This is a keyword rank tracker I build using Node.js that tracks pixel position as well as standard position in Google. To do this requires a proxy provider. I used Trusted Proxies because they were really easy to use but I'm sure others would work.
This Google position rank tracker can track pixel positions on both mobile and desktop browsers. Right now it runs sychnronously, but I'm playing around with adding async functionality to it, maybe I'll finish that eventually.
I'm sure that the CSS selectors I was using to find specific desktop/mobile elements on Google's pages no longer work completely because Google constantly changes them and I haven't kept them up to date. But for anyone looking to get pixel rankings from Google this Puppeteer cralwer is a great start!