code: function(evt, pinchData) {
          var scale = pinchData.scale;
          var containerOrigin = this.map.layerContainerOriginPx;
          var pinchOrigin = this.pinchOrigin;
          var current = (this.preserveCenter) ?
              this.map.getPixelFromLonLat(this.map.getCenter()) : evt.xy;
  
          var dx = Math.round((containerOrigin.x + current.x - pinchOrigin.x) + (scale - 1) * (containerOrigin.x - pinchOrigin.x));
          var dy = Math.round((containerOrigin.y + current.y - pinchOrigin.y) + (scale - 1) * (containerOrigin.y - pinchOrigin.y));
  
          this.map.applyTransform(dx, dy, scale);
          this.currentCenter = current;
      }
docs: Method: pinchMove
  
  Parameters:
  evt - {Event}
  pinchData - {Object} pinch data object related to the current touchmove
  of the pinch gesture. This give us the current scale of the pinch.