//** jquery scroll to top control script- (c) dynamic drive dhtml code library: http://www.dynamicdrive.com.
//** available/ usage terms at http://www.dynamicdrive.com (march 30th, 09')
//** v1.1 (april 7th, 09'):
//** 1) adds ability to scroll to an absolute position (from top of page) or specific element on the page instead.
//** 2) fixes scroll animation not working in opera. 


var scrolltotop={
	//startline: integer. number of pixels from top of doc scrollbar is scrolled before showing control
	//scrollto: keyword (integer, or "scroll_to_element_id"). how far to scroll document up when control is clicked on (0=top).
	setting: {startline:100, scrollto: 0, scrollduration:1000, fadeduration:[500, 100]},
	controlhtml: '<img src="/hdimg/hdbas/up.gif"/>', //html for control, which is auto wrapped in div w/ id="topcontrol"
	controlattrs: {offsetx:20, offsety:20}, //offset of control relative to right/ bottom of window corner
	anchorkeyword: '#top', //enter href value of html anchors on the page that should also act as "scroll up" links

	state: {isvisible:false, shouldvisible:false},

	scrollup:function(){
		if (!this.cssfixedsupport) //if control is positioned using javascript
			this.$control.css({opacity:0}) //hide control immediately after clicking it
		var dest=isnan(this.setting.scrollto)? this.setting.scrollto : parseint(this.setting.scrollto)
		if (typeof dest=="string" && jquery('#'+dest).length==1) //check element set by string exists
			dest=jquery('#'+dest).offset().top
		else
			dest=0
		this.$body.animate({scrolltop: dest}, this.setting.scrollduration);
	},

	keepfixed:function(){
		var $window=jquery(window)
		var controlx=$window.scrollleft() + $window.width() - this.$control.width() - this.controlattrs.offsetx
		var controly=$window.scrolltop() + $window.height() - this.$control.height() - this.controlattrs.offsety
		this.$control.css({left:controlx+'px', top:controly+'px'})
	},

	togglecontrol:function(){
		var scrolltop=jquery(window).scrolltop()
		if (!this.cssfixedsupport)
			this.keepfixed()
		this.state.shouldvisible=(scrolltop>=this.setting.startline)? true : false
		if (this.state.shouldvisible && !this.state.isvisible){
			this.$control.stop().animate({opacity:1}, this.setting.fadeduration[0])
			this.state.isvisible=true
		}
		else if (this.state.shouldvisible==false && this.state.isvisible){
			this.$control.stop().animate({opacity:0}, this.setting.fadeduration[1])
			this.state.isvisible=false
		}
	},
	
	init:function(){
		jquery(document).ready(function($){
			var mainobj=scrolltotop
			var iebrws=document.all
			mainobj.cssfixedsupport=!iebrws || iebrws && document.compatmode=="css1compat" && window.xmlhttprequest //not ie or ie7+ browsers in standards mode
			mainobj.$body=(window.opera)? (document.compatmode=="css1compat"? $('html') : $('body')) : $('html,body')
			mainobj.$control=$('<div id="topcontrol">'+mainobj.controlhtml+'</div>')
				.css({position:mainobj.cssfixedsupport? 'fixed' : 'absolute', bottom:mainobj.controlattrs.offsety, right:mainobj.controlattrs.offsetx, opacity:0, cursor:'pointer'})
				.attr({title:'点击这里回到页面顶部'})
				.click(function(){mainobj.scrollup(); return false})
				.appendto('body')
			if (document.all && !window.xmlhttprequest && mainobj.$control.text()!='') //loose check for ie6 and below, plus whether control contains any text
				mainobj.$control.css({width:mainobj.$control.width()}) //ie6- seems to require an explicit width on a div containing text
			mainobj.togglecontrol()
			$('a[href="' + mainobj.anchorkeyword +'"]').click(function(){
				mainobj.scrollup()
				return false
			})
			$(window).bind('scroll resize', function(e){
				mainobj.togglecontrol()
			})
		})
	}
}

scrolltotop.init()