Custom Hit Detection Render

circle 4 feature 12 vector 69 render 4 custom 6 hitDetectionRenderer 1

Example of a custom hit detection renderer.

This example demonstrates the use of 'ol/style/Style' hitDetectionRender option function in detecting if pointer is over a particular feature. Move pointer over the label for Columbus Circle feature and see that only label is used in hit detection.

main.js

import 'ol/ol.css';
import Feature from 'ol/Feature';
import Map from 'ol/Map';
import View from 'ol/View';
import {Circle} from 'ol/geom';
import {OSM, Vector as VectorSource} from 'ol/source';
import {Style} from 'ol/style';
import {Tile as TileLayer, Vector as VectorLayer} from 'ol/layer';
import {fromLonLat} from 'ol/proj';

const columbusCircleCoords = fromLonLat([-73.98189, 40.76805]);
const labelTextStroke = 'rgba(120, 120, 120, 1)';
const labelText = 'Columbus Circle';

let pointerOverFeature = null;

const renderLabelText = (ctx, x, y, stroke) => {
  ctx.fillStyle = 'rgba(255,0,0,1)';
  ctx.strokeStyle = stroke;
  ctx.lineWidth = 1;
  ctx.textAlign = 'center';
  ctx.textBaseline = 'middle';
  ctx.font = `bold 30px verdana`;
  ctx.filter = 'drop-shadow(7px 7px 2px #e81)';
  ctx.fillText(labelText, x, y);
  ctx.strokeText(labelText, x, y);
};

const circleFeature = new Feature({
  geometry: new Circle(columbusCircleCoords, 50),
});

circleFeature.set('label-color', labelTextStroke);

circleFeature.setStyle(
  new Style({
    renderer(coordinates, state) {
      const [[x, y], [x1, y1]] = coordinates;
      const ctx = state.context;
      const dx = x1 - x;
      const dy = y1 - y;
      const radius = Math.sqrt(dx * dx + dy * dy);

      const innerRadius = 0;
      const outerRadius = radius * 1.4;

      const gradient = ctx.createRadialGradient(
        x,
        y,
        innerRadius,
        x,
        y,
        outerRadius
      );
      gradient.addColorStop(0, 'rgba(255,0,0,0)');
      gradient.addColorStop(0.6, 'rgba(255,0,0,0.2)');
      gradient.addColorStop(1, 'rgba(255,0,0,0.8)');
      ctx.beginPath();
      ctx.arc(x, y, radius, 0, 2 * Math.PI, true);
      ctx.fillStyle = gradient;
      ctx.fill();
      ctx.strokeStyle = 'rgba(255,0,0,1)';
      ctx.stroke();

      renderLabelText(ctx, x, y, circleFeature.get('label-color'));
    },
    hitDetectionRenderer(coordinates, state) {
      const [x, y] = coordinates[0];
      const ctx = state.context;
      renderLabelText(ctx, x, y, circleFeature.get('label-color'));
    },
  })
);

const map = new Map({
  layers: [
    new TileLayer({
      source: new OSM(),
      visible: true,
    }),
    new VectorLayer({
      source: new VectorSource({
        features: [circleFeature],
      }),
    }),
  ],
  target: 'map',
  view: new View({
    center: columbusCircleCoords,
    zoom: 19,
  }),
});

map.on('pointermove', (evt) => {
  const featureOver = map.forEachFeatureAtPixel(evt.pixel, (feature) => {
    feature.set('label-color', 'rgba(255,255,255,1)');
    return feature;
  });

  if (pointerOverFeature && pointerOverFeature != featureOver) {
    pointerOverFeature.set('label-color', labelTextStroke);
  }
  pointerOverFeature = featureOver;
});

index.html

<!DOCTYPE html>
<html lang="en">
  <head>
    <meta charset="UTF-8">
    <title>Custom Hit Detection Render</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;
      }
    </style>
  </head>
  <body>
    <div id="map" class="map"></div>    <script src="main.js"></script>
  </body>
</html>

package.json

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