made WrapMemory() public + test case demonstrating using Image.WrapMemory() to draw over a System.Drawing.Bitmap instance

src/ImageSharp/Image.WrapMemory.cs

@@ -26,7 +26,7 @@ namespace SixLabors.ImageSharp
         /// <param name="height">The height of the memory image</param>
         /// <param name="metaData">The <see cref="ImageMetaData"/></param>
         /// <returns>An <see cref="Image{TPixel}"/> instance</returns>
-        internal static Image<TPixel> WrapMemory<TPixel>(
+        public static Image<TPixel> WrapMemory<TPixel>(
             Configuration config,
             Memory<TPixel> pixelMemory,
             int width,
@@ -46,7 +46,7 @@ namespace SixLabors.ImageSharp
         /// <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>
-        internal static Image<TPixel> WrapMemory<TPixel>(
+        public static Image<TPixel> WrapMemory<TPixel>(
             Memory<TPixel> pixelMemory,
             int width,
             int height)

src/ImageSharp/PixelFormats/Bgra32.cs

@@ -11,6 +11,7 @@ namespace SixLabors.ImageSharp.PixelFormats
     /// <summary>
     /// Packed pixel type containing four 8-bit unsigned normalized values ranging from 0 to 255.
     /// The color components are stored in blue, green, red, and alpha order (least significant to most significant byte).
+    /// The format is binary compatible with System.Drawing.Imaging.PixelFormat.Format32bppArgb
     /// <para>
     /// Ranges from [0, 0, 0, 0] to [1, 1, 1, 1] in vector form.
     /// </para>

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

@@ -2,7 +2,14 @@
 // Licensed under the Apache License, Version 2.0.
 
 using System;
+using System.Buffers;
+using System.Drawing;
+using System.Drawing.Imaging;
+
+using SixLabors.ImageSharp.PixelFormats;
 using SixLabors.Memory;
+using SixLabors.Shapes;
+using SixLabors.ImageSharp.Processing;
 using Xunit;
 
 // ReSharper disable InconsistentNaming
@@ -12,6 +19,73 @@ namespace SixLabors.ImageSharp.Tests
     {
         public class WrapMemory
         {
+            class BitmapMemoryManager : MemoryManager<Bgra32>
+            {
+                private System.Drawing.Bitmap bitmap;
+
+                private BitmapData bmpData;
+
+                private int length;
+
+                public BitmapMemoryManager(Bitmap bitmap)
+                {
+                    if (bitmap.PixelFormat != PixelFormat.Format32bppArgb)
+                    {
+                        throw new ArgumentException("bitmap.PixelFormat != PixelFormat.Format32bppArgb", nameof(bitmap));
+                    }
+
+                    this.bitmap = bitmap;
+                    var rectangle = new Rectangle(0, 0, bitmap.Width, bitmap.Height);
+                    this.bmpData = bitmap.LockBits(rectangle, ImageLockMode.ReadWrite, bitmap.PixelFormat);
+                    this.length = bitmap.Width * bitmap.Height;
+                }
+
+                protected override void Dispose(bool disposing)
+                {
+                    this.bitmap.UnlockBits(this.bmpData);
+                }
+
+                public override unsafe Span<Bgra32> GetSpan()
+                {
+                    void* ptr = (void*) this.bmpData.Scan0;
+                    return new Span<Bgra32>(ptr, this.length);
+                }
+
+                public override unsafe MemoryHandle Pin(int elementIndex = 0)
+                {
+                    void* ptr = (void*)this.bmpData.Scan0;
+                    return new MemoryHandle(ptr);
+                }
+
+                public override void Unpin()
+                {
+                }
+            }
+
+            [Fact]
+            public void WrapSystemDrawingBitmap()
+            {
+                using (var bmp = new Bitmap(51, 23))
+                {
+                    using (var memoryManager = new BitmapMemoryManager(bmp))
+                    {
+                        Memory<Bgra32> memory = memoryManager.Memory;
+                        Bgra32 bg = NamedColors<Bgra32>.Red;
+                        Bgra32 fg = NamedColors<Bgra32>.Green;
+
+                        using (var image = Image.WrapMemory(memory, bmp.Width, bmp.Height))
+                        {
+                            image.Mutate(c => c.Fill(bg).Fill(fg, new RectangularPolygon(10, 10, 10, 10)));
+                        }
+                    }
+
+                    string fn = System.IO.Path.Combine(
+                        TestEnvironment.ActualOutputDirectoryFullPath,
+                        "WrapSystemDrawingBitmap.bmp");
+
+                    bmp.Save(fn, ImageFormat.Bmp);
+                }
+            }
         }
     }
 }