Finite State Machines in Games

1
Finite State Machines in Games

• Jarret Raim
• 2004
• Based on
• AI Game Programming Wisdom 2

2
FSM Example

• States
• Attack
• Chase
• Spawn
• Wander
• Events
• E see an enemy
• S hear a sound
• D die

Attack
E
D
E
Wander
E
E
Spawn
D
Problem Cant remember what we were doing
3
FSM Implementation - Code

• Simplest method
• After an action, the state might change.
• Requires a recompile for changes
• No pluggable AI
• Not accessible to non-programmers
• No set structure
• Can be a bottleneck.

void RunLogic( int state ) switch( state )
case 0 //Wander Wander()
if( SeeEnemy() ) state 1
if( Dead() ) state 2
break case 1 //Attack
Attack() state 0 if(
Dead() ) state 2 break
case 3 //Dead SlowlyRot()
break
4
FSM Example
Attack
Problem Cant remember what we were doing
E
D
E
Wander
E
E
Spawn
D
Solution Add an stack to keep track of the
states I have visited
5
Stack FSM Thief 3
Stack allows AI to move back and forth between
states.
Leads to more realistic behavior without
increasing FSM complexity.