Synthetic Lines

<!--
  示例：OpenLayers 合成线要素
  要点：一次性构造数千条线要素，VectorLayer 直接渲染，不依赖任何数据文件
  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>合成线要素</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;flex-wrap:wrap;font-size:12px;color:#58606e}
  .bar label{display:flex;gap:5px;align-items:center;cursor:pointer}
  .bar select,.bar input[type=range]{font-size:12px}
  .bar .val{font-family:ui-monospace,Consolas,monospace;color:#1f5fd0;min-width:44px}
  .bar .sep{width:1px;height:16px;background:#d8dce2}
  #map{flex:1 1 auto;min-height:0;background:#eef0f3}
</style>
</head>
<body>
<div class="bar">
  <label><input type="checkbox" id="tglVec" checked> 线要素图层</label>
  <span class="sep"></span>
  <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').textContent = 'OpenLayers 加载失败，请检查能否访问 cdn.jsdelivr.net';
    return;
  }


  var center = ol.proj.fromLonLat([116.391, 39.907]);
  var view = new ol.View({
    center: center,
    zoom: 12,
    minZoom: 2,
    maxZoom: 19
  });

  var base = 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'})});

  var features = [];
  var lon = 116.20;
  var lat = 39.78;
  var signX = 1;
  var signY = -1;
  for (var i = 0; i < 3000; ++i) {
    var delta = (i + 1) * 0.000018;
    if (i % 2 === 0) {
      signY *= -1;
    } else {
      signX *= -1;
    }
    var endLon = lon + delta * signX;
    var endLat = lat + delta * signY;
    features.push(new ol.Feature({
      geometry: new ol.geom.LineString([
        ol.proj.fromLonLat([lon, lat]),
        ol.proj.fromLonLat([endLon, endLat])
      ])
    }));
    lon = endLon;
    lat = endLat;
  }

  var vector = new ol.layer.Vector({
    source: new ol.source.Vector({features: features, wrapX: false}),
    opacity: 0.8,
    style: new ol.style.Style({
      stroke: new ol.style.Stroke({color: '#1f5fd0', width: 1})
    })
  });

  var map = new ol.Map({
    target: 'map',
    layers: [base, vector],
    view: view
  });

  document.getElementById('tglVec').addEventListener('change', function () {
    vector.setVisible(this.checked);
  });

  map.on('singleclick', function (evt) {
    var lonlat = ol.proj.toLonLat(evt.coordinate);
    document.getElementById('info').textContent =
      lonlat[0].toFixed(5) + ', ' + lonlat[1].toFixed(5);
  });

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