introduced CoreCompat.SystemDrawing as reference utility for tests, implemented ToSystemDrawingBitmap()

tests/ImageSharp.Tests/ImageComparer.cs

@@ -72,9 +72,13 @@ namespace ImageSharp.Tests
         /// This is a sampling factor we sample a grid of average pixels <paramref name="scalingFactor"/> width by <paramref name="scalingFactor"/> high
         /// The default undefined value is <see cref="DefaultScalingFactor"/>
         /// </param>
-        public static void CheckSimilarity<TPixelA, TPixelB>(Image<TPixelA> expected, Image<TPixelB> actual, float imageTheshold = DefaultImageThreshold, byte segmentThreshold = DefaultSegmentThreshold, int scalingFactor = DefaultScalingFactor)
-           where TPixelA : struct, IPixel<TPixelA>
-           where TPixelB : struct, IPixel<TPixelB>
+        public static void CheckSimilarity<TPixelA, TPixelB>(
+            Image<TPixelA> expected,
+            Image<TPixelB> actual,
+            float imageTheshold = DefaultImageThreshold,
+            byte segmentThreshold = DefaultSegmentThreshold,
+            int scalingFactor = DefaultScalingFactor)
+            where TPixelA : struct, IPixel<TPixelA> where TPixelB : struct, IPixel<TPixelB>
         {
             float percentage = expected.PercentageDifference(actual, segmentThreshold, scalingFactor);
 

tests/ImageSharp.Tests/ImageSharp.Tests.csproj

@@ -10,6 +10,7 @@
     <None Include="PixelFormats\PixelOperationsTests.Blender.cs" />
   </ItemGroup>
   <ItemGroup>
+    <PackageReference Include="CoreCompat.System.Drawing" Version="1.0.0-beta006" />
     <PackageReference Include="Microsoft.NET.Test.Sdk" Version="15.0.0" />
     <PackageReference Include="Moq" Version="4.7.1" />
     <PackageReference Include="xunit" Version="2.3.0-beta3-build3705" />

tests/ImageSharp.Tests/TestUtilities/Integration/IntegrationTestUtils.cs

@@ -0,0 +1,65 @@
+namespace ImageSharp.Tests.TestUtilities.Integration
+{
+    using System;
+    using System.Drawing.Imaging;
+
+    using ImageSharp.Memory;
+    using ImageSharp.PixelFormats;
+
+    public static class IntegrationTestUtils
+    {
+        // TODO: It would be nice to have this method in PixelOperations<T>
+        private static void ToArgb32<TPixel>(Span<TPixel> source, Span<Argb32> dest)
+            where TPixel : struct, IPixel<TPixel>
+        {
+            int length = source.Length;
+            Guard.MustBeSizedAtLeast(dest, length, nameof(dest));
+            
+            using (var rgbaBuffer = new Buffer<Rgba32>(length))
+            {
+                PixelOperations<TPixel>.Instance.ToRgba32(source, rgbaBuffer, length);
+
+                for (int i = 0; i < length; i++)
+                {
+                    ref Rgba32 s = ref rgbaBuffer[i];
+                    ref Argb32 d = ref dest[i];
+
+                    d.PackFromRgba32(s);
+                }
+            }
+        }
+
+        internal static unsafe System.Drawing.Bitmap ToSystemDrawingBitmap<TPixel>(Image<TPixel> image)
+            where TPixel : struct, IPixel<TPixel>
+        {
+            int w = image.Width;
+            int h = image.Height;
+            
+            var resultBitmap = new System.Drawing.Bitmap(w, h, PixelFormat.Format32bppArgb);
+            var fullRect = new System.Drawing.Rectangle(0, 0, w, h);
+            BitmapData data = resultBitmap.LockBits(fullRect, ImageLockMode.ReadWrite, resultBitmap.PixelFormat);
+            byte* destPtrBase = (byte*)data.Scan0;
+
+            long destRowByteCount= data.Stride;
+            long sourceRowByteCount = w * sizeof(Argb32);
+
+            using (var workBuffer = new Buffer<Argb32>(w))
+            {
+                var sourcePtr = (Argb32*) workBuffer.Pin();
+                
+                for (int y = 0; y < h; y++)
+                {
+                    Span<TPixel> row = image.GetRowSpan(y);
+                    ToArgb32(row, workBuffer);
+                    byte* destPtr = destPtrBase + data.Stride * y;
+
+                    Buffer.MemoryCopy(sourcePtr, destPtr, destRowByteCount, sourceRowByteCount);
+                }
+            }
+                
+            resultBitmap.UnlockBits(data);
+
+            return resultBitmap;
+        }
+    }
+}

tests/ImageSharp.Tests/TestUtilities/Integration/ReferenceEncoder.cs

@@ -0,0 +1,21 @@
+using System;
+using System.Collections.Generic;
+using System.Text;
+
+namespace ImageSharp.Tests.TestUtilities.Integration
+{
+    using System.IO;
+
+    using ImageSharp.Formats;
+    using ImageSharp.PixelFormats;
+
+    public class ReferenceEncoder : IImageEncoder
+    {
+        public void Encode<TPixel>(Image<TPixel> image, Stream stream, IEncoderOptions options)
+            where TPixel : struct, IPixel<TPixel>
+        {
+            System.Drawing.Bitmap sdBitmap = IntegrationTestUtils.ToSystemDrawingBitmap(image);
+            throw new NotImplementedException();
+        }
+    }
+}

tests/ImageSharp.Tests/TestUtilities/Tests/IntegrationTestUtilsTests.cs

@@ -0,0 +1,33 @@
+namespace ImageSharp.Tests
+{
+    using ImageSharp.PixelFormats;
+    using ImageSharp.Tests.TestUtilities.Integration;
+
+    using Xunit;
+    using Xunit.Abstractions;
+
+    public class IntegrationTestUtilsTests
+    {
+        private ITestOutputHelper Output { get; }
+
+        public IntegrationTestUtilsTests(ITestOutputHelper output)
+        {
+            this.Output = output;
+        }
+
+        [Theory]
+        [WithTestPatternImages(20, 20, PixelTypes.Rgba32 | PixelTypes.Bgra32)]
+        public void ToSystemDrawingBitmap<TPixel>(TestImageProvider<TPixel> provider)
+            where TPixel : struct, IPixel<TPixel>
+        {
+            using (Image<TPixel> image = provider.GetImage())
+            {
+                using (System.Drawing.Bitmap sdBitmap = IntegrationTestUtils.ToSystemDrawingBitmap(image))
+                {
+                    string fileName = provider.Utility.GetTestOutputFileName("png");
+                    sdBitmap.Save(fileName, System.Drawing.Imaging.ImageFormat.Png);
+                }
+            }
+        }
+    }
+}