refactor

- ResizeWindow -> ResizeWorker
- Most logic moved to ResizeWorker

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

@@ -237,11 +237,9 @@ namespace SixLabors.ImageSharp.Processing.Processors.Transforms
 
             BufferArea<TPixel> sourceArea = source.PixelBuffer.GetArea(sourceRectangle);
 
-            // Interpolate the image using the calculated weights.
-            // A 2-pass 1D algorithm appears to be faster than splitting a 1-pass 2D algorithm
-            // First process the columns. Since we are not using multiple threads startY and endY
-            // are the upper and lower bounds of the source rectangle.
-            using (var resizeWindow = new ResizeWindow<TPixel>(
+            // If we want to reintroduce processing:
+            // it's possible to launch multiple workers for different regions of the image
+            using (var worker = new ResizeWorker<TPixel>(
                 configuration,
                 sourceArea,
                 conversionModifiers,
@@ -250,39 +248,9 @@ namespace SixLabors.ImageSharp.Processing.Processors.Transforms
                 width,
                 destWorkingRect,
                 startX))
-            using (IMemoryOwner<Vector4> tempBuffer = source.MemoryAllocator.Allocate<Vector4>(width))
             {
-                resizeWindow.Initialize();
-
-                // Now process the rows.
-                Span<Vector4> tempColSpan = tempBuffer.GetSpan();
-
-                for (int y = destWorkingRect.Top; y < destWorkingRect.Bottom; y++)
-                {
-                    // Ensure offsets are normalized for cropping and padding.
-                    ResizeKernel kernel = this.verticalKernelMap.GetKernel(y - startY);
-
-                    while (kernel.StartIndex + kernel.Length > resizeWindow.Bottom)
-                    {
-                        resizeWindow.Slide();
-                    }
-
-                    ref Vector4 tempRowBase = ref MemoryMarshal.GetReference(tempColSpan);
-
-                    int top = kernel.StartIndex - resizeWindow.Top;
-
-                    for (int x = 0; x < width; x++)
-                    {
-                        Span<Vector4> firstPassColumn = resizeWindow.GetColumnSpan(x).Slice(top);
-
-                        // Destination color components
-                        Unsafe.Add(ref tempRowBase, x) = kernel.ConvolveCore(firstPassColumn);
-                    }
-
-                    Span<TPixel> targetRowSpan = destination.GetPixelRowSpan(y);
-
-                    PixelOperations<TPixel>.Instance.FromVector4Destructive(configuration, tempColSpan, targetRowSpan, conversionModifiers);
-                }
+                worker.Initialize();
+                worker.FillDestinationPixels(destWorkingRect.Top, destWorkingRect.Bottom, startY, destination.PixelBuffer);
             }
         }
 

src/ImageSharp/Processing/Processors/Transforms/Resize/ResizeWindow.cs → src/ImageSharp/Processing/Processors/Transforms/Resize/ResizeWorker.cs

@@ -5,6 +5,7 @@ using System;
 using System.Buffers;
 using System.Numerics;
 using System.Runtime.CompilerServices;
+using System.Runtime.InteropServices;
 
 using SixLabors.ImageSharp.Memory;
 using SixLabors.ImageSharp.PixelFormats;
@@ -13,7 +14,7 @@ using SixLabors.Primitives;
 
 namespace SixLabors.ImageSharp.Processing.Processors.Transforms
 {
-    internal class ResizeWindow<TPixel> : IDisposable
+    internal class ResizeWorker<TPixel> : IDisposable
         where TPixel : struct, IPixel<TPixel>
     {
         private readonly Buffer2D<Vector4> buffer;
@@ -32,15 +33,19 @@ namespace SixLabors.ImageSharp.Processing.Processors.Transforms
 
         private readonly IMemoryOwner<Vector4> tempRowBuffer;
 
+        private readonly IMemoryOwner<Vector4> tempColumnBuffer;
+
         private readonly ResizeKernelMap verticalKernelMap;
 
+        private readonly int destWidth;
+
         private readonly Rectangle destWorkingRect;
 
         private readonly int diameter;
 
         private readonly int windowHeight;
 
-        public ResizeWindow(
+        public ResizeWorker(
             Configuration configuration,
             BufferArea<TPixel> source,
             PixelConversionModifiers conversionModifiers,
@@ -56,6 +61,7 @@ namespace SixLabors.ImageSharp.Processing.Processors.Transforms
             this.conversionModifiers = conversionModifiers;
             this.horizontalKernelMap = horizontalKernelMap;
             this.verticalKernelMap = verticalKernelMap;
+            this.destWidth = destWidth;
             this.destWorkingRect = destWorkingRect;
             this.startX = startX;
 
