Merge pull request unoplatform#14959 from Youssef1313/rendertargetbit…

…map-unmanagedmem

perf: Avoid LOH allocations in RenderTargetBitmap

src/Uno.UI/UI/Xaml/Media/Imaging/RenderTargetBitmap.cs

@@ -14,6 +14,7 @@
 using Uno.UI.Xaml.Media;
 using Buffer = Windows.Storage.Streams.Buffer;
 using System.Buffers;
+using System.Runtime.InteropServices;
 
 using WinUICoreServices = Uno.UI.Xaml.Core.CoreServices;
 
@@ -22,8 +23,84 @@ namespace Microsoft.UI.Xaml.Media.Imaging
 #if NOT_IMPLEMENTED
 	[global::Uno.NotImplemented("IS_UNIT_TESTS", "__WASM__", "__NETSTD_REFERENCE__")]
 #endif
-	public partial class RenderTargetBitmap : ImageSource, IDisposable
+	public partial class RenderTargetBitmap : ImageSource
 	{
+#if !__ANDROID__
+		// This is to avoid LOH array allocations
+		private unsafe class UnmanagedArrayOfBytes
+		{
+			public nint Pointer;
+			public int Length { get; }
+
+			public UnmanagedArrayOfBytes(int length)
+			{
+				Length = length;
+				Pointer = Marshal.AllocHGlobal(length);
+				GC.AddMemoryPressure(length);
+			}
+
+			public byte this[int index]
+			{
+				get
+				{
+					return ((byte*)Pointer.ToPointer())[index];
+				}
+				set
+				{
+					((byte*)Pointer.ToPointer())[index] = value;
+				}
+			}
+
+			~UnmanagedArrayOfBytes()
+			{
+				Marshal.FreeHGlobal(Pointer);
+				GC.RemoveMemoryPressure(Length);
+			}
+		}
+
+		// https://stackoverflow.com/questions/52190423/c-sharp-access-unmanaged-array-using-memoryt-or-arraysegmentt
+		private sealed unsafe class UnmanagedMemoryManager<T> : MemoryManager<T>
+			where T : unmanaged
+		{
+			private readonly T* _pointer;
+			private readonly int _length;
+
+			/// <summary>
+			/// Create a new UnmanagedMemoryManager instance at the given pointer and size
+			/// </summary>
+			public UnmanagedMemoryManager(T* pointer, int length)
+			{
+				if (length < 0) throw new ArgumentOutOfRangeException(nameof(length));
+				_pointer = pointer;
+				_length = length;
+			}
+			/// <summary>
+			/// Obtains a span that represents the region
+			/// </summary>
+			public override Span<T> GetSpan() => new Span<T>(_pointer, _length);
+
+			/// <summary>
+			/// Provides access to a pointer that represents the data (note: no actual pin occurs)
+			/// </summary>
+			public override MemoryHandle Pin(int elementIndex = 0)
+			{
+				if (elementIndex < 0 || elementIndex >= _length)
+					throw new ArgumentOutOfRangeException(nameof(elementIndex));
+				return new MemoryHandle(_pointer + elementIndex);
+			}
+
+			/// <summary>
+			/// Has no effect
+			/// </summary>
+			public override void Unpin() { }
+
+			/// <summary>
+			/// Releases all resources associated with this object
+			/// </summary>
+			protected override void Dispose(bool disposing) { }
+		}
+#endif
+
 #if NOT_IMPLEMENTED
 		internal const bool IsImplemented = false;
 #else
@@ -65,7 +142,11 @@ public int PixelHeight
 		}
 		#endregion
 
+#if !__ANDROID__
+		private UnmanagedArrayOfBytes? _buffer;
+#else
 		private byte[]? _buffer;
+#endif
 		private int _bufferSize;
 
 		/// <inheritdoc />
@@ -74,19 +155,19 @@ private protected override bool TryOpenSourceSync(int? targetWidth, int? targetH
 			var width = PixelWidth;
 			var height = PixelHeight;
 
-			if (_buffer is null || _bufferSize <= 0 || width <= 0 || height <= 0)
+			if (_buffer is not { } buffer || _bufferSize <= 0 || width <= 0 || height <= 0)
 			{
 				image = default;
 				return false;
 			}
 
