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function scrollTo(Y, duration, easingFunction, callback) {
var start = Date.now(),
elem = document.documentElement.scrollTop?document.documentElement:document.body,
from = elem.scrollTop;
if(from === Y) {
callback();
return; /* Prevent scrolling to the Y point if already there */
}
function min(a,b) {
return a<b?a:b;
}
function scroll(timestamp) {
var currentTime = Date.now(),
time = min(1, ((currentTime - start) / duration)),
easedT = easingFunction(time);
elem.scrollTop = (easedT * (Y - from)) + from;
if(time < 1) requestAnimationFrame(scroll);
else
if(callback) callback();
}
requestAnimationFrame(scroll)
}
/* bits and bytes of the scrollTo function inspired by the works of Benjamin DeCock */
/*
* Easing Functions - inspired from http://gizma.com/easing/
* only considering the t value for the range [0, 1] => [0, 1]
*/
var easing = {
// no easing, no acceleration
linear: function (t) { return t },
// accelerating from zero velocity
easeInQuad: function (t) { return t*t },
// decelerating to zero velocity
easeOutQuad: function (t) { return t*(2-t) },
// acceleration until halfway, then deceleration
easeInOutQuad: function (t) { return t<.5 ? 2*t*t : -1+(4-2*t)*t },
// accelerating from zero velocity
easeInCubic: function (t) { return t*t*t },
// decelerating to zero velocity
easeOutCubic: function (t) { return (--t)*t*t+1 },
// acceleration until halfway, then deceleration
easeInOutCubic: function (t) { return t<.5 ? 4*t*t*t : (t-1)*(2*t-2)*(2*t-2)+1 },
// accelerating from zero velocity
easeInQuart: function (t) { return t*t*t*t },
// decelerating to zero velocity
easeOutQuart: function (t) { return 1-(--t)*t*t*t },
// acceleration until halfway, then deceleration
easeInOutQuart: function (t) { return t<.5 ? 8*t*t*t*t : 1-8*(--t)*t*t*t },
// accelerating from zero velocity
easeInQuint: function (t) { return t*t*t*t*t },
// decelerating to zero velocity
easeOutQuint: function (t) { return 1+(--t)*t*t*t*t },
// acceleration until halfway, then deceleration
easeInOutQuint: function (t) { return t<.5 ? 16*t*t*t*t*t : 1+16*(--t)*t*t*t*t }
}
/* Add the following to you main js file
// http://paulirish.com/2011/requestanimationframe-for-smart-animating/
// http://my.opera.com/emoller/blog/2011/12/20/requestanimationframe-for-smart-er-animating
// requestAnimationFrame polyfill by Erik Möller
// fixes from Paul Irish and Tino Zijdel
(function() {
var lastTime = 0;
var vendors = ['ms', 'moz', 'webkit', 'o'];
for(var x = 0; x < vendors.length && !window.requestAnimationFrame; ++x) {
window.requestAnimationFrame = window[vendors[x]+'RequestAnimationFrame'];
window.cancelAnimationFrame = window[vendors[x]+'CancelAnimationFrame']
|| window[vendors[x]+'CancelRequestAnimationFrame'];
}
if (!window.requestAnimationFrame)
window.requestAnimationFrame = function(callback, element) {
var currTime = new Date().getTime();
var timeToCall = Math.max(0, 16 - (currTime - lastTime));
var id = window.setTimeout(function() { callback(currTime + timeToCall); },
timeToCall);
lastTime = currTime + timeToCall;
return id;
};
if (!window.cancelAnimationFrame)
window.cancelAnimationFrame = function(id) {
clearTimeout(id);
};
}()); */
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