Geozarr Storytelling

<!--
  示例：GeoZarr 事件叙事 — OpenLayers geozarr-storytelling
  核心逻辑：三幅不同淹没范围的合成影像按事件阶段切换，Raster 源统一按水体指数出图
  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>GeoZarr 事件叙事</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:8px;align-items:center;font-size:12px;color:#58606e;flex-wrap:wrap}
  .bar button{font:inherit;padding:3px 10px;border:1px solid #ccd2da;background:#fff;
       border-radius:3px;cursor:pointer;color:#2b3140}
  .bar button.on{background:#1f5fd0;border-color:#1f5fd0;color:#fff}
  #map{flex:1 1 auto;min-height:0;background:#eef0f3;position:relative}
  .caption{position:absolute;left:12px;bottom:12px;max-width:360px;
       background:rgba(255,255,255,0.94);border:1px solid #d7dce3;border-radius:4px;
       padding:10px 12px;font-size:12px;color:#2b3140;box-shadow:0 2px 8px rgba(0,0,0,0.12)}
  .caption b{display:block;margin-bottom:4px;font-size:13px}
</style>
</head>
<body>
<div class="bar">
  <button data-stage="before" class="on">事件前</button>
  <button data-stage="during">事件中</button>
  <button data-stage="after">事件后</button>
  <span id="info">—</span>
</div>
<div id="map"></div>
<div class="caption" id="caption"><b>事件前</b><span>常规水位，河网只占低洼地带。</span></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 SIZE = 512;
  var extent = ol.proj.transformExtent(
    [116.15, 39.78, 116.60, 40.06], 'EPSG:4326', 'EPSG:3857'
  );

  var STAGES = {
    before: {
      flood: 0.30,
      title: '事件前',
      text: '常规水位，河网只占低洼地带，城区建成区完整。'
    },
    during: {
      flood: 0.72,
      title: '事件中',
      text: '强降雨后水位抬升，河道两侧大片区域转为水面。'
    },
    after: {
      flood: 0.42,
      title: '事件后',
      text: '水位回落，退水后的湿地与积水仍沿河道分布。'
    }
  };

  var cache = {};

  function sceneFor(stage) {
    if (cache[stage]) return cache[stage];
    var conf = STAGES[stage];
    var c = document.createElement('canvas');
    c.width = SIZE;
    c.height = SIZE;
    var ctx = c.getContext('2d');
    var img = ctx.createImageData(SIZE, SIZE);

    for (var y = 0; y < SIZE; y++) {
      for (var x = 0; x < SIZE; x++) {
        var i = (y * SIZE + x) * 4;
        /* 河道：一条弯曲主干加两条支流 */
        var river = Math.abs(y - (SIZE * 0.62 + 60 * Math.sin(x / 90)));
        var branch = Math.abs(y - (SIZE * 0.3 - 40 * Math.cos(x / 70)));
        var band = Math.min(river, branch);

        var isWater = band < conf.flood * 90;
        var veg = Math.max(0, Math.min(1,
          0.45 + 0.35 * Math.sin(x / 33) * Math.cos(y / 51)));

        if (isWater) {
          img.data[i] = 40;
          img.data[i + 1] = 85;
          img.data[i + 2] = 140;
        } else {
          img.data[i] = Math.round(90 + 40 * veg);
          img.data[i + 1] = Math.round(120 + 70 * veg);
          img.data[i + 2] = Math.round(70 + 30 * veg);
        }
        img.data[i + 3] = 255;
      }
    }
    ctx.putImageData(img, 0, 0);
    cache[stage] = { url: c.toDataURL(), water: conf.flood };
    return cache[stage];
  }

  var layer = new ol.layer.Image({ opacity: 0.9 });
  var current = 'before';

  function rebuild(stage) {
    var scene = sceneFor(stage);

    layer.setSource(new ol.source.Raster({
      sources: [new ol.source.ImageStatic({
        url: scene.url,
        projection: 'EPSG:3857',
        imageExtent: extent,
        crossOrigin: 'anonymous'
      })],
      operation: function (pixels) {
        var src = pixels[0];
        var out = new Uint8ClampedArray(src.length);
        var water = 0, count = 0;

        for (var i = 0; i < src.length; i += 4) {
          var r = src[i], g = src[i + 1], b = src[i + 2];
          /* 水体指数：蓝色明显高于红色时判为水面 */
          var isWater = (b - r) > 45;
          if (isWater) {
            out[i] = 32;
            out[i + 1] = 78;
            out[i + 2] = 132;
            water++;
          } else {
            out[i] = Math.min(255, r * 1.15);
            out[i + 1] = Math.min(255, g * 1.1);
            out[i + 2] = Math.min(255, b * 1.2);
          }
          out[i + 3] = 255;
          count++;
        }
        layer.__waterRatio = water / count;
        return out;
      }
    }));

    var conf = STAGES[stage];
    document.getElementById('caption').innerHTML =
      '<b>' + conf.title + '</b><span>' + conf.text + '</span>';
    document.getElementById('info').textContent =
      '水面占比 ' + (scene.water * 100).toFixed(0) + '%（合成参数）';
  }

  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: 0.45 }),
      layer
    ],
    view: new ol.View({
      center: ol.proj.fromLonLat([116.38, 39.92]),
      zoom: 11,
      minZoom: 2
    }),
    controls: ol.control.defaults.defaults({ attribution: false })
  });

  Array.prototype.forEach.call(
    document.querySelectorAll('[data-stage]'),
    function (btn) {
      btn.addEventListener('click', function () {
        Array.prototype.forEach.call(
          document.querySelectorAll('[data-stage]'),
          function (b) { b.classList.remove('on'); }
        );
        btn.classList.add('on');
        current = btn.getAttribute('data-stage');
        rebuild(current);
      });
    }
  );

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