/*
plugin: jquery parallax
version 1.1.3
author: ian lunn
twitter: @ianlunn
author url: http://www.ianlunn.co.uk/
plugin url: http://www.ianlunn.co.uk/plugins/jquery-parallax/

dual licensed under the mit and gpl licenses:
http://www.opensource.org/licenses/mit-license.php
http://www.gnu.org/licenses/gpl.html
*/

(function( jquery ){
	var jquerywindow = jquery(window);
	var windowheight = jquerywindow.height();

	jquerywindow.resize(function () {
		windowheight = jquerywindow.height();
	});

	jquery.fn.parallax = function(xpos, speedfactor, outerheight) {
		var jquerythis = jquery(this);
		var getheight;
		var firsttop;
		var paddingtop = 0;
		
		//get the starting position of each element to have parallax applied to it		
		jquerythis.each(function(){
		    firsttop = jquerythis.offset().top;
		});

		if (outerheight) {
			getheight = function(jqo) {
				return jqo.outerheight(true);
			};
		} else {
			getheight = function(jqo) {
				return jqo.height();
			};
		}
			
		// setup defaults if arguments aren't specified
		if (arguments.length < 1 || xpos === null) xpos = "50%";
		if (arguments.length < 2 || speedfactor === null) speedfactor = 0.1;
		if (arguments.length < 3 || outerheight === null) outerheight = true;
		
		// function to be called whenever the window is scrolled or resized
		function update(){
			var pos = jquerywindow.scrolltop();				

			jquerythis.each(function(){
				var jqueryelement = jquery(this);
				var top = jqueryelement.offset().top;
				var height = getheight(jqueryelement);

				// check if totally above or totally below viewport
				if (top + height < pos || top > pos + windowheight) {
					return;
				}


				jquerythis.css('backgroundposition', xpos + " " + math.round((top - pos) * speedfactor) + "px");


			});
		}		

		jquerywindow.bind('scroll', update).resize(update);
		update();
	};
})(jquery);