private static async Task <IStorageFile> SaveThumbnail(int id, DjvuDocument document)
{
var page = await document.GetPageAsync(1);
var maxWidth = 140 * DisplayInformation.GetForCurrentView().RawPixelsPerViewPixel;
var aspectRatio = (double)page.Width / page.Height;
var width = (uint)Math.Min(maxWidth, page.Width);
var height = (uint)(width / aspectRatio);
var bitmap = new WriteableBitmap((int)width, (int)height);
await page.RenderRegionAsync(
bitmap : bitmap,
rescaledPageSize : new BitmapSize {
Width = width, Height = height
},
renderRegion : new BitmapBounds {
Width = width, Height = height
});
var booksFolder = await ApplicationData.Current.LocalFolder.CreateFolderAsync("Books", CreationCollisionOption.OpenIfExists);
var thumbnailFile = await booksFolder.CreateFileAsync($"{id}.jpg", CreationCollisionOption.ReplaceExisting);
using (var thumbnailStream = await thumbnailFile.OpenAsync(FileAccessMode.ReadWrite))
{
var encoder = await BitmapEncoder.CreateAsync(BitmapEncoder.JpegEncoderId, thumbnailStream);
encoder.SetPixelData(
pixelFormat: BitmapPixelFormat.Bgra8,
alphaMode: BitmapAlphaMode.Ignore,
width: (uint)bitmap.PixelWidth,
height: (uint)bitmap.PixelHeight,
dpiX: 96.0,
dpiY: 96.0,
pixels: bitmap.PixelBuffer.ToArray());
await encoder.FlushAsync();
}
return(thumbnailFile);
}
