Hit Tolerance

 No feature got hit.

Area:  

Example using the hitTolerance parameter.

By default, the map.forEachFeatureAtPixel() function only considers features that are directly under the provided pixel. This can make it difficult to interact with features on touch devices. To consider features within some distance of the provided pixel, use the hitTolerance option. For example, map.forEachFeatureAtPixel(pixel, callback, {hitTolerance: 3}) will call the callback with all features that are within three pixels of the provided pixel.

<!DOCTYPE html>
<html>
  <head>
    <title>Hit Tolerance</title>
    <link rel="stylesheet" href="https://openlayers.org/en/v4.6.4/css/ol.css" type="text/css">
    <!-- The line below is only needed for old environments like Internet Explorer and Android 4.x -->
    <script src=""></script>
    <script src="https://openlayers.org/en/v4.6.4/build/ol.js"></script>
  </head>
  <body>
    <div id="map" class="map"></div>
    <form class="form-inline">
      <span id="status">&nbsp;No feature got hit.</span>
      <br />
      <label>Hit tolerance for selecting features </label>
      <select id="hitTolerance" class="form-control">
        <option value="0" selected>0 Pixels</option>
        <option value="5">5 Pixels</option>
        <option value="10">10 Pixels</option>
      </select>
      <br />
      Area: &nbsp;<canvas id="circle" style="vertical-align: middle"/>
    </form>
    <script>
      var raster = new ol.layer.Tile({
        source: new ol.source.OSM()
      });

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

      var feature = new ol.Feature(new ol.geom.LineString([[-4000000, 0], [4000000, 0]]));

      var vector = new ol.layer.Vector({
        source: new ol.source.Vector({
          features: [feature]
        }),
        style: style
      });

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

      var hitTolerance;

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

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

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

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

        var size = 2 * hitTolerance + 2;
        circleCanvas.width = size;
        circleCanvas.height = size;
        var 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();
    </script>
  </body>
</html>