@@ -67,22 +73,29 @@ namespace SixLabors.ImageSharp.Processing.Processors.Transforms
                 this.windowHeight,
                 destWidth,
                 AllocationOptions.Clean);
+
             this.tempRowBuffer = configuration.MemoryAllocator.Allocate<Vector4>(this.sourceRectangle.Width);
+            this.tempColumnBuffer = configuration.MemoryAllocator.Allocate<Vector4>(destWidth);
+
+            this.CurrentMinY = 0;
+            this.CurrentMaxY = this.windowHeight;
         }
 
-        public int Bottom { get; private set; }
+        public int CurrentMaxY { get; private set; }
 
-        public int Top { get; private set; }
+        public int CurrentMinY { get; private set; }
 
         public void Dispose()
         {
             this.buffer.Dispose();
+            this.tempRowBuffer.Dispose();
+            this.tempColumnBuffer.Dispose();
         }
 
         [MethodImpl(MethodImplOptions.AggressiveInlining)]
         public Span<Vector4> GetColumnSpan(int x, int startY)
         {
-            return this.buffer.GetRowSpan(x).Slice(startY - this.Top);
+            return this.buffer.GetRowSpan(x).Slice(startY - this.CurrentMinY);
         }
 
         [MethodImpl(MethodImplOptions.AggressiveInlining)]
@@ -93,23 +106,52 @@ namespace SixLabors.ImageSharp.Processing.Processors.Transforms
 
         public void Initialize()
         {
-            this.Initialize(0, this.windowHeight);
+            this.CalculateFirstPassValues(0, this.windowHeight);
         }
 
-        public void Slide()
+        public void FillDestinationPixels(int minY, int maxY, int startY, Buffer2D<TPixel> destination)
         {
-            int top = this.Top + this.diameter;
-            int bottom = Math.Min(this.Bottom + this.diameter, this.sourceRectangle.Height);
-            this.Initialize(top, bottom);
+            Span<Vector4> tempColSpan = this.tempColumnBuffer.GetSpan();
+
+            for (int y = minY; y < maxY; y++)
+            {
+                // Ensure offsets are normalized for cropping and padding.
+                ResizeKernel kernel = this.verticalKernelMap.GetKernel(y - startY);
+
+                while (kernel.StartIndex + kernel.Length > this.CurrentMaxY)
+                {
+                    this.Slide();
+                }
+
+                ref Vector4 tempRowBase = ref MemoryMarshal.GetReference(tempColSpan);
+
+                int top = kernel.StartIndex - this.CurrentMinY;
+
+                for (int x = 0; x < this.destWidth; x++)
+                {
+                    Span<Vector4> firstPassColumn = this.GetColumnSpan(x).Slice(top);
+
+                    // Destination color components
+                    Unsafe.Add(ref tempRowBase, x) = kernel.ConvolveCore(firstPassColumn);
+                }
+
+                Span<TPixel> targetRowSpan = destination.GetRowSpan(y);
+
+                PixelOperations<TPixel>.Instance.FromVector4Destructive(configuration, tempColSpan, targetRowSpan, conversionModifiers);
+            }
         }
 
-        private void Initialize(int top, int bottom)
+        public void Slide()
         {
-            this.Top = top;
-            this.Bottom = bottom;
+            this.CurrentMinY = this.CurrentMinY + this.diameter;
+            this.CurrentMaxY = Math.Min(this.CurrentMaxY + this.diameter, this.sourceRectangle.Height);
+            this.CalculateFirstPassValues(this.CurrentMinY, this.CurrentMaxY);
+        }
 
+        private void CalculateFirstPassValues(int minY, int maxY)
+        {
             Span<Vector4> tempRowSpan = this.tempRowBuffer.GetSpan();
-            for (int y = top; y < bottom; y++)
+            for (int y = minY; y < maxY; y++)
             {
                 Span<TPixel> sourceRow = this.source.GetRowSpan(y);
 
@@ -120,7 +162,7 @@ namespace SixLabors.ImageSharp.Processing.Processors.Transforms
                     this.conversionModifiers);
 
                 //ref Vector4 firstPassBaseRef = ref this.buffer.Span[y - top];
-                Span<Vector4> firstPassSpan = this.buffer.Span.Slice(y - top);
+                Span<Vector4> firstPassSpan = this.buffer.Span.Slice(y - minY);
 
                 for (int x = this.destWorkingRect.Left; x < this.destWorkingRect.Right; x++)
                 {