anchor.diff:    /**
      * Put the pivot point into the center of the sprite.
      */
  -  void center() {
  +  void centerPivot() {
       pivotX = bitmapData.width / 2;
       pivotY = bitmapData.height / 2;
     }
  
positive.code:   /**
     * Removes the sprite from the world and juggler.
     */
    removeFromWorld() {
      alive = false;
      _context.game.world.removeChild(this);
      if (isMovable) {
  
negative.code: 
    StageXL.Vector _newDirection;
  
    final StageXL.Vector _zeroVector = new StageXL.Vector.zero();
  
    final StageXL.Vector _zeroOneVector = new StageXL.Vector(0, 1);
  
    final StageXL.Vector _oneZeroVector = new StageXL.Vector(1, 0);
  