Transcript Individual NPC Behavior

Individual NPC
Behavior
Elizabeth Carter
CSE 348
2/11/2010
Agenda
• Realistic Character Animation
• Responding to the Player
• Simulated Animals
• Autonomous Characters
• More Humanlike NPCs
Realistic Animation
Realistic Character Animation
• No longer acceptable to animate one part at a time
• Want character to be able to do multiple things at
once
• Walk, wave, hair blown by breeze
• Layering of animation
• Two methods
• Animation Controller
• Layered / prioritized animation system
Animation Controller and
Layering
• Animation Controller approach
• Use separate animation controller for each body part
• Can lead to over complicated code and
interdependencies
• Layering
• Made possible via skeletal animation systems
• Layers categorized by regions of body that they affect
Prioritization and
Categorization
• Each animation receives priority and category
• In implementation discussed…
• Priority
• Integer, with zero being lowest
• Category
• Bit flag enumerator describing affected body area
Animation Controller for
Priory and Categorization
• In one implementation
• Animation controller class has one
• Member variable
• Map of animation instances
• Animation instance = struct storing animation resource file
refrance and instance data
• Sorted by category
• Core function
• Requests play of animation
• Priority utilized to determine if it should be allowed to play
Important Assumptions
• Each frame stored as list of bone rotations [p 66]
• Rotations stored relative to same default pose
• Applying animation to bone overrides any
previously applied animation bone rotations
Keeping the Motion Natural
• Blend between animations during transition
• Keeps animation from becoming choppy
• Implementation
• Store array of quaternions (cache)
• Quaternion algebra is method for representing 3
dimensional orientation
• Animation refers to array to gradually blend the
animation
Reputation
Responding to the Player
• NPCs should
• React to player’s ability
• React in situation appropriate manner
• One way to implement this – Reputation system
• Prevents
• NPC Omniscience
• NPC Bob shouldn’t know what happened with NPC Larry if
not involved
Types of Reputation Systems
• Create global reputations based on average of other’s
opinions
• Use Centralized authorities to create global
reputations inherited by all
Problems with Existing
Systems
• Identity
• Usually every individual has one known identity
• Problem – identity easily faked
• Ratings
• Excessive negative or positive ratings with no
substantiation
Surreal Software
Implementation
• Event Driven
• Data Structures
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Event Template
Reputation Event
Master Event List
Long Term Memory (per NPC)
Reputation Table (per NPC)
• Only stores
• Events involving player
• Events where NPC killed someone
Reputation Event
• Triggered when player does something that has
positive or negative affect on their reputation
• Example
• Kills NPC’s friend
• Kills NPC’s enemy
Master Event List
• Holds all important actions NPCs privy to
• Stored as list of Reputation Events
• Reputation Event added to this when its created
• Stores complete information about all events
• Events no NPC knows about deleted to keep list
small
• Multiple copies of same event receive one entry
Long Term Memory
• References all events in Master Event List that NPC
in question was involved in
• Witnessed
• Heard About
Reputation Table
• Stores NPC’s opinion of player
• Each NPC has own opinions
• Is list of groups
• Group for Player
• Group for members of each group
• On recognition of reputation event, reputation effect
applied
Reputation Details
• Implemented via dynamic array
• Contains reputation meters
• One meter for each group
• One meter for player
• Meter has
• Group ID
• 2 Float Variables
• Like
• Hate
Long Term Memory
• Contains compressed versions of
• Reputation events known to NPC
• Data
• Event ID
• Magnitude of event
• Time encountered
Long Term Memory Example
• NPC Bob and NPC Lisa witness the same event
• Lisa watches to see player kill another NPC
• Bob runs away
• Lisa ‘remembers’ Killed
• Bob ‘remembers’ ShootAt
Long Term Memory Physical
Memory Management
• Table consists of references instead of the actual
data
• Don’t let NPC learn something they shouldn’t know
• Not witness or recipient of information, shouldn’t
know it
• If a tree falls in a forest and no one is there to hear it...
