//// mouse events ////
/**
 * To make hovertips appear correctly we need the exact mouse position.
 * These functions make that possible.
 */
// use globals to track mouse position
var hovertipMouseX = "";
var hovertipMouseY = "";
function hovertipMouseUpdate(e) {
  var mouse = hovertipMouseXY(e);
  hovertipMouseX = mouse[0];
  hovertipMouseY = mouse[1];
}

// http://www.howtocreate.co.uk/tutorials/javascript/eventinfo
function hovertipMouseXY(e) {
  if( !e ) {
    if( window.event ) {
      //Internet Explorer
      e = window.event;
    } else {
      //total failure, we have no way of referencing the event
      return;
    }
  }
  if( typeof( e.pageX ) == 'number' ) {
    //most browsers
    var xcoord = e.pageX;
    var ycoord = e.pageY;
  } else if( typeof( e.clientX ) == 'number' ) {
    //Internet Explorer and older browsers
    //other browsers provide this, but follow the pageX/Y branch
    var xcoord = e.clientX;
    var ycoord = e.clientY;
    var badOldBrowser = ( window.navigator.userAgent.indexOf( 'Opera' ) + 1 ) ||
      ( window.ScriptEngine && ScriptEngine().indexOf( 'InScript' ) + 1 ) ||
      ( navigator.vendor == 'KDE' );
    if( !badOldBrowser ) {
      if( document.body && ( document.body.scrollLeft || document.body.scrollTop ) ) {
        //IE 4, 5 & 6 (in non-standards compliant mode)
        xcoord += document.body.scrollLeft;
        ycoord += document.body.scrollTop;
      } else if( document.documentElement && ( document.documentElement.scrollLeft || document.documentElement.scrollTop ) ) {
        //IE 6 (in standards compliant mode)
        xcoord += document.documentElement.scrollLeft;
        ycoord += document.documentElement.scrollTop;
      }
    }
  } else {
    //total failure, we have no way of obtaining the mouse coordinates
    return;
  }
  return [xcoord, ycoord];
}