Enlarging extent to include new center

Question

I have a map with some layers, and the layers have different features on them. I have a function that iterates through each layer and creates an extent from all the features' geometry extent. Then I fit the map to this extent. I want to have a different center for the map and still fit all the features in the view of the map.

Is there a function that can enlarge/extend a given extent to have a new center?

I'm using OpenLayers 4.6.4 Example of code, below, so in essence I want to give a center parameter and have a function that extends/enlarges the extent already calculated.

 /**
 * Fits all the features in a layer on the map.
 * @param {*Layer on map which should get all the features from} layer 
 */
function fitLayersFeatureOnMap(layers, center) {
    var featuresOnLayers = [];
    _.each(layers, function(layer) {
        featuresOnLayers.push(mapLayers[layer].getSource().getFeatures());
    });

    var extentOfAllFeatures = ol.extent.createEmpty();

    _.each(_.flatten(featuresOnLayers), function (feature) {
        ol.extent.extend(extentOfAllFeatures, feature.getGeometry().getExtent());
    });

    map.getView().fit(extentOfAllFeatures);
}

Answer 1

I've been adapting the answer of @lambertj to #openlayers-5

/**
 * Fits all the features of all layers on the map.
 * @author massimoi
 * @since 4/1/2019
 * @param map on which we will center
 * @param layers set of layers which will be analyzed 
 */
function centraTuttiLayer(map, layers)
{
  var featuresOnLayers = [];
  layers.forEach(function(layer) {
      featuresOnLayers.push(layer.getSource().getFeatures());
  });

  var extentOfAllFeatures = createEmpty();
  var flatFeatures = featuresOnLayers.flat();

  flatFeatures.forEach(function (feature) {
      extend(extentOfAllFeatures, feature.getGeometry().getExtent());
  });

  map.getView().fit(extentOfAllFeatures);
}