1Idx) error++;
+						if (indices[i] != max1Idx) error++;
 					}
 				}
 
@@ -110,8 +125,20 @@ public static int[] Rank3SubsetPartitions(ClusterIndices4X4 reducedIndicesBlock,
 		{
 			var output = Enumerable.Range(0, 64).ToArray();
 
+			// Copy struct to array before the closure so that reducedIndicesBlock is not
+			// heap-captured. On .NET Framework, MemoryMarshalPolyfills.CreateSpan uses
+			// Unsafe.AsPointer, which is only GC-safe for stack-allocated structs.
+			#if NETSTANDARD2_0
+			var indices = new int[16];
+			reducedIndicesBlock.AsSpan.CopyTo(indices);
+			#endif
+
 			int CalculatePartitionError(int partitionIndex)
 			{
+				#if NETSTANDARD2_1
+				var indices = reducedIndicesBlock.AsSpan;
+				#endif
+
 				var error = 0;
 				ReadOnlySpan<int> partitionTable = Bc7Block.Subsets3PartitionTable[partitionIndex];
 
@@ -122,12 +149,12 @@ int CalculatePartitionError(int partitionIndex)
 				var max1Idx = 0;
 				var max2Idx = 0;
 
-				//Calculate largest cluster index for each subset 
+				//Calculate largest cluster index for each subset
 				for (var i = 0; i < 16; i++)
 				{
 					if (partitionTable[i] == 0)
 					{
-						var r = reducedIndicesBlock[i];
+						var r = indices[i];
 						subset0[r]++;
 						var count = subset0[r];
 						if (count > subset0[max0Idx])
@@ -137,7 +164,7 @@ int CalculatePartitionError(int partitionIndex)
 					}
 					else if (partitionTable[i] == 1)
 					{
-						var r = reducedIndicesBlock[i];
+						var r = indices[i];
 						subset1[r]++;
 						var count = subset1[r];
 						if (count > subset1[max1Idx])
@@ -147,7 +174,7 @@ int CalculatePartitionError(int partitionIndex)
 					}
 					else
 					{
-						var r = reducedIndicesBlock[i];
+						var r = indices[i];
 						subset2[r]++;
 						var count = subset2[r];
 						if (count > subset2[max2Idx])
@@ -162,15 +189,15 @@ int CalculatePartitionError(int partitionIndex)
 				{
 					if (partitionTable[i] == 0)
 					{
-						if (reducedIndicesBlock[i] != max0Idx) error++;
+						if (indices[i] != max0Idx) error++;
 					}
 					else if (partitionTable[i] == 1)
 					{
-						if (reducedIndicesBlock[i] != max1Idx) error++;
+						if (indices[i] != max1Idx) error++;
 					}
 					else
 					{
-						if (reducedIndicesBlock[i] != max2Idx) error++;
+						if (indices[i] != max2Idx) error++;
 					}
 				}
 

BCnEnc.Net/Encoder/LeastSquares.cs

@@ -5,6 +5,10 @@
 using BCnEncoder.Encoder.Bptc;
 using BCnEncoder.Shared;
 
+#if NETSTANDARD2_0
+using Math = BCnEncoder.Shared.MathPolyfills;
+#endif
+
 namespace BCnEncoder.Encoder
 {
 	/// <summary>

BCnEnc.Net/Shared/Colors.cs

@@ -1241,7 +1241,7 @@ public static ColorLab XyzToLab(ColorXyz xyz)
 
 		private static float PivotXyz(float n)
 		{
-			var i = MathF.Cbrt(n);
+			var i = MathCbrt.Cbrt(n);
 			return n > 0.008856f ? i : 7.787f * n + 16 / 116f;
 		}
 	}

BCnEnc.Net/Shared/HdrImage.cs

@@ -73,7 +73,7 @@ private static string ReadFromStream(Stream stream)
 				c = (char)b;
 				buffer[i++] = c;
 			} while (c != (char)10);
-			return new string(buffer.AsSpan().Slice(0, i)).Trim();
+			return new string(buffer, 0, i).Trim();
 		}
 
 		private static void WriteLineToStream(BinaryWriter br, string s)

BCnEnc.Net/Shared/LinearClustering.cs

@@ -1,6 +1,10 @@
 using System;
 using System.Collections.Generic;
 
