select visible nodes in a dgrid

gistfile1.txt

  			var dh = domGeom.getMarginBox(grid.contentNode).h;
				var scrollPos = grid.getScrollPosition();
				var rows = Query(".dgrid-row",grid.contentNode).filter(function(node){
					return ((node.offsetTop>=scrollPos.y) &&  ((node.offsetTop + (.75 * node.offsetHeight)) <(scrollPos.y+dh))); 
				});
				grid.clearSelection();
				grid.select(rows[0], rows[rows.length-1]);