Originally Posted by KevinH
Also you would not need get all of calibre running, just the viewers part of the code. I agree this would be a lot of work but should be doable depending on the requirements of the viewer software.
The viewer requires the entire conversion engine. Which requires Qt. The viewer only supports displaying EPUB. So, every format is first converted to EPUB before being displayed. This can take a few minutes on a modern desktop so I don't want to think trying it on a phone. The viewer also uses a QWebView (WebKit widget) to display the pages.