Add tests for new Image.WrapMemory APIs

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

@@ -6,10 +6,10 @@ using System.Buffers;
 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 +80,52 @@ namespace SixLabors.ImageSharp.Tests
                 }
             }
 
+            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()
+                {
+                    if (MemoryMarshal.TryGetArray(this.memory, out ArraySegment<TFrom> arraySegment))
+                    {
+                        return MemoryMarshal.Cast<TFrom, TTo>(arraySegment.AsSpan());
+                    }
+
+                    if (MemoryMarshal.TryGetMemoryManager<TFrom, MemoryManager<TFrom>>(this.memory, out MemoryManager<TFrom> memoryManager))
+                    {
+                        return MemoryMarshal.Cast<TFrom, TTo>(memoryManager.GetSpan());
+                    }
+
+                    ThrowHelper.ThrowArgumentException("The input Memory<byte> instance was not valid.", nameof(this.memory));
+
+                    return default;
+                }
+
+                /// <inheritdoc/>
+                public override MemoryHandle Pin(int elementIndex = 0)
+                {
+                    return this.memory.Pin();
+                }
+
+                /// <inheritdoc/>
+                public override void Unpin()
+                {
+                }
+            }
+
             [Fact]
             public void WrapMemory_CreatedImageIsCorrect()
             {
@@ -173,6 +219,65 @@ namespace SixLabors.ImageSharp.Tests
                 }
             }
 
+            [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))
+                        {
+                            Assert.Equal(pixelMemory, image.GetRootFramePixelBuffer().GetSingleMemory());
+                            Assert.True(image.TryGetSinglePixelSpan(out Span<Bgra32> 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");
         }