Make processors public, refactor cloning.

src/ImageSharp.Drawing/Processing/Processors/Drawing/DrawImageProcessor{TPixelBg,TPixelFg}.cs

@@ -91,7 +91,7 @@ protected override void OnFrameApply(ImageFrame<TPixelBg> source)
 
             var workingRect = Rectangle.FromLTRB(minX, minY, maxX, maxY);
 
-            // not a valid operation because rectangle does not overlap with this image.
+            // Not a valid operation because rectangle does not overlap with this image.
             if (workingRect.Width <= 0 || workingRect.Height <= 0)
             {
                 throw new ImageProcessingException(
@@ -102,14 +102,14 @@ protected override void OnFrameApply(ImageFrame<TPixelBg> source)
                 workingRect,
                 configuration,
                 rows =>
+                {
+                    for (int y = rows.Min; y < rows.Max; y++)
                     {
-                        for (int y = rows.Min; y < rows.Max; y++)
-                        {
-                            Span<TPixelBg> background = source.GetPixelRowSpan(y).Slice(minX, width);
-                            Span<TPixelFg> foreground = targetImage.GetPixelRowSpan(y - locationY).Slice(targetX, width);
-                            blender.Blend<TPixelFg>(configuration, background, background, foreground, this.Opacity);
-                        }
-                    });
+                        Span<TPixelBg> background = source.GetPixelRowSpan(y).Slice(minX, width);
+                        Span<TPixelFg> foreground = targetImage.GetPixelRowSpan(y - locationY).Slice(targetX, width);
+                        blender.Blend<TPixelFg>(configuration, background, background, foreground, this.Opacity);
+                    }
+                });
         }
     }
 }

src/ImageSharp/Advanced/AotCompilerTools.cs

@@ -2,13 +2,12 @@
 // Licensed under the Apache License, Version 2.0.
 
 using System.Numerics;
+using System.Runtime.CompilerServices;
 using SixLabors.ImageSharp.Formats;
 using SixLabors.ImageSharp.Formats.Jpeg.Components;
 using SixLabors.ImageSharp.PixelFormats;
-using SixLabors.ImageSharp.Processing;
 using SixLabors.ImageSharp.Processing.Processors.Dithering;
 using SixLabors.ImageSharp.Processing.Processors.Quantization;
-using SixLabors.ImageSharp.Processing.Processors.Transforms;
 
 namespace SixLabors.ImageSharp.Advanced
 {
@@ -81,9 +80,8 @@ private static void Seed<TPixel>()
             AotCompileWuQuantizer<TPixel>();
             AotCompileDithering<TPixel>();
             AotCompilePixelOperations<TPixel>();
-            AotCompileResizeOperations<TPixel>();
 
-            System.Runtime.CompilerServices.Unsafe.SizeOf<TPixel>();
+            Unsafe.SizeOf<TPixel>();
 
             AotCodec<TPixel>(new Formats.Png.PngDecoder(), new Formats.Png.PngEncoder());
             AotCodec<TPixel>(new Formats.Bmp.BmpDecoder(), new Formats.Bmp.BmpEncoder());
@@ -107,8 +105,10 @@ private static void Seed<TPixel>()
         private static void AotCompileOctreeQuantizer<TPixel>()
             where TPixel : struct, IPixel<TPixel>
         {
-            var test = new OctreeFrameQuantizer<TPixel>(new OctreeQuantizer(false));
-            test.AotGetPalette();
+            using (var test = new OctreeFrameQuantizer<TPixel>(new OctreeQuantizer(false)))
+            {
+                test.AotGetPalette();
+            }
         }
 
         /// <summary>
@@ -118,9 +118,11 @@ private static void AotCompileOctreeQuantizer<TPixel>()
         private static void AotCompileWuQuantizer<TPixel>()
             where TPixel : struct, IPixel<TPixel>
         {
-            var test = new WuFrameQuantizer<TPixel>(Configuration.Default.MemoryAllocator, new WuQuantizer(false));
-            test.QuantizeFrame(new ImageFrame<TPixel>(Configuration.Default, 1, 1));
-            test.AotGetPalette();
+            using (var test = new WuFrameQuantizer<TPixel>(Configuration.Default.MemoryAllocator, new WuQuantizer(false)))
+            {
+                test.QuantizeFrame(new ImageFrame<TPixel>(Configuration.Default, 1, 1));
+                test.AotGetPalette();
+            }
         }
 
         /// <summary>
@@ -132,7 +134,10 @@ private static void AotCompileDithering<TPixel>()
         {
             var test = new FloydSteinbergDiffuser();
             TPixel pixel = default;
-            test.Dither(new ImageFrame<TPixel>(Configuration.Default, 1, 1), pixel, pixel, 0, 0, 0, 0, 0, 0);
+            using (var image = new ImageFrame<TPixel>(Configuration.Default, 1, 1))
+            {
+                test.Dither(image, pixel, pixel, 0, 0, 0, 0, 0, 0);
+            }
         }
 
