Replace ImageMagick with ImageSharp for render test comparisons.

Avalonia.sln

@@ -99,7 +99,6 @@ Project("{2150E333-8FDC-42A3-9474-1A3956D46DE8}") = "Props", "Props", "{F3AC8BC1
 		build\HarfBuzzSharp.props = build\HarfBuzzSharp.props
 		build\JetBrains.Annotations.props = build\JetBrains.Annotations.props
 		build\JetBrains.dotMemoryUnit.props = build\JetBrains.dotMemoryUnit.props
-		build\Magick.NET-Q16-AnyCPU.props = build\Magick.NET-Q16-AnyCPU.props
 		build\Microsoft.CSharp.props = build\Microsoft.CSharp.props
 		build\Microsoft.Reactive.Testing.props = build\Microsoft.Reactive.Testing.props
 		build\Moq.props = build\Moq.props
@@ -118,6 +117,7 @@ Project("{2150E333-8FDC-42A3-9474-1A3956D46DE8}") = "Props", "Props", "{F3AC8BC1
 		build\System.Memory.props = build\System.Memory.props
 		build\UnitTests.NetFX.props = build\UnitTests.NetFX.props
 		build\XUnit.props = build\XUnit.props
+		build\ImageSharp.props = build\ImageSharp.props
 	EndProjectSection
 EndProject
 Project("{2150E333-8FDC-42A3-9474-1A3956D46DE8}") = "Targets", "Targets", "{4D6FAF79-58B4-482F-9122-0668C346364C}"

build/Magick.NET-Q16-AnyCPU.props → build/ImageSharp.props

@@ -1,5 +1,5 @@
 <Project DefaultTargets="Build" xmlns="http://schemas.microsoft.com/developer/msbuild/2003">
   <ItemGroup>
-    <PackageReference Include="Magick.NET-Q16-AnyCPU" Version="7.9.0.2" />
+    <PackageReference Include="SixLabors.ImageSharp" Version="2.1.1" />
   </ItemGroup>
 </Project>

tests/Avalonia.Direct2D1.RenderTests/Avalonia.Direct2D1.RenderTests.csproj

@@ -19,6 +19,6 @@
   <Import Project="..\..\build\Moq.props" />
   <Import Project="..\..\build\Rx.props" />
   <Import Project="..\..\build\XUnit.props" />
-  <Import Project="..\..\build\Magick.NET-Q16-AnyCPU.props" />
+  <Import Project="..\..\build\ImageSharp.props" />
   <Import Project="..\..\build\SharedVersion.props" />
 </Project>

tests/Avalonia.RenderTests/TestBase.cs

@@ -1,10 +1,9 @@
 using System.IO;
 using System.Runtime.CompilerServices;
-using ImageMagick;
 using Avalonia.Controls;
 using Avalonia.Media.Imaging;
 using Avalonia.Rendering;
-
+using SixLabors.ImageSharp;
 using Xunit;
 using Avalonia.Platform;
 using System.Threading.Tasks;
@@ -12,6 +11,8 @@ using System;
 using System.Threading;
 using Avalonia.Media;
 using Avalonia.Threading;
+using SixLabors.ImageSharp.PixelFormats;
+using Image = SixLabors.ImageSharp.Image;
 #if AVALONIA_SKIA
 using Avalonia.Skia;
 #else
@@ -119,12 +120,12 @@ namespace Avalonia.Direct2D1.RenderTests
             var immediatePath = Path.Combine(OutputPath, testName + ".immediate.out.png");
             var deferredPath = Path.Combine(OutputPath, testName + ".deferred.out.png");
 
-            using (var expected = new MagickImage(expectedPath))
-            using (var immediate = new MagickImage(immediatePath))
-            using (var deferred = new MagickImage(deferredPath))
+            using (var expected = Image.Load<Rgba32>(expectedPath))
+            using (var immediate = Image.Load<Rgba32>(immediatePath))
+            using (var deferred = Image.Load<Rgba32>(deferredPath))
             {
-                double immediateError = expected.Compare(immediate, ErrorMetric.RootMeanSquared);
-                double deferredError = expected.Compare(deferred, ErrorMetric.RootMeanSquared);
+                var immediateError = CompareImages(immediate, expected);
+                var deferredError = CompareImages(deferred, expected);
 
                 if (immediateError > 0.022)
                 {
@@ -143,10 +144,10 @@ namespace Avalonia.Direct2D1.RenderTests
             var expectedPath = Path.Combine(OutputPath, testName + ".expected.png");
             var actualPath = Path.Combine(OutputPath, testName + ".out.png");
 
-            using (var expected = new MagickImage(expectedPath))
-            using (var actual = new MagickImage(actualPath))
+            using (var expected = Image.Load<Rgba32>(expectedPath))
+            using (var actual = Image.Load<Rgba32>(actualPath))
             {
-                double immediateError = expected.Compare(actual, ErrorMetric.RootMeanSquared);
+                double immediateError = CompareImages(actual, expected);
 
                 if (immediateError > 0.022)
                 {
@@ -154,6 +155,53 @@ namespace Avalonia.Direct2D1.RenderTests
                 }
             }
         }
+        
+        /// <summary>
+        /// Calculates root mean square error for given two images.
+        /// Based roughly on ImageMagick implementation to ensure consistency.
+        /// </summary>
+        private static double CompareImages(Image<Rgba32> actual, Image<Rgba32> expected)
+        {
+            if (actual.Width != expected.Width || actual.Height != expected.Height)
+            {
+                throw new ArgumentException("Images have different resolutions");
+            }
+
+            var quantity = actual.Width * actual.Height;
+            double squaresError = 0;
+
+            const double scale = 1 / 255d;
+            
+            for (var x = 0; x < actual.Width; x++)
+            {
+                double localError = 0;
+                
+                for (var y = 0; y < actual.Height; y++)
+                {
+                    var expectedAlpha = expected[x, y].A * scale;
+                    var actualAlpha = actual[x, y].A * scale;
+                    
+                    var r = scale * (expectedAlpha * expected[x, y].R - actualAlpha * actual[x, y].R);
+                    var g = scale * (expectedAlpha * expected[x, y].G - actualAlpha * actual[x, y].G);
+                    var b = scale * (expectedAlpha * expected[x, y].B - actualAlpha * actual[x, y].B);
+                    var a = expectedAlpha - actualAlpha;
+
+                    var error = r * r + g * g + b * b + a * a;
+
+                    localError += error;
+                }
+
+                squaresError += localError;
+            }
+
+            var meanSquaresError = squaresError / quantity;
+
+            const int channelCount = 4;
+            
+            meanSquaresError = meanSquaresError / channelCount;
+            
+            return Math.Sqrt(meanSquaresError);
+        }
 
         private string GetTestsDirectory()
         {

tests/Avalonia.Skia.RenderTests/Avalonia.Skia.RenderTests.csproj

@@ -20,7 +20,7 @@
   <Import Project="..\..\build\Moq.props" />
   <Import Project="..\..\build\Rx.props" />
   <Import Project="..\..\build\XUnit.props" />
-  <Import Project="..\..\build\Magick.NET-Q16-AnyCPU.props" />
+  <Import Project="..\..\build\ImageSharp.props" />
   <Import Project="..\..\build\SkiaSharp.props" />
   <Import Project="..\..\build\SharedVersion.props" />
 </Project>