Cover KernelMap with tests

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

@@ -17,6 +17,8 @@ namespace SixLabors.ImageSharp.Processing.Processors.Transforms
     {
         private readonly Buffer2D<float> data;
 
+        private readonly ResizeKernel[] kernels;
+
         /// <summary>
         /// Initializes a new instance of the <see cref="KernelMap"/> class.
         /// </summary>
@@ -25,15 +27,13 @@ namespace SixLabors.ImageSharp.Processing.Processors.Transforms
         /// <param name="kernelRadius">The radius of the kernel</param>
         public KernelMap(MemoryAllocator memoryAllocator, int destinationSize, float kernelRadius)
         {
+            this.DestinationSize = destinationSize;
             int width = (int)Math.Ceiling(kernelRadius * 2);
             this.data = memoryAllocator.Allocate2D<float>(width, destinationSize, AllocationOptions.Clean);
-            this.Kernels = new ResizeKernel[destinationSize];
+            this.kernels = new ResizeKernel[destinationSize];
         }
 
-        /// <summary>
+        public int DestinationSize { get; }
-        /// Gets the calculated <see cref="Kernels"/> values.
-        /// </summary>
-        public ResizeKernel[] Kernels { get; }
 
         /// <summary>
         /// Disposes <see cref="KernelMap"/> instance releasing it's backing buffer.
@@ -43,6 +43,12 @@ namespace SixLabors.ImageSharp.Processing.Processors.Transforms
             this.data.Dispose();
         }
 
+        /// <summary>
+        /// Returns a <see cref="ResizeKernel"/> for an index value between 0 and destinationSize - 1.
+        /// </summary>
+        [MethodImpl(InliningOptions.ShortMethod)]
+        public ref ResizeKernel GetKernel(int destIdx) => ref this.kernels[destIdx];
+
         /// <summary>
         /// Computes the weights to apply at each pixel when resizing.
         /// </summary>
@@ -88,7 +94,7 @@ namespace SixLabors.ImageSharp.Processing.Processors.Transforms
                 float sum = 0;
 
                 ResizeKernel ws = result.CreateKernel(i, left, right);
-                result.Kernels[i] = ws;
+                result.kernels[i] = ws;
 
                 ref float weightsBaseRef = ref MemoryMarshal.GetReference(ws.GetValues());
 

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

@@ -269,9 +269,9 @@ namespace SixLabors.ImageSharp.Processing.Processors.Transforms
 
                                 for (int x = minX; x < maxX; x++)
                                 {
-                                    ResizeKernel window = this.horizontalKernelMap.Kernels[x - startX];
+                                    ResizeKernel kernel = this.horizontalKernelMap.GetKernel(x - startX);
                                     Unsafe.Add(ref firstPassBaseRef, x * sourceHeight) =
-                                        window.Convolve(tempRowSpan);
+                                        kernel.Convolve(tempRowSpan);
                                 }
                             }
                         });
@@ -289,7 +289,7 @@ namespace SixLabors.ImageSharp.Processing.Processors.Transforms
                             for (int y = rows.Min; y < rows.Max; y++)
                             {
                                 // Ensure offsets are normalized for cropping and padding.
-                                ResizeKernel window = this.verticalKernelMap.Kernels[y - startY];
+                                ResizeKernel kernel = this.verticalKernelMap.GetKernel(y - startY);
 
                                 ref Vector4 tempRowBase = ref MemoryMarshal.GetReference(tempRowSpan);
 
@@ -298,7 +298,7 @@ namespace SixLabors.ImageSharp.Processing.Processors.Transforms
                                     Span<Vector4> firstPassColumn = firstPassPixelsTransposed.GetRowSpan(x).Slice(sourceY);
 
                                     // Destination color components
-                                    Unsafe.Add(ref tempRowBase, x) = window.Convolve(firstPassColumn);
+                                    Unsafe.Add(ref tempRowBase, x) = kernel.Convolve(firstPassColumn);
                                 }
 
                                 Vector4Utils.UnPremultiply(tempRowSpan);