         /// <summary>
@@ -171,16 +176,5 @@ private static void AotCompilePixelOperations<TPixel>()
             var pixelOp = new PixelOperations<TPixel>();
             pixelOp.GetPixelBlender(PixelColorBlendingMode.Normal, PixelAlphaCompositionMode.Clear);
         }
-
-        /// <summary>
-        /// This method pre-seeds the ResizeProcessor for the AoT compiler on iOS.
-        /// </summary>
-        /// <typeparam name="TPixel">The pixel format.</typeparam>
-        private static void AotCompileResizeOperations<TPixel>()
-            where TPixel : struct, IPixel<TPixel>
-        {
-            var genericResizeProcessor = (ResizeProcessor<TPixel>)new ResizeProcessor(new ResizeOptions(), default).CreatePixelSpecificProcessor(new Image<TPixel>(0, 0), default);
-            genericResizeProcessor.AotCreateDestination();
-        }
     }
 }

src/ImageSharp/Processing/DefaultImageProcessorContext{TPixel}.cs

@@ -29,6 +29,8 @@ public DefaultImageProcessorContext(Image<TPixel> source, bool mutate)
         {
             this.mutate = mutate;
             this.source = source;
+
+            // Mutate acts upon the source image only.
             if (this.mutate)
             {
                 this.destination = source;
@@ -43,7 +45,8 @@ public Image<TPixel> GetResultImage()
         {
             if (!this.mutate && this.destination is null)
             {
-                // Ensure we have cloned it if we are not mutating as we might have failed to register any processors
+                // Ensure we have cloned the source if we are not mutating as we might have failed
+                // to register any processors.
                 this.destination = this.source.Clone();
             }
 
@@ -64,26 +67,25 @@ public IImageProcessingContext ApplyProcessor(IImageProcessor processor, Rectang
         {
             if (!this.mutate && this.destination is null)
             {
-                // This will only work if the first processor applied is the cloning one thus
-                // realistically for this optimization to work the resize must the first processor
-                // applied any only up processors will take the double data path.
-                using (IImageProcessor<TPixel> specificProcessor = processor.CreatePixelSpecificProcessor(this.source, rectangle))
+                // When cloning an image we can optimize the processing pipeline by avoiding an unnecessary
+                // interim clone if the first processor in the pipeline is a cloning processor.
+                if (processor is ICloningImageProcessor cloningImageProcessor)
                 {
-                    // TODO: if 'specificProcessor' is not an ICloningImageProcessor<TPixel> we are unnecessarily disposing and recreating it.
-                    // This should be solved in a future refactor.
-                    if (specificProcessor is ICloningImageProcessor<TPixel> cloningImageProcessor)
+                    using (ICloningImageProcessor<TPixel> pixelProcessor = cloningImageProcessor.CreatePixelSpecificCloningProcessor(this.source, rectangle))
                     {
-                        this.destination = cloningImageProcessor.CloneAndApply();
+                        this.destination = pixelProcessor.CloneAndExecute();
                         return this;
                     }
                 }
 
+                // Not a cloning processor? We need to create a clone to operate on.
                 this.destination = this.source.Clone();
             }
 
+            // Standard processing pipeline.
             using (IImageProcessor<TPixel> specificProcessor = processor.CreatePixelSpecificProcessor(this.destination, rectangle))
             {
-                specificProcessor.Apply();
+                specificProcessor.Execute();
             }
 
             return this;

src/ImageSharp/Processing/Processors/CloningImageProcessor.cs

@@ -0,0 +1,22 @@
+// Copyright (c) Six Labors and contributors.
+// Licensed under the Apache License, Version 2.0.
+
+using SixLabors.ImageSharp.PixelFormats;
+using SixLabors.Primitives;
+
+namespace SixLabors.ImageSharp.Processing.Processors
+{
+    /// <summary>
+    /// The base class for all cloning image processors.
+    /// </summary>
+    public abstract class CloningImageProcessor : ICloningImageProcessor
+    {
+        /// <inheritdoc/>
+        public abstract ICloningImageProcessor<TPixel> CreatePixelSpecificCloningProcessor<TPixel>(Image<TPixel> source, Rectangle sourceRectangle)
+            where TPixel : struct, IPixel<TPixel>;
+
+        /// <inheritdoc/>
+        IImageProcessor<TPixel> IImageProcessor.CreatePixelSpecificProcessor<TPixel>(Image<TPixel> source, Rectangle sourceRectangle)
+            => this.CreatePixelSpecificCloningProcessor(source, sourceRectangle);
+    }
+}

src/ImageSharp/Processing/Processors/CloningImageProcessor{TPixel}.cs

@@ -2,17 +2,21 @@
 // Licensed under the Apache License, Version 2.0.
 
