code: function (e) {
          var scale = this._map.getZoomScale(e.zoom),
              offset = this._map._latLngToNewLayerPoint(this._map.getBounds().getNorthWest(), e.zoom, e.center);
  
          L.DomUtil.setTransform(this._glMap._actualCanvas, offset.subtract(this._offset), scale);
          }
docs: borrowed from L.ImageOverlay https://github.com/Leaflet/Leaflet/blob/master/src/layer/ImageOverlay.js#L139-L144