Steps to Reproduce

run fiddle
http://zkfiddle.org/sample/2mete3i/2-Dynamic-Listbox-Columns-Performance#source-2

scroll down to trigger load on demand

Current Result

Load on demand trigger a large number of zUtl fireSized, which cause as many computation of isRealVisible which takes a lot of rendering time.
average rendering time after receiving the response for a batch or ROD entries is around 10s

Expected Result

rendering a batch of ROD entries should only be a few seconds.
rendering shouldn't call fireSized for each individual elements (one fireSized at the end should be triggered anyway by Listbox)

Debug Info

fireSized triggered by
fireSized (rod.zul:1119)
jq.fn.(anonymous function) (zk.wpd:formatted:12164)
_asBodyChild (zk.wpd:formatted:26211)
mtAU (zk.wpd:formatted:25028)
zkx (zk.wpd:formatted:25249)
zkx_ (zk.wpd:formatted:25267)
addChd (zk.wpd:formatted:27844)
doProcess (zk.wpd:formatted:26051)
doCmdsNow (zk.wpd:formatted:26161)
_doCmds (zk.wpd:formatted:26541)
afterResponse (zk.wpd:formatted:27097)
_onResponseReady (zk.wpd:formatted:26944)
XMLHttpRequest.send (async)
ajaxSendNow (zk.wpd:formatted:26128)
sendNow (zk.wpd:formatted:26799)
(anonymous) (zk.wpd:formatted:26097)
setTimeout (async)
ajaxSend2 (zk.wpd:formatted:26096)
ajaxSend (zk.wpd:formatted:26089)
send (zk.wpd:formatted:26427)
sendAU_ (zk.wpd:formatted:21969)
fireX (zk.wpd:formatted:21907)
fire (zk.wpd:formatted:22007)
_scrollPage (zk.wpd:formatted:43585)
(anonymous) (zk.wpd:formatted:11062)
setTimeout (async)
_fireOnScrollPos (zk.wpd:formatted:43435)
_doScroll (zul.mesh.wpd:1013)
$supers (zk.wpd:formatted:11219)
$super (zk.wpd:formatted:11164)
_doScroll (zul.sel.wpd:1810)
(anonymous) (zk.wpd:formatted:18039)
dispatch (zk.wpd:formatted:4912)
elemData.handle (zk.wpd:formatted:4609)

Root Cause

Workaround

prevent element firesized when added at DOM root during rendering.
WARNING: not fully tested, may prevent automatic resizing of root-level elements such as popups / modal windows

 	<script><![CDATA[
	zk.afterLoad('zk', function() {
		var xzUtl = {};
		zk.skipFireSized = false;
		zk.override(zUtl, xzUtl ,{
			fireSized : function(a,b) {
				var result;	
				if(!(!(a.className == "zk.Page" ) && (a.$n().parentElement == document.body))){
					result = xzUtl.fireSized.apply(this, arguments);
				}
				return result;
			}
		});//zk.override
	});//zk.afterLoad
	]]></script>