 using System;
+using System.Collections.Generic;
+using System.Linq;
 using SixLabors.ImageSharp.Advanced;
 using SixLabors.ImageSharp.PixelFormats;
 using SixLabors.Primitives;
 
 namespace SixLabors.ImageSharp.Processing.Processors
 {
     /// <summary>
-    /// Allows the application of processing algorithms to a clone of the original image.
+    /// The base class for all pixel specific cloning image processors.
+    /// Allows the application of processing algorithms to the image.
+    /// The image is cloned before operating upon and the buffers swapped upon completion.
     /// </summary>
     /// <typeparam name="TPixel">The pixel format.</typeparam>
-    internal abstract class CloningImageProcessor<TPixel> : ICloningImageProcessor<TPixel>
+    public abstract class CloningImageProcessor<TPixel> : ICloningImageProcessor<TPixel>
         where TPixel : struct, IPixel<TPixel>
     {
         /// <summary>
@@ -38,21 +42,17 @@ protected CloningImageProcessor(Image<TPixel> source, Rectangle sourceRectangle)
         protected Rectangle SourceRectangle { get; }
 
         /// <summary>
-        /// Gets the <see cref="ImageSharp.Configuration"/> instance to use when performing operations.
+        /// Gets the <see cref="Configuration"/> instance to use when performing operations.
         /// </summary>
         protected Configuration Configuration { get; }
 
         /// <inheritdoc/>
-        public Image<TPixel> CloneAndApply()
+        Image<TPixel> ICloningImageProcessor<TPixel>.CloneAndExecute()
         {
             try
             {
-                Image<TPixel> clone = this.CreateDestination();
-
-                if (clone.Frames.Count != this.Source.Frames.Count)
-                {
-                    throw new ImageProcessingException($"An error occurred when processing the image using {this.GetType().Name}. The processor changed the number of frames.");
-                }
+                Image<TPixel> clone = this.CreateTarget();
+                this.CheckFrameCount(this.Source, clone);
 
                 Configuration configuration = this.Source.GetConfiguration();
                 this.BeforeImageApply(clone);
@@ -84,17 +84,24 @@ public Image<TPixel> CloneAndApply()
         }
 
         /// <inheritdoc/>
-        public void Apply()
+        void IImageProcessor<TPixel>.Execute()
         {
-            using (Image<TPixel> cloned = this.CloneAndApply())
+            // Create an interim clone of the source image to operate on.
+            // Doing this allows for the application of transforms that will alter
+            // the dimensions of the image.
+            Image<TPixel> clone = default;
+            try
             {
-                // we now need to move the pixel data/size data from one image base to another
-                if (cloned.Frames.Count != this.Source.Frames.Count)
-                {
-                    throw new ImageProcessingException($"An error occurred when processing the image using {this.GetType().Name}. The processor changed the number of frames.");
-                }
+                clone = ((ICloningImageProcessor<TPixel>)this).CloneAndExecute();
 
-                this.Source.SwapOrCopyPixelsBuffersFrom(cloned);
+                // We now need to move the pixel data/size data from the clone to the source.
+                this.CheckFrameCount(this.Source, clone);
+                this.Source.SwapOrCopyPixelsBuffersFrom(clone);
+            }
+            finally
+            {
+                // Dispose of the clone now that we have swapped the pixel/size data.
+                clone?.Dispose();
             }
         }
 
@@ -106,10 +113,10 @@ public void Dispose()
         }
 
         /// <summary>
-        /// Generates a deep clone of the source image that operations should be applied to.
+        /// Gets the size of the target image.
         /// </summary>
-        /// <returns>The cloned image.</returns>
-        protected virtual Image<TPixel> CreateDestination() => this.Source.Clone();
+        /// <returns>The <see cref="Size"/>.</returns>
+        protected abstract Size GetTargetSize();
 
         /// <summary>
         /// This method is called before the process is applied to prepare the processor.
@@ -160,5 +167,30 @@ protected virtual void AfterImageApply(Image<TPixel> destination)
         protected virtual void Dispose(bool disposing)
         {
         }
+
+        private Image<TPixel> CreateTarget()
+        {
+            Image<TPixel> source = this.Source;
+            Size targetSize = this.GetTargetSize();
+
+            // We will always be creating the clone even for mutate because we may need to resize the canvas
+            IEnumerable<ImageFrame<TPixel>> frames = source.Frames.Select<ImageFrame<TPixel>, ImageFrame<TPixel>>(
+                x => new ImageFrame<TPixel>(
+                    source.GetConfiguration(),
+                    targetSize.Width,
+                    targetSize.Height,
+                    x.Metadata.DeepClone()));
+
+            // Use the overload to prevent an extra frame being added
+            return new Image<TPixel>(this.Configuration, source.Metadata.DeepClone(), frames);
+        }
+
+        private void CheckFrameCount(Image<TPixel> a, Image<TPixel> b)
+        {
+            if (a.Frames.Count != b.Frames.Count)
+            {
+                throw new ImageProcessingException($"An error occurred when processing the image using {this.GetType().Name}. The processor changed the number of frames.");
+            }
+        }
     }
 }

src/ImageSharp/Processing/Processors/Convolution/EdgeDetector2DProcessor{TPixel}.cs

