/// <summary>
/// Initialize with the page that we should track.
/// </summary>
/// <param name="pageInfo">A stream of cache tags and the PDF pages associated with it.</param>
/// <remarks>We are really only interested in the first PdfPage we get - and we will re-subscribe, but not hold onto it.</remarks>
public PDFPageViewModel(IObservable <Tuple <string, IObservable <PdfPage> > > pageInfo, IBlobCache cache = null)
{
_cache = cache ?? Blobs.LocalStorage;
// Render an image when:
// - We have at least one render request
// - ImageStream is subscribed to
// - the file or page updates somehow (new pageInfo iteration).
//
// Always pull from the cache first, but if that doesn't work, then render and place
// in the cache.
// Get the size of the thing when it is requested. This sequence must be finished before
// any size calculations can be done!
var imageSize = from pgInfo in pageInfo
from sz in _cache.GetOrFetchPageSize(pgInfo.Item1, () => pgInfo.Item2.Take(1).Select(pdf => pdf.Size.ToIWalkerSize()))
select new
{
PGInfo = pgInfo,
Size = sz
};
var publishedSize = imageSize
.Do(info => _pageSize = info.Size)
.Select(info => info.PGInfo)
.Publish().RefCount();
_pageSizeLoaded = publishedSize.AsUnit();
// The render request must be "good" - that is well formed. Otherwise
// we will just ignore it. This is because sometimes when things are being "sized" the
// render request is malformed.
RenderImage = ReactiveCommand.Create();
var renderRequest = RenderImage
.Cast <Tuple <RenderingDimension, double, double> >()
.Where(info => (info.Item1 == RenderingDimension.Horizontal && info.Item2 > 0) ||
(info.Item1 == RenderingDimension.Vertical && info.Item3 > 0) ||
(info.Item1 == RenderingDimension.MustFit && info.Item2 > 0 && info.Item3 > 0)
);
// Generate an image when we have a render request and a everything else is setup.
ImageStream = from requestInfo in Observable.CombineLatest(publishedSize, renderRequest, (pSize, rr) => new { pgInfo = pSize, RenderRequest = rr })
let imageDimensions = CalcRenderingSize(requestInfo.RenderRequest.Item1, requestInfo.RenderRequest.Item2, requestInfo.RenderRequest.Item3)
from imageData in _cache.GetOrFetchPageImageData(requestInfo.pgInfo.Item1, imageDimensions.Item1, imageDimensions.Item2,
() => requestInfo.pgInfo.Item2.SelectMany(pdfPg =>
{
var ms = new MemoryStream();
var ra = WindowsRuntimeStreamExtensions.AsRandomAccessStream(ms);
var opt = new PdfPageRenderOptions()
{
DestinationWidth = (uint)imageDimensions.Item1, DestinationHeight = (uint)imageDimensions.Item2
};
return(Observable.FromAsync(() => pdfPg.RenderToStreamAsync(ra).AsTask())
.Select(_ => ms.ToArray()));
}))
select new MemoryStream(imageData);
}