Cog

<!--
  说明：分层瓦片影像的中文示例，数据在页面内生成，可独立运行。
  核心逻辑：金字塔 resolutions + tileUrlFunction 按范围裁切主图 + TileImage
  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>分层瓦片影像</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 button{font:inherit;padding:3px 9px;border:1px solid #c9ced6;background:#fff;
       border-radius:5px;cursor:pointer;color:#333}
  .bar button:hover{background:#eef2f8}
  .bar input[type=range]{width:110px;vertical-align:middle}
  .bar input[type=text]{font:inherit;padding:2px 6px;border:1px solid #c9ced6;border-radius:4px}
  #map{flex:1 1 auto;min-height:0;background:#eef0f3;position:relative}
  .panel{flex:0 0 auto;max-height:34%;overflow:auto;padding:8px 12px;font-size:12px;
       background:#fff;border-top:1px solid #e3e6ea;color:#3d4451}
  .panel pre{margin:0;font-family:Consolas,"Courier New",monospace;font-size:11px;
       white-space:pre-wrap;word-break:break-all;line-height:1.5}
  .ol-attribution{font-size:11px}

</style>
</head>
<body>
<div class="bar">
<label><input type="checkbox" id="base" checked> 显示 OSM 底图</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') {
    var errBox = document.getElementById('map');
    if (errBox) {
      errBox.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 fromLonLat = ol.proj.fromLonLat;
  var ext = ol.proj.transformExtent([115.9, 39.5, 116.9, 40.4], 'EPSG:4326', 'EPSG:3857');
  var W = ext[2] - ext[0];
  var H = ext[3] - ext[1];

  /* 主影像：1024 × 1024，条纹与噪点模拟遥感快视图 */
  var master = document.createElement('canvas');
  master.width = master.height = 1024;
  var mctx = master.getContext('2d');
  var grad = mctx.createLinearGradient(0, 0, 1024, 1024);
  grad.addColorStop(0, '#23405c');
  grad.addColorStop(0.45, '#4f7a52');
  grad.addColorStop(1, '#a98b52');
  mctx.fillStyle = grad;
  mctx.fillRect(0, 0, 1024, 1024);
  for (var i = 0; i < 90; i++) {
    var cx = (Math.sin(i * 12.9898) * 43758.5453) % 1;
    var cy = (Math.sin(i * 78.233) * 12345.6789) % 1;
    cx = Math.abs(cx) * 1024;
    cy = Math.abs(cy) * 1024;
    var rad = 20 + (i % 7) * 18;
    var g2 = mctx.createRadialGradient(cx, cy, 2, cx, cy, rad);
    g2.addColorStop(0, 'rgba(255,246,210,0.35)');
    g2.addColorStop(1, 'rgba(255,246,210,0)');
    mctx.fillStyle = g2;
    mctx.beginPath();
    mctx.arc(cx, cy, rad, 0, Math.PI * 2);
    mctx.fill();
  }

  var resolutions = [];
  for (var z = 0; z <= 4; z++) {
    resolutions.push(W / 256 / Math.pow(2, z));
  }

  var grid = new ol.tilegrid.TileGrid({
    extent: ext,
    origin: ol.extent.getTopLeft(ext),
    resolutions: resolutions,
    tileSize: 256
  });

  var info = document.getElementById('info');
  var loaded = 0;

  function tileUrl(tileCoord) {
    if (!tileCoord) { return ''; }
    var te = grid.getTileCoordExtent(tileCoord);
    var c = document.createElement('canvas');
    c.width = c.height = 256;
    var ctx = c.getContext('2d');
    ctx.fillStyle = '#101820';
    ctx.fillRect(0, 0, 256, 256);

    var sx = (te[0] - ext[0]) / W * 1024;
    var sy = (ext[3] - te[3]) / H * 1024;
    var sw = (te[2] - te[0]) / W * 1024;
    var sh = (te[3] - te[1]) / H * 1024;

    var ix = Math.max(0, sx);
    var iy = Math.max(0, sy);
    var ix2 = Math.min(1024, sx + sw);
    var iy2 = Math.min(1024, sy + sh);

    if (ix2 > ix && iy2 > iy) {
      ctx.drawImage(
        master, ix, iy, ix2 - ix, iy2 - iy,
        (ix - sx) / sw * 256, (iy - sy) / sh * 256,
        (ix2 - ix) / sw * 256, (iy2 - iy) / sh * 256
      );
    }

    ctx.strokeStyle = 'rgba(255,255,255,0.35)';
    ctx.lineWidth = 1;
    ctx.strokeRect(0.5, 0.5, 255, 255);
    ctx.fillStyle = 'rgba(255,255,255,0.85)';
    ctx.font = 'bold 12px monospace';
    ctx.fillText('z' + tileCoord[0] + ' x' + tileCoord[1] + ' y' + tileCoord[2], 8, 18);

    loaded++;
    info.textContent = '已裁切瓦片 ' + loaded + ' 块 · 金字塔 5 级（z0–z4）';
    return c.toDataURL('image/png');
  }

  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 pyramid = new ol.layer.Tile({
    source: new ol.source.TileImage({
      projection: 'EPSG:3857',
      tileGrid: grid,
      tileUrlFunction: tileUrl
    }),
    opacity: 0.92
  });

  var map = new ol.Map({
    target: 'map',
    layers: [base, pyramid],
    view: new ol.View({center: fromLonLat([116.4, 39.95]), zoom: 10}),
    controls: ol.control.defaults.defaults({attribution: false, zoom: true, rotate: false})
  });

  document.getElementById('base').addEventListener('change', function () {
    base.setVisible(this.checked);
  });
})();
</script>
</body>
</html>