Style renderer

vector 69 geojson 8 style 22 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 'ol/ol.css';
import GeoJSON from 'ol/format/GeoJSON';
import Map from 'ol/Map';
import VectorLayer from 'ol/layer/Vector';
import VectorSource from 'ol/source/Vector';
import View from 'ol/View';
import {Fill, Stroke, Style} from 'ol/style';
import {getBottomLeft, getHeight, getWidth} from 'ol/extent';
import {toContext} from 'ol/render';

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>
    <!-- Pointer events polyfill for old browsers, see https://caniuse.com/#feat=pointer -->
    <script src="https://unpkg.com/elm-pep@1.0.6/dist/elm-pep.js"></script>
    <!-- The lines below are only needed for old environments like Internet Explorer and Android 4.x -->
    <script src="https://cdn.polyfill.io/v3/polyfill.min.js?features=fetch,requestAnimationFrame,Element.prototype.classList,TextDecoder"></script>
    <script src="https://cdnjs.cloudflare.com/ajax/libs/core-js/3.18.3/minified.js"></script>
    <style>
      .map {
        width: 100%;
        height:400px;
      }
      #map {
        background: #75d0f0;
      }
    </style>
  </head>
  <body>
    <div id="map" class="map"></div>
    <div id="info">&nbsp;</div>
    <script src="main.js"></script>
  </body>
</html>

package.json

{
  "name": "style-renderer",
  "dependencies": {
    "ol": "6.13.1-dev"
  },
  "devDependencies": {
    "parcel": "^2.0.0"
  },
  "scripts": {
    "start": "parcel index.html",
    "build": "parcel build --public-url . index.html"
  }
}