Earthquakes with custom symbols

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

const symbol = [
  [0, 0],
  [4, 2],
  [6, 0],
  [10, 5],
  [6, 3],
  [4, 5],
  [0, 0],
];
let scale;
const scaleFunction = function (coordinate) {
  return [coordinate[0] * scale, coordinate[1] * scale];
};

const styleCache = {};
const styleFunction = function (feature) {
  // 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.
  const name = feature.get('name');
  const magnitude = parseFloat(name.substr(2));
  const size = parseInt(10 + 40 * (magnitude - 5), 10);
  scale = size / 10;
  let style = styleCache[size];
  if (!style) {
    const canvas = document.createElement('canvas');
    const vectorContext = toContext(canvas.getContext('2d'), {
      size: [size, size],
      pixelRatio: 1,
    });
    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(new Polygon([symbol.map(scaleFunction)]));
    style = new Style({
      image: new Icon({
        img: canvas,
        rotation: 1.2,
      }),
    });
    styleCache[size] = style;
  }
  return style;
};

const vector = new VectorLayer({
  source: new VectorSource({
    url: 'data/kml/2012_Earthquakes_Mag5.kml',
    format: new KML({
      extractStyles: false,
    }),
  }),
  style: styleFunction,
});

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>

Earthquakes with custom symbols

main.js

index.html

package.json