XAML-Map-Control/MapControl/Avalonia/ImageLoader.Avalonia.cs

using Avalonia;
using Avalonia.Media;
using Avalonia.Media.Imaging;
using Avalonia.Platform;
using System;
using System.IO;
using System.Threading;
using System.Threading.Tasks;

namespace MapControl
{
    public static partial class ImageLoader
    {
        public static IImage LoadImage(Uri uri)
        {
            return new Bitmap(AssetLoader.Open(uri));
        }

        public static IImage LoadImage(Stream stream)
        {
            return new Bitmap(stream);
        }

        public static IImage LoadImage(string path)
        {
            return File.Exists(path) ? new Bitmap(path) : null;
        }

        public static Task<IImage> LoadImageAsync(Stream stream)
        {
            return Thread.CurrentThread.IsThreadPoolThread ?
                Task.FromResult(LoadImage(stream)) :
                Task.Run(() => LoadImage(stream));
        }

        public static Task<IImage> LoadImageAsync(string path)
        {
            return Thread.CurrentThread.IsThreadPoolThread ?
                Task.FromResult(LoadImage(path)) :
                Task.Run(() => LoadImage(path));
        }

        internal static async Task<IImage> LoadMergedImageAsync(Uri uri1, Uri uri2, IProgress<double> progress)
        {
            WriteableBitmap mergedBitmap = null;
            var p1 = 0d;
            var p2 = 0d;

            var images = await Task.WhenAll(
                LoadImageAsync(uri1, new Progress<double>(p => { p1 = p; progress.Report((p1 + p2) / 2d); })),
                LoadImageAsync(uri2, new Progress<double>(p => { p2 = p; progress.Report((p1 + p2) / 2d); })));

            if (images.Length == 2 &&
                images[0] is Bitmap bitmap1 &&
                images[1] is Bitmap bitmap2 &&
                bitmap1.PixelSize.Height == bitmap2.PixelSize.Height &&
                bitmap1.Format.HasValue &&
                bitmap1.Format == bitmap2.Format &&
                bitmap1.AlphaFormat.HasValue &&
                bitmap1.AlphaFormat == bitmap2.AlphaFormat)
            {
                var bpp = bitmap1.Format.Value == PixelFormat.Rgb565 ? 2 : 4;
                var pixelSize = new PixelSize(bitmap1.PixelSize.Width + bitmap2.PixelSize.Width, bitmap1.PixelSize.Height);
                var stride1 = bpp * bitmap1.PixelSize.Width;
                var stride = bpp * pixelSize.Width;
                var bufferSize = stride * pixelSize.Height;

                unsafe
                {
                    fixed (byte* ptr = new byte[stride * pixelSize.Height])
                    {
                        var buffer = (nint)ptr;

                        bitmap1.CopyPixels(new PixelRect(bitmap1.PixelSize), buffer, bufferSize, stride);
                        bitmap2.CopyPixels(new PixelRect(bitmap2.PixelSize), buffer + stride1, bufferSize, stride);

                        mergedBitmap = new WriteableBitmap(bitmap1.Format.Value, bitmap1.AlphaFormat.Value, buffer, pixelSize, bitmap1.Dpi, stride);
                    }
                }
            }

            return mergedBitmap;
        }
    }
}