Immediate Geographic

<!--
  示例：立即渲染（地理坐标） — OpenLayers immediate-geographic
  核心逻辑：postrender 中取 ol.render.toContext，把经纬度几何转换后逐帧绘制脉冲圆环
  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>立即渲染（地理坐标）</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:12px;align-items:center;font-size:12px;color:#58606e;flex-wrap:wrap}
  .bar label{display:flex;gap:5px;align-items:center;cursor:pointer}
  #map{flex:1 1 auto;min-height:0;background:#eef0f3}
</style>
</head>
<body>
<div class="bar">
  <label><input type="checkbox" id="run" checked> 动画</label>
  <span>圆环直接画在渲染上下文中，不经过图层与要素</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 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'}) })
    ],
    view: new ol.View({
      center: ol.proj.fromLonLat([116.391, 39.907]),
      zoom: 12,
      minZoom: 2
    }),
    controls: ol.control.defaults.defaults({ attribution: false })
  });

  var sites = [
    [116.391263, 39.907359],
    [116.410600, 39.914700],
    [116.374200, 39.909700]
  ];

  var start = Date.now();
  var running = true;

  /* 每帧都重新绘制，不走图层体系 */
  function drawPulse(event) {
    if (!running) return;

    var t = (Date.now() - start) / 1000;
    var ctx = ol.render.toContext(event.context, {
      size: event.frameState.size,
      pixelRatio: event.frameState.pixelRatio
    });

    sites.forEach(function (lonlat, i) {
      var center = ol.proj.fromLonLat(lonlat);
      var phase = (t * 0.45 + i * 0.33) % 1;

      /* 半径在 3857 下以米为单位，按视口分辨率换算成像素感更稳 */
      var res = map.getView().getResolution();
      var pixelRadius = 8 + phase * 46;

      ctx.setStyle(new ol.style.Style({
        stroke: new ol.style.Stroke({
          color: 'rgba(31,95,208,' + (0.75 * (1 - phase)) + ')',
          width: 2
        })
      }));

      ctx.drawCircle(center, pixelRadius * res);

      ctx.setStyle(new ol.style.Style({
        image: new ol.style.Circle({
          radius: 5,
          fill: new ol.style.Fill({ color: '#1f5fd0' }),
          stroke: new ol.style.Stroke({ color: '#ffffff', width: 2 })
        }),
        text: new ol.style.Text({
          text: '监测点 ' + (i + 1),
          offsetY: -16,
          font: '500 12px sans-serif',
          fill: new ol.style.Fill({ color: '#16181d' }),
          stroke: new ol.style.Stroke({ color: '#ffffff', width: 3 })
        })
      }));

      ctx.drawGeometry(new ol.geom.Point(center));
    });
  }

  map.on('postrender', drawPulse);

  /* 持续请求重绘，让圆环动起来 */
  function loop() {
    if (running) map.render();
    requestAnimationFrame(loop);
  }
  loop();

  document.getElementById('run').addEventListener('change', function () {
    running = this.checked;
    if (running) start = Date.now();
    map.render();
  });
})();
</script>
</body>
</html>