Draw Freehand

<!--
  示例：自由手绘 — OpenLayers draw-freehand
  核心逻辑：Draw 交互打开 freehand，指针移动即追加顶点，抬手结束一条线或一个面
  依赖：OpenLayers 10.3.1 · jsDelivr CDN
-->
<!DOCTYPE html>
<html lang="zh-CN">
<head>
<meta name="robots" content="noindex,follow">
<meta charset="utf-8">
<meta name="viewport" content="width=device-width, initial-scale=1">
<title>自由手绘</title>
<link rel="stylesheet" href="https://cdn.jsdelivr.net/npm/ol@10.3.1/ol.css">
<style>
  html,body{height:100%;margin:0}
  body{display:flex;flex-direction:column;overflow:hidden;
       font:13px/1.6 -apple-system,"Segoe UI","PingFang SC",sans-serif}
  .bar{flex:0 0 auto;padding:8px 12px;background:#f6f7f9;border-bottom:1px solid #e3e6ea;
       display:flex;gap:10px;align-items:center;font-size:12px;color:#58606e;flex-wrap:wrap}
  .bar button{font:inherit;padding:3px 9px;border:1px solid #ccd2da;background:#fff;
       border-radius:3px;cursor:pointer;color:#2b3140}
  .bar button.on{background:#1f5fd0;border-color:#1f5fd0;color:#fff}
  #map{flex:1 1 auto;min-height:0;background:#eef0f3}
  #map canvas{cursor:crosshair}
</style>
</head>
<body>
<div class="bar">
  <button data-type="LineString" class="on">自由画线</button>
  <button data-type="Polygon">自由画面</button>
  <button id="undo">撤销一笔</button>
  <button id="clear">清空</button>
  <span id="info">—</span>
</div>
<div id="map"></div>
<script src="https://cdn.jsdelivr.net/npm/ol@10.3.1/dist/ol.js"></script>
<script>
(function () {
  'use strict';

  if (typeof ol === 'undefined') {
    document.getElementById('map').innerHTML =
      '<div style="padding:20px;color:#b42318">OpenLayers 加载失败，请检查能否访问 cdn.jsdelivr.net</div>';
    return;
  }

  var infoEl = document.getElementById('info');
  var source = new ol.source.Vector();
  var draw = null;

  var vectorLayer = new ol.layer.Vector({
    source: source,
    style: new ol.style.Style({
      fill: new ol.style.Fill({ color: 'rgba(232,89,12,0.20)' }),
      stroke: new ol.style.Stroke({ color: '#e8590c', width: 3, lineCap: 'round', lineJoin: 'round' })
    })
  });

  var map = new ol.Map({
    target: 'map',
    layers: [
      new ol.layer.Tile({ source: new ol.source.XYZ({url: 'https://server.arcgisonline.com/ArcGIS/rest/services/World_Street_Map/MapServer/tile/{z}/{y}/{x}', attributions: 'Tiles © Esri'}) }),
      vectorLayer
    ],
    view: new ol.View({
      center: ol.proj.fromLonLat([116.391, 39.907]),
      zoom: 13,
      minZoom: 2
    }),
    controls: ol.control.defaults.defaults({ attribution: false })
  });

  function updateInfo() {
    infoEl.textContent = '已绘制 ' + source.getFeatures().length + ' 笔';
  }

  function startDraw(type) {
    if (draw) map.removeInteraction(draw);
    draw = new ol.interaction.Draw({
      source: source,
      type: type,
      freehand: true,
      /* 手绘条件直接放行，桌面鼠标也能连续加点 */
      freehandCondition: ol.events.condition.always
    });
    draw.on('drawend', updateInfo);
    map.addInteraction(draw);
  }

  Array.prototype.forEach.call(
    document.querySelectorAll('[data-type]'),
    function (btn) {
      btn.addEventListener('click', function () {
        Array.prototype.forEach.call(
          document.querySelectorAll('[data-type]'),
          function (b) { b.classList.remove('on'); }
        );
        btn.classList.add('on');
        startDraw(btn.getAttribute('data-type'));
      });
    }
  );

  document.getElementById('undo').addEventListener('click', function () {
    var fs = source.getFeatures();
    if (fs.length) source.removeFeature(fs[fs.length - 1]);
    updateInfo();
  });

  document.getElementById('clear').addEventListener('click', function () {
    source.clear();
    updateInfo();
  });

  startDraw('LineString');
  updateInfo();
})();
</script>
</body>
</html>