anchor.diff:        _accelerationDirection = -1;
       }
     }
  -
  +  
  +  /**
  +   * Stop the acceleration, both speed up and slow down.
  +   */
     stopSpeedChange() {
       _accelerationDirection = 0;
     }
  
positive.code:       _accelerationDirection = 1;
      }
    }
  
    slowDown() {
      if (_speedUnderEqualMinSpeed() && _accelerationDirection == -1) {
        _accelerationDirection = 0;
  
negative.code:   stop() {
      if (!mainDirection.isZero) mainDirection = zeroVector;
    }
    
    /**
     * Speed up the sprite's movement.
     */
    speedUP() {
      if (_speedOverEqualMaxSpeed() && _accelerationDirection == 1) {
        _accelerationDirection = 0;
  