Image.WrapMemory<TPixel> APIs wrapping Memory<byte>

src/ImageSharp/Image.WrapMemory.cs

@@ -150,5 +150,70 @@ public static Image<TPixel> WrapMemory<TPixel>(
             int height)
             where TPixel : unmanaged, IPixel<TPixel>
             => WrapMemory(Configuration.Default, pixelMemoryOwner, width, height);
+
+        /// <summary>
+        /// Wraps an existing contiguous memory area of 'width' x 'height' pixels,
+        /// allowing to view/manipulate it as an ImageSharp <see cref="Image{TPixel}"/> instance.
+        /// </summary>
+        /// <typeparam name="TPixel">The pixel type</typeparam>
+        /// <param name="configuration">The <see cref="Configuration"/></param>
+        /// <param name="byteMemory">The byte memory representing the pixel data.</param>
+        /// <param name="width">The width of the memory image.</param>
+        /// <param name="height">The height of the memory image.</param>
+        /// <param name="metadata">The <see cref="ImageMetadata"/>.</param>
+        /// <exception cref="ArgumentNullException">The configuration is null.</exception>
+        /// <exception cref="ArgumentNullException">The metadata is null.</exception>
+        /// <returns>An <see cref="Image{TPixel}"/> instance</returns>
+        public static Image<TPixel> WrapMemory<TPixel>(
+            Configuration configuration,
+            Memory<byte> byteMemory,
+            int width,
+            int height,
+            ImageMetadata metadata)
+            where TPixel : unmanaged, IPixel<TPixel>
+        {
+            Guard.NotNull(configuration, nameof(configuration));
+            Guard.NotNull(metadata, nameof(metadata));
+
+            var memoryManager = new ByteMemoryManager<TPixel>(byteMemory);
+            var memorySource = MemoryGroup<TPixel>.Wrap(memoryManager.Memory);
+            return new Image<TPixel>(configuration, memorySource, width, height, metadata);
+        }
+
+        /// <summary>
+        /// Wraps an existing contiguous memory area of 'width' x 'height' pixels,
+        /// allowing to view/manipulate it as an ImageSharp <see cref="Image{TPixel}"/> instance.
+        /// </summary>
+        /// <typeparam name="TPixel">The pixel type</typeparam>
+        /// <param name="configuration">The <see cref="Configuration"/></param>
+        /// <param name="byteMemory">The byte memory representing the pixel data.</param>
+        /// <param name="width">The width of the memory image.</param>
+        /// <param name="height">The height of the memory image.</param>
+        /// <exception cref="ArgumentNullException">The configuration is null.</exception>
+        /// <returns>An <see cref="Image{TPixel}"/> instance.</returns>
+        public static Image<TPixel> WrapMemory<TPixel>(
+            Configuration configuration,
+            Memory<byte> byteMemory,
+            int width,
+            int height)
+            where TPixel : unmanaged, IPixel<TPixel>
+            => WrapMemory<TPixel>(configuration, byteMemory, width, height, new ImageMetadata());
+
+        /// <summary>
+        /// Wraps an existing contiguous memory area of 'width' x 'height' pixels,
+        /// allowing to view/manipulate it as an ImageSharp <see cref="Image{TPixel}"/> instance.
+        /// The memory is being observed, the caller remains responsible for managing it's lifecycle.
+        /// </summary>
+        /// <typeparam name="TPixel">The pixel type.</typeparam>
+        /// <param name="byteMemory">The byte memory representing the pixel data.</param>
+        /// <param name="width">The width of the memory image.</param>
+        /// <param name="height">The height of the memory image.</param>
+        /// <returns>An <see cref="Image{TPixel}"/> instance.</returns>
+        public static Image<TPixel> WrapMemory<TPixel>(
+            Memory<byte> byteMemory,
+            int width,
+            int height)
+            where TPixel : unmanaged, IPixel<TPixel>
+            => WrapMemory<TPixel>(Configuration.Default, byteMemory, width, height);
     }
 }

