How do i track view count of different div blocks on single page while scrolling without clicking them.

I have many cards (div blocks) on my single page application. I want to track view counts when user scroll through this page. Means whenever one card visible on screen or in screen viewport area while scrolling just increment view count for that perticular card (div blocks). Its like Facebook tracking pixel thing but i want ot create custom and different tracking pixel for my cards which track view counts when div is visible.
I am using Ruby on Rails and Angularjs.
Thank you.