Google图表：在物料折线图中，点大小不起作用

Question

在以下物料折线图的代码中，pointSize属性未按预期工作。虽然在文档中写了pointSize的默认值为0并将其设置为大于0的值会使其可见，但它在我的情况下不起作用。< / p>

简而言之，我想让我的图表上的点可见，但它不起作用。

Jsfiddle Here

    google.charts.load('current', {'packages':['line']});
    google.charts.setOnLoadCallback(drawChart);
    function drawChart() {

      var data = new google.visualization.DataTable();
      data.addColumn('number', 'Day');
      data.addColumn('number', 'Guardians of the Galaxy');
      data.addColumn('number', 'The Avengers');
      data.addColumn('number', 'Transformers: Age of Extinction');
      data.addRows([
        [1, 0, 0, 41.8],
        [2, 30.9, 69.5, 32.4],
        [3, 25.4, 57, 25.7],
        [4, 11.7, 18.8, 10.5],
        [5, 11.9, 17.6, 10.4],
        [6, 8.8, 13.6, 7.7],
        [7, 7.6, 12.3, 9.6],
        [8, 12.3, 29.2, 10.6],
        [9, 16.9, 0, 14.8],
        [10, 12.8, 30.9, 11.6],
        [11, 5.3, 7.9, 4.7],
        [12, 6.6, 8.4, 5.2],
        [13, 4.8, 6.3, 3.6],
        [14, 4.2, 6.2, 3.4],
        [15, 4.5, 5.9, 41.8],
        [16, 30.9, 69.5, 32.4],
        [17, 25.4, 57, 25.7],
        [18, 11.7, 18.8, 10.5],
        [19, 11.9, 17.6, 10.4],
        [20, 8.8, 13.6, 7.7],
        [21, 7.6, 12.3, 9.6],
        [22, 12.3, 29.2,10.6],
        [23, 16.9, 0, 14.8],
        [24, 12.8, 30.9, 11.6],
        [25, 5.3, 7.9, 4.7],
        [26, 6.6, 8.4, 5.2],
        [27, 4.8, 6.3, 3.6],
        [28, 30.2, 45.2, 25.4],
        [29, 40.2, 25.2, 36.4],
        [30, 25.2, 35.2, 30.4]
      ]);

      var options = {
        chart: {
          title: 'Box Office Earnings in First Two Weeks of Opening',
          subtitle: 'in millions of dollars (USD)',
        },
        pointSize: 20,
        pointShape: 'square',
        width: 600,
        height: 400
      };
      var chart = new google.charts.Line(document.getElementById('linechart_material'));
chart.draw(data, options);
}

 <script type="text/javascript" src="https://www.gstatic.com/charts/loader.js"></script>
 <div id="linechart_material"></div>