anchor.diff:    /**
      * Stop the acceleration, both speed up and slow down.
      */
  -  stopSpeedChange() {
  +  void stopSpeedChange() {
       _accelerationDirection = _NO_ACCELERATION_DIRECTION;
     }
   
  
positive.code:   /**
     * Slows down the sprite's movement.
     */
    slowDown() {
      if (_speedUnderEqualMinSpeed() && _accelerationDirection == -1) {
        _accelerationDirection = _NO_ACCELERATION_DIRECTION;
      } else {
  
negative.code:   /**
     * Stops the movement of the sprite.
     */
    void stop() {
      if (!mainDirection.isZero) mainDirection = _zeroVector;
    }
  
    /**
     * Speed up the sprite's movement.
     */
    void speedUP() {
      if (_speedOverEqualMaxSpeed() && _accelerationDirection == 1) {
        _accelerationDirection = _NO_ACCELERATION_DIRECTION;
      } else {
  