This example uses OpenLayers v10.9.0. The latest is v.
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#### Earthquakes with custom symbols

KML 9 vector 86 style 27 canvas 6 symbol 3

#####

Demonstrates the use of `toContext` to create custom icon symbols.

This example parses a KML file and renders the features as a vector layer. The layer is given a `style` that renders earthquake locations with a custom lightning symbol and a size relative to their magnitude.

##### main.js

    import Map from 'ol/Map.js';
    import View from 'ol/View.js';
    import {getBottomLeft, getTopRight} from 'ol/extent.js';
    import KML from 'ol/format/KML.js';
    import Polygon from 'ol/geom/Polygon.js';
    import {DEVICE_PIXEL_RATIO} from 'ol/has.js';
    import TileLayer from 'ol/layer/Tile.js';
    import VectorLayer from 'ol/layer/Vector.js';
    import {toContext} from 'ol/render.js';
    import StadiaMaps from 'ol/source/StadiaMaps.js';
    import VectorSource from 'ol/source/Vector.js';
    import Fill from 'ol/style/Fill.js';
    import Icon from 'ol/style/Icon.js';
    import Stroke from 'ol/style/Stroke.js';
    import Style from 'ol/style/Style.js';

    const getSymbolOutline = (function () {
      const path = [
        [0, 0],
        [4, 2],
        [6, 0],
        [10, 5],
        [6, 3],
        [4, 5],
        [0, 0],
      ];
      const symbolOutline = new Polygon([path]);
      symbolOutline.rotate(1.2, path[0]);
      return function (scale, offset) {
        const outline = symbolOutline.clone();
        outline.scale(scale, scale, path[0]);
        const origin = getBottomLeft(outline.getExtent());
        outline.translate(offset - origin[0], offset - origin[1]);
        return outline;
      };
    })();

    const styleCache = {};

    const vector = new VectorLayer({
      source: new VectorSource({
        url: 'data/kml/2012_Earthquakes_Mag5.kml',
        format: new KML({
          extractStyles: false,
        }),
      }),
      style: function (feature) {
        const magnitude = feature.get('magnitude');
        let style = styleCache[magnitude];
        if (!style) {
          const scale = 1 + 4 * (magnitude - 5);
          const lineWidth = 2;
          const outline = getSymbolOutline(scale, Math.ceil(lineWidth / 2));
          const canvas = document.createElement('canvas');
          const vectorContext = toContext(canvas.getContext('2d'), {
            size: getTopRight(outline.getExtent()).map((n) =>
              Math.ceil(n + lineWidth / 2),
            ),
            pixelRatio: DEVICE_PIXEL_RATIO,
          });
          vectorContext.setStyle(
            new Style({
              fill: new Fill({color: 'rgba(255, 153, 0, 0.4)'}),
              stroke: new Stroke({
                color: 'rgba(255, 204, 0, 0.2)',
                width: 2,
              }),
            }),
          );
          vectorContext.drawGeometry(outline);
          style = new Style({
            image: new Icon({
              img: canvas,
              scale: 1 / DEVICE_PIXEL_RATIO,
            }),
          });
          styleCache[magnitude] = style;
        }
        return style;
      },
    });
    // 2012_Earthquakes_Mag5.kml stores the magnitude of each earthquake in a
    // standards-violating <magnitude> tag in each Placemark.  We extract it from
    // the Placemark's name instead.
    function parseMagnitudeFromName(name) {
      return parseFloat(name.substr(2));
    }
    vector.getSource().on('featuresloadend', function (evt) {
      evt.features.forEach((f) => {
        f.set('magnitude', parseMagnitudeFromName(f.get('name')), true);
      });
    });

    const raster = new TileLayer({
      source: new StadiaMaps({
        layer: 'stamen_toner',
      }),
    });

    const map = new Map({
      layers: [raster, vector],
      target: 'map',
      view: new View({
        center: [0, 0],
        zoom: 2,
      }),
    });

##### index.html

    <!DOCTYPE html>
    <html lang="en">
      <head>
        <meta charset="UTF-8">
        <title>Earthquakes with custom symbols</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>

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

##### package.json

    {
      "name": "earthquake-custom-symbol",
      "dependencies": {
        "ol": "10.9.0"
      },
      "devDependencies": {
        "vite": "^3.2.3"
      },
      "scripts": {
        "start": "vite",
        "build": "vite build"
      }
    }