void add_upgrade(const Vector& pos, Direction dir, UpgradeKind kind);
bool add_bullet(const Vector& pos, float xm, Direction dir);
bool add_smoke_cloud(const Vector& pos);
bool add_particles(const Vector& epicenter, const Vector& velocity, const Vector& acceleration, int number, Color color, int size, int life_time);
void add_upgrade(const Vector& pos, Direction dir, UpgradeKind kind);
bool add_bullet(const Vector& pos, float xm, Direction dir);
bool add_smoke_cloud(const Vector& pos);
bool add_particles(const Vector& epicenter, const Vector& velocity, const Vector& acceleration, int number, Color color, int size, int life_time);