Avoid reset of scroll positions

[arrix]

by adding the page scroll offsets to the bounding rect.

[niklasvh]

Global within html2canvas should be fine (everything within the script gets wrapped anyway). Caching does matter: http://jsperf.com/cache-scroll

[sjamaan]

I would really like to see a fix like this.

I've been debugging for a full work day today only to find out that Android's Webview, like the piece of shit that it is, won't update the page.scrollYOffset upon window.scrollTo(). (the view is visually scrolled up, however!)

This means the scroll position is also not reflected in the calculations that are performed by getBoundingClientRect(), which means that if you take a "screenshot" of one HTML element while scrolled down, you'll end up with a canvas that "has its head chopped off". In other words, html2canvas thinks it's still scrolled down so it'll skip too many Y coordinates in the source canvas when copying the image to the destination canvas.

The horrible hacky workaround I have now is that I hook the scroll event using jQuery.one(), then scroll up. The event handler for the scroll event will call html2canvas. So far it looks like the event is consistently fired after the position has been updated.

[niklasvh]

This is fixed in 0.5