document.getElementById("fs").style.height = (document.body.scrollHeight + 80) + "px";
var fspic=document.getElementById("fspic");
var fs=document.getElementById("fs");
var fscontent=document.getElementById("fscontent");
var trickpic=document.getElementById("trickpic");

function setoffset () {

    var freeH = document.documentElement.clientHeight;
    freeH -= fspic.height;
    var standoffH = document.getElementsByTagName("html")[0].scrollTop + 2*freeH/5;
    fspic.style.margin = standoffH + "px auto 0";
    document.getElementsByTagName("html")[0].style.overflow="hidden";
    fs.style.visibility="visible";
    fscontent.style.visibility="visible";
}

function fscreen (src) {
  fspic.src="img/fscreen/"+src+".jpg";
  fspic.onload = function() {fspic.onload=setoffset()}
  setoffset();
}

function goback () {
fspic.onload = function () {}
  fscontent.style.visibility="hidden";
  fs.style.visibility="hidden";
  document.getElementsByTagName("html")[0].style.overflow="auto";
  fspic.src="img/fscreen/blank.gif";
}

function chkscroll(evt) {
  if (fs.style.visibility=="visible") {
  evt.returnValue = false;
  if(evt.preventDefault) evt.preventDefault(); 
  if(evt.stopPropagation) evt.stopPropagation();
  }
}

function chkkey(evt) {

  if (fs.style.visibility=="visible") {
    if (evt.keyCode==27) goback();
    else {
      evt.returnValue = false;
      if(evt.preventDefault) evt.preventDefault(); 
      if(evt.stopPropagation) evt.stopPropagation();
    }
  }
}

function chkclick(evt) {
if (fs.style.visibility=="visible") goback();
}