SwapOrCopyContent() works

src/ImageSharp/Memory/DiscontiguousBuffers/MemoryGroupView{T}.cs

@@ -21,12 +21,11 @@ namespace SixLabors.ImageSharp.Memory
     internal class MemoryGroupView<T> : IMemoryGroup<T>
         where T : struct
     {
-        private readonly Memory.MemoryGroup<T> owner;
+        private MemoryGroup<T> owner;
         private readonly MemoryOwnerWrapper[] memoryWrappers;
 
-        public MemoryGroupView(Memory.MemoryGroup<T> owner)
+        public MemoryGroupView(MemoryGroup<T> owner)
         {
-            this.IsValid = true;
             this.owner = owner;
             this.memoryWrappers = new MemoryOwnerWrapper[owner.Count];
 
@@ -36,20 +35,68 @@ namespace SixLabors.ImageSharp.Memory
             }
         }
 
-        public int Count => this.owner.Count;
+        public int Count
+        {
+            get
+            {
+                this.EnsureIsValid();
+                return this.owner.Count;
+            }
+        }
 
-        public int BufferLength => this.owner.BufferLength;
+        public int BufferLength
+        {
+            get
+            {
+                this.EnsureIsValid();
+                return this.owner.BufferLength;
+            }
+        }
 
-        public long TotalLength => this.owner.TotalLength;
+        public long TotalLength
+        {
+            get
+            {
+                this.EnsureIsValid();
+                return this.owner.TotalLength;
+            }
+        }
 
-        public bool IsValid { get; internal set; }
+        public bool IsValid => this.owner != null;
 
-        public Memory<T> this[int index] => throw new NotImplementedException();
+        public Memory<T> this[int index]
+        {
+            get
+            {
+                this.EnsureIsValid();
+                return this.memoryWrappers[index].Memory;
+            }
+        }
 
-        public IEnumerator<Memory<T>> GetEnumerator() => throw new NotImplementedException();
+        public IEnumerator<Memory<T>> GetEnumerator()
+        {
+            this.EnsureIsValid();
+            for (int i = 0; i < this.Count; i++)
+            {
+                yield return this.memoryWrappers[i].Memory;
+            }
+        }
 
         IEnumerator IEnumerable.GetEnumerator() => this.GetEnumerator();
 
+        internal void Invalidate()
+        {
+            this.owner = null;
+        }
+
+        private void EnsureIsValid()
+        {
+            if (!this.IsValid)
+            {
+                throw new InvalidMemoryOperationException("Can not access an invalidated MemoryGroupView!");
+            }
+        }
+
         private class MemoryOwnerWrapper : MemoryManager<T>
         {
             private readonly MemoryGroupView<T> view;
@@ -68,17 +115,20 @@ namespace SixLabors.ImageSharp.Memory
 
             public override Span<T> GetSpan()
             {
-                if (!this.view.IsValid)
-                {
-                    throw new InvalidOperationException();
-                }
-
-                return this.view[this.index].Span;
+                this.view.EnsureIsValid();
+                return this.view.owner[this.index].Span;
             }
 
-            public override MemoryHandle Pin(int elementIndex = 0) => throw new NotImplementedException();
+            public override MemoryHandle Pin(int elementIndex = 0)
+            {
+                this.view.EnsureIsValid();
+                return this.view.owner[this.index].Pin();
+            }
 
-            public override void Unpin() => throw new NotImplementedException();
+            public override void Unpin()
+            {
+                throw new NotSupportedException();
+            }
         }
     }
 }

src/ImageSharp/Memory/DiscontiguousBuffers/MemoryGroup{T}.Consumed.cs

@@ -17,6 +17,7 @@ namespace SixLabors.ImageSharp.Memory
                 : base(bufferLength, totalLength)
             {
                 this.source = source;
+                this.View = new MemoryGroupView<T>(this);
             }
 
             public override int Count => this.source.Length;
@@ -33,7 +34,7 @@ namespace SixLabors.ImageSharp.Memory
 
             public override void Dispose()
             {
-                // No ownership nothing to dispose
+                this.View.Invalidate();
             }
         }
     }

src/ImageSharp/Memory/DiscontiguousBuffers/MemoryGroup{T}.Owned.cs

@@ -19,15 +19,9 @@ namespace SixLabors.ImageSharp.Memory
                 : base(bufferLength, totalLength)
             {
                 this.memoryOwners = memoryOwners;
+                this.View = new MemoryGroupView<T>(this);
             }
 
