openlayers/examples/hit-tolerance.js

import Map from 'ol/Map';
import View from 'ol/View';
import {Tile as TileLayer, Vector as VectorLayer} from 'ol/layer';
import {OSM, Vector as VectorSource} from 'ol/source';
import Feature from 'ol/Feature';
import LineString from 'ol/geom/LineString';
import {Stroke, Style} from 'ol/style';

const raster = new TileLayer({
  source: new OSM()
});

const style = new Style({
  stroke: new Stroke({
    color: 'black',
    width: 1
  })
});

const feature = new Feature(new LineString([[-4000000, 0], [4000000, 0]]));

const vector = new VectorLayer({
  source: new VectorSource({
    features: [feature]
  }),
  style: style
});

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

let hitTolerance;

const statusElement = document.getElementById('status');

map.on('singleclick', function(e) {
  let hit = false;
  map.forEachFeatureAtPixel(e.pixel, function() {
    hit = true;
  }, {
    hitTolerance: hitTolerance
  });
  if (hit) {
    style.getStroke().setColor('green');
    statusElement.innerHTML = ' A feature got hit!';
  } else {
    style.getStroke().setColor('black');
    statusElement.innerHTML = ' No feature got hit.';
  }
  feature.changed();
});

const selectHitToleranceElement = document.getElementById('hitTolerance');
const circleCanvas = document.getElementById('circle');

const changeHitTolerance = function() {
  hitTolerance = parseInt(selectHitToleranceElement.value, 10);

  const size = 2 * hitTolerance + 2;
  circleCanvas.width = size;
  circleCanvas.height = size;
  const ctx = circleCanvas.getContext('2d');
  ctx.clearRect(0, 0, size, size);
  ctx.beginPath();
  ctx.arc(hitTolerance + 1, hitTolerance + 1, hitTolerance + 0.5, 0, 2 * Math.PI);
  ctx.fill();
  ctx.stroke();
};

selectHitToleranceElement.onchange = changeHitTolerance;
changeHitTolerance();