function get_scroll_top() 
{
  if (typeof(window.pageYOffset) == 'number')
    return window.pageYOffset;
  if (document.documentElement && document.documentElement.scrollTop)
    return document.documentElement.scrollTop;
  if (document.body && document.body.scrollTop) 
    return document.body.scrollTop;
  return 0;
}

var floating_menu__y=120;

function floating_menu__update(eid,y,min_y,lowpass) {
  var e=document.getElementById(eid);
  var st=get_scroll_top();
  var to_y=st>0?Math.max(st+y,min_y):min_y;
  floating_menu__y+=(to_y-floating_menu__y)*lowpass;
  e.style.top=floating_menu__y+'px';
}