-            public override IEnumerator<Memory<T>> GetEnumerator()
-            {
-                this.EnsureNotDisposed();
-                return this.memoryOwners.Select(mo => mo.Memory).GetEnumerator();
-            }
-
-
             public override int Count
             {
                 get
@@ -46,6 +40,12 @@ namespace SixLabors.ImageSharp.Memory
                 }
             }
 
+            public override IEnumerator<Memory<T>> GetEnumerator()
+            {
+                this.EnsureNotDisposed();
+                return this.memoryOwners.Select(mo => mo.Memory).GetEnumerator();
+            }
+
             public override void Dispose()
             {
                 if (this.memoryOwners == null)
@@ -53,6 +53,8 @@ namespace SixLabors.ImageSharp.Memory
                     return;
                 }
 
+                this.View.Invalidate();
+
                 foreach (IMemoryOwner<T> memoryOwner in this.memoryOwners)
                 {
                     memoryOwner.Dispose();
@@ -69,6 +71,29 @@ namespace SixLabors.ImageSharp.Memory
                     throw new ObjectDisposedException(nameof(MemoryGroup<T>));
                 }
             }
+
+            internal static void SwapContents(Owned a, Owned b)
+            {
+                a.EnsureNotDisposed();
+                b.EnsureNotDisposed();
+
+                IMemoryOwner<T>[] tempOwners = a.memoryOwners;
+                long tempTotalLength = a.TotalLength;
+                int tempBufferLength = a.BufferLength;
+
+                a.memoryOwners = b.memoryOwners;
+                a.TotalLength = b.TotalLength;
+                a.BufferLength = b.BufferLength;
+
+                b.memoryOwners = tempOwners;
+                b.TotalLength = tempTotalLength;
+                b.BufferLength = tempBufferLength;
+
+                a.View.Invalidate();
+                b.View.Invalidate();
+                a.View = new MemoryGroupView<T>(a);
+                b.View = new MemoryGroupView<T>(b);
+            }
         }
     }
 }

src/ImageSharp/Memory/DiscontiguousBuffers/MemoryGroup{T}.cs

@@ -26,41 +26,60 @@ namespace SixLabors.ImageSharp.Memory
             this.TotalLength = totalLength;
         }
 
+        /// <inheritdoc />
         public abstract int Count { get; }
 
-        public int BufferLength { get; }
+        /// <inheritdoc />
+        public int BufferLength { get; private set; }
 
-        public long TotalLength { get; }
+        /// <inheritdoc />
+        public long TotalLength { get; private set; }
 
+        /// <inheritdoc />
         public bool IsValid { get; private set; } = true;
 
+        public MemoryGroupView<T> View { get; private set; }
+
+        /// <inheritdoc />
         public abstract Memory<T> this[int index] { get; }
 
+        /// <inheritdoc />
         public abstract void Dispose();
 
+        /// <inheritdoc />
         public abstract IEnumerator<Memory<T>> GetEnumerator();
 
+        /// <inheritdoc />
         IEnumerator IEnumerable.GetEnumerator() => this.GetEnumerator();
 
-        // bufferLengthAlignment == image.Width in row-major images
+        /// <summary>
+        /// Creates a new memory group, allocating it's buffers with the provided allocator.
+        /// </summary>
+        /// <param name="allocator">The <see cref="MemoryAllocator"/> to use.</param>
+        /// <param name="totalLength">The total length of the buffer.</param>
+        /// <param name="bufferAlignment">The expected alignment (eg. to make sure image rows fit into single buffers).</param>
+        /// <param name="options">The <see cref="AllocationOptions"/>.</param>
+        /// <returns>A new <see cref="MemoryGroup{T}"/>.</returns>
+        /// <exception cref="InvalidMemoryOperationException">Thrown when 'blockAlignment' converted to bytes is greater than the buffer capacity of the allocator.</exception>
         public static MemoryGroup<T> Allocate(
             MemoryAllocator allocator,
             long totalLength,
-            int blockAlignment,
-            AllocationOptions allocationOptions = AllocationOptions.None)
+            int bufferAlignment,
+            AllocationOptions options = AllocationOptions.None)
         {
             Guard.NotNull(allocator, nameof(allocator));
             Guard.MustBeGreaterThanOrEqualTo(totalLength, 0, nameof(totalLength));
-            Guard.MustBeGreaterThan(blockAlignment, 0, nameof(blockAlignment));
+            Guard.MustBeGreaterThan(bufferAlignment, 0, nameof(bufferAlignment));
 
