Add row action overload

src/ImageSharp/Advanced/ParallelUtils/IRowAction.cs

@@ -0,0 +1,37 @@
+// Copyright (c) Six Labors and contributors.
+// Licensed under the Apache License, Version 2.0.
+
+using System.Runtime.CompilerServices;
+using SixLabors.ImageSharp.Memory;
+
+namespace SixLabors.ImageSharp.Advanced.ParallelUtils
+{
+    /// <summary>
+    /// Defines the contract for.
+    /// </summary>
+    public interface IRowAction
+    {
+        /// <summary>
+        /// Invokes the method passing the row interval.
+        /// </summary>
+        /// <param name="rows">The row interval.</param>
+        void Invoke(in RowInterval rows);
+    }
+
+    internal readonly struct WrappingRowAction<T> : IRowAction
+        where T : struct, IRowAction
+    {
+        private readonly T action;
+
+        public WrappingRowAction(ref T action)
+        {
+            this.action = action;
+        }
+
+        [MethodImpl(InliningOptions.ShortMethod)]
+        public void Invoke(in RowInterval rows)
+        {
+            this.action.Invoke(in rows);
+        }
+    }
+}

src/ImageSharp/Advanced/ParallelUtils/ParallelHelper.cs

@@ -28,19 +28,86 @@ namespace SixLabors.ImageSharp.Advanced.ParallelUtils
         {
             var parallelSettings = ParallelExecutionSettings.FromConfiguration(configuration);
 
-            IterateRows(rectangle, parallelSettings, body);
+            IterateRows(rectangle, in parallelSettings, body);
         }
 
         /// <summary>
         /// Iterate through the rows of a rectangle in optimized batches defined by <see cref="RowInterval"/>-s.
         /// </summary>
+        /// <typeparam name="T">The type of row action to perform.</typeparam>
         /// <param name="rectangle">The <see cref="Rectangle"/>.</param>
-        /// <param name="parallelSettings">The <see cref="ParallelExecutionSettings"/>.</param>
+        /// <param name="configuration">The <see cref="Configuration"/> to get the parallel settings from.</param>
         /// <param name="body">The method body defining the iteration logic on a single <see cref="RowInterval"/>.</param>
-        public static void IterateRows(
+        public static void IterateRowsFast<T>(Rectangle rectangle, Configuration configuration, ref T body)
+            where T : struct, IRowAction
+        {
+            var parallelSettings = ParallelExecutionSettings.FromConfiguration(configuration);
+
+            IterateRowsFast(rectangle, in parallelSettings, ref body);
+        }
+
+        internal static void IterateRowsFast<T>(
             Rectangle rectangle,
             in ParallelExecutionSettings parallelSettings,
-            Action<RowInterval> body)
+            ref T body)
+            where T : struct, IRowAction
+        {
+            ValidateRectangle(rectangle);
+
+            int maxSteps = DivideCeil(
+                rectangle.Width * rectangle.Height,
+                parallelSettings.MinimumPixelsProcessedPerTask);
+
+            int numOfSteps = Math.Min(parallelSettings.MaxDegreeOfParallelism, maxSteps);
+
+            // Avoid TPL overhead in this trivial case:
+            if (numOfSteps == 1)
+            {
+                var rows = new RowInterval(rectangle.Top, rectangle.Bottom);
+                body.Invoke(in rows);
+                return;
+            }
+
+            int verticalStep = DivideCeil(rectangle.Height, numOfSteps);
+
+            var parallelOptions = new ParallelOptions { MaxDegreeOfParallelism = numOfSteps };
+
+            int top = rectangle.Top;
+            int bottom = rectangle.Bottom;
+
+            var rowAction = new WrappingRowAction<T>(ref body);
+
+            Parallel.For(
+                0,
+                numOfSteps,
+                parallelOptions,
+                i =>
+                {
+                    int yMin = top + (i * verticalStep);
+
+                    if (yMin >= bottom)
+                    {
+                        return;
+                    }
+
+                    int yMax = Math.Min(yMin + verticalStep, bottom);
+
+                    var rows = new RowInterval(yMin, yMax);
+
+                    rowAction.Invoke(in rows);
+                });
+        }
+
+        /// <summary>
+        /// Iterate through the rows of a rectangle in optimized batches defined by <see cref="RowInterval"/>-s.
+        /// </summary>
+        /// <param name="rectangle">The <see cref="Rectangle"/>.</param>
+        /// <param name="parallelSettings">The <see cref="ParallelExecutionSettings"/>.</param>
+        /// <param name="body">The method body defining the iteration logic on a single <see cref="RowInterval"/>.</param>
+        public static void IterateRows(
+        Rectangle rectangle,
+        in ParallelExecutionSettings parallelSettings,
+        Action<RowInterval> body)
         {
             ValidateRectangle(rectangle);
 
