-class Rock : public MovingSprite, public Portable, public Serializable
+class Rock : public MovingSprite, public Portable, protected UsesPhysic, public Serializable
HitResponse collision(GameObject& other, const CollisionHit& hit);
void update(float elapsed_time);
void write(lisp::Writer& writer);
HitResponse collision(GameObject& other, const CollisionHit& hit);
void update(float elapsed_time);
void write(lisp::Writer& writer);