jquery - parallax scrolling - jumps when used mouse scroll wheel -

i have come across problem parallax scrolling. when mouse scroll wheel used starts jumping , bad on chrome , little jump in ie fine in firefox.

here link site.

the code using parallax

 <script> var topdiv = document.getelementbyid("topdiv"); var speed = 1.5;  window.onscroll = function() {     var yoffset = window.pageyoffset;     topdiv.style.backgroundposition = "center "+ (yoffset / speed) + "px";         scrolling = true; }  </script> 

if can me have looked answers not able find.

thanks in advance

this known issue... check parallax site on chrome mouse , jump. there workaround seems work me: use nicescroll plugin don't use default scroll...

i used here: http://www.xboxeventsus.com/

here link nicescroll plugin: http://areaaperta.com/nicescroll/