matt buckland : ai book excerpts

Buckland, Mat.
Programming game AI by example / by Mat Buckland.
p. cm.
Includes index.
ISBN 1-55622-078-2 (pbk.)
1. Computer games — Design. 2. Computer games — Programming. 3.Computer
graphics. I. Title.
QA76.76.C672B85 2004
794.8'1526 — dc22

class State
{
public:
virtual void Execute (Troll* troll) = 0;
};

Now imagine a Troll class that has member variables for attributes such as health, anger, stamina, etc., and an interface allowing a client to query and adjust those values. A Troll can be given the functionality of a finite state machine by adding a pointer to an instance of a derived object of the State class, and a method permitting a client to change the instance the pointer is pointing to.

class Troll
{
/* ATTRIBUTES OMITTED */

State* m_pCurrentState;

public:

/* INTERFACE TO ATTRIBUTES OMITTED */

void Update()
{
m_pCurrentState->Execute(this);
}

void ChangeState(const State* pNewState)
{
delete m_pCurrentState;
m_pCurrentState = pNewState;
}
};