@@ -54,7 +54,7 @@ protected override void BeforeImageApply()
         {
             if (this.Grayscale)
             {
-                new GrayscaleBt709Processor(1F).Apply(this.Source, this.SourceRectangle);
+                new GrayscaleBt709Processor(1F).Execute(this.Source, this.SourceRectangle);
             }
 
             base.BeforeImageApply();

src/ImageSharp/Processing/Processors/Convolution/EdgeDetectorCompassProcessor{TPixel}.cs

@@ -45,7 +45,7 @@ protected override void BeforeImageApply()
         {
             if (this.Grayscale)
             {
-                new GrayscaleBt709Processor(1F).Apply(this.Source, this.SourceRectangle);
+                new GrayscaleBt709Processor(1F).Execute(this.Source, this.SourceRectangle);
             }
 
             base.BeforeImageApply();

src/ImageSharp/Processing/Processors/Convolution/EdgeDetectorProcessor{TPixel}.cs

@@ -41,7 +41,7 @@ protected override void BeforeImageApply()
         {
             if (this.Grayscale)
             {
-                new GrayscaleBt709Processor(1F).Apply(this.Source, this.SourceRectangle);
+                new GrayscaleBt709Processor(1F).Execute(this.Source, this.SourceRectangle);
             }
 
             base.BeforeImageApply();

src/ImageSharp/Processing/Processors/Filters/LomographProcessor{TPixel}.cs

@@ -29,7 +29,7 @@ public LomographProcessor(LomographProcessor definition, Image<TPixel> source, R
         /// <inheritdoc/>
         protected override void AfterImageApply()
         {
-            new VignetteProcessor(VeryDarkGreen).Apply(this.Source, this.SourceRectangle);
+            new VignetteProcessor(VeryDarkGreen).Execute(this.Source, this.SourceRectangle);
             base.AfterImageApply();
         }
     }

src/ImageSharp/Processing/Processors/Filters/PolaroidProcessor{TPixel}.cs

@@ -31,8 +31,8 @@ public PolaroidProcessor(PolaroidProcessor definition, Image<TPixel> source, Rec
         /// <inheritdoc/>
         protected override void AfterImageApply()
         {
-            new VignetteProcessor(VeryDarkOrange).Apply(this.Source, this.SourceRectangle);
-            new GlowProcessor(LightOrange, this.Source.Width / 4F).Apply(this.Source, this.SourceRectangle);
+            new VignetteProcessor(VeryDarkOrange).Execute(this.Source, this.SourceRectangle);
+            new GlowProcessor(LightOrange, this.Source.Width / 4F).Execute(this.Source, this.SourceRectangle);
             base.AfterImageApply();
         }
     }

src/ImageSharp/Processing/Processors/ICloningImageProcessor.cs

@@ -0,0 +1,27 @@
+// Copyright (c) Six Labors and contributors.
+// Licensed under the Apache License, Version 2.0.
+
+using SixLabors.ImageSharp.PixelFormats;
+using SixLabors.Primitives;
+
+namespace SixLabors.ImageSharp.Processing.Processors
+{
+    /// <summary>
+    /// Defines an algorithm to alter the pixels of a cloned image.
+    /// </summary>
+    public interface ICloningImageProcessor : IImageProcessor
+    {
+        /// <summary>
+        /// Creates a pixel specific <see cref="ICloningImageProcessor{TPixel}"/> that is capable of executing
+        /// the processing algorithm on an <see cref="Image{TPixel}"/>.
+        /// </summary>
+        /// <typeparam name="TPixel">The pixel type.</typeparam>
+        /// <param name="source">The source image. Cannot be null.</param>
+        /// <param name="sourceRectangle">
+        /// The <see cref="Rectangle"/> structure that specifies the portion of the image object to draw.
+        /// </param>
+        /// <returns>The <see cref="ICloningImageProcessor{TPixel}"/></returns>
+        ICloningImageProcessor<TPixel> CreatePixelSpecificCloningProcessor<TPixel>(Image<TPixel> source, Rectangle sourceRectangle)
+            where TPixel : struct, IPixel<TPixel>;
+    }
+}