4/10/20151 State Driven Agents CIS 479/579 Bruce R. Maxim UM-Dearborn.

04/18/23 1

State Driven Agents

CIS 479/579

Bruce R. Maxim

UM-Dearborn

04/18/23 2

Buckland Software

• The executables and source code availablehttp://www.wordware.com/files/ai

The Boost library is available from

http://www.boost.org/

• The Visual C++ environment need to be configured to compile the source code by setting the appropriate paths

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Paths• Include file paths

C:\boostC:\AI_Source\CommonC:\AI_Source\Common\lua-5.0\includeC:\AI_Source\Common\laubind

• Source file pathsC:\AI_Source\CommonC:\AI_Source\Common\lua-5.0C:\AI_Source\Common\laubind

• Library file pathsC:\AI_Source\Common\lua-5.0\lib

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FSM Agent Advantages

• Quick design and simple to code• Easy to debug• Low computational overhead• Intuitive so they make sense to domain

experts• Flexible, easy for programmers to tweak to

modify behaviors

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FSM State Examples

• Pacman ghosts– evade, chase

• Quake bots– find armor, find health, seek cover, run away

• FIFA soccer players– strike, dribble, chase ball, mark player

• NPC’s in real time strategy games– move to position, patrol, follow path

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Switch Implementation - 1

• Define an enumerated type with the state namesenum StateType(RunAway, Patrol, Attack);

• Then define method that manages the transitionsvoid Agent::Update(StateType CurrentState){

switch (CurrentState) { case Runaway:

EvadeEnemy( );if (Safe( )) ChangeState(Patrol);

break;…

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Switch Implementation - 2

• This works OK for simple FSM’s• Becomes overly complicated for FSM’s with

lots of states and transitions• Requires recompilation if states are changed• Not easy to have simultaneous behaviors

implemented (run and shoot) without defining lots of states

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State Transition Table -1

Current State Condition State Transition

Runaway Safe Patrol

Attack Weaker than enemy Runaway

Patrol Threatened and stronger than enemy

Attack

Patrol Threatened and

weaker than enemy

Runaway

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State Transition Table - 2

• Agent queries table as needed• Table can stored in file and edited without

recompiling the program• Each state can be modeled as a separate

objects or functions called by the agent• Fairly easy to extend and modify

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State Design Pattern - 1

• The state transition rules can be embedded in the states themselves

• All states share a common interface using a pure virtual class

class State

{

public:

virtual void Execute(Troll* troll) = 0;

}

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State Design Pattern - 2class Troll{ State* m_pCurrentState; public: void Update() { m_pCurrentState->Execute(this); } void ChangeState(const State* pNewState) { delete m_pCurrentState; m_pCurrentState = pNewState; }}

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State Design Pattern - 3

class State_Runaway : public State

{

public:

void Execute(Troll* troll)

{

if (troll->isSafe())

troll->ChangeState(new State_Sleep());

else

troll->MoveAwayFromEnemy();

}

}

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State Design Pattern - 4

class State_Sleep : public State

{

public:

void Execute(Troll* troll)

{

if (troll->isThreatned())

troll->ChangeState(new State_RunAway());

else

troll->Snore();

}

}

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West World Miner States

EnterMineDigForGold

QuenchThirstSaloonVisitBankDepositGold

GoHomeSleepwealthy enough

not thirstynot wealthy

rested

thirstypockets full

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Classes

• All West World inhabitants are derived from the base class BaseGameEntity

• Each entity will be assigned a unique identifier

• The Miner class is an example of one such class

• The State class is the base abstract class and each of the four Miner states needs its own class definition

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Reusable Classes

• The State base class and the Miner owned classes would be more easily reused if were templates

• Creating a StateMachine class with ways of tracking the Miner’s current, previous, and global states gives the FSM a crude memory to allow more complex (context sensitive) behaviors

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Adding New NPC

• Elsa only visits two states VisitBathroom (1 chance in 10) or DoHouseWork

• This makes use of the template version of the State class and required the definition of a new global state WifeGlobalState to deal with the bathroom visits

• This requires adding classes MinersWife and MinersWifeOwnedStates

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Adding NPC Communication

• Good games make use of event driven architectures

• When events occur they are broadcast to other game objects who are programmed to react to the event or ignore it

• Intelligent game agents can send messages to each other to allow cooperative behaviors

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Telegram Structurestruct Telegram{ //the entity that sent this telegram int Sender; //the entity that is to receive this telegram int Receiver; //the message itself. These are all enumerated in the file //"MessageTypes.h" int Msg; //If a delay is necessary this field is stamped with the time //the message should be dispatched. double DispatchTime; //any additional information that may accompany the message void* ExtraInfo; // constructors not shown here}

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Message Types#include <string>

enum message_type{ Msg_HiHoneyImHome, Msg_StewReady,};

inline std::string MsgToStr(int msg){ switch (msg) { case 1: return "HiHoneyImHome"; case 2: return "StewReady"; default: return "Not recognized!"; }}

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Elsa’s New States

CookStew

VisitBathroom

DoHouseWorkprevious state

Previous state

Receive “honey I’m home”

Delayed message to self“Stew Ready”

1 chance in 10

1 chance in 10

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Message Management

• Creation, dispatch, and management of telegrams is handled by the class MessageDispatcher

• The method DispatchMessage is used by every agent to send a message to entity with a known ID

• The database of ID’s are managed by the class EntityManager

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Use Priority Queue

• Telegrams with delays are store in a priority queue ordered by their Time Stamp data

• Telegrams without delays (e.g. “I just shot you with my crossbow”) are sent right away

• The front queue message is removed long with any unprocessed expired telegrams

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FSM Changes

• The BaseEntity class needs to be modified (add HandleMessage) so that any derived class can receive messages

• The State class needs to be modified so that BaseEntity states can choose to accept and handle messages (add OnMessage method)

• The StateMachine class needs its own version of HandleMessage

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Elsa Cooks Dinner

• Miner enters shack and sends “honey I’m home” message

• Elsa receives “honey I’m home” and changes state to CookStew

• Elsa puts Stew in oven and sends delayed message “Stew ready”

• Elsa receives “Stew ready”, takes out stew, and sends Miner “Dinner ready” message

• Miner receives “Dinner ready” and changes state to EatStew

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What happens?

• In between messages the NPC’s are free to respond to all state appropriate inputs

• This may means that the Miner has left the building before receiving the “Dinner ready” message

• Sometimes you need two FSM’s working in parallel (one for character movement and one for character’s weapon)

• Sometimes you need nested state machines (aka hierarchical FSM’s)