HBitmap -> WPF BitmapSource -> Avalonia Bitmap

GetBitmapFromHBitmap.cs

// First attempt
public static Bitmap GetBitmapFromHBitmap_1(IntPtr nativeHBitmap)
{
    var bitmapSource = Imaging.CreateBitmapSourceFromHBitmap(
        nativeHBitmap, IntPtr.Zero, Int32Rect.Empty, BitmapSizeOptions.FromEmptyOptions());

    // There were missing parentheses here (they are important because this is integer arithmetic.
    // Also worth noting, the code below only supports 32bpp images. In this case, stride
    // is always equal to width, so a micro-optim would be to not compute the stride.
    var stride = 4 * ((bitmapSource.PixelWidth * bitmapSource.Format.BitsPerPixel + 31) / 32);

    var destinationBuffer = new byte[stride * bitmapSource.PixelHeight];
    bitmapSource.CopyPixels(destinationBuffer, stride, 0);

    var pinned = GCHandle.Alloc(destinationBuffer, GCHandleType.Pinned);
    try
    {
        var pointer = pinned.AddrOfPinnedObject();

        var dpi = new Avalonia.Vector(bitmapSource.DpiX, bitmapSource.DpiY);
        var size = new PixelSize(bitmapSource.PixelWidth, bitmapSource.PixelHeight);
        var pixelFormat = bitmapSource.Format.BitsPerPixel == 32
            ? PixelFormat.Bgra8888
            : throw new NotSupportedException("Only 32bpp images are supported");

        return new Bitmap(pixelFormat, AlphaFormat.Unpremul, pointer, size, dpi, stride);
    }
    finally
    {
        pinned.Free();
    }
}

// Better attempt
public static Bitmap GetBitmapFromHBitmap_2(IntPtr nativeHBitmap)
{
    var bitmapSource = Imaging.CreateBitmapSourceFromHBitmap(
        nativeHBitmap, IntPtr.Zero, Int32Rect.Empty, BitmapSizeOptions.FromEmptyOptions());

    var dpi = new Avalonia.Vector(bitmapSource.DpiX, bitmapSource.DpiY);
    var size = new PixelSize(bitmapSource.PixelWidth, bitmapSource.PixelHeight);
    var pixelFormat = bitmapSource.Format.BitsPerPixel == 32
        ? PixelFormat.Bgra8888
        : throw new NotSupportedException("Only 32bpp images are supported");

    var bitmap = new Avalonia.Media.Imaging.WriteableBitmap(size, dpi, pixelFormat, AlphaFormat.Unpremul);
    using (var buffer = bitmap.Lock())
        bitmapSource.CopyPixels(new Int32Rect(0, 0, size.Width, size.Height), buffer.Address, buffer.RowBytes * size.Height, buffer.RowBytes);
    return bitmap;
}