function cycleImages(source,imgstr) {
   var imgarray=imgstr.split(" ");
   var mod = imgarray.length;
   var i=0;
   while(source.src.search(imgarray[i]) <= 0)
      i++;
   i = (++i % mod);
   source.src = imgarray[i];
} 

function replayAnimatedGIF(place) {
	orig = place.src;
	place.src = "../images/loading.gif";
	place.src = orig;
}

function truncateDecimals(n,p)
{
   v = Math.pow(10,p);
   return Math.round(n * v)/v;
}
function computeLens()
{
   var lens = document.lens;
   ior = lens.ior.value;
   iorm1 = ior-1;
   fl = lens.fl.value;
   lr = lens.desrad.value;
   sr = 2 * iorm1 * fl;
   sr = truncateDecimals(sr,4);
   lens.radius.value = sr;
   q = 4 * fl * fl * iorm1 * iorm1 - lr * lr;
   if(q < 0) {
      offset = "Error";
      code_str = "Error";
   }
   else {
      offset = Math.sqrt(q);
      offset = truncateDecimals(offset,4);
      code_str="intersection {\n\t"
      + "sphere{\n\t\t<0,+" + offset + ",0>, " + sr + "\n\t}\n\t"
      + "sphere{\n\t\t<0,-" + offset + ",0>, " + sr + "\n\t}"
      + "\n}\n";
   }
   lens.offset.value = offset;
   lens.povcode.value = code_str;
}