title: Features added to vector layer are not visible
body: <p>I am trying to add new features to a vector layer.</p>
  
  <p>I do it with this code:</p>
  
  <pre><code>layer.getSource().addFeatures(features);
  </code></pre>
  
  <p>Where <strong>layer</strong> is an instance of ol.vector.Layer and <strong>features</strong> is an array of ol.Feature</p>
  
  <p>The features are added but they are not visible. And unfortunately even calling</p>
  
  <pre><code>map.render()
  </code></pre>
  
  <p>does not help.
  The only solution that works is reloading all features for the layer:</p>
  
  <pre><code>layer.getSource().clear();
  view = map.getView();
  layer.getSource().loadFeatures(map.getExtent(), view.getResolution(), view.getProjection());
  </code></pre>
  
  <p>But it is quite annoying to wait for the whole layer reload each time you want to add a feature.</p>
  
  <p>Any ideas what I might be doing wrong ?</p>