_onFabricMouseMove(fEvent) {
    const canvas = this.getCanvas();
    const pointer = canvas.getPointer(fEvent.e);
    const { x, y } = pointer;
    const cropzone = this._cropzone;

    if (Math.abs(x - this._startX) + Math.abs(y - this._startY) > MOUSE_MOVE_THRESHOLD) {
      canvas.remove(cropzone);
      cropzone.set(this._calcRectDimensionFromPoint(x, y, cropzone.presetRatio));

      canvas.add(cropzone);
      canvas.setActiveObject(cropzone);
    }
  }
onMousemove handler in fabric canvas
@param {{target: fabric.Object, e: MouseEvent}} fEvent - Fabric event
@private