jparalax

/** paralax plugin **/
(function($) {
$.fn.jparalax = function ( options, startcallback, finishcallback ) {
    var $this = this;
    var settings = {
		effect 		: 'fixedbackground',
		speed		: 100,
		container	: window
	};

    startcallback 	= startcallback ? startcallback : [];
    finishcallback 	= finishcallback ? finishcallback : [];

    var options = $.extend( {}, settings, options );

    return this.each(function (i) {
    	if($(this).attr('data-parent')) {
    		var parent 		= "#" + $(this).attr('data-parent');
    		var element		= $(parent);
    		var child 		= $(this);
    		var childpos 	= $(child).position();

    		/** data center **/
            if($(child).attr('data-top') == 'center'){
            	var datatop = ( $(window).height() - $(child).height()) / 2;
            	$(child).attr('data-top', datatop).css("top", datatop + "px");
            }
    	} else {
    		var element		= $(this);
    	}

    	var position 	= $(element).offset();
		var o 			= options;
		var $container 	= $(o.container);
		var speed 		= o.speed;
		var effect		= o.effect;
        var bgpos 		= $(element).css('backgroundPosition').split(" ");

        var useragent	= detectbrowser();



        function detectbrowser() {
        	 if (navigator.userAgent.indexOf('Firefox') != -1 && parseFloat(navigator.userAgent.substring(navigator.userAgent.indexOf('Firefox') + 8)) >= 3.6){//Firefox
        		 return "firefox";
    		 } else if (navigator.userAgent.indexOf('Chrome') != -1 && parseFloat(navigator.userAgent.substring(navigator.userAgent.indexOf('Chrome') + 7).split(' ')[0]) >= 15){//Chrome
    			 return "chrome";
    		 } else if(navigator.userAgent.indexOf('Safari') != -1 && navigator.userAgent.indexOf('Version') != -1 && parseFloat(navigator.userAgent.substring(navigator.userAgent.indexOf('Version') + 8).split(' ')[0]) >= 5){//Safari
    			 return "safari";
    		 } else{
    			 return "unknown";
    		 }
        }

		function calcpos() {
			var minpos = position.top - $container.height();
			var maxpos = position.top + $(element).height() + $('nav').height();

			return {
				'min'	: minpos,
				'max'	: maxpos,
				'diff'	: ( maxpos - minpos )
			};
		}

		function fixedbackground(ratio, scrollpos, dpos){
			var bgposresult = parseInt(bgpos[1]) - ( ratio * speed );
			var newposition = bgpos[0] + " " + bgposresult + "px";
			 $(element).css('background-position', newposition);
		}

		function staytop(scrollpos, ratio, dpos) {

			var thistop = scrollpos - position.top + parseInt($(child).attr("data-top")) + $('nav').height();
			thistop = ( thistop - ( ratio * speed ) ) + "px";
			$(child).css("top", thistop);

			/*
			if( scrollpos > ( position.top - $('nav').height() ) ) {
				var unknownvar = ( ( position.top - $('nav').height() ) / dpos.diff ) * speed;
				var thistop = ( scrollpos - position.top + parseInt($(child).attr("data-top")) + $('nav').height() + unknownvar );
				thistop = ( thistop - ( ratio * speed ) ) + "px";
				$(child).css("top", thistop);
			} else {
				$(child).css("top", $(child).attr("data-top") + "px");
			}
			*/
		}

		function staytopfixed(scrollpos, ratio, dpos) {
			if( scrollpos > ( position.top - $('nav').height() )) {
			} else {
				$(child).css("top", $(child).attr("data-top") + "px").css("position", "relative");
			}
		}

	    function doparalax() {
	    	var dpos = calcpos();
	    	var scrollpos = $(window).scrollTop();

	    	if( scrollpos >= dpos.min && scrollpos <= dpos.max) {
	    		if(effect == 'fixedbackground') {
		    		var ratio = ( scrollpos - dpos.min ) / dpos.diff;
		    		fixedbackground(ratio, scrollpos, dpos);
	    		} else if (effect = 'staytop') {
	    			var ratio = ( scrollpos - dpos.min ) / dpos.diff;

	    			if(useragent == "firefox") {
	    				staytop(scrollpos, ratio, dpos);
	    			} else {
	    				staytopfixed(scrollpos, ratio, dpos);
	    			}
	    		}
	    	}
	    }


	    $container.bind('scroll load resize', function(e){
      	  	doparalax();
        });
    });
};
})(jQuery);