src/ImageSharp/Memory/ByteMemoryManager{T}.cs

@@ -0,0 +1,57 @@
+// Copyright (c) Six Labors.
+// Licensed under the Apache License, Version 2.0.
+using System;
+using System.Buffers;
+using System.Runtime.CompilerServices;
+using System.Runtime.InteropServices;
+
+namespace SixLabors.ImageSharp.Memory
+{
+    /// <summary>
+    /// A custom <see cref="MemoryManager{T}"/> that can wrap <see cref="Memory{T}"/> of <see cref="byte"/> instances
+    /// and cast them to be <see cref="Memory{T}"/> for any arbitrary unmanaged <typeparamref name="T"/> value type.
+    /// </summary>
+    /// <typeparam name="T">The value type to use when casting the wrapped <see cref="Memory{T}"/> instance.</typeparam>
+    internal sealed class ByteMemoryManager<T> : MemoryManager<T>
+        where T : unmanaged
+    {
+        /// <summary>
+        /// The wrapped <see cref="Memory{T}"/> of <see cref="byte"/> instance.
+        /// </summary>
+        private readonly Memory<byte> memory;
+
+        /// <summary>
+        /// Initializes a new instance of the <see cref="ByteMemoryManager{T}"/> class.
+        /// </summary>
+        /// <param name="memory">The <see cref="Memory{T}"/> of <see cref="byte"/> instance to wrap.</param>
+        public ByteMemoryManager(Memory<byte> memory)
+        {
+            this.memory = memory;
+        }
+
+        /// <inheritdoc/>
+        protected override void Dispose(bool disposing)
+        {
+        }
+
+        /// <inheritdoc/>
+        public override Span<T> GetSpan()
+        {
+            return MemoryMarshal.Cast<byte, T>(this.memory.Span);
+        }
+
+        /// <inheritdoc/>
+        public override MemoryHandle Pin(int elementIndex = 0)
+        {
+            // We need to adjust the offset into the wrapped byte segment,
+            // as the input index refers to the target-cast memory of T.
+            // We just have to shift this index by the byte size of T.
+            return this.memory.Slice(elementIndex * Unsafe.SizeOf<T>()).Pin();
+        }
+
+        /// <inheritdoc/>
+        public override void Unpin()
+        {
+        }
+    }
+}

tests/ImageSharp.Tests/Image/ImageTests.WrapMemory.cs

@@ -6,10 +6,10 @@
 using System.Drawing;
 using System.Drawing.Imaging;
 using System.Runtime.CompilerServices;
+using System.Runtime.InteropServices;
 
 using SixLabors.ImageSharp.Advanced;
 using SixLabors.ImageSharp.Common.Helpers;
-using SixLabors.ImageSharp.Memory;
 using SixLabors.ImageSharp.Metadata;
 using SixLabors.ImageSharp.PixelFormats;
 using Xunit;
@@ -80,6 +80,48 @@ public override void Unpin()
                 }
             }
 
+            public sealed class CastMemoryManager<TFrom, TTo> : MemoryManager<TTo>
+                where TFrom : unmanaged
+                where TTo : unmanaged
+            {
+                private readonly Memory<TFrom> memory;
+
+                public CastMemoryManager(Memory<TFrom> memory)
+                {
+                    this.memory = memory;
+                }
+
+                /// <inheritdoc/>
+                protected override void Dispose(bool disposing)
+                {
+                }
+
+                /// <inheritdoc/>
+                public override Span<TTo> GetSpan()
+                {
+                    return MemoryMarshal.Cast<TFrom, TTo>(this.memory.Span);
+                }
+
+                /// <inheritdoc/>
+                public override MemoryHandle Pin(int elementIndex = 0)
+                {
+                    int byteOffset = elementIndex * Unsafe.SizeOf<TTo>();
+                    int shiftedOffset = Math.DivRem(byteOffset, Unsafe.SizeOf<TFrom>(), out int remainder);
+
+                    if (remainder != 0)
+                    {
+                        ThrowHelper.ThrowArgumentException("The input index doesn't result in an aligned item access", nameof(elementIndex));
+                    }
+
+                    return this.memory.Slice(shiftedOffset).Pin();
+                }
+
+                /// <inheritdoc/>
+                public override void Unpin()
+                {
+                }
+            }
+
             [Fact]
             public void WrapMemory_CreatedImageIsCorrect()
             {
@@ -173,6 +215,73 @@ public void WrapSystemDrawingBitmap_WhenOwned()
                 }
             }
 
