Tutorial

Achei um tutorial bem legal no blog Cherry Bomb é o tutorial Volta ao topo com efeito.Funciona da seguinte maneira,quando você clica no volta ao topo ele sobe até o topo deslizando e a imagem de voltar ao topo só aparece se você deslizar um pouco pelo blog.É bem simples,e útil.Vamos aprender?
Vá em Design>>>Layout>>>Adicionar Gadget>>>HTML/JavaScript >>>Cole o código abaixo↓:

<script type="text/javascript" src="http://ajax.googleapis.com/ajax/libs/jquery/1.3.2/jquery.min.js"></script>
<script type='text/javascript' language='Javascript'>
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 (1=top).
setting: {startline:100, scrollto: 0, scrollduration:1000, fadeduration:[500, 100]},
controlHTML: '<img src="COLOQUE AQUI O URL DA IMAGEM"/>', //HTML for control, which is auto wrapped in DIV w/ ID="topcontrol"
controlattrs: {offsetx:5, offsety:5}, //offset of control relative to right/ center 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=$('<div id="topcontrol">'+mainobj.controlHTML+'</div>')
.css({position:mainobj.cssfixedsupport? 'fixed' : 'absolute', bottom:mainobj.controlattrs.offsety, right:mainobj.controlattrs.offsetx, opacity:0, cursor:'pointer'})
.attr({title:'Scroll Back to Top'})
.click(function(){mainobj.scrollup(); return false})
.appendTo('body')
if (document.all && !window.XMLHttpRequest && mainobj.$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()
</script>

Mude a parte destacada em vermelho pelo que se pede(o URL da sua imagem)

Créditos de código