Check if element is visible for certain percentage on screen (viewport)?

javascript, jquery

Solution

Jquery.fracs plugin seems to do exactly what you need.

function callback(fracs: Fractions, previousFracs: Fractions) {
    if(fracs > 0.5)
      doSomething();
};

var fracs = $("img").fracs(callback);

Problem

How can i detect if some element is visible? For better understading look at the image below. I want to fire event when the image is half-visible. It would be great if it would work for all browsers and devices (tablets and smartphones).

Original source