• the NPC doesn’t remember the sound of it falling
• Let NPC forget
• Choke Points
How Learning Occurs
• Event Announcers
• Sharing Information
• Memory Match and Updates
Event Announcers
• Spawned by actions at position of object of event
• On NPC Bob’s death event announced immediately
• Announcer at body stays and continually announces
Bob’s death
Sharing
• Let the NPCs Gossip
• If Eve likes Lisa, they’ll share
• If Eve dislikes Lisa she’ll keep the info to herself
Memory Match and Update
• For each event
• NPC checks to see if this event matches something it’s
already stored
• Checks subject group, verb, object group, object individual
• What needs to match
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Check group, verb, etc, exactly
Group, verb, object match but not individual ID
Unknown subject group but matches everything else
Subject group known of new event but not old event
Seven Rules For Updating (1)
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Ignore:
1. MagnitudenewEvent <= MagnitudeoldEvent
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New Event Subject group Unknown
Same subject group for both
Object individual ID the same for both events
2. Subject groups match and are already known
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Old event has maximum magnitude
Seven Rules for Updating (2)
• Update Magnitude in Long Term Memory, apply
reputation effects
MagnitudeNewEvent > MagnitudeOldEvent
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New Event contains unknown subject group or subject
groups equal
Object individual IDs the same
Seven Rules for Updating (3)
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Remove existing event and add the one with the
greater magnitude, applying reputation effects
1. New event subject group known
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Existing event subject group unknown
Object individual IDs match
New Event has new information
2. Subject groups known and match
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New event has maximum magnitude
Seven Rules for Updating (4)
• Add new event and apply reputation effects
1. Subject groups for either or both unknown
• Object individual IDs different
2. Subject groups known and match
• Object individual IDs different
• Neither even has maximum magnitude
Applying Updates and
Incomplete Information
• Applying Update
• Modifies own Long Term Memory first
• Then notifies Master Event List
• If exists there already, update and increase reference count
• Incomplete Information
• Complete the information with peer data
• Bob has an event with an unknown subject group
• Lisa has a matching event with a known subject group
Simulating Animals
Animal NPC Behavior
• Usage
• Ambient animals
• Scenery
• Secondary animals
• Some interaction but not focus
• Chickens in Zelda
• Primary animals
• Primary focus of a game
• Hunting situations
• Real Life behavior must be taken into account
Behavior – Simple Animals
• Bugs, Solitary Animals, Flocks of Birds, Schools of
Fish
• General behaviors studied and mimicked
• Birds and fish unique because travel in flocks/schools
• Allow for low level multiagent system behavior
Behavior – Primary and
Secondary Animals
• Generally concerns large mammals
• Real behavior more varied and intelligent than that of
bugs, fish, etc
• Best programmed via state machines
• FSMs adequate
• Fuzzy logic presents more realistic behavior
Autonomous Characters
Autonomous Characters
• Emergent Gameplay
• Players have freedom to explore and solve problems
without restraint
• Game world responds appropriately
• Player rewarded for creativity and exploration
• Example: The Sims, NOLF2
Controlling Autonomous
Characters (1)
• Need to not stray too far from what it was meant for
• Ownership of objects prevents NPC Bob from
stealing Lisa’s desk when she uses the restroom
• Dependencies
• Couple two items together to create atomic behavior
• Toilet usage and hand washing
Controlling Autonomous
Characters (2)
• Responsibility
• Helps player decide what to do appropriately
• Relevance
• NPC’s understanding of relevance to the storyline helps
decrease overreaction of system
• Example: NOLF2 rabbit being scared off triggered very
intense music, this is undesirable
• Priority
• High priority implies urgency to NPC
Controlling Autonomous
Characters (3)
• State of Consciousness
• If character is sleeping or unconscious it shouldn’t be
responding to sensory input
• Expected State
• Character might expect compatriot to be patrolling,
therefore expects to see patrolling behavior
• Unconsciousness would be unexpected and dealt with
according to the game
Character Introspection
• Suggested questions that agent should ask itself in
an emergent environment
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Ownership – is this mine?