-			image = Open(_buffer, _bufferSize, width, height);
+			image = Open(buffer, _bufferSize, width, height);
 			InvalidateImageSource();
 			return image.HasData;
 		}
 
 #if NOT_IMPLEMENTED
-		private static ImageData Open(byte[] buffer, int bufferLength, int width, int height)
+		private static ImageData Open(UnmanagedArrayOfBytes buffer, int bufferLength, int width, int height)
 			=> default;
 #endif
 
@@ -156,36 +237,42 @@ public IAsyncOperation<IBuffer> GetPixelsAsync()
 				{
 					return Task.FromResult<IBuffer>(new Buffer(Array.Empty<byte>()));
 				}
+
+#if !__ANDROID__
+				unsafe
+				{
+					var mem = new UnmanagedMemoryManager<byte>((byte*)_buffer.Pointer.ToPointer(), _bufferSize);
+					return Task.FromResult<IBuffer>(new Buffer(mem.Memory.Slice(0, _bufferSize)));
+				}
+#else
 				return Task.FromResult<IBuffer>(new Buffer(_buffer.AsMemory().Slice(0, _bufferSize)));
+#endif
 			});
 
 #if NOT_IMPLEMENTED
-		private (int ByteCount, int Width, int Height) RenderAsBgra8_Premul(UIElement element, ref byte[]? buffer, Size? scaledSize = null)
+		private (int ByteCount, int Width, int Height) RenderAsBgra8_Premul(UIElement element, ref UnmanagedArrayOfBytes? buffer, Size? scaledSize = null)
 			=> throw new NotImplementedException("RenderTargetBitmap is not supported on this platform.");
 #endif
 
-		void IDisposable.Dispose()
-		{
-			if (_buffer is not null)
-			{
-				ArrayPool<byte>.Shared.Return(_buffer);
-			}
-		}
-
 		#region Misc static helpers
 #if !NOT_IMPLEMENTED
+#if __ANDROID__
 		private static void EnsureBuffer(ref byte[]? buffer, int length)
 		{
-			if (buffer is null)
+			if (buffer is null || buffer.Length < length)
 			{
-				buffer = ArrayPool<byte>.Shared.Rent(length);
+				buffer = new byte[length];
 			}
-			else if (buffer.Length < length)
+		}
+#else
+		private static void EnsureBuffer(ref UnmanagedArrayOfBytes? buffer, int length)
+		{
+			if (buffer is null || buffer.Length < length)
 			{
-				ArrayPool<byte>.Shared.Return(buffer);
-				buffer = ArrayPool<byte>.Shared.Rent(length);
+				buffer = new UnmanagedArrayOfBytes(length);
 			}
 		}
+#endif
 #endif
 		#endregion
 	}

src/Uno.UI/UI/Xaml/Media/Imaging/RenderTargetBitmap.iOS.cs

@@ -23,11 +23,11 @@ partial class RenderTargetBitmap
 		private protected override bool IsSourceReady => _buffer != null;
 
 		/// <inheritdoc />
-		private static ImageData Open(byte[] buffer, int bufferLength, int width, int height)
+		private static ImageData Open(UnmanagedArrayOfBytes buffer, int bufferLength, int width, int height)
 		{
 			using var colorSpace = CGColorSpace.CreateDeviceRGB();
 			using var context = new CGBitmapContext(
-				buffer,
+				buffer.Pointer,
 				width,
 				height,
 				_bitsPerComponent,
@@ -44,7 +44,7 @@ private static ImageData Open(byte[] buffer, int bufferLength, int width, int he
 			return default;
 		}
 
-		private static (int ByteCount, int Width, int Height) RenderAsBgra8_Premul(UIElement element, ref byte[]? buffer, Size? scaledSize = null)
+		private static (int ByteCount, int Width, int Height) RenderAsBgra8_Premul(UIElement element, ref UnmanagedArrayOfBytes? buffer, Size? scaledSize = null)
 		{
 			var size = new Size(element.ActualSize.X, element.ActualSize.Y);
 			if (size == default)
@@ -85,7 +85,7 @@ private static (int ByteCount, int Width, int Height) RenderAsBgra8_Premul(UIEle
 
 				using var colorSpace = CGColorSpace.CreateDeviceRGB();
 				using var context = new CGBitmapContext(
-					buffer,
+					buffer!.Pointer,
 					width,
 					height,
 					_bitsPerComponent,

src/Uno.UI/UI/Xaml/Media/Imaging/RenderTargetBitmap.macOS.cs

@@ -21,11 +21,11 @@ partial class RenderTargetBitmap
 		/// <inheritdoc />
 		private protected override bool IsSourceReady => _buffer != null;
 