             int blockCapacityInElements = allocator.GetBufferCapacityInBytes() / ElementSize;
-            if (blockAlignment > blockCapacityInElements)
+            if (bufferAlignment > blockCapacityInElements)
             {
-                throw new InvalidMemoryOperationException();
+                throw new InvalidMemoryOperationException(
+                    $"The buffer capacity of the provided MemoryAllocator is insufficient for the requested buffer alignment: {bufferAlignment}.");
             }
 
-            int numberOfAlignedSegments = blockCapacityInElements / blockAlignment;
-            int bufferLength = numberOfAlignedSegments * blockAlignment;
+            int numberOfAlignedSegments = blockCapacityInElements / bufferAlignment;
+            int bufferLength = numberOfAlignedSegments * bufferAlignment;
             if (totalLength > 0 && totalLength < bufferLength)
             {
                 bufferLength = (int)totalLength;
@@ -81,12 +100,12 @@ namespace SixLabors.ImageSharp.Memory
             var buffers = new IMemoryOwner<T>[bufferCount];
             for (int i = 0; i < buffers.Length - 1; i++)
             {
-                buffers[i] = allocator.Allocate<T>(bufferLength, allocationOptions);
+                buffers[i] = allocator.Allocate<T>(bufferLength, options);
             }
 
             if (bufferCount > 0)
             {
-                buffers[^1] = allocator.Allocate<T>(sizeOfLastBuffer, allocationOptions);
+                buffers[^1] = allocator.Allocate<T>(sizeOfLastBuffer, options);
             }
 
             return new Owned(buffers, bufferLength, totalLength);
@@ -115,10 +134,27 @@ namespace SixLabors.ImageSharp.Memory
             return new Consumed(source, bufferLength, totalLength);
         }
 
-        // Analogous to current MemorySource.SwapOrCopyContent()
-        public static void SwapOrCopyContent(MemoryGroup<T> destination, MemoryGroup<T> source)
+        /// <summary>
+        /// Swaps the contents of 'target' with 'source' if the buffers are allocated (1),
+        /// copies the contents of 'source' to 'target' otherwise (2).
+        /// Groups should be of same TotalLength in case 2.
+        /// </summary>
+        public static void SwapOrCopyContent(MemoryGroup<T> target, MemoryGroup<T> source)
         {
-            throw new NotImplementedException();
+            if (source is Owned ownedSrc && target is Owned ownedTarget)
+            {
+                Owned.SwapContents(ownedTarget, ownedSrc);
+            }
+            else
+            {
+                if (target.TotalLength != source.TotalLength)
+                {
+                    throw new InvalidMemoryOperationException(
+                        "Trying to copy/swap incompatible buffers. This is most likely caused by applying an unsupported processor to wrapped-memory images.");
+                }
+
+                source.CopyTo(target);
+            }
         }
     }
 }

src/ImageSharp/Memory/MemoryAllocatorExtensions.cs

@@ -17,7 +17,7 @@ namespace SixLabors.ImageSharp.Memory
         /// <typeparam name="T">The type of buffer items to allocate.</typeparam>
         /// <param name="memoryAllocator">The memory allocator.</param>
         /// <param name="width">The buffer width.</param>
-        /// <param name="height">The buffer heght.</param>
+        /// <param name="height">The buffer height.</param>
         /// <param name="options">The allocation options.</param>
         /// <returns>The <see cref="Buffer2D{T}"/>.</returns>
         public static Buffer2D<T> Allocate2D<T>(
@@ -50,13 +50,13 @@ namespace SixLabors.ImageSharp.Memory
             Allocate2D<T>(memoryAllocator, size.Width, size.Height, options);
 