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

@@ -0,0 +1,99 @@
+using System;
+using System.Collections.Generic;
+
+using SixLabors.ImageSharp.Processing.Processors.Transforms;
+
+namespace SixLabors.ImageSharp.Tests.Processing.Processors.Transforms
+{
+    public partial class KernelMapTests
+    {
+        /// <summary>
+        /// Simplified reference implementation for <see cref="KernelMap"/> functionality.
+        /// </summary>
+        public class ReferenceKernelMap
+        {
+            private readonly ReferenceKernel[] kernels;
+
+            public ReferenceKernelMap(ReferenceKernel[] kernels)
+            {
+                this.kernels = kernels;
+            }
+
+            public int DestinationSize => this.kernels.Length;
+
+            public ReferenceKernel GetKernel(int destinationIndex) => this.kernels[destinationIndex];
+
+            public static ReferenceKernelMap Calculate(IResampler sampler, int destinationSize, int sourceSize)
+            {
+                float ratio = (float)sourceSize / destinationSize;
+                float scale = ratio;
+
+                if (scale < 1F)
+                {
+                    scale = 1F;
+                }
+
+                float radius = MathF.Ceiling(scale * sampler.Radius);
+                
+                var result = new List<ReferenceKernel>();
+
+                for (int i = 0; i < destinationSize; i++)
+                {
+                    float center = ((i + .5F) * ratio) - .5F;
+
+                    // Keep inside bounds.
+                    int left = (int)MathF.Ceiling(center - radius);
+                    if (left < 0)
+                    {
+                        left = 0;
+                    }
+
+                    int right = (int)MathF.Floor(center + radius);
+                    if (right > sourceSize - 1)
+                    {
+                        right = sourceSize - 1;
+                    }
+
+                    float sum = 0;
+
+                    float[] values = new float[right - left + 1];
+
+                    for (int j = left; j <= right; j++)
+                    {
+                        float weight = sampler.GetValue((j - center) / scale);
+                        sum += weight;
+
+                        values[j - left] = weight;
+                    }
+
+                    result.Add(new ReferenceKernel(left, values));
+
+                    if (sum > 0)
+                    {
+                        for (int w = 0; w < values.Length; w++)
+                        {
+                            values[w] /= sum;
+                        }
+                    }
+                }
+
+                return new ReferenceKernelMap(result.ToArray());
+            }
+        }
+
+        public struct ReferenceKernel
+        {
+            public ReferenceKernel(int left, float[] values)
+            {
+                this.Left = left;
+                this.Values = values;
+            }
+
+            public int Left { get; }
+
+            public float[] Values { get; }
+
+            public int Length => this.Values.Length;
+        }
+    }
+}

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

@@ -12,7 +12,7 @@ using Xunit.Abstractions;
 
 namespace SixLabors.ImageSharp.Tests.Processing.Processors.Transforms
 {
-    public class KernelMapTests
+    public partial class KernelMapTests
     {
         private ITestOutputHelper Output { get; }
 
@@ -30,34 +30,52 @@ namespace SixLabors.ImageSharp.Tests.Processing.Processors.Transforms
         [InlineData(100, 80, nameof(KnownResamplers.Lanczos8))]
         [InlineData(100, 10, nameof(KnownResamplers.Lanczos8))]
         [InlineData(10, 100, nameof(KnownResamplers.Lanczos8))]
-        public void PrintKernelMap(int srcSize, int destSize, string resamplerName)
+        public void KernelMapContentIsCorrect(int srcSize, int destSize, string resamplerName)
         {
             var resampler = (IResampler)typeof(KnownResamplers).GetProperty(resamplerName).GetValue(null);
             
             var kernelMap = KernelMap.Calculate(resampler, destSize, srcSize, Configuration.Default.MemoryAllocator);
 
+            var referenceMap = ReferenceKernelMap.Calculate(resampler, destSize, srcSize);
+
+#if DEBUG
+            string text = PrintKernelMap(kernelMap);
+            this.Output.WriteLine(text);
+#endif
+
+            for (int i = 0; i < kernelMap.DestinationSize; i++)
+            {
+                ResizeKernel kernel = kernelMap.GetKernel(i);
+
+                ReferenceKernel referenceKernel = referenceMap.GetKernel(i);
+
+                Assert.Equal(referenceKernel.Length, kernel.Length);
+                Assert.Equal(referenceKernel.Left, kernel.Left);
+                Assert.True(kernel.GetValues().SequenceEqual(referenceKernel.Values));
+            }
+        }
+
+        private static string PrintKernelMap(KernelMap kernelMap)
+        {
             var bld = new StringBuilder();
 
-            foreach (ResizeKernel kernel in kernelMap.Kernels)
+            for (int i = 0; i < kernelMap.DestinationSize; i++)
             {
+                ResizeKernel kernel = kernelMap.GetKernel(i);
                 bld.Append($"({kernel.Left:D3}) || ");
                 Span<float> span = kernel.GetValues();
-                for (int i = 0; i < kernel.Length; i++)
+
+                for (int j = 0; j < kernel.Length; j++)
                 {
-                    float value = span[i];
+                    float value = span[j];
-                    bld.Append($"{value,7:F5}");
+                    bld.Append($"{value,8:F5}");
                     bld.Append(" | ");
                 }
 
                 bld.AppendLine();
             }
 
-            string outDir = TestEnvironment.CreateOutputDirectory("." + nameof(this.PrintKernelMap));
+            return bld.ToString();
-            string fileName = $@"{outDir}\{resamplerName}_{srcSize}_{destSize}.MD";
-
-            File.WriteAllText(fileName, bld.ToString());
-
-            this.Output.WriteLine(bld.ToString());
         }
     }
 }