Temp

gistfile1.txt

$(document).scroll(function() {
    var currentScrollTop = $(this).scrollTop();
    if (currentScrollTop > prevScrollTop) {
        //down
        var lasthiddenbox = $('.fadeboxhidden:last');
        var nextbox = (lasthiddenbox.length > 0) ? lasthiddenbox.next('.fadebox') : $('.fadebox:first');
        while (nextbox.length) {
            if (nextbox.offset().top < currentScrollTop) {
                nextbox.css('opacity', (currentScrollTop - nextbox.offset().top) / nextbox.outerHeight());
            }
            if ((nextbox.offset().top + nextbox.outerHeight()) < currentScrollTop)
            nextbox = nextbox.next('.fadebox');
        }        
    } else {
        //up          
    }
    prevScrollTop = currentScrollTop ;
});

//create an object to hold a list of box top locations
var boxtops = new Object;
//track whether user has scrolled up or down
var prevScrollTop = $(document).scrollTop();

//gather all boxes and store their top location
$('.fadebox').each( function(index) {    
    //you may want to dynamically generate div ids here based on index. I didn't do this
    //because i was already using the id for positioning.
    var divid = $(this).prop('id');
    boxtops[divid] = $(this).offset().top;
    //console.log(boxtops[divid]);    
});

​