Layer Z Index

<!--
  示例：图层叠放次序 — OpenLayers layer-z-index
  核心逻辑：三个图层用 setZIndex 调整绘制顺序，改变遮挡关系
  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>图层叠放次序</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:6px;align-items:center}
  .bar select{font:inherit;padding:3px 6px;border:1px solid #ccd2da;border-radius:3px;background:#fff}
  #map{flex:1 1 auto;min-height:0;background:#eef0f3}
</style>
</head>
<body>
<div class="bar">
  <label>A 区 zIndex <select id="zA"><option>0</option><option>1</option><option>2</option><option>3</option></select></label>
  <label>B 区 zIndex <select id="zB"><option>0</option><option>1</option><option>2</option><option>3</option></select></label>
  <label>C 区 zIndex <select id="zC"><option>0</option><option>1</option><option>2</option><option>3</option></select></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;
  }

  function zoneFeature(west, south, east, north, name) {
    return new ol.Feature({
      geometry: new ol.geom.Polygon([[
        [west, south], [east, south], [east, north], [west, north], [west, south]
      ]]).transform('EPSG:4326', 'EPSG:3857'),
      name: name
    });
  }

  function makeLayer(color, name, features) {
    return new ol.layer.Vector({
      source: new ol.source.Vector({ features: features }),
      style: new ol.style.Style({
        fill: new ol.style.Fill({ color: color }),
        stroke: new ol.style.Stroke({ color: 'rgba(255,255,255,0.9)', width: 2 }),
        text: new ol.style.Text({
          text: name,
          font: '600 16px sans-serif',
          fill: new ol.style.Fill({ color: 'rgba(255,255,255,0.95)' })
        })
      })
    });
  }

  var layerA = makeLayer('rgba(31,95,208,0.72)', 'A 区', [
    zoneFeature(116.32, 39.88, 116.42, 39.94, 'A 区')
  ]);
  var layerB = makeLayer('rgba(232,89,12,0.72)', 'B 区', [
    zoneFeature(116.37, 39.90, 116.47, 39.96, 'B 区')
  ]);
  var layerC = makeLayer('rgba(47,158,68,0.72)', 'C 区', [
    zoneFeature(116.41, 39.87, 116.50, 39.93, 'C 区')
  ]);

  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'}) }),
      layerA, layerB, layerC
    ],
    view: new ol.View({
      center: ol.proj.fromLonLat([116.41, 39.915]),
      zoom: 12,
      minZoom: 2
    }),
    controls: ol.control.defaults.defaults({ attribution: false })
  });

  function apply() {
    layerA.setZIndex(Number(document.getElementById('zA').value));
    layerB.setZIndex(Number(document.getElementById('zB').value));
    layerC.setZIndex(Number(document.getElementById('zC').value));

    document.getElementById('info').textContent =
      'A=' + layerA.getZIndex() + ' · B=' + layerB.getZIndex() +
      ' · C=' + layerC.getZIndex();
  }

  ['zA', 'zB', 'zC'].forEach(function (id) {
    document.getElementById(id).addEventListener('change', apply);
  });

  document.getElementById('zA').value = '0';
  document.getElementById('zB').value = '1';
  document.getElementById('zC').value = '2';
  apply();
})();
</script>
</body>
</html>