Applying Blackboard Systems to First Person Shooters
Jeff Orkin
Monolith Productions
http://www.jorkin.com
No One Lives Forever 2:A Spy in H.A.R.M.’s Way
aka NOLF2
A.I. Systems
re-used:– TRON 2.0– Contract J.A.C.K.
No One Lives Forever 2:A Spy in H.A.R.M.’s Way
Agenda
Blackboards are wicked cool. What is a blackboard? Inter-agent coordination Intra-agent coordination
What if there was an architecture that…
…was simple to implement. …was flexible & maintainable. …handled coordinated behavior:
– Coordinated timing of behaviors.– Coordinated pathfinding.– Coordinated tactics.
But wait! There’s more!
…simplifies agent architecture. …reduces code bloat. …facilitates AI LOD system. …facilitates variations, re-use, and sharing. …allows complex reasoning.
Blackboards: the magical animal
Homer: “What about bacon?”
Lisa: “No!”
Homer: “Ham?”
Lisa: “No!”
Homer: “Pork chops?!?”
Lisa: “Dad! Those all come from the same animal!”
Homer: “Yeah right Lisa. A wonderful magical animal.”
What is a blackboard?
A blackboard is a metaphor
Physical blackboard– Publicly read/writeable.– Possibly organized.
Maybe more like a bulletin board– Post requests and information.– Respond to items of interest.
A blackboard is shared memory
Read/write memory Working memory Like a hard-drive Like a database No processing (other than sorting)
A blackboard is a means of communication
Centralized communication Agents communicate Sub-systems of an agent communicate
A blackboard is an architecture
Changes how agents and/or sub-systems interact
Like an interface Reduces coupling of sub-systems
Blackboard implementation
There’s no wrong way to eat a blackboard.
Two flavors:– Static– Dynamic
Static blackboards
class CBlackboard{ private: Vector m_vPos; Vector m_vVelocity; int m_nHealth; // etc…
public: // access functions…};
Static blackboards (cont.)
Predetermined data to share. Static amount of data. Best for intra-agent coordination.
Dynamic blackboards
struct BBRECORD { … };typedef std::vector<BBRECORD*> BBRECORD_LIST;
class CBlackboard{ private: BBRECORD_LIST m_lstBBRecords;
public: // query functions…};
Dynamic blackboards (cont.)
struct BBRECORD
{
ENUM_BBRECORD_TYPE eType;
HANDLE hSubject;
HANDLE hTarget;
float fData;
};
Dynamic blackboards (cont.)
enum ENUM_BBRECORD_TYPE
{
kBB_Invalid = -1,
kBB_Attacking,
kBB_Crouching,
kBB_NextDisappearTime,
kBB_ReservedVolume,
// etc…
};
Dynamic blackboards (cont.)
// query functions
int CountRecords( ENUM_BBRECORD_TYPE eType );
int CountRecords( ENUM_BBRECORD_TYPE eType, HANDLE hTarget );
float GetRecordData( ENUM_BBRECORD_TYPE eType );
float GetRecordData( ENUM_BBRECORD_TYPE eType, HANDLE hTarget );
Dynamic blackboards (cont.)
Data to share is not predetermined. Dynamic amount of data. Best for inter-agent coordination. Also useful for intra-agent complex reasoning.
Inter-agent Coordination
Using a blackboard to solve coordination
problems on NOLF2.
Inter-agent Coordination Problems
1. Agents doing the same thing at the same time.
2. Agents doing things too often.
3. Special constraints for tactics.
4. Agents take same paths.
5. Agents clump at destinations.
NOLF2 Blackboard
Add Records:– Enumerated type– Subject ID– Optional Target ID– Optional float data
Remove Records:– Specific by type and Subject ID– All by type
Replace Records
NOLF2 Blackboard (cont.)
Query:– Count matching records– Retrieve data from matching records
Problem #1: Agents doing same thing at same time
Examples: Soldiers Crouching
– Random chance of crouch
– Dodge roll into crouch– Crouch to get out of
firing line
Ninja Lunging
Blackboard Solution: Agents doing same thing at same time
Should I crouch?
if( g_pAIBB->CountRecords( kBB_Crouching ) == 0 )
{
// Crouch…
g_pAIBB->AddRecord( kBB_Crouching, m_hObject );
}
Problem #2: Agents doing things too often
Examples: Soldiers going Prone Ninja Disappear-Reappear Combat/Search sounds
Blackboard Solution: Agents doing things too often
Should I go prone?
if( fCurTime > g_pAIBB->GetRecordFloat( kBB_NextProneTime ) )
{// Go prone…
g_pAIBB->ReplaceRecord( kBB_NextProneTime, m_hObject, fCurTime + fDelay );
}
Problem #3: Tactical behavior has special constraints
Example: Ninja only attacks from a rooftop if two other ninja are
already attacking on ground, and no one is on a roof.
