<!DOCTYPE html>
<html>
  <meta charset="UTF-8">
  <meta name="viewport" content="width=device-width, initial-scale=1">
  <title>shadow test</title>
  <style type="text/css">
    html,body{margin:0px;height:100%;width:100%}
    .container{width:800px;height:800px}
    .btn{width:80px;height:30px;margin-left: 10px;cursor: pointer;}
  </style>
  <script type="text/javascript" src="https://cdn.jsdelivr.net/npm/maptalks/dist/maptalks.min.js"></script>
  <script src="../../packages/gl/dist/maptalksgl-dev.js" type