https://codepen.io/almosnow/pen/abEXBZP?editors=0011

(at the end of the blur pass it prints the elapsed time to the console)

You're right, it does get kind of slow at 2x, but not that slow, on my laptop it takes around 1 sec/page, while on your site takes 20-30 secs/page. Also, my very naive code does not take into account "warming up" and some other code optimizations to make the blur much faster, you could easily get it down to 100ms/page, I'm sure!

Best luck!

1. https://gist.github.com/andyrbell/25c8632e15d17c83a54602f6ac...

There's something extremely wrong with your implementation as it just takes too much to render every page.

I've done plenty of work in the past with both canvas and pdf.js (which is what you're using) and it shouldn't be that slow, at all. Perhaps you have a rogue loop that's calling a very expensive function on each pixel of every page, maybe?

Who knows, but for sure performance on that could be near real-time.