$(document).ready(function() {

    $("#button1").click(function() {
        scrollToPage(0, this);
        return false;
    });

    $("#button2").click(function() {
        scrollToPage(1, this);
        return false;
    });

    $("#button3").click(function() {
        scrollToPage(2, this);
        return false;
    });

    scrollToPage(0, $("#button1"));
});

function scrollToPage(page, el) {
    updateSelectedPage(el);

    var bgOffset = -page * 1000;
    var layer1Offset = -page * 2250;
    var layer2Offset = -page * 1750;

    $("#layer_bkgrd .wrapper").animate({ left: bgOffset }, { duration: 1500, queue: false, complete: function() { updateSelectedPage(el); } });
    $("#layer_2 .wrapper").animate({ left: layer2Offset }, { duration: 1500, queue: false });
    $("#layer_1 .wrapper").animate({ left: layer1Offset }, { duration: 1500, queue: false });
}

function updateSelectedPage(el) {
    $('#slide_nav li a').removeClass('on');
    $(el).addClass('on');
}