XYZ Retina

<!--
  示例：OpenLayers 高分辨率 XYZ
  要点：tilePixelRatio 为 2 时，512 像素瓦片按 256 CSS 像素显示，细节更锐利
  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>高分辨率 XYZ</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 select,.bar input[type=range]{font-size:12px}
  .bar .val{font-family:ui-monospace,Consolas,monospace;color:#1f5fd0;min-width:44px}
  .bar .sep{width:1px;height:16px;background:#d8dce2}
  #map{flex:1 1 auto;min-height:0;background:#eef0f3}
</style>
</head>
<body>
<div class="bar">
  <label><input type="checkbox" id="retina" checked> 2 倍瓦片</label>
  <span class="sep"></span>
  <span id="info">当前：512 px 图片 / 256 CSS px</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').textContent = 'OpenLayers 加载失败，请检查能否访问 cdn.jsdelivr.net';
    return;
  }


  function tilePreview(tile, pixels) {
    var coord = tile.getTileCoord();
    var canvas = document.createElement('canvas');
    canvas.width = pixels;
    canvas.height = pixels;
    var ctx = canvas.getContext('2d');
    var step = pixels / 4;
    ctx.clearRect(0, 0, pixels, pixels);
    ctx.strokeStyle = 'rgba(255, 255, 255, 0.65)';
    ctx.lineWidth = pixels / 128;
    for (var i = 1; i < 4; ++i) {
      ctx.beginPath();
      ctx.moveTo(i * step, 0);
      ctx.lineTo(i * step, pixels);
      ctx.stroke();
      ctx.beginPath();
      ctx.moveTo(0, i * step);
      ctx.lineTo(pixels, i * step);
      ctx.stroke();
    }
    ctx.fillStyle = 'rgba(20, 40, 60, 0.82)';
    ctx.font = '600 ' + Math.round(pixels / 18) + 'px ui-monospace,Consolas,monospace';
    ctx.textAlign = 'center';
    ctx.textBaseline = 'middle';
    ctx.fillText(coord[0] + '/' + coord[1] + '/' + coord[2], pixels / 2, pixels / 2);
    tile.getImage().src = canvas.toDataURL('image/png');
  }

  var normal = new ol.source.XYZ({
    url: 'https://demo.invalid/retina/{z}/{x}/{y}.png',
    tilePixelRatio: 1,
    maxZoom: 18,
    tileLoadFunction: function (tile) {
      tilePreview(tile, 256);
    }
  });

  var retina = new ol.source.XYZ({
    url: 'https://demo.invalid/retina/{z}/{x}/{y}@2x.png',
    tilePixelRatio: 2,
    maxZoom: 18,
    tileLoadFunction: function (tile) {
      tilePreview(tile, 512);
    }
  });

  var normalLayer = new ol.layer.Tile({source: normal, visible: false, opacity: 0.9});
  var retinaLayer = new ol.layer.Tile({source: retina, visible: true, opacity: 0.9});

  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: 0.6}),
      normalLayer,
      retinaLayer
    ],
    view: new ol.View({
      center: ol.proj.fromLonLat([116.391, 39.907]),
      zoom: 12
    })
  });

  document.getElementById('retina').addEventListener('change', function (evt) {
    var useRetina = evt.target.checked;
    retinaLayer.setVisible(useRetina);
    normalLayer.setVisible(!useRetina);
    document.getElementById('info').textContent = useRetina
      ? '当前：512 px 图片 / 256 CSS px'
      : '当前：256 px 图片 / 256 CSS px';
  });

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