Blackboard Solution: Tactical behavior has special constraints
Should I attack from the roof?
if( g_pAIBB->CountRecords( kBB_AttackingRoof, m_hTarget ) > 0 )
{
return false;
}
Blackboard Solution: Tactical behavior has special constraints (cont.)
if( g_pAIBB->CountRecords( kBB_Attacking, m_hTarget ) < 2 )
{return false;
}
// Attack from the roof…
g_pAIBB->AddRecord( kBB_Attacking, m_hObject, m_hTarget );
g_pAIBB->AddRecord( kBB_AttackingRoof, m_hObject, m_hTarget );
Problem #4: Agents take same paths
Example: Player runs around the corner, and characters
follow in a congo line and get killed one by one.
Problem #4: Agents take same paths (cont.)
NOLF2 AIVolume system:
Problem #4: Agents take same paths (cont.)
NOLF2 AIVolume system:
Problem #4: Agents take same paths (cont.)
NOLF2 AIVolume system:
P
AB
Problem #4: Agents take same paths (cont.)
NOLF2 AIVolume system:
P
AB
Problem #4: Agents take same paths (cont.)
NOLF2 AIVolume system:
P
AB
Blackboard Solution: Agents take same paths
Volume reservation system: Reserve the Volume before the destination. Reserved Volume Cost == Cost + 500
Blackboard Solution: Agents take same paths (cont.)
Volume reservation system:
P
AB6
1 1
1
1
1
1
1
1 1
Blackboard Solution: Agents take same paths (cont.)
Volume reservation system:
P
AB6
1 1
1
1
1
1
1
1 1
P
AB6
1 1
1
1
1
1
1
1 1
Blackboard Solution: Agents take same paths (cont.)
Volume reservation system:
P
AB6
1 1
1
1
1
1
1
1 1
P
AB6
1 501
1
1
1
1
1
1 1
Reserved!
Blackboard Solution: Agents take same paths (cont.)
// Pathfinding
if( g_pAIBB->CountRecords( kBB_ReservedVolume, hVolume ) > 0 )
{
fNodeCost += 500.f;
}
Blackboard Solution: Agents take same paths (cont.)
// Movement
g_pAIBB->RemoveRecord( kBB_ReservedVolume,
m_hObject );
g_pAIBB->AddRecord( kBB_ReservedVolume,
m_hObject,
hVolume );
Problem #5: Agents crowd at destination
Examples: Player knocks over a bottle. Characters
converge on bottle position. Characters discover dead body and converge.
Blackboard Solution: Agents crowd at destination
First agent claims volume for investigation. Other agents stop at edge of volume.
Blackboard Solution: Agents crowd at destination (cont.)
A
B
D
Blackboard Solution: Agents crowd at destination (cont.)
A
B
D
A
B
D
Blackboard Solution: Agents crowd at destination (cont.)
A
B
D
A
B
D
Blackboard Solution: Agents crowd at destination (cont.)
// AI reached the dest volume first.
if( g_pAIBB->CountRecords( kBB_InvestigatingVolume, hVolume ) == 0 )
{g_pAIBB->AddRecord( kBB_InvestigatingVolume,
m_hObject );}
// AI did not reach the dest volume first.
else { // Look at dest. }
Einstein says…
“Hang in there, we’re half-way done!”
Why use blackboards??
Why use blackboards??
“Less is more”: Less to debug Less to maintain Less to port Less to compile Less to document Less to learn Less data (per volume)
Why use blackboards??
Decouple data from game-specific purpose: Designs change Re-use systems in other games (other
genres?) OO design is not always the right choice.
What about performance?!
Problem: Pathfinder needs to look up Volume
Reservation status every iteration thru A*.
What about performance?! (cont.)
Solution:A* flags arraychar astarFlags[NUM_VOLUMES]; enum ASTAR_FLAGS{
kNone = 0x00,kOpen = 0x01,kClosed = 0x02,
};
What about performance?! (cont.)
Solution:A* flags arraychar astarFlags[NUM_VOLUMES]; enum ASTAR_FLAGS{
kNone = 0x00,kOpen = 0x01,kClosed = 0x02,kReserved = 0x04,
};
What about performance?! (cont.)
RunAStar(){ClearFlags();Search();
}
What about performance?! (cont.)
RunAStar(){ClearFlags();MarkReserved();Search();
}
Intra-agent Coordination
Intra-agent Coordination
A character is an entire world. Sub-systems are characters in the world.
– Navigation– Movement– Target/Attention selection– Senses– Animation– Weapons– Decision-Making
NOLF2 Agent Architecture
Animation
Navigation
Movement
Sensory
Target Selection
W eapons
Decision-Making
NOLF2 Agent Architecture
Animation
Navigation
Movement
Sensory
Target Selection
W eapons
Decision-MakingAnimation
Navigation
Movement
Sensory
Target Selection
W eapons
Decision-Making
Blackboard Agent Architecture
Animation
Navigation
Movement
Sensory
Target Selection
W eapons
Decision-MakingAnimation
Navigation
Movement
Sensory
Target Selection
W eapons
Decision-Making
Blackboard
Blackboard Agent Architecture
class AgentBlackBoard{
private:Vector m_vDest;NAV_STATUS m_eNavStatus;HANDLE m_hTarget;AISenses m_aSenses[MAX_SENSES];// etc…
public:// Access functions…
}
Benefits of Decoupling Sub-systems
Benefits of Decoupling:
1. Development/Maintenance
2. Flexibility
3. Performance
Benefit #1: Development/Maintenance Benefits
Problem: Difficult to upgrade or replace old systems.
