anchor.diff:  
     }
   
  +  void setGravityDirection(String direction) {
  +    switch (direction) {
  +      case Direction.UP:
  +        gravityDirection = upDirection;
  +        break;
  +      case Direction.DOWN:
  +        gravityDirection = downDirection;
  +        break;
  +      case Direction.LEFT:
  +        gravityDirection = leftDirection;
  +        break;
  +      case Direction.RIGHT:
  +        gravityDirection = rightDirection;
  +        break;
  +
  +    }
  +  }
  +  
  +  void rotateGravityDirectionsInAngles(num angles) {
  +    rotateGravityDirectionsInRads(angles * (math.PI / 180));
  +  }
  +  
  +  void rotateGravityDirectionsInRads(num rads) {
  +    upDirection = upDirection.rotate(rads);
  +    downDirection = downDirection.rotate(rads);
  +    leftDirection = leftDirection.rotate(rads);
  +    rightDirection = rightDirection.rotate(rads);
  +  }
  +
   }
  
positive.code:    *      });
     * 
     */
    void collison(var object1, var object2, Function
        collisonHandler(item1, itme2)) {
  
      if (object1 is Group && object2 is Group) {
  
  
negative.code:  */
  
  class Physics {
  
    num garvitySpeed = 0;
  
    StageXL.Vector gravityDirection = new StageXL.Vector.zero();
  
    StageXL.Vector upDirection = new StageXL.Vector(0, -1);
    StageXL.Vector downDirection = new StageXL.Vector(0, 1);
    StageXL.Vector leftDirection = new StageXL.Vector(-1, 0);
    StageXL.Vector rightDirection = new StageXL.Vector(1, 0);
  
    /**
     * Resolve collison between two gameobject.
     * 
  