Sorry I just noticed there was a bug with Safari iOS where webp was not being show so the viewport for the browser was invisible. This could have affected a lot of people. Fixed now.
Sorry there's a bug where you can bork it with "while(true)" I'm working on a better sandbox. I'll probably repost later if I have something that works! :)
So it's not open source, but... a big part is open source[1]
[1]: https://github.com/i5ik/ViewFinderJS
You can check it out. :) Thank you for saying nice tool, I appreciate that! :)