code: function _touchMove(event) {
          if (!this.options.enabled) {
              return;
          }
  
          // Process the touch event
          var primaryTouch;
          for (var i = 0; i < event.changedTouches.length; i++) {
              var changedTouch = event.changedTouches[i];
              for (var j = 0; j < this._scroll.activeTouches.length; j++) {
                  var touch = this._scroll.activeTouches[j];
                  if (touch.id === changedTouch.identifier) {
  
                      // When a thresshold is configured, check whether the move operation (x/y ratio)
                      // lies within the thresshold. A move of 10 pixels x and 10 pixels y is considered 45 deg,
                      // which corresponds to a thresshold of 0.5.
                      var moveDirection = Math.atan2(
                          Math.abs(changedTouch.clientY - touch.prev[1]),
                          Math.abs(changedTouch.clientX - touch.prev[0])) / (Math.PI / 2.0);
                      var directionDiff = Math.abs(this._direction - moveDirection);
                      if ((this.options.touchMoveDirectionThreshold === undefined) || (directionDiff <= this.options.touchMoveDirectionThreshold)){
                          touch.prev = touch.current;
                          touch.current = [changedTouch.clientX, changedTouch.clientY];
                          touch.prevTime = touch.time;
                          touch.direction = moveDirection;
                          touch.time = _getEventTimestamp(event);
                          primaryTouch = (j === 0) ? touch : undefined;
                      }
                  }
              }
          }
  
          // Update move offset and emit event
          if (primaryTouch) {
              var delta = primaryTouch.current[this._direction] - primaryTouch.start[this._direction];
              this.updateScrollForce(this._scroll.touchDelta, delta);
              this._scroll.touchDelta = delta;
          }
      }
docs: Called whenever the user is moving his/her fingers to scroll the view.
  Updates the moveOffset so that the scroll-offset on the view is updated.