Steps to Reproduce

https://zkfiddle.org/sample/2ciuc58/3-grid-extra-rendering

Run locally (not fiddle), using chrome debugger tools with sensors > touch (force enabled)

to emulate an hybrid device like a touchscreen laptop (touch + mouse)

With zkmax

make sure that zk.touchEnabled is "true" after loading

Click button

Current Result

grid loads initial items, then send onRender for all items in the grid

Expected Result

grids load items when user scrolls

Debug Information

caused by zul.mesh.Scrollbar.getScrollPosV from the grid-touch zkmax override.

The grid may have wgt_padsz == {}

as set by grid-rod.js $init override

This cause getScrollPosV to return NaN.

This causes grid#_onRender to have min and max == NaN

min = zul.mesh.Scrollbar.getScrollPosV(this),
 max = min + this.ebody.offsetHeight;

because of this, the following conditions are never met:

if (top + $row.offsetHeight() < min) continue;
 if (top > max) break; //Bug 1822517

which causes all of the grid rows to be processed and added to the items to render

Workaround

<script><![CDATA[ 
		zk.afterLoad("zul.mesh, zkmax", function () {
			zul.mesh.Scrollbar.getScrollPosV = function (wgt) {
				var ebody = wgt.ebody,
					ebodytbl = wgt.ebodytbl,
					scrollTop = jq(ebody).offset().top - jq(ebodytbl).offset().top;
				
				return (wgt._padsz && wgt._padsz['tpad']) ? scrollTop + wgt._padsz['tpad'] : scrollTop;
			};
		});
	]]></script>