function toggle(div_id) {
   var el = document.getElementById(div_id);
   if ( el.style.display == 'none' ) {   el.style.display = 'block';}
   else {el.style.display = 'none';}
}
function blanket_size(popUpDivVar) {
   if (typeof window.innerWidth != 'undefined') {
      viewportheight = window.innerHeight;
   } else {
      viewportheight = document.documentElement.clientHeight;
   }
   if ((viewportheight > document.body.parentNode.scrollHeight) && (viewportheight > document.body.parentNode.clientHeight)) {
      blanket_height = viewportheight;
   } else {
      if (document.body.parentNode.clientHeight > document.body.parentNode.scrollHeight) {
         blanket_height = document.body.parentNode.clientHeight;
      } else {
         blanket_height = document.body.parentNode.scrollHeight;
      }
   }
   var blanket = document.getElementById('blanket');
   blanket.style.height = blanket_height + 'px';
   var popUpDiv = document.getElementById(popUpDivVar);
   popUpDiv_height=blanket_height/2-500;//150 is half popup's height
   popUpDiv.style.top = popUpDiv_height + 'px';
}
function window_pos(popUpDivVar) {
   if (typeof window.innerWidth != 'undefined') {
      viewportwidth = window.innerHeight;
   } else {
      viewportwidth = document.documentElement.clientHeight;
   }
   if ((viewportwidth > document.body.parentNode.scrollWidth) && (viewportwidth > document.body.parentNode.clientWidth)) {
      window_width = viewportwidth;
   } else {
      if (document.body.parentNode.clientWidth > document.body.parentNode.scrollWidth) {
         window_width = document.body.parentNode.clientWidth;
      } else {
         window_width = document.body.parentNode.scrollWidth;
      }
   }
   var popUpDiv = document.getElementById(popUpDivVar);
   window_width=window_width/2-280;//150 is half popup's width
   popUpDiv.style.left = window_width + 'px';
}
function popup(windowname) {
   blanket_size(windowname);
   window_pos(windowname);
   toggle('blanket');
   toggle(windowname);      
}