This example uses OpenLayers v10.9.0. The latest is v.
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#### Style renderer

vector 86 geojson 11 style 27 custom 6 renderer 1

#####

Example of a style with a custom renderer.

A custom style renderer and a clip path are used to render the flag of a country as fill for the country shape.

##### main.js

    import Map from 'ol/Map.js';
    import View from 'ol/View.js';
    import {getBottomLeft, getHeight, getWidth} from 'ol/extent.js';
    import GeoJSON from 'ol/format/GeoJSON.js';
    import VectorLayer from 'ol/layer/Vector.js';
    import {toContext} from 'ol/render.js';
    import VectorSource from 'ol/source/Vector.js';
    import Fill from 'ol/style/Fill.js';
    import Stroke from 'ol/style/Stroke.js';
    import Style from 'ol/style/Style.js';

    const fill = new Fill();
    const stroke = new Stroke({
      color: 'rgba(255,255,255,0.8)',
      width: 2,
    });
    const style = new Style({
      renderer: function (pixelCoordinates, state) {
        const context = state.context;
        const geometry = state.geometry.clone();
        geometry.setCoordinates(pixelCoordinates);
        const extent = geometry.getExtent();
        const width = getWidth(extent);
        const height = getHeight(extent);
        const flag = state.feature.get('flag');
        if (!flag || height < 1 || width < 1) {
          return;
        }

        // Stitch out country shape from the blue canvas
        context.save();
        const renderContext = toContext(context, {
          pixelRatio: 1,
        });
        renderContext.setFillStrokeStyle(fill, stroke);
        renderContext.drawGeometry(geometry);
        context.clip();

        // Fill transparent country with the flag image
        const bottomLeft = getBottomLeft(extent);
        const left = bottomLeft[0];
        const bottom = bottomLeft[1];
        context.drawImage(flag, left, bottom, width, height);
        context.restore();
      },
    });

    const vectorLayer = new VectorLayer({
      source: new VectorSource({
        url: 'https://openlayersbook.github.io/openlayers_book_samples/assets/data/countries.geojson',
        format: new GeoJSON(),
      }),
      style: style,
    });

    // Load country flags and set them as `flag` attribute on the country feature
    vectorLayer.getSource().on('addfeature', function (event) {
      const feature = event.feature;
      const img = new Image();
      img.onload = function () {
        feature.set('flag', img);
      };
      img.src =
        'https://flagcdn.com/w320/' + feature.get('iso_a2').toLowerCase() + '.png';
    });

    new Map({
      layers: [vectorLayer],
      target: 'map',
      view: new View({
        center: [0, 0],
        zoom: 1,
      }),
    });

##### index.html

    <!DOCTYPE html>
    <html lang="en">
      <head>
        <meta charset="UTF-8">
        <title>Style renderer</title>
        <link rel="stylesheet" href="node_modules/ol/ol.css">
        <style>
          .map {
            width: 100%;
            height: 400px;
          }
          #map {
            background: #75d0f0;
          }
        </style>
      </head>
      <body>
        <div id="map" class="map"></div>
        <div id="info">&nbsp;</div>

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

##### package.json

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