Individual NPC Behavior

1. Individual NPC Behavior Elizabeth Carter CSE 348 2/11/2010

2. Agenda • Realistic Character Animation • Responding to the Player • Simulated Animals • Autonomous Characters • More Humanlike NPCs

3. Realistic Animation

4. 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

5. 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

6. 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

7. 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

8. 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

9. 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

10. Reputation

11. 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

12. Types of Reputation Systems • Create global reputations based on average of other’s opinions • Use Centralized authorities to create global reputations inherited by all

13. 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

14. Surreal Software Implementation • Event Driven • Data Structures • 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

15. 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

16. 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

17. Long Term Memory • References all events in Master Event List that NPC in question was involved in • Witnessed • Heard About

18. 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

19. 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

20. Long Term Memory • Contains compressed versions of • Reputation events known to NPC • Data • Event ID • Magnitude of event • Time encountered

21. 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

22. 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

23. How Learning Occurs • Event Announcers • Sharing Information • Memory Match and Updates

24. 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

25. Sharing • Let the NPCs Gossip • If Eve likes Lisa, they’ll share • If Eve dislikes Lisa she’ll keep the info to herself

26. 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 • 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

27. Seven Rules For Updating (1) • Ignore: • MagnitudenewEvent <= MagnitudeoldEvent • New Event Subject group Unknown • Same subject group for both • Object individual ID the same for both events • Subject groups match and are already known • Old event has maximum magnitude

28. Seven Rules for Updating (2) • Update Magnitude in Long Term Memory, apply reputation effects • MagnitudeNewEvent > MagnitudeOldEvent • New Event contains unknown subject group or subject groups equal • Object individual IDs the same

29. Seven Rules for Updating (3) • Remove existing event and add the one with the greater magnitude, applying reputation effects • New event subject group known • Existing event subject group unknown • Object individual IDs match • New Event has new information • Subject groups known and match • New event has maximum magnitude

30. Seven Rules for Updating (4) • Add new