@@ -72,6 +139,7 @@ namespace SixLabors.ImageSharp.Advanced.ParallelUtils
                         int yMax = Math.Min(yMin + verticalStep, rectangle.Bottom);
 
                         var rows = new RowInterval(yMin, yMax);
+
                         body(rows);
                     });
         }

src/ImageSharp/Processing/Processors/Transforms/CropProcessor{TPixel}.cs

@@ -2,8 +2,10 @@
 // Licensed under the Apache License, Version 2.0.
 
 using System;
+using System.Runtime.CompilerServices;
 using SixLabors.ImageSharp.Advanced;
 using SixLabors.ImageSharp.Advanced.ParallelUtils;
+using SixLabors.ImageSharp.Memory;
 using SixLabors.ImageSharp.PixelFormats;
 
 namespace SixLabors.ImageSharp.Processing.Processors.Transforms
@@ -50,18 +52,49 @@ namespace SixLabors.ImageSharp.Processing.Processors.Transforms
             ParallelExecutionSettings parallelSettings = ParallelExecutionSettings.FromConfiguration(this.Configuration)
                 .MultiplyMinimumPixelsPerTask(4);
 
-            ParallelHelper.IterateRows(
+            // ParallelHelper.IterateRows(
+            //    bounds,
+            //    parallelSettings,
+            //    rows =>
+            //        {
+            //            for (int y = rows.Min; y < rows.Max; y++)
+            //            {
+            //                Span<TPixel> sourceRow = source.GetPixelRowSpan(y).Slice(bounds.Left);
+            //                Span<TPixel> targetRow = destination.GetPixelRowSpan(y - bounds.Top);
+            //                sourceRow.Slice(0, bounds.Width).CopyTo(targetRow);
+            //            }
+            //        });
+            var rowAction = new RowAction(ref bounds, source, destination);
+
+            ParallelHelper.IterateRowsFast(
                 bounds,
-                parallelSettings,
-                rows =>
-                    {
-                        for (int y = rows.Min; y < rows.Max; y++)
-                        {
-                            Span<TPixel> sourceRow = source.GetPixelRowSpan(y).Slice(bounds.Left);
-                            Span<TPixel> targetRow = destination.GetPixelRowSpan(y - bounds.Top);
-                            sourceRow.Slice(0, bounds.Width).CopyTo(targetRow);
-                        }
-                    });
+                in parallelSettings,
+                ref rowAction);
+        }
+
+        private readonly struct RowAction : IRowAction
+        {
+            private readonly Rectangle bounds;
+            private readonly ImageFrame<TPixel> source;
+            private readonly ImageFrame<TPixel> destination;
+
+            public RowAction(ref Rectangle bounds, ImageFrame<TPixel> source, ImageFrame<TPixel> destination)
+            {
+                this.bounds = bounds;
+                this.source = source;
+                this.destination = destination;
+            }
+
+            [MethodImpl(InliningOptions.ShortMethod)]
+            public void Invoke(in RowInterval rows)
+            {
+                for (int y = rows.Min; y < rows.Max; y++)
+                {
+                    Span<TPixel> sourceRow = this.source.GetPixelRowSpan(y).Slice(this.bounds.Left);
+                    Span<TPixel> targetRow = this.destination.GetPixelRowSpan(y - this.bounds.Top);
+                    sourceRow.Slice(0, this.bounds.Width).CopyTo(targetRow);
+                }
+            }
         }
     }
 }