Example: Re-writing navigation system
Benefit #1: Development/Maintenance (cont.)
Various calls to sub-system:
pAI->GetPathManager()->SetPath(vDest);
pAI->GetPathManager()->UpdatePath();
if( pAI->GetPathManager()->IsPathDone() )
...
AIVolume* GetNextVolume(AIVolume* pVolume, AIVolume::EnumVolumeType
eVolumeType);
Benefit #2: Flexibility
Problem: Different characters have
different needs.
Example: Humans plan paths to a
dest. Rats and Rabbits wander
randomly to a dest.
Benefit #2: Flexibility (cont.)
Example (cont.):
AIStatePatrol::Update( AI* pAI ){
pAI->GetPathManager()->SetPath(vDest);
if( pAI->GetPathManager()->IsPathComplete() ){
// etc…}
Benefit #2: Flexibility (cont.)
Blackboard Solution:
AIStatePatrol::Update( AI* pAI ){
pAI->GetAIBlackboard()->SetDest(vDest);
if( pAI->GetAIBlackboard()->GetNavStatus() == kNavStatus_Done )
{// etc…
}
Benefit #2: Flexibility (cont.)
Example: Humans need a lot of sensory information to
make complex goal-based decisions. Rats and Rabbits need very little info for
simplistic behavior.
Benefit #2: Flexibility (cont.)
Benefit #2: Flexibility (cont.)
Friend?
Benefit #2: Flexibility (cont.)
Benefit #3: Performance
Problem: All characters in NOLF2 are
active all of the time, regardless of player location.
Example: Characters are pathfinding,
moving, animating, and sensing as they work at desks, go to the bathroom, etc.
Benefit #3: Performance (cont.)
Blackboard Solution: Sub-systems communicate through the
blackboard. LOD system swaps sub-systems behind the
scenes.
Benefit #3: Performance (cont.)
LOD 5:
Benefit #3: Performance (cont.)
LOD 5:
Benefit #3: Performance (cont.)
LOD 5:
Benefit #3: Performance (cont.)
LOD 2:
Benefit #3: Performance (cont.)
LOD 2:
Don’t run away…
We’re almost done!
Intra-agent Dynamic Blackboard
MIT Media Lab
Synthetic Characters Group
C4
GDC 2001
Creature Smarts: The Art and Architecture of the
Virtual Brain
Intra-agent Dynamic Blackboard (cont.)
Intra-agent Dynamic Blackboard (cont.)
Intra-agent Dynamic Blackboard (cont.)
Percept Memory Records: Only form of knowledge representation.
– Game objects (characters, objects of interest, etc)
– Desires– Damage– AI hints (AINodes, AIVolumes)– Tasks
Can group multiple records for same object.
Intra-agent Dynamic Blackboard (cont.)
Benefits: Keep track of multiple types of information in a
consistent way. Open-ended architecture: different games may
use different data in different ways. Complex reasoning.
Intra-agent Dynamic Blackboard:Complex Reasoning
Queries: “Is there food near me?” Find the “red object that is making the most
noise.” “Find an object that is humanoid-shaped and
go to it.”
Intra-agent Dynamic Blackboard:Complex Reasoning (cont.)
Spatial Reasoning: Agent is more alarmed if multiple disturbances
are found near each other.
Intra-agent Dynamic Blackboard:Complex Reasoning (cont.)
Temporal Reasoning: Anticipation and surprise.
Intra-agent Dynamic Blackboard:Complex Reasoning (cont.)
Deductive Reasoning: Agent sees dead body. Agent sees player with a gun. Agent draws the conclusion that the player was
the killer.
Intra-agent Dynamic Blackboard:Complex Reasoning (cont.)
Multi-tasking: Agent targets enemyA. Agent targets enemyB. Agent kills enemyB. Agent is aware that he
was also fighting enemyA.
Take-away
Use blackboard systems!– Less is more.– Decouple your data from its game-specific purpose.– Decouple your subsystems.
More Information
December 2003:
AI Game Programming Wisdom 2“Simple Techniques for Coordinated Behavior”
More Information
NOLF2 Source, Toolkit & SDK:
http://nolf2.sierra.com
( AICentralKnowledgeMgr == Blackboard )
Slides:
http://www.jorkin.com/talks/UT_blackboards.zip
Questions?
NOLF2 Source, Toolkit & SDK:
http://nolf2.sierra.com
( AICentralKnowledgeMgr == Blackboard )
Slides:
http://www.jorkin.com
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