function _fnVisbleColumns(settings) {
		var layout = settings.aoHeader;
		var columns = settings.aoColumns;
		var vis = 0;

		if (layout.length) {
			for (var i = 0, ien = layout[0].length; i < ien; i++) {
				if (columns[i].bVisible && $(layout[0][i].cell).css('display') !== 'none') {
					vis++;
				}
			}
		}

		return vis;
	}
Get the number of visible columns
 @param {object} oSettings dataTables settings object
 @returns {int} i the number of visible columns
 @memberof DataTable#oApi