SKCGSurfaceFactory.cs

using System;
using System.Runtime.InteropServices;
using CoreGraphics;
using Foundation;

#if __TVOS__
namespace SkiaSharp.Views.tvOS
#elif __WATCHOS__
namespace SkiaSharp.Views.watchOS
#elif __IOS__
namespace SkiaSharp.Views.iOS
#elif __MACOS__
namespace SkiaSharp.Views.Mac
#endif
{
	internal class SKCGSurfaceFactory : IDisposable
	{
		private const int BitsPerByte = 8; // 1 byte = 8 bits
		private const CGBitmapFlags BitmapFlags = CGBitmapFlags.ByteOrder32Big | CGBitmapFlags.PremultipliedLast;

		private NSMutableData bitmapData;
		private CGDataProvider dataProvider;

		public SKImageInfo Info { get; private set; }

		public SKSurface CreateSurface(CGRect contentsBounds, nfloat scale, out SKImageInfo info)
		{
			// apply a scale
			contentsBounds.Width *= scale;
			contentsBounds.Height *= scale;

			// get context details
			Info = info = CreateInfo((int)contentsBounds.Width, (int)contentsBounds.Height);

			// if there are no pixels, clean up and return
			if (info.Width == 0 || info.Height == 0)
			{
				Dispose();
				return null;
			}

			// if the memory size has changed, then reset the underlying memory
			if (bitmapData?.Length != (nuint)info.BytesSize)
				FreeBitmap();

			// allocate a memory block for the drawing process
			if (bitmapData == null)
			{
				bitmapData = NSMutableData.FromLength(info.BytesSize);
				dataProvider = new CGDataProvider(bitmapData.MutableBytes, info.BytesSize, Dummy);

				void Dummy(IntPtr data)
				{
					// do nothing as we manage the memory separately
				}
			}

			return SKSurface.Create(info, bitmapData.MutableBytes, info.RowBytes);
		}

		public void DrawSurface(CGContext ctx, CGRect viewBounds, SKImageInfo info, SKSurface surface)
		{
			if (info.Width == 0 || info.Height == 0)
				return;

			surface.Canvas.Flush();

			// draw the image onto the context
			using (var colorSpace = CGColorSpace.CreateDeviceRGB())
			using (var image = new CGImage(info.Width, info.Height, BitsPerByte, info.BytesPerPixel * BitsPerByte, info.RowBytes, colorSpace, BitmapFlags, dataProvider, null, false, CGColorRenderingIntent.Default))
			{
#if __IOS__ || __TVOS__ || __WATCHOS__ || HAS_UNO
				// we need to flip the image as we are mixing CoreGraphics and UIKit functions:
				// https://developer.apple.com/library/ios/documentation/2DDrawing/Conceptual/DrawingPrintingiOS/GraphicsDrawingOverview/GraphicsDrawingOverview.html#//apple_ref/doc/uid/TP40010156-CH14-SW26
				ctx.SaveState();
				ctx.TranslateCTM(0, viewBounds.Height);
				ctx.ScaleCTM(1, -1);
				// draw the image
				ctx.DrawImage(viewBounds, image);
				ctx.RestoreState();
#elif __MACOS__
				// draw the image
				ctx.DrawImage(viewBounds, image);
#else
#error Plaform-specific code missing
#endif
			}
		}

		public void Dispose()
		{
			// make sure we free the image data
			FreeBitmap();
			Info = CreateInfo(0, 0);
		}

		private void FreeBitmap()
		{
			dataProvider?.Dispose();
			dataProvider = null;
			bitmapData?.Dispose();
			bitmapData = null;
		}

		private SKImageInfo CreateInfo(int width, int height) =>
			new SKImageInfo(width, height, SKColorType.Rgba8888, SKAlphaType.Premul);
	}
}