Edit

Example of Retina / HiDPI mercator tiles (512x512px) available as XYZ.

The XYZ source accepts a tilePixelRatio option.

main.js
import Map from 'ol/Map';
import OSM from 'ol/source/OSM';
import TileLayer from 'ol/layer/Tile';
import View from 'ol/View';
import XYZ from 'ol/source/XYZ';
import {transform} from 'ol/proj';

const key = 'Get your own API key at https://www.maptiler.com/cloud/';
const attributions =
  '<a href="https://www.maptiler.com/copyright/" target="_blank">&copy; MapTiler</a> ' +
  '<a href="https://www.openstreetmap.org/copyright" target="_blank">&copy; OpenStreetMap contributors</a>';

const map = new Map({
  target: 'map',
  layers: [
    new TileLayer({
      source: new OSM(),
    }),
    new TileLayer({
      source: new XYZ({
        attributions: attributions,
        url:
          'https://api.maptiler.com/maps/outdoor/256/{z}/{x}/{y}@2x.png?key=' +
          key,
        tilePixelRatio: 2, // THIS IS IMPORTANT
      }),
    }),
  ],
  view: new View({
    projection: 'EPSG:3857',
    center: transform([-112.18688965, 36.057944835], 'EPSG:4326', 'EPSG:3857'),
    zoom: 12,
  }),
});
index.html
<!DOCTYPE html>
<html lang="en">
  <head>
    <meta charset="UTF-8">
    <title>XYZ Retina Tiles</title>
    <link rel="stylesheet" href="node_modules/ol/ol.css">
    <style>
      .map {
        width: 100%;
        height: 400px;
      }
    </style>
  </head>
  <body>
    <div id="map" class="map"></div>
    <!-- Pointer events polyfill for old browsers, see https://caniuse.com/#feat=pointer -->
    <script src="https://unpkg.com/[email protected]/dist/elm-pep.js"></script>
    <script type="module" src="main.js"></script>
  </body>
</html>
package.json
{
  "name": "xyz-retina",
  "dependencies": {
    "ol": "7.1.0"
  },
  "devDependencies": {
    "vite": "^3.0.3",
    "@babel/core": "latest"
  },
  "scripts": {
    "start": "vite",
    "build": "vite build"
  }
}