code: function _doubleTapHandler(e) {
        var pos,
            ratio,
            animation;
  
        if (e.touches && e.touches.length === 1 && _settings('touchEnabled')) {
          _doubleTap = true;
  
          ratio = 1 / _settings('doubleClickZoomingRatio');
  
          pos = position(e.touches[0]);
          _self.dispatchEvent('doubleclick',
            sigma.utils.mouseCoords(e, pos.x, pos.y));
  
          if (_settings('doubleClickEnabled')) {
            pos = _camera.cameraPosition(
              pos.x - sigma.utils.getCenter(e).x,
              pos.y - sigma.utils.getCenter(e).y,
              true
            );
  
            animation = {
              duration: _settings('doubleClickZoomDuration'),
              onComplete: function() {
                _doubleTap = false;
              }
            };
  
            sigma.utils.zoomTo(_camera, pos.x, pos.y, ratio, animation);
          }
  
          if (e.preventDefault)
            e.preventDefault();
          else
            e.returnValue = false;
  
          e.stopPropagation();
          return false;
        }
      }
docs: The handler listening to the double tap custom event. It will
  basically zoom into the graph.
  
  @param {event} e A touch event.