Dependency – is there something I need to do before x?
Responsibility – what am I supposed to be doing?
Relevance – how will my actions affect gameplay?
Priority – what’s most important right now?
Consciousness – am I conscious?
Expected state – is everything as I expect it to be?
Others – how will what I do affect other NPCs
Coordinated Behavior
Splitting Up
• Don’t have all agents take the same path
• Solutions
• Reserve path
• Agents reserve pathfinding nodes for themselves so that
everyone doesn’t go the same way
• Adopt maximum occupancy rule
• Only allow a certain number of agents at a given location
• Use inter-agent communication to find out what other
agents are doing and plan accordingly
Getting Out Of The Way
• Obstruction by ally can be resolved in 4 ways
(regarding firing)
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Do nothing
Fire anyway (killing ally)
Agent moves
Ally moves
Inter Agent Communication
• Efficient and intelligent utilization of inter agent
communication can enable the agents to behave, as a
group, much more intelligently than they otherwise
might
• NPC can share knowledge with another NPC
• NPCs can coordinate behavior
More Humanlike NPCs
Sensory Perception (1)
• First step in making an NPC more humanlike
• Tactile
• Achieved through collision detection systems and smart
terrain
• Range
• Immediate surrounding area on all sides
Sensory Perception (2)
• Visual
• Need to model NPC visual system after a person
• Sensing region should be cone shaped
• should extend to limited distance in front of agent to
simulate binocular vision
• Lighting conditions can effect NPC’s sight realistically
• Audio
• Sound attenuates with distance therefore NPC hearing
should degrade with distance from sound
• NPC should be able to hear same things player can hear
Sensory Perception (3)
• Olfactory
• Smell should be emitted across some radius depending
on strength of smell
• Smell should deteriorate over time as disperses or get
stronger over time if appropriate
• Corpse smells worse as time goes by
• Taste
• aka Gustatory sensing
• Not used very often, could be used for game beasts –
they could get more aggressive when taste raw meat
Memory
• Humans have 3 different kinds of memory
• Sensory, short term, long term
• NPC memory
• Sensory memory linked to sensory input
• Short term memory accomplished by utilizing
timestamp degradation and importance levels
• Many ways to implement long term memory
• Size management can become an issue
Personality
• Model
• “The Big Five”
• Extraversion, agreeableness, conscientiousness,
neuroticism, openness
• Implement via a desirability algorithm
• Add bias to decision algorithms depending on agent
personality
Emotions
• Eight primary emotions in people
• Joy, acceptance, fear, surprise, sadness, disgust, anger,
anticipation
• Current game emotions generally scripted
• Could implement such that different actions instill
different emotions
• Killing an NPC could invoke sadness, disgust, fear, etc
Emotions – An
Implementation
• One way that Emotions could be given to an agent is
by providing an emotional model to the system
• Could be divided into 3 parts
• Input
• Internal reaction
• External Reaction
Human Emotions
• Are three popular theories to how we interpret
emotion from external stimulus
• After external stimulus emotional state alters as result
of physiological state change
• Physiological and emotional states simultaneously
affected after receipt of stiumuls
• Emotional states determined by perceived cause of
stiumulus
NPC Emotion
• Example implementation from “IPD for Emotional
NPC Societies in Games”
• 5 basic emotions modeled
• Fear, anger, disgust, sadness, happiness
• Implementation of Norms was included to include
social acceptability of an action as a consideration
• Drives included to simulate real world stimulus
• Social, energy, rest, and heat
Physiological Stressors
• Anything that causes significant change in human
body to occur
• Muscle fatigue, pain, health, anxiety/fear, exposure to
cold/hot/chemicals, hunger
• If agent is hot, should be sweating
• If agent comes into contact with chemicals, should
receive chemical burns