-		private static ImageData Open(byte[] buffer, int bufferLength, int width, int height)
+		private static ImageData Open(UnmanagedArrayOfBytes buffer, int bufferLength, int width, int height)
 		{
 			using var colorSpace = CGColorSpace.CreateDeviceRGB();
 			using var context = new CGBitmapContext(
-				buffer,
+				buffer.Pointer,
 				width,
 				height,
 				_bitsPerComponent,
@@ -42,7 +42,7 @@ private static ImageData Open(byte[] buffer, int bufferLength, int width, int he
 			return default;
 		}
 
-		private static (int ByteCount, int Width, int Height) RenderAsBgra8_Premul(UIElement element, ref byte[]? buffer, Size? scaledSize = null)
+		private static (int ByteCount, int Width, int Height) RenderAsBgra8_Premul(UIElement element, ref UnmanagedArrayOfBytes? buffer, Size? scaledSize = null)
 		{
 			var size = new Size(element.ActualSize.X, element.ActualSize.Y);
 
@@ -87,7 +87,7 @@ private static (int ByteCount, int Width, int Height) RenderAsBgra8_Premul(UIEle
 
 				using var colorSpace = CGColorSpace.CreateDeviceRGB();
 				using var context = new CGBitmapContext(
-					buffer,
+					buffer!.Pointer,
 					width,
 					height,
 					_bitsPerComponent,

src/Uno.UI/UI/Xaml/Media/Imaging/RenderTargetBitmap.skia.cs

@@ -15,30 +15,25 @@ partial class RenderTargetBitmap
 		private const int _bitsPerComponent = 8;
 		private const int _bytesPerPixel = _bitsPerPixel / _bitsPerComponent;
 
-		private static ImageData Open(byte[] buffer, int bufferLength, int width, int height)
+		private static ImageData Open(UnmanagedArrayOfBytes buffer, int bufferLength, int width, int height)
 		{
-			var bufferHandle = GCHandle.Alloc(buffer, GCHandleType.Pinned);
 			try
 			{
 				// Note: We use the FromPixelCopy which will create a clone of the buffer, so we are ready to be re-used to render another UIElement.
 				// (It's needed also if we swapped the buffer since we are not maintaining a ref on the swappedBuffer)
 				var bytesPerRow = width * _bytesPerPixel;
 				var info = new SKImageInfo(width, height, SKColorType.Bgra8888, SKAlphaType.Premul);
-				var image = SKImage.FromPixelCopy(info, bufferHandle.AddrOfPinnedObject(), bytesPerRow);
+				var image = SKImage.FromPixelCopy(info, buffer.Pointer, bytesPerRow);
 
 				return ImageData.FromCompositionSurface(new SkiaCompositionSurface(image));
 			}
 			catch (Exception error)
 			{
 				return ImageData.FromError(error);
 			}
-			finally
-			{
-				bufferHandle.Free();
-			}
 		}
 
-		private static (int ByteCount, int Width, int Height) RenderAsBgra8_Premul(UIElement element, ref byte[]? buffer, Size? scaledSize = null)
+		private static (int ByteCount, int Width, int Height) RenderAsBgra8_Premul(UIElement element, ref UnmanagedArrayOfBytes? buffer, Size? scaledSize = null)
 		{
 			var renderSize = element.RenderSize;
 			var visual = element.Visual;
@@ -74,7 +69,10 @@ private static (int ByteCount, int Width, int Height) RenderAsBgra8_Premul(UIEle
 
 			var byteCount = bitmap.ByteCount;
 			EnsureBuffer(ref buffer, byteCount);
-			bitmap.GetPixelSpan().CopyTo(buffer);
+			unsafe
+			{
+				bitmap.GetPixelSpan().CopyTo(new Span<byte>(buffer!.Pointer.ToPointer(), byteCount));
+			}
 			bitmap?.Dispose();
 			return (byteCount, width, height);
 		}