Add missing file contents.

VS 2015 definitely has a bug that deletes the contents of files when
dragging/dropping within a solution.

src/ImageSharp/Filters/Effects/Pixelate.cs

@@ -0,0 +1,55 @@
+// <copyright file="Pixelate.cs" company="James Jackson-South">
+// Copyright (c) James Jackson-South and contributors.
+// Licensed under the Apache License, Version 2.0.
+// </copyright>
+
+namespace ImageSharp
+{
+    using System;
+
+    using Processors;
+
+    /// <summary>
+    /// Extension methods for the <see cref="Image{TColor, TPacked}"/> type.
+    /// </summary>
+    public static partial class ImageExtensions
+    {
+        /// <summary>
+        /// Pixelates an image with the given pixel size.
+        /// </summary>
+        /// <typeparam name="TColor">The pixel format.</typeparam>
+        /// <typeparam name="TPacked">The packed format. <example>uint, long, float.</example></typeparam>
+        /// <param name="source">The image this method extends.</param>
+        /// <param name="size">The size of the pixels.</param>
+        /// <returns>The <see cref="Image{TColor, TPacked}"/>.</returns>
+        public static Image<TColor, TPacked> Pixelate<TColor, TPacked>(this Image<TColor, TPacked> source, int size = 4)
+            where TColor : struct, IPackedPixel<TPacked>
+            where TPacked : struct
+        {
+            return Pixelate(source, size, source.Bounds);
+        }
+
+        /// <summary>
+        /// Pixelates an image with the given pixel size.
+        /// </summary>
+        /// <typeparam name="TColor">The pixel format.</typeparam>
+        /// <typeparam name="TPacked">The packed format. <example>uint, long, float.</example></typeparam>
+        /// <param name="source">The image this method extends.</param>
+        /// <param name="size">The size of the pixels.</param>
+        /// <param name="rectangle">
+        /// The <see cref="Rectangle"/> structure that specifies the portion of the image object to alter.
+        /// </param>
+        /// <returns>The <see cref="Image{TColor, TPacked}"/>.</returns>
+        public static Image<TColor, TPacked> Pixelate<TColor, TPacked>(this Image<TColor, TPacked> source, int size, Rectangle rectangle)
+            where TColor : struct, IPackedPixel<TPacked>
+            where TPacked : struct
+        {
+            if (size <= 0 || size > source.Height || size > source.Width)
+            {
+                throw new ArgumentOutOfRangeException(nameof(size));
+            }
+
+            return source.Process(rectangle, new PixelateProcessor<TColor, TPacked>(size));
+        }
+    }
+}

tests/ImageSharp.Tests/Processors/Filters/OilPaintTest.cs

@@ -0,0 +1,60 @@
+// <copyright file="OilPaintTest.cs" company="James Jackson-South">
+// Copyright (c) James Jackson-South and contributors.
+// Licensed under the Apache License, Version 2.0.
+// </copyright>
+
+namespace ImageSharp.Tests
+{
+    using System;
+    using System.IO;
+
+    using Xunit;
+
+    public class OilPaintTest : FileTestBase
+    {
+        public static readonly TheoryData<Tuple<int, int>> OilPaintValues
+            = new TheoryData<Tuple<int, int>>
+            {
+                new Tuple<int, int>(15,10),
+                new Tuple<int, int>(6,5)
+            };
+
+        [Theory]
+        [MemberData(nameof(OilPaintValues))]
+        public void ImageShouldApplyOilPaintFilter(Tuple<int, int> value)
+        {
+            string path = CreateOutputDirectory("OilPaint");
+
+            foreach (TestFile file in Files)
+            {
+                string filename = file.GetFileName(value);
+                Image image = file.CreateImage();
+
+                using (FileStream output = File.OpenWrite($"{path}/{filename}"))
+                {
+                    image.OilPaint(value.Item1, value.Item2)
+                          .Save(output);
+                }
+            }
+        }
+
+        [Theory]
+        [MemberData(nameof(OilPaintValues))]
+        public void ImageShouldApplyOilPaintFilterInBox(Tuple<int, int> value)
+        {
+            string path = CreateOutputDirectory("OilPaint");
+
+            foreach (TestFile file in Files)
+            {
+                string filename = file.GetFileName(value + "-InBox");
+                Image image = file.CreateImage();
+
+                using (FileStream output = File.OpenWrite($"{path}/{filename}"))
+                {
+                    image.OilPaint(value.Item1, value.Item2, new Rectangle(10, 10, image.Width / 2, image.Height / 2))
+                          .Save(output);
+                }
+            }
+        }
+    }
+}

tests/ImageSharp.Tests/Processors/Filters/PixelateTest.cs

@@ -0,0 +1,59 @@
+// <copyright file="PixelateTest.cs" company="James Jackson-South">
+// Copyright (c) James Jackson-South and contributors.
+// Licensed under the Apache License, Version 2.0.
+// </copyright>
+
+namespace ImageSharp.Tests
+{
+    using System.IO;
+
+    using Xunit;
+
+    public class PixelateTest : FileTestBase
+    {
+        public static readonly TheoryData<int> PixelateValues
+        = new TheoryData<int>
+        {
+            4 ,
+            8
+        };
+
+        [Theory]
+        [MemberData(nameof(PixelateValues))]
+        public void ImageShouldApplyPixelateFilter(int value)
+        {
+            string path = CreateOutputDirectory("Pixelate");
+
+            foreach (TestFile file in Files)
+            {
+                string filename = file.GetFileName(value);
+                Image image = file.CreateImage();
+
+                using (FileStream output = File.OpenWrite($"{path}/{filename}"))
+                {
+                    image.Pixelate(value)
+                          .Save(output);
+                }
+            }
+        }
+
+        [Theory]
+        [MemberData(nameof(PixelateValues))]
+        public void ImageShouldApplyPixelateFilterInBox(int value)
+        {
+            string path = CreateOutputDirectory("Pixelate");
+
+            foreach (TestFile file in Files)
+            {
+                string filename = file.GetFileName(value + "-InBox");
+                Image image = file.CreateImage();
+
+                using (FileStream output = File.OpenWrite($"{path}/{filename}"))
+                {
+                    image.Pixelate(value, new Rectangle(10, 10, image.Width / 2, image.Height / 2))
+                         .Save(output);
+                }
+            }
+        }
+    }
+}