Apply fix and tests

src/ImageSharp/Processing/Processors/Transforms/Linear/AffineTransformProcessor{TPixel}.cs

@@ -64,7 +64,14 @@ namespace SixLabors.ImageSharp.Processing.Processors.Transforms
             if (matrix.Equals(default) || matrix.Equals(Matrix3x2.Identity))
             {
                 // The clone will be blank here copy all the pixel data over
-                source.GetPixelMemoryGroup().CopyTo(destination.GetPixelMemoryGroup());
+                var interest = Rectangle.Intersect(this.SourceRectangle, destination.Bounds());
+                Buffer2DRegion<TPixel> sourceBuffer = source.PixelBuffer.GetRegion(interest);
+                Buffer2DRegion<TPixel> destbuffer = destination.PixelBuffer.GetRegion(interest);
+                for (int y = 0; y < sourceBuffer.Height; y++)
+                {
+                    sourceBuffer.DangerousGetRowSpan(y).CopyTo(destbuffer.DangerousGetRowSpan(y));
+                }
+
                 return;
             }
 

src/ImageSharp/Processing/Processors/Transforms/Linear/ProjectiveTransformProcessor{TPixel}.cs

@@ -63,7 +63,14 @@ namespace SixLabors.ImageSharp.Processing.Processors.Transforms
             if (matrix.Equals(default) || matrix.Equals(Matrix4x4.Identity))
             {
                 // The clone will be blank here copy all the pixel data over
-                source.GetPixelMemoryGroup().CopyTo(destination.GetPixelMemoryGroup());
+                var interest = Rectangle.Intersect(this.SourceRectangle, destination.Bounds());
+                Buffer2DRegion<TPixel> sourceBuffer = source.PixelBuffer.GetRegion(interest);
+                Buffer2DRegion<TPixel> destbuffer = destination.PixelBuffer.GetRegion(interest);
+                for (int y = 0; y < sourceBuffer.Height; y++)
+                {
+                    sourceBuffer.DangerousGetRowSpan(y).CopyTo(destbuffer.DangerousGetRowSpan(y));
+                }
+
                 return;
             }
 

tests/ImageSharp.Tests/Processing/Processors/Transforms/AffineTransformTests.cs

@@ -4,6 +4,7 @@
 using System;
 using System.Numerics;
 using System.Reflection;
+using SixLabors.ImageSharp.Metadata;
 using SixLabors.ImageSharp.PixelFormats;
 using SixLabors.ImageSharp.Processing;
 using SixLabors.ImageSharp.Processing.Processors.Transforms;
@@ -224,6 +225,16 @@ namespace SixLabors.ImageSharp.Tests.Processing.Transforms
                 c => c.Transform(builder));
         }
 
+        [Fact]
+        public void Issue1911()
+        {
+            using var image = new Image<Rgba32>(100, 100);
+            image.Mutate(x => x = x.Transform(new Rectangle(0, 0, 99, 100), Matrix3x2.Identity, new Size(99, 100), KnownResamplers.Lanczos2));
+
+            Assert.Equal(99, image.Width);
+            Assert.Equal(100, image.Height);
+        }
+
         private static IResampler GetResampler(string name)
         {
             PropertyInfo property = typeof(KnownResamplers).GetTypeInfo().GetProperty(name);

tests/ImageSharp.Tests/Processing/Transforms/ProjectiveTransformTests.cs

@@ -147,6 +147,16 @@ namespace SixLabors.ImageSharp.Tests.Processing.Transforms
             }
         }
 
+        [Fact]
+        public void Issue1911()
+        {
+            using var image = new Image<Rgba32>(100, 100);
+            image.Mutate(x => x = x.Transform(new Rectangle(0, 0, 99, 100), Matrix4x4.Identity, new Size(99, 100), KnownResamplers.Lanczos2));
+
+            Assert.Equal(99, image.Width);
+            Assert.Equal(100, image.Height);
+        }
+
         private static IResampler GetResampler(string name)
         {
             PropertyInfo property = typeof(KnownResamplers).GetTypeInfo().GetProperty(name);