         /// <summary>
-        /// Allocates padded buffers for BMP encoder/decoder. (Replacing old PixelRow/PixelArea)
+        /// Allocates padded buffers for BMP encoder/decoder. (Replacing old PixelRow/PixelArea).
         /// </summary>
-        /// <param name="memoryAllocator">The <see cref="MemoryAllocator"/></param>
+        /// <param name="memoryAllocator">The <see cref="MemoryAllocator"/>.</param>
         /// <param name="width">Pixel count in the row</param>
-        /// <param name="pixelSizeInBytes">The pixel size in bytes, eg. 3 for RGB</param>
-        /// <param name="paddingInBytes">The padding</param>
-        /// <returns>A <see cref="IManagedByteBuffer"/></returns>
+        /// <param name="pixelSizeInBytes">The pixel size in bytes, eg. 3 for RGB.</param>
+        /// <param name="paddingInBytes">The padding.</param>
+        /// <returns>A <see cref="IManagedByteBuffer"/>.</returns>
         internal static IManagedByteBuffer AllocatePaddedPixelRowBuffer(
             this MemoryAllocator memoryAllocator,
             int width,
@@ -66,5 +66,22 @@ namespace SixLabors.ImageSharp.Memory
             int length = (width * pixelSizeInBytes) + paddingInBytes;
             return memoryAllocator.AllocateManagedByteBuffer(length);
         }
+
+        /// <summary>
+        /// Allocates a <see cref="MemoryGroup{T}"/>.
+        /// </summary>
+        /// <param name="memoryAllocator">The <see cref="MemoryAllocator"/> to use.</param>
+        /// <param name="totalLength">The total length of the buffer.</param>
+        /// <param name="bufferAlignment">The expected alignment (eg. to make sure image rows fit into single buffers).</param>
+        /// <param name="options">The <see cref="AllocationOptions"/>.</param>
+        /// <returns>A new <see cref="MemoryGroup{T}"/>.</returns>
+        /// <exception cref="InvalidMemoryOperationException">Thrown when 'blockAlignment' converted to bytes is greater than the buffer capacity of the allocator.</exception>
+        internal static MemoryGroup<T> AllocateGroup<T>(
+            this MemoryAllocator memoryAllocator,
+            long totalLength,
+            int bufferAlignment,
+            AllocationOptions options = AllocationOptions.None)
+            where T : struct
+            => MemoryGroup<T>.Allocate(memoryAllocator, totalLength, bufferAlignment, options);
     }
 }

tests/ImageSharp.Tests/Memory/DiscontiguousBuffers/MemoryGroupIndex.cs

@@ -112,12 +112,9 @@ namespace SixLabors.ImageSharp.Tests.Memory.DiscontiguousBuffers
         public static MemoryGroupIndex MaxIndex<T>(this MemoryGroup<T> group)
             where T : struct
         {
-            if (group.Count == 0)
-            {
-                return new MemoryGroupIndex(group.BufferLength, 0, 0);
-            }
-
-            return new MemoryGroupIndex(group.BufferLength, group.Count - 1, group[^1].Length - 1);
+            return group.Count == 0
+                ? new MemoryGroupIndex(group.BufferLength, 0, 0)
+                : new MemoryGroupIndex(group.BufferLength, group.Count - 1, group[^1].Length);
         }
     }
 }

tests/ImageSharp.Tests/Memory/DiscontiguousBuffers/MemoryGroupTests.Allocate.cs

@@ -1,6 +1,7 @@
 // Copyright (c) Six Labors and contributors.
 // Licensed under the Apache License, Version 2.0.
 
+using System;
 using System.Collections.Generic;
 using System.Linq;
 using SixLabors.ImageSharp.Memory;

tests/ImageSharp.Tests/Memory/DiscontiguousBuffers/MemoryGroupTests.SwapOrCopyContent.cs