+#if NETSTANDARD2_0
+using Array = BCnEncoder.Shared.ArrayPolyfills;
+#endif
+
 namespace BCnEncoder.Shared
 {
 	/// <summary>
@@ -133,7 +137,7 @@
 			return ClusterPixels(floats, width, height, clusters, m, maxIterations, enforceConnectivity);
 
 			//Grid interval S
 			var s = MathF.Sqrt(pixels.Length / (float)clusters);
 			var clusterIndices = new int[pixels.Length];
 
 			var labXys = ConvertToLabXy(pixels, width, height);
@@ -194,7 +198,7 @@
 			if (enforceConnectivity) {
 				clusterIndices = EnforceConnectivity(clusterIndices, width, height, clusters);
 			}
-			
+
 			return clusterIndices;
 		}
 
@@ -427,7 +431,7 @@
 		{
 			ReadOnlySpan<int> neighborX = new[] { -1, 0, 1, 0 };
 			ReadOnlySpan<int> neighborY = new[] { 0, -1, 0, 1 };
-			
+
 			var sSquared = width * height / clusters;
 
 			var clusterX = new List<int>(sSquared);

BCnEnc.Net/Shared/MipMapper.cs

@@ -164,15 +164,14 @@ public static void CalculateMipLevelSize(int width, int height, int mipIdx, out
 			mipHeight = Math.Max(1, height >> mipIdx);
 		}
 
-		private static ColorRgba32[,] ResizeToHalf(ReadOnlySpan2D<ColorRgba32> pixelsRgba)
+		private static Memory2D<ColorRgba32> ResizeToHalf(ReadOnlySpan2D<ColorRgba32> pixelsRgba)
 		{
-
 			var oldWidth = pixelsRgba.Width;
 			var oldHeight = pixelsRgba.Height;
 			var newWidth = Math.Max(1, oldWidth >> 1);
 			var newHeight = Math.Max(1, oldHeight >> 1);
 
-			var result = new ColorRgba32[newHeight, newWidth];
+			var result = new ColorRgba32[newHeight * newWidth];
 
 			int ClampW(int x) => Math.Max(0, Math.Min(oldWidth - 1, x));
 			int ClampH(int y) => Math.Max(0, Math.Min(oldHeight - 1, y));
@@ -186,22 +185,21 @@ public static void CalculateMipLevelSize(int width, int height, int mipIdx, out
 					var ll = pixelsRgba[ClampH(y2 * 2 + 1), ClampW(x2 * 2)].ToFloat();
 					var lr = pixelsRgba[ClampH(y2 * 2 + 1), ClampW(x2 * 2 + 1)].ToFloat();
 
-					result[y2, x2] = ((ul + ur + ll + lr) / 4).ToRgba32();
+					result[y2 * newWidth + x2] = ((ul + ur + ll + lr) / 4).ToRgba32();
 				}
 			}
 
-			return result;
+			return ((Memory<ColorRgba32>)result).AsMemory2D(newHeight, newWidth);
 		}
 
-		private static ColorRgbFloat[,] ResizeToHalf(ReadOnlySpan2D<ColorRgbFloat> pixelsRgba)
+		private static Memory2D<ColorRgbFloat> ResizeToHalf(ReadOnlySpan2D<ColorRgbFloat> pixelsRgba)
 		{
-
 			var oldWidth = pixelsRgba.Width;
 			var oldHeight = pixelsRgba.Height;
 			var newWidth = Math.Max(1, oldWidth >> 1);
 			var newHeight = Math.Max(1, oldHeight >> 1);
 
-			var result = new ColorRgbFloat[newHeight, newWidth];
+			var result = new ColorRgbFloat[newHeight * newWidth];
 
 			int ClampW(int x) => Math.Max(0, Math.Min(oldWidth - 1, x));
 			int ClampH(int y) => Math.Max(0, Math.Min(oldHeight - 1, y));
@@ -215,11 +213,11 @@ public static void CalculateMipLevelSize(int width, int height, int mipIdx, out
 					var ll = pixelsRgba[ClampH(y2 * 2 + 1), ClampW(x2 * 2)];
 					var lr = pixelsRgba[ClampH(y2 * 2 + 1), ClampW(x2 * 2 + 1)];
 
-					result[y2, x2] = ((ul + ur + ll + lr) / 4);
+					result[y2 * newWidth + x2] = ((ul + ur + ll + lr) / 4);
 				}
 			}
 
-			return result;
+			return ((Memory<ColorRgbFloat>)result).AsMemory2D(newHeight, newWidth);
 		}
 	}
 }