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/**
 * Behaves the same as setTimeout except uses requestAnimationFrame() where possible for better performance
 * @param {function} fn The callback function
 * @param {int} delay The delay in milliseconds
 */

window.requestTimeout = function(fn, delay) {
	if( !window.requestAnimationFrame      	&& 
		!window.webkitRequestAnimationFrame && 
		!(window.mozRequestAnimationFrame && window.mozCancelRequestAnimationFrame) && // Firefox 5 ships without cancel support
		!window.oRequestAnimationFrame      && 
		!window.msRequestAnimationFrame)
			return window.setTimeout(fn, delay);
			
	var start = new Date().getTime(),
		handle = new Object();
		
	function loop(){
		var current = new Date().getTime(),
			delta = current - start;
			
		delta >= delay ? fn.call() : handle.value = requestAnimFrame(loop);
	};
	
	handle.value = requestAnimFrame(loop);
	return handle;
};

/**
 * Behaves the same as clearTimeout except uses cancelRequestAnimationFrame() where possible for better performance
 * @param {int|object} fn The callback function
 */
window.clearRequestTimeout = function(handle) {
    window.cancelAnimationFrame ? window.cancelAnimationFrame(handle.value) :
    window.webkitCancelAnimationFrame ? window.webkitCancelAnimationFrame(handle.value) :
    window.webkitCancelRequestAnimationFrame ? window.webkitCancelRequestAnimationFrame(handle.value) : /* Support for legacy API */
    window.mozCancelRequestAnimationFrame ? window.mozCancelRequestAnimationFrame(handle.value) :
    window.oCancelRequestAnimationFrame	? window.oCancelRequestAnimationFrame(handle.value) :
    window.msCancelRequestAnimationFrame ? window.msCancelRequestAnimationFrame(handle.value) :
    clearTimeout(handle);
};

/**
 * Behaves the same as setInterval except uses requestAnimationFrame() where possible for better performance
 * @param {function} fn The callback function
 * @param {int} delay The delay in milliseconds
 */
window.requestInterval = function(fn, delay) {
	if( !window.requestAnimationFrame       && 
		!window.webkitRequestAnimationFrame && 
		!(window.mozRequestAnimationFrame && window.mozCancelRequestAnimationFrame) && // Firefox 5 ships without cancel support
		!window.oRequestAnimationFrame      && 
		!window.msRequestAnimationFrame)
			return window.setInterval(fn, delay);
			
	var start = new Date().getTime(),
		handle = new Object();
		
	function loop() {
		var current = new Date().getTime(),
			delta = current - start;
			
		if(delta >= delay) {
			fn.call();
			start = new Date().getTime();
		}

		handle.value = requestAnimFrame(loop);
	};
	
	handle.value = requestAnimFrame(loop);
	return handle;
}

/**
 * Behaves the same as clearInterval except uses cancelRequestAnimationFrame() where possible for better performance
 * @param {int|object} fn The callback function
 */
    window.clearRequestInterval = function(handle) {
    window.cancelAnimationFrame ? window.cancelAnimationFrame(handle.value) :
    window.webkitCancelAnimationFrame ? window.webkitCancelAnimationFrame(handle.value) :
    window.webkitCancelRequestAnimationFrame ? window.webkitCancelRequestAnimationFrame(handle.value) : /* Support for legacy API */
    window.mozCancelRequestAnimationFrame ? window.mozCancelRequestAnimationFrame(handle.value) :
    window.oCancelRequestAnimationFrame	? window.oCancelRequestAnimationFrame(handle.value) :
    window.msCancelRequestAnimationFrame ? window.msCancelRequestAnimationFrame(handle.value) :
    clearInterval(handle);
};

// requestAnimationFrame() shim by Paul Irish
// http://paulirish.com/2011/requestanimationframe-for-smart-animating/
window.requestAnimFrame = (function() {
	return  window.requestAnimationFrame       || 
			window.webkitRequestAnimationFrame || 
			window.mozRequestAnimationFrame    || 
			window.oRequestAnimationFrame      || 
			window.msRequestAnimationFrame     || 
			function(/* function */ callback, /* DOMElement */ element){
				window.setTimeout(callback, 1000 / 60);
			};
})();

Drop in replace functions for setTimeout() & setInterval() that 
make use of requestAnimationFrame() for performance where available
http://www.joelambert.co.uk

Copyright 2011, Joe Lambert.
Free to use under the MIT license.
http://www.opensource.org/licenses/mit-license.php