@@ -0,0 +1,105 @@
+// Copyright (c) Six Labors and contributors.
+// Licensed under the Apache License, Version 2.0.
+
+using System;
+using SixLabors.ImageSharp.Memory;
+using SixLabors.ImageSharp.PixelFormats;
+using Xunit;
+
+namespace SixLabors.ImageSharp.Tests.Memory.DiscontiguousBuffers
+{
+    public partial class MemoryGroupTests
+    {
+        public class SwapOrCopyContent : MemoryGroupTestsBase
+        {
+            [Fact]
+            public void WhenBothAreMemoryOwners_ShouldSwap()
+            {
+                this.MemoryAllocator.BufferCapacityInBytes = sizeof(int) * 50;
+                using MemoryGroup<int> a = this.MemoryAllocator.AllocateGroup<int>(100, 50);
+                using MemoryGroup<int> b = this.MemoryAllocator.AllocateGroup<int>(120, 50);
+
+                Memory<int> a0 = a[0];
+                Memory<int> a1 = a[1];
+                Memory<int> b0 = b[0];
+                Memory<int> b1 = b[1];
+
+                MemoryGroup<int>.SwapOrCopyContent(a, b);
+
+                Assert.Equal(b0, a[0]);
+                Assert.Equal(b1, a[1]);
+                Assert.Equal(a0, b[0]);
+                Assert.Equal(a1, b[1]);
+                Assert.NotEqual(a[0], b[0]);
+            }
+
+            [Fact]
+            public void WhenBothAreMemoryOwners_ShouldReplaceViews()
+            {
+                using MemoryGroup<int> a = this.MemoryAllocator.AllocateGroup<int>(100, 100);
+                using MemoryGroup<int> b = this.MemoryAllocator.AllocateGroup<int>(120, 100);
+
+                a[0].Span[42] = 1;
+                b[0].Span[33] = 2;
+                MemoryGroupView<int> aView0 = a.View;
+                MemoryGroupView<int> bView0 = b.View;
+
+                MemoryGroup<int>.SwapOrCopyContent(a, b);
+                Assert.False(aView0.IsValid);
+                Assert.False(bView0.IsValid);
+                Assert.ThrowsAny<InvalidOperationException>(() => _ = aView0[0].Span);
+                Assert.ThrowsAny<InvalidOperationException>(() => _ = bView0[0].Span);
+
+                Assert.True(a.View.IsValid);
+                Assert.True(b.View.IsValid);
+                Assert.Equal(2, a.View[0].Span[33]);
+                Assert.Equal(1, b.View[0].Span[42]);
+            }
+
+            [Theory]
+            [InlineData(false)]
+            [InlineData(true)]
+            public void WhenDestIsNotAllocated_SameSize_ShouldCopy(bool sourceIsAllocated)
+            {
+                var data = new Rgba32[21];
+                var color = new Rgba32(1, 2, 3, 4);
+
+                using var destOwner = new TestMemoryManager<Rgba32>(data);
+                using var dest = MemoryGroup<Rgba32>.Wrap(destOwner.Memory);
+
+                using MemoryGroup<Rgba32> source = this.MemoryAllocator.AllocateGroup<Rgba32>(21, 30);
+
+                source[0].Span[10] = color;
+
+                // Act:
+                MemoryGroup<Rgba32>.SwapOrCopyContent(dest, source);
+
+                // Assert:
+                Assert.Equal(color, dest[0].Span[10]);
+                Assert.NotEqual(source[0], dest[0]);
+            }
+
+            [Theory]
+            [InlineData(false)]
+            [InlineData(true)]
+            public void WhenDestIsNotMemoryOwner_DifferentSize_Throws(bool sourceIsOwner)
+            {
+                var data = new Rgba32[21];
+                var color = new Rgba32(1, 2, 3, 4);
+
+                using var destOwner = new TestMemoryManager<Rgba32>(data);
+                var dest = MemoryGroup<Rgba32>.Wrap(destOwner.Memory);
+
+                using MemoryGroup<Rgba32> source = this.MemoryAllocator.AllocateGroup<Rgba32>(22, 30);
+
+                source[0].Span[10] = color;
+
+                // Act:
+                Assert.ThrowsAny<InvalidOperationException>(() => MemoryGroup<Rgba32>.SwapOrCopyContent(dest, source));
+
+                Assert.Equal(color, source[0].Span[10]);
+                Assert.NotEqual(color, dest[0].Span[10]);
+            }
+        }
+    }
+}

