Proper queued, progress, failed states

[aseemk]

Thanks @nein09 for implementing some handling of not-ready state in the embed!

Not urgent, but at some point, we should revisit that and round it out:

• We should use proper accessible HTML etc., rather than a DZI.
• Ideally, it'd be a proper progress bar, requiring us to actually track progress on the back-end.
• Either way, the queued/progress UI should auto-update.

Most importantly, the view page needs this feature too. To achieve that, we should:

• Make a shared "viewer" component that both the embed and the view page use.

From memory, Zoom.it did that. There was a shared component that was a thin wrapper around the Seadragon combo viewer, which took the content info and showed either an error message, queued/progress state, or the actual DZI, depending on the content info.

[nein09]

It seems to me that the most elegant solution to this is to implement some kind of progress callback in the DeepZoomTools, but maybe there's a better way to do it in Node that I don't know about.

[aseemk]

That would work (perhaps the more "Node" way is to emit a progress event instead), but I think the trickier thing might be seeing if VIPS conveys progress at all.

[nein09]

If VIPS won't do it, we could look at the number of levels that need to be written versus what's actually on disk at the moment.

[aseemk]

Nice idea! Could even look at the actual generated tiles.

So this'd be setInterval (+ clearInterval when done) + fs.readdir.

[aseemk]

Expanded the title to cover that we need to display a "failed" state too.

E.g. http://zoomhub.net/v1/content/Yev6 reports failed: true, but http://zoomhub.net/Yev6 doesn't.

[aseemk]

Opened zoomhub/node-deepzoomtools#10 to emit progress there.