Fill Extrusion

<!--
  示例：3D 挤出
  核心逻辑：fill-extrusion 图层按属性算高度与颜色，俯仰 55 度观察体块，滑块统一调高
  依赖：MapLibre GL JS 4 · jsDelivr CDN · demotiles 样式
-->
<!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>3D 挤出</title>
<link rel="stylesheet" href="https://cdn.jsdelivr.net/npm/maplibre-gl@4/dist/maplibre-gl.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;color:#16181d}
  .bar{flex:0 0 auto;display:flex;gap:12px;align-items:center;padding:8px 12px;
       background:#f6f7f9;border-bottom:1px solid #e3e6ea;font-size:12px;color:#58606e;flex-wrap:wrap}
  .bar b{color:#16181d;font-weight:600}
  .bar input[type=range]{width:130px}
  #map{flex:1 1 auto;min-height:0}
</style>
</head>
<body>
<div class="bar">
  <label>高度倍数 <input id="k" type="range" min="0.5" max="2.5" step="0.1" value="1"> <b id="kv">1.0</b></label>
  <span>最高 <b>120 m</b> · 俯仰 <b id="p">—</b></span>
  <span>拖动右键改变俯仰与方向</span>
</div>
<div id="map"></div>
<script src="https://cdn.jsdelivr.net/npm/maplibre-gl@4/dist/maplibre-gl.js"></script>
<script>
(function () {
  'use strict';

  if (typeof maplibregl === 'undefined') {
    document.body.innerHTML =
      '<div style="padding:24px;color:#b42318">MapLibre 加载失败，请检查能否访问 cdn.jsdelivr.net</div>';
    return;
  }

  var blocks = [];
  var rows = 7, cols = 7;
  for (var r = 0; r < rows; r++) {
    for (var c = 0; c < cols; c++) {
      var x0 = 121.40 + c * 0.012;
      var y0 = 31.18 + r * 0.010;
      var h = 20 + ((r * cols + c) % 9) * 12;
      if ((r + c) % 4 === 0) h += 24;
      blocks.push({
        type: 'Feature',
        properties: { height: h },
        geometry: {
          type: 'Polygon',
          coordinates: [[
            [x0, y0],
            [x0 + 0.008, y0],
            [x0 + 0.008, y0 + 0.007],
            [x0, y0 + 0.007],
            [x0, y0]
          ]]
        }
      });
    }
  }

  var map = new maplibregl.Map({
    container: 'map',
    style: 'https://demotiles.maplibre.org/style.json',
    center: [121.445, 31.215],
    zoom: 13.2,
    pitch: 55,
    bearing: -18,
    maxPitch: 85,
    attributionControl: { compact: true, customAttribution: 'MapLibre demo tiles' }
  });

  map.addControl(new maplibregl.NavigationControl({ visualizePitch: true }), 'top-right');

  function heightExpr(k) {
    return ['*', ['get', 'height'], k];
  }

  map.on('load', function () {
    map.addSource('blocks', {
      type: 'geojson',
      data: { type: 'FeatureCollection', features: blocks }
    });

    map.addLayer({
      id: 'blocks',
      type: 'fill-extrusion',
      source: 'blocks',
      paint: {
        'fill-extrusion-height': heightExpr(1),
        'fill-extrusion-base': 0,
        'fill-extrusion-opacity': 0.85,
        'fill-extrusion-color': [
          'interpolate', ['linear'], ['get', 'height'],
          20, '#b6d3ea',
          80, '#4a90c9',
          130, '#1f5fd0'
        ]
      }
    });
  });

  document.getElementById('k').addEventListener('input', function () {
    var v = parseFloat(this.value);
    document.getElementById('kv').textContent = v.toFixed(1);
    if (map.getLayer('blocks')) {
      map.setPaintProperty('blocks', 'fill-extrusion-height', heightExpr(v));
    }
  });

  map.on('moveend', function () {
    document.getElementById('p').textContent = map.getPitch().toFixed(0) + '°';
  });

  map.on('error', function (e) {
    if (e.error) console.warn('地图错误：' + e.error.message);
  });
})();
</script>
</body>
</html>