+            [Fact]
+            public void WrapMemory_FromBytes_CreatedImageIsCorrect()
+            {
+                Configuration cfg = Configuration.Default.Clone();
+                var metaData = new ImageMetadata();
+
+                var array = new byte[25 * Unsafe.SizeOf<Rgba32>()];
+                var memory = new Memory<byte>(array);
+
+                using (var image = Image.WrapMemory<Rgba32>(cfg, memory, 5, 5, metaData))
+                {
+                    Assert.True(image.TryGetSinglePixelSpan(out Span<Rgba32> imageSpan));
+                    ref Rgba32 pixel0 = ref imageSpan[0];
+                    Assert.True(Unsafe.AreSame(ref Unsafe.As<byte, Rgba32>(ref array[0]), ref pixel0));
+
+                    Assert.Equal(cfg, image.GetConfiguration());
+                    Assert.Equal(metaData, image.Metadata);
+                }
+            }
+
+            [Fact]
+            public void WrapSystemDrawingBitmap_FromBytes_WhenObserved()
+            {
+                if (ShouldSkipBitmapTest)
+                {
+                    return;
+                }
+
+                using (var bmp = new Bitmap(51, 23))
+                {
+                    using (var memoryManager = new BitmapMemoryManager(bmp))
+                    {
+                        Memory<Bgra32> pixelMemory = memoryManager.Memory;
+                        Memory<byte> byteMemory = new CastMemoryManager<Bgra32, byte>(pixelMemory).Memory;
+                        Bgra32 bg = Color.Red;
+                        Bgra32 fg = Color.Green;
+
+                        using (var image = Image.WrapMemory<Bgra32>(byteMemory, bmp.Width, bmp.Height))
+                        {
+                            Span<Bgra32> pixelSpan = pixelMemory.Span;
+                            Span<Bgra32> imageSpan = image.GetRootFramePixelBuffer().GetSingleMemory().Span;
+
+                            // We can't compare the two Memory<T> instances directly as they wrap different memory managers.
+                            // To check that the underlying data matches, we can just manually check their lenth, and the
+                            // fact that a reference to the first pixel in both spans is actually the same memory location.
+                            Assert.Equal(pixelSpan.Length, imageSpan.Length);
+                            Assert.True(Unsafe.AreSame(ref pixelSpan.GetPinnableReference(), ref imageSpan.GetPinnableReference()));
+
+                            Assert.True(image.TryGetSinglePixelSpan(out imageSpan));
+                            imageSpan.Fill(bg);
+                            for (var i = 10; i < 20; i++)
+                            {
+                                image.GetPixelRowSpan(i).Slice(10, 10).Fill(fg);
+                            }
+                        }
+
+                        Assert.False(memoryManager.IsDisposed);
+                    }
+
+                    string fn = System.IO.Path.Combine(
+                        TestEnvironment.ActualOutputDirectoryFullPath,
+                        $"{nameof(this.WrapSystemDrawingBitmap_WhenObserved)}.bmp");
+
+                    bmp.Save(fn, ImageFormat.Bmp);
+                }
+            }
+
             private static bool ShouldSkipBitmapTest =>
                 !TestEnvironment.Is64BitProcess || (TestHelpers.ImageSharpBuiltAgainst != "netcoreapp3.1" && TestHelpers.ImageSharpBuiltAgainst != "netcoreapp2.1");
         }