/*  *****  JavaScript Sheet - venter.org, 'top level' index   *****   */


 addLoadEvent(sf_time)

/*   ***********   function 'set_backgnd'   ***********   */

/*   This function selects the background photo of San Francisco 
     according to the time of day in San Francisco.   */
   
  function set_backgnd(this_tab)
   {
                              // First set all the 'visibility' properties to 'hidden'
     document.getElementById('home').style.visibility = 'hidden';
     document.getElementById('surname').style.visibility = 'hidden';
     document.getElementById('dna').style.visibility = 'hidden';
     document.getElementById('venter').style.visibility = 'hidden';
     document.getElementById('sisters').style.visibility = 'hidden';
                             //  Then set 'visibility' of the selected tab to 'visible'
     document.getElementById(this_tab).style.visibility = 'visible';
   }
   
/*   ***********   End function 'set_backgnd'   ***********   */


/*   ***********   function 'sf_time'   ***********   */

/*   This function determines the time of day in San Francisco.   */
   
 function sf_time()
   {
                             // Create a 'date' instance
      var timenow = new Date();
                             // Determine viewer's offset from GMT
      var gmtOffset = timenow.getTimezoneOffset()/60;
                             // get viewer's locale time   
      var ltime = timenow.getHours();
                             // Calculate SF time from view's time vieqwer's GMT offset
      var gmt = ltime + gmtOffset;
      var sfTime = gmt - 7;
                            //  Choose correct photo for SF time
      if ( sfTime < 0) sfTime = sfTime + 24;
      if ( sfTime > 24) sfTime = sfTime - 24;
 
      var mastpic = document.getElementById("masthead");
      
       if ( sfTime >= 6 && sfTime < 17 )    // daytime
           {
              mastpic.style.backgroundImage = "url(soke1/top/mast_sf_day.jpg)";
           }
         else if ( sfTime >= 17 && sfTime <= 19 )    // sunset
           {
             mastpic.style.backgroundImage = "url(soke1/top/mast_sf_sunset.jpg)";
           }
         else if ( (sfTime > 19 && sfTime < 24 ) | (sfTime > 0 && sfTime < 6 ) )   // nighttime
           {
             mastpic.style.backgroundImage = "url(soke1/top/mast_sf_night.jpg)";
           }
  }           

/*   ********   End function 'sf_time'   ********   */


/*   ******** Revisions   ********   */

//   Rev 0; (7-25-2010) original issue

//   Rev. 1 (8-19-2010) changed ".png" to '.gif' due to a
//                      problem with the way IE7 handles 'png's

/*   *****************************   */