// cacule la hauteur de la fenetre
function GetBodyHeight() {
  var BodyHeight = 0, BodyHeight = 0;
  
  if( typeof( window.innerHeight ) == 'number' ) {
    //Non-IE
    BodyHeight = window.innerHeight;
  } else if( document.documentElement && document.documentElement.clientHeight ) {
    //IE 6+ in 'standards compliant mode'
    BodyHeight = document.documentElement.clientHeight;
  } else if( document.body &&  document.body.clientHeight ) {
    //IE 4 compatible
    BodyHeight = document.body.clientHeight;
  }
  return BodyHeight;
}
function getScrollY() {
  var scrOfY = 0;
  if( typeof( window.pageYOffset ) == 'number' ) {
    //Netscape compliant
    scrOfY = window.pageYOffset;
  } else if( document.body && document.body.scrollTop  ) {
    //DOM compliant
    scrOfY = document.body.scrollTop;
  } else if( document.documentElement && document.documentElement.scrollTop ) {
    //IE6 standards compliant mode
    scrOfY = document.documentElement.scrollTop;
  }
  return scrOfY;
}