code: function getInterpolateFunction(c) {
        var swiper = this;
        if (!swiper.controller.spline) {
          swiper.controller.spline = swiper.params.loop
            ? new Controller.LinearSpline(swiper.slidesGrid, c.slidesGrid)
            : new Controller.LinearSpline(swiper.snapGrid, c.snapGrid);
        }
      }
docs: xxx: for now i will just save one spline function to to