Layer Extent

<!--
  示例：限制图层范围 — OpenLayers layer-extent
  核心逻辑：layer.setExtent 缩小渲染范围，范围外即使有数据也不绘制
  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>限制图层范围</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:14px;align-items:center;font-size:12px;color:#58606e;flex-wrap:wrap}
  .bar label{display:flex;gap:5px;align-items:center;cursor:pointer}
  .bar input[type=range]{width:200px}
  #map{flex:1 1 auto;min-height:0;background:#eef0f3}
</style>
</head>
<body>
<div class="bar">
  <label><input type="checkbox" id="limit" checked> 启用范围限制</label>
  <label>范围宽度 <input type="range" id="width" min="20" max="100" value="60"></label>
  <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 FULL = ol.proj.transformExtent(
    [116.24, 39.84, 116.54, 40.00], 'EPSG:4326', 'EPSG:3857'
  );

  /* 覆盖整幅范围的热力格网 */
  var features = [];
  var COLS = 18, ROWS = 12;

  for (var i = 0; i < COLS; i++) {
    for (var j = 0; j < ROWS; j++) {
      var x0 = FULL[0] + (FULL[2] - FULL[0]) * i / COLS;
      var x1 = FULL[0] + (FULL[2] - FULL[0]) * (i + 1) / COLS;
      var y0 = FULL[1] + (FULL[3] - FULL[1]) * j / ROWS;
      var y1 = FULL[1] + (FULL[3] - FULL[1]) * (j + 1) / ROWS;
      features.push(new ol.Feature({
        geometry: new ol.geom.Polygon([[
          [x0, y0], [x1, y0], [x1, y1], [x0, y1], [x0, y0]
        ]]),
        v: Math.abs(Math.sin(i / 3.4) * Math.cos(j / 2.8))
      }));
    }
  }

  var layer = new ol.layer.Vector({
    source: new ol.source.Vector({ features: features }),
    style: function (f) {
      var v = f.get('v');
      return new ol.style.Style({
        fill: new ol.style.Fill({
          color: 'rgba(' + Math.round(40 + 200 * v) + ',' +
            Math.round(150 - 70 * v) + ',70,0.55)'
        }),
        stroke: new ol.style.Stroke({ color: 'rgba(255,255,255,0.35)', width: 0.6 })
      });
    }
  });

  /* 范围提示框 */
  var outline = new ol.layer.Vector({
    source: new ol.source.Vector({}),
    style: new ol.style.Style({
      stroke: new ol.style.Stroke({ color: '#1f5fd0', width: 2, lineDash: [8, 6] })
    })
  });

  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'}), opacity: 0.5 }),
      layer,
      outline
    ],
    view: new ol.View({
      center: ol.proj.fromLonLat([116.39, 39.92]),
      zoom: 11,
      minZoom: 2
    }),
    controls: ol.control.defaults.defaults({ attribution: false })
  });

  function apply() {
    var enabled = document.getElementById('limit').checked;
    var pct = Number(document.getElementById('width').value) / 100;

    var extent = enabled
      ? [FULL[0], FULL[1], FULL[0] + (FULL[2] - FULL[0]) * pct, FULL[3]]
      : null;

    layer.setExtent(extent);

    outline.getSource().clear();
    if (extent) {
      var ring = [
        [extent[0], extent[1]], [extent[2], extent[1]],
        [extent[2], extent[3]], [extent[0], extent[3]],
        [extent[0], extent[1]]
      ];
      outline.getSource().addFeature(new ol.Feature({
        geometry: new ol.geom.Polygon([ring])
      }));
    }

    document.getElementById('info').textContent = enabled
      ? '仅渲染宽度 ' + Math.round(pct * 100) + '% 的范围'
      : '整幅范围渲染';
  }

  document.getElementById('limit').addEventListener('change', apply);
  document.getElementById('width').addEventListener('input', apply);
  apply();
})();
</script>
</body>
</html>