This example uses OpenLayers v10.9.0. The latest is v.
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#### High DPI WMTS

hidpi 4 retina 3 wmts 7

#####

Example of a WMTS based HiDPI layer.

The WMTS source has a `tilePixelRatio` option. A HiDPI capable WMTS could provide tiles with 512x512 pixel tiles, but use them in a 256x256 pixel tile grid. In this case `tilePixelRatio` needs to be set to `2`.

##### main.js

    import Map from 'ol/Map.js';
    import View from 'ol/View.js';
    import WMTSCapabilities from 'ol/format/WMTSCapabilities.js';
    import {DEVICE_PIXEL_RATIO} from 'ol/has.js';
    import TileLayer from 'ol/layer/Tile.js';
    import WMTS, {optionsFromCapabilities} from 'ol/source/WMTS.js';

    const capabilitiesUrl =
      'https://mapsneu.wien.gv.at/basemapneu/1.0.0/WMTSCapabilities.xml';

    // HiDPI support:
    // * Use 'bmaphidpi' layer (pixel ratio 2) for device pixel ratio > 1
    // * Use 'geolandbasemap' layer (pixel ratio 1) for device pixel ratio == 1
    const hiDPI = DEVICE_PIXEL_RATIO > 1;
    const layer = hiDPI ? 'bmaphidpi' : 'geolandbasemap';
    const tilePixelRatio = hiDPI ? 2 : 1;

    const map = new Map({
      target: 'map',
      view: new View({
        center: [1823849, 6143760],
        zoom: 11,
      }),
    });

    fetch(capabilitiesUrl)
      .then(function (response) {
        return response.text();
      })
      .then(function (text) {
        const result = new WMTSCapabilities().read(text);
        const options = optionsFromCapabilities(result, {
          layer: layer,
          matrixSet: 'google3857',
          style: 'normal',
        });
        options.tilePixelRatio = tilePixelRatio;
        options.attributions =
          'Grundkarte: <a target="_blank" href="https://basemap.at/">basemap.at</a>';
        map.addLayer(
          new TileLayer({
            source: new WMTS(options),
          }),
        );
      });

##### index.html

    <!DOCTYPE html>
    <html lang="en">
      <head>
        <meta charset="UTF-8">
        <title>High DPI WMTS</title>
        <link rel="stylesheet" href="node_modules/ol/ol.css">
        <style>
          .map {
            width: 100%;
            height: 400px;
          }
          .map {
            background: white;
          }
        </style>
      </head>
      <body>
        <div id="map" class="map"></div>

        <script type="module" src="main.js"></script>
      </body>
    </html>

##### package.json

    {
      "name": "wmts-hidpi",
      "dependencies": {
        "ol": "10.9.0"
      },
      "devDependencies": {
        "vite": "^3.2.3"
      },
      "scripts": {
        "start": "vite",
        "build": "vite build"
      }
    }