Draw Features Style

<!--
  说明：绘制样式配置
  核心逻辑：Draw 的 style 只管绘制预览，图层 style 决定定稿外观，主题切换时重建交互
  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>绘制样式配置</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:8px;align-items:center;font-size:12px;color:#58606e;flex-wrap:wrap}
  .bar button{font:inherit;padding:4px 10px;border:1px solid #c9d0da;border-radius:5px;
              background:#fff;color:#1f2a37;cursor:pointer}
  .bar button.on{background:#1f5fd0;border-color:#1f5fd0;color:#fff}
  #info{margin-left:auto}
  #map{flex:1 1 auto;min-height:0;background:#eef0f3}
</style>
</head>
<body>
<div class="bar">
  <button data-theme="normal" class="on">常规</button>
  <button data-theme="contrast">高对比</button>
  <button id="clear">清空</button>
  <span id="info">按住拖拽绘制多边形</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 fromLonLat = ol.proj.fromLonLat;

  var themes = {
    normal: {
      fill: 'rgba(31,95,208,0.16)', stroke: '#1f5fd0',
      previewFill: 'rgba(226,72,60,0.10)', previewStroke: '#e2483c'
    },
    contrast: {
      fill: 'rgba(255,196,0,0.22)', stroke: '#123b78',
      previewFill: 'rgba(18,59,120,0.12)', previewStroke: '#123b78'
    }
  };

  var source = new ol.source.Vector();
  var draw = null;
  var current = 'normal';

  function layerStyle() {
    var t = themes[current];
    return new ol.style.Style({
      fill: new ol.style.Fill({ color: t.fill }),
      stroke: new ol.style.Stroke({ color: t.stroke, width: 2.5 })
    });
  }

  var layer = new ol.layer.Vector({ source: source, style: layerStyle });

  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'}) }), layer],
    view: new ol.View({ center: fromLonLat([116.391, 39.907]), zoom: 12, minZoom: 2, maxZoom: 19 }),
    controls: ol.control.defaults.defaults({ attribution: false, rotate: false })
  });

  var info = document.getElementById('info');

  function build() {
    var t = themes[current];
    if (draw) map.removeInteraction(draw);
    draw = new ol.interaction.Draw({
      source: source,
      type: 'Polygon',
      style: new ol.style.Style({
        fill: new ol.style.Fill({ color: t.previewFill }),
        stroke: new ol.style.Stroke({ color: t.previewStroke, width: 2, lineDash: [7, 6] }),
        image: new ol.style.Circle({
          radius: 5,
          fill: new ol.style.Fill({ color: t.previewStroke }),
          stroke: new ol.style.Stroke({ color: '#ffffff', width: 1.5 })
        })
      })
    });
    draw.on('drawend', function () {
      info.textContent = '已绘制 ' + source.getFeatures().length + ' 个面';
    });
    map.addInteraction(draw);
  }

  Array.prototype.forEach.call(document.querySelectorAll('.bar button[data-theme]'), function (btn) {
    btn.addEventListener('click', function () {
      Array.prototype.forEach.call(document.querySelectorAll('.bar button[data-theme]'), function (b) {
        b.classList.remove('on');
      });
      btn.classList.add('on');
      current = btn.getAttribute('data-theme');
      build();
      layer.changed();
      info.textContent = current === 'normal' ? '已切换到常规配色' : '已切换到高对比配色';
    });
  });

  document.getElementById('clear').addEventListener('click', function () {
    source.clear();
    info.textContent = '已清空';
  });

  build();
})();
</script>
</body>
</html>