fx.js

/*
---
name: fx
description: very basic animation logic.
authors:
- "[Valerio Proietti](http://mad4milk.net)"
- "[Thomas Aylott](http://subtlegradient.com)"
license: "[MIT](http://mootools.net/license.txt)"
provides: fx
...
*/


(function(exports){

var UID = 0, toString = ({}).toString,
	instances = {}, timer, fps = 60;

function isArray(object){
	return toString.call(object) == '[object Array]';
}

exports.fx = fx;

function fx(options){
	if (!this instanceof fx) return new fx(options);

	options = options || {};
	
	var self = this,
		
		uid = (UID++).toString(36),
		duration = options.duration || 500,
		behavior = options.behavior || 'cancel',
		
		render = options.render || function(){},
		callBack = options.callBack || function(){},
		equation = options.equation || function(p){
			return -(Math.cos(Math.PI * p) - 1) / 2;
		},
	
		stack = [], from, to, time, timer
	;
	
	self.start = function(f, t){
		
		if (timer){
			if (behavior == 'cancel') self.stop();
			else {
				if (behavior == 'stack') stack.push(function(){
					self.start(f, t);
				});
				return self;
			}
		}
		
		from = !isArray(f) ? [f] : f;
		to = !isArray(t) ? [t] : t;
		
		time = +(new Date);
		timer = addInstance(uid, self);

		return self;
	};
	
	self.step = function(){
		var now = +(new Date),
			factor = (now - time) / duration;
		
		if (factor >= 1) factor = 1;
		
		var computations = [],
			delta = equation(factor);
		
		for (var i = 0, l = from.length; i < l; i++)
			computations[i] = compute(from[i], to[i], delta);
		
		render.apply(self, computations);
		
		if (factor == 1){
			self.stop();
			var next = stack.shift();
			if (next) next();
			callBack();
		}
	};
	
	self.stop = function(){
		timer = removeInstance(uid, self);
		return self;
	};
	
};

function compute(from, to, delta){
	return (to - from) * delta + from;
};

function loop(){
	for (var uid in instances) instances[uid].step();
};

function addInstance(uid, instance){
	instances[uid] = instance;
	if (!timer) timer = setInterval(loop, Math.round(1000 / fps));
	return 1;
};

function removeInstance(uid, instance){
	delete instances[uid];
	if (timer){
		var length = 0;
		for (uid in instances) length++;
		if (!length) timer = clearInterval(timer);
	}
	return 0;
};

})(typeof exports != 'undefined' ? exports : this);