Screenshot.uwp.cs

using System;
using System.IO;
using System.Runtime.InteropServices.WindowsRuntime;
using System.Threading.Tasks;
using Windows.Graphics.Imaging;
using Windows.Storage.Streams;
using Windows.UI.Xaml;
using Windows.UI.Xaml.Media.Imaging;

namespace Xamarin.Essentials
{
    public static partial class Screenshot
    {
        internal static bool PlatformIsCaptureSupported =>
            true;

        static async Task<ScreenshotResult> PlatformCaptureAsync()
        {
            var element = Window.Current?.Content as FrameworkElement;
            if (element == null)
                throw new InvalidOperationException("Unable to find main window content.");

            var bmp = new RenderTargetBitmap();

            // NOTE: Return to the main thread so we can access view properties such as
            //       width and height. Do not ConfigureAwait!
            await bmp.RenderAsync(element);

            // get the view information first
            var width = bmp.PixelWidth;
            var height = bmp.PixelHeight;

            // then potentially move to a different thread
            var pixels = await bmp.GetPixelsAsync().AsTask().ConfigureAwait(false);

            return new ScreenshotResult(width, height, pixels);
        }
    }

    public partial class ScreenshotResult
    {
        readonly byte[] bytes;

        public ScreenshotResult(int width, int height, IBuffer pixels)
        {
            Width = width;
            Height = height;
            bytes = pixels?.ToArray() ?? throw new ArgumentNullException(nameof(pixels));
        }

        internal async Task<Stream> PlatformOpenReadAsync(ScreenshotFormat format)
        {
            var f = format switch
            {
                ScreenshotFormat.Jpeg => BitmapEncoder.JpegEncoderId,
                _ => BitmapEncoder.PngEncoderId
            };

            var ms = new InMemoryRandomAccessStream();

            var encoder = await BitmapEncoder.CreateAsync(f, ms).AsTask().ConfigureAwait(false);
            encoder.SetPixelData(BitmapPixelFormat.Bgra8, BitmapAlphaMode.Ignore, (uint)Width, (uint)Height, 96, 96, bytes);
            await encoder.FlushAsync().AsTask().ConfigureAwait(false);

            return ms.AsStreamForRead();
        }
    }
}