tests/ImageSharp.Tests/Memory/DiscontiguousBuffers/MemoryGroupTests.View.cs

@@ -0,0 +1,84 @@
+// Copyright (c) Six Labors and contributors.
+// Licensed under the Apache License, Version 2.0.
+
+using System;
+using SixLabors.ImageSharp.Memory;
+using Xunit;
+
+namespace SixLabors.ImageSharp.Tests.Memory.DiscontiguousBuffers
+{
+    public partial class MemoryGroupTests
+    {
+        public class View : MemoryGroupTestsBase
+        {
+            [Fact]
+            public void RefersToOwnerGroupContent()
+            {
+                using MemoryGroup<int> group = this.CreateTestGroup(240, 80, true);
+
+                MemoryGroupView<int> view = group.View;
+                Assert.True(view.IsValid);
+                Assert.Equal(group.Count, view.Count);
+                Assert.Equal(group.BufferLength, view.BufferLength);
+                Assert.Equal(group.TotalLength, view.TotalLength);
+                int cnt = 1;
+                foreach (Memory<int> memory in view)
+                {
+                    Span<int> span = memory.Span;
+                    foreach (int t in span)
+                    {
+                        Assert.Equal(cnt, t);
+                        cnt++;
+                    }
+                }
+            }
+
+            [Fact]
+            public void IsInvalidatedOnOwnerGroupDispose()
+            {
+                MemoryGroupView<int> view;
+                using (MemoryGroup<int> group = this.CreateTestGroup(240, 80, true))
+                {
+                    view = group.View;
+                }
+
+                Assert.False(view.IsValid);
+
+                Assert.ThrowsAny<InvalidMemoryOperationException>(() =>
+                {
+                    _ = view.Count;
+                });
+
+                Assert.ThrowsAny<InvalidMemoryOperationException>(() =>
+                {
+                    _ = view.BufferLength;
+                });
+
+                Assert.ThrowsAny<InvalidMemoryOperationException>(() =>
+                {
+                    _ = view.TotalLength;
+                });
+
+                Assert.ThrowsAny<InvalidMemoryOperationException>(() =>
+                {
+                    _ = view[0];
+                });
+            }
+
+            [Fact]
+            public void WhenInvalid_CanNotUseMemberMemory()
+            {
+                Memory<int> memory;
+                using (MemoryGroup<int> group = this.CreateTestGroup(240, 80, true))
+                {
+                    memory = group.View[0];
+                }
+
+                Assert.ThrowsAny<InvalidMemoryOperationException>(() =>
+                {
+                    _ = memory.Span;
+                });
+            }
+        }
+    }
+}

tests/ImageSharp.Tests/Memory/DiscontiguousBuffers/MemoryGroupTests.cs

@@ -2,6 +2,7 @@
 // Licensed under the Apache License, Version 2.0.
 
 using System;
+using System.Buffers;
 using System.Runtime.InteropServices;
 using SixLabors.ImageSharp.Memory;
 using Xunit;
@@ -103,8 +104,6 @@ namespace SixLabors.ImageSharp.Tests.Memory.DiscontiguousBuffers
 
                     Assert.True(b == 2 * a, $"Mismatch @ {pos} Expected: {a} Actual: {b}");
                 }
-
-
             }
 
             [Fact]
@@ -117,7 +116,6 @@ namespace SixLabors.ImageSharp.Tests.Memory.DiscontiguousBuffers
             }
         }
 
-
         [Theory]
         [InlineData(100, 5)]
         [InlineData(100, 101)]
@@ -136,6 +134,26 @@ namespace SixLabors.ImageSharp.Tests.Memory.DiscontiguousBuffers
             }
         }
 
+        [Fact]
+        public void Wrap()
+        {
+            int[] data0 = { 1, 2, 3, 4 };
+            int[] data1 = { 5, 6, 7, 8 };
+            int[] data2 = { 9, 10 };
+            using var mgr0 = new TestMemoryManager<int>(data0);
+            using var mgr1 = new TestMemoryManager<int>(data1);
+
+            using var group = MemoryGroup<int>.Wrap(mgr0.Memory, mgr1.Memory, data2);
+
+            Assert.Equal(3, group.Count);
+            Assert.Equal(4, group.BufferLength);
+            Assert.Equal(10, group.TotalLength);
+
+            Assert.True(group[0].Span.SequenceEqual(data0));
+            Assert.True(group[1].Span.SequenceEqual(data1));
+            Assert.True(group[2].Span.SequenceEqual(data2));
+        }
+
         private static void MultiplyAllBy2(ReadOnlySpan<int> source, Span<int> target)
         {
             Assert.Equal(source.Length, target.Length);

tests/ImageSharp.Tests/Memory/DiscontiguousBuffers/MemoryGroupTestsBase.cs

@@ -9,6 +9,9 @@ namespace SixLabors.ImageSharp.Tests.Memory.DiscontiguousBuffers
     {
         internal readonly TestMemoryAllocator MemoryAllocator = new TestMemoryAllocator();
 
+        /// <summary>
+        /// Create a group, either uninitialized or filled with incrementing numbers starting with 1.
+        /// </summary>
         internal MemoryGroup<int> CreateTestGroup(long totalLength, int bufferLength, bool fillSequence = false)
         {
             this.MemoryAllocator.BufferCapacityInBytes = bufferLength * sizeof(int);