//--------------------------------------------------------------------------------------------------------
// Show popup window of given size in centre of screen
// For full screen popup, set width and height to zero
//--------------------------------------------------------------------------------------------------------
function popup(mylink, windowname, width, height)
{
if (! window.focus)return true;
var href;
if (width == 0) width = screen.width;
if (height == 0) height = screen.height;
var left = (screen.width  - width)/2;
var top  = (screen.height - height)/2;
if (typeof(mylink) == 'string')
   href=mylink;
else
   href=mylink.href;
var params = 'width=' + width + ',height=' + height;
params += ',left=' + left + ',top=' + top;
params += ',scrollbars=yes,resizable=yes,dependent=yes';
window.open(href,windowname,params);
return false;
}