fixed a bug in KernelMap caused by overlapping memory areas

src/ImageSharp/Processing/Processors/Transforms/KernelMap.cs

@@ -35,7 +35,7 @@ namespace SixLabors.ImageSharp.Processing.Processors.Transforms
             this.periodicRegionMin = period + radius;
             this.periodicRegionMax = destinationSize - radius;
 
-            int width = radius * 2;
+            int width = (radius * 2) + 1;
             this.data = memoryAllocator.Allocate2D<float>(width, destinationSize, AllocationOptions.Clean);
             this.kernels = new ResizeKernel[destinationSize];
         }
@@ -141,8 +141,15 @@ namespace SixLabors.ImageSharp.Processing.Processors.Transforms
         /// </summary>
         private ResizeKernel CreateKernel(int destIdx, int left, int rightIdx)
         {
-            int flatStartIndex = destIdx * this.data.Width;
             int length = rightIdx - left + 1;
+
+            if (length > this.data.Width)
+            {
+                throw new InvalidOperationException($"Error in KernelMap.CreateKernel({destIdx},{left},{rightIdx}): left > this.data.Width");
+            }
+
+            int flatStartIndex = destIdx * this.data.Width;
+
             Memory<float> bufferSlice = this.data.Memory.Slice(flatStartIndex, length);
             return new ResizeKernel(left, bufferSlice);
         }

tests/ImageSharp.Tests/Processing/Processors/Transforms/KernelMapTests.cs

@@ -1,5 +1,6 @@
 using System;
 using System.IO;
+using System.Runtime.InteropServices;
 using System.Text;
 
 using SixLabors.ImageSharp.PixelFormats;
@@ -40,25 +41,22 @@ namespace SixLabors.ImageSharp.Tests.Processing.Processors.Transforms
             { nameof(KnownResamplers.Lanczos3), 9, 12 },
             { nameof(KnownResamplers.Lanczos3), 6, 8 },
             { nameof(KnownResamplers.Lanczos3), 8, 6 },
-
-            // TODO: What's wrong here:
             { nameof(KnownResamplers.Lanczos3), 20, 12 },
 
-            {nameof(KnownResamplers.Lanczos8), 500, 200 },
-            {nameof(KnownResamplers.Lanczos8), 100, 10 },
-            {nameof(KnownResamplers.Lanczos8), 100, 80 },
-            {nameof(KnownResamplers.Lanczos8), 10, 100 },
+            { nameof(KnownResamplers.Lanczos8), 500, 200 },
+            { nameof(KnownResamplers.Lanczos8), 100, 10 },
+            { nameof(KnownResamplers.Lanczos8), 100, 80 },
+            { nameof(KnownResamplers.Lanczos8), 10, 100 },
         };
 
         [Theory]
         [MemberData(nameof(KernelMapData))]
         public void KernelMapContentIsCorrect(string resamplerName, int srcSize, int destSize)
         {
-            var resampler = (IResampler)typeof(KnownResamplers).GetProperty(resamplerName).GetValue(null);
-            
-            var kernelMap = KernelMap.Calculate(resampler, destSize, srcSize, Configuration.Default.MemoryAllocator);
+            IResampler resampler = TestUtils.GetResampler(resamplerName);
 
             var referenceMap = ReferenceKernelMap.Calculate(resampler, destSize, srcSize);
+            var kernelMap = KernelMap.Calculate(resampler, destSize, srcSize, Configuration.Default.MemoryAllocator);
 
 #if DEBUG
             this.Output.WriteLine($"Actual KernelMap:\n{PrintKernelMap(kernelMap)}\n");

tests/ImageSharp.Tests/Processing/Processors/Transforms/SkewTest.cs

@@ -60,7 +60,7 @@ namespace SixLabors.ImageSharp.Tests.Processing.Processors.Transforms
         {
             foreach (string resamplerName in ResamplerNames)
             {
-                IResampler sampler = GetResampler(resamplerName);
+                IResampler sampler = TestUtils.GetResampler(resamplerName);
                 using (Image<TPixel> image = provider.GetImage())
                 {
                     image.Mutate(i => i.Skew(x, y, sampler));
@@ -68,17 +68,5 @@ namespace SixLabors.ImageSharp.Tests.Processing.Processors.Transforms
                 }
             }
         }
-
-        private static IResampler GetResampler(string name)
-        {
-            PropertyInfo property = typeof(KnownResamplers).GetTypeInfo().GetProperty(name);
-
-            if (property is null)
-            {
-                throw new Exception($"No resampler named '{name}");
-            }
-
-            return (IResampler)property.GetValue(null);
-        }
     }
 }

tests/ImageSharp.Tests/TestUtilities/TestUtils.cs

@@ -10,6 +10,7 @@ using SixLabors.ImageSharp.Advanced;
 using SixLabors.ImageSharp.Memory;
 using SixLabors.ImageSharp.PixelFormats;
 using SixLabors.ImageSharp.Processing;
+using SixLabors.ImageSharp.Processing.Processors.Transforms;
 using SixLabors.ImageSharp.Tests.TestUtilities.ImageComparison;
 using SixLabors.Primitives;
 
@@ -284,5 +285,17 @@ namespace SixLabors.ImageSharp.Tests
         }
 
         public static string AsInvariantString(this FormattableString formattable) => System.FormattableString.Invariant(formattable);
+
+        public static IResampler GetResampler(string name)
+        {
+            PropertyInfo property = typeof(KnownResamplers).GetTypeInfo().GetProperty(name);
+
+            if (property is null)
+            {
+                throw new Exception($"No resampler named '{name}");
+            }
+
+            return (IResampler)property.GetValue(null);
+        }
     }
 }