/* Скрипт Скроллинга 
HTML на странице: <a id="gotop" href="#" onclick="top.goTop(); return false;"></a> 
------------------------------------*/
 (function() {
 

function $(id){
 return document.getElementById(id);
 }
 
function goTop(acceleration, time) {
 acceleration = acceleration || 0.1;
 time = time || 12;
 
var dx = 0;
 var dy = 0;
 var bx = 0;
 var by = 0;
 var wx = 0;
 var wy = 0;
 
if (document.documentElement) {
 dx = document.documentElement.scrollLeft || 0;
 dy = document.documentElement.scrollTop || 0;
 }
 if (document.body) {
 bx = document.body.scrollLeft || 0;
 by = document.body.scrollTop || 0;
 }
 var wx = window.scrollX || 0;
 var wy = window.scrollY || 0;
 
var x = Math.max(wx, Math.max(bx, dx));
 var y = Math.max(wy, Math.max(by, dy));
 
var speed = 1 + acceleration;
 window.scrollTo(Math.floor(x / speed), Math.floor(y / speed));
 if(x > 0 || y > 0) {
 var invokeFunction = "top.goTop(" + acceleration + ", " + time + ")"
 window.setTimeout(invokeFunction, time);
 }
 return false;
 }
 
//*
 function scrollTop(){
 var el = $('gotop');
 var stop = (document.body.scrollTop || document.documentElement.scrollTop);
 if(stop>400){
 if(el.style.display!='block'){ 
el.style.display='block'; 
smoothopaque(el, 0, 100, 1); 
}
 }
 else 
el.style.display='none';

 return false;
 }
 
// Плавная смена прозрачности
 function smoothopaque(el, startop, endop, inc){
 op = startop;
 // Устанавливаем прозрачность
setopacity(el, op);
 // Начинаем изменение прозрачности
setTimeout(slowopacity, 1);
 function slowopacity(){
 if(startop < endop){
 op = op + inc;
 if(op < endop){
 setTimeout(slowopacity, 1);
 }
 }else{
 op = op - inc;
 if(op > endop){
 setTimeout(slowopacity, 1);
 }
 }
 setopacity(el, op); 
};
 };
 // установка opacity
 function setopacity(el, opacity){
 el.style.opacity = (opacity/100);
 el.style.filter = 'alpha(opacity=' + opacity + ')';
 };
 
if (window.addEventListener){
 window.addEventListener("scroll", scrollTop, false);
 window.addEventListener("load", scrollTop, false);
 }
 else if (window.attachEvent){
 window.attachEvent("onscroll", scrollTop);
 window.attachEvent("onload", scrollTop);
 } 


window['top'] = {};
 window['top']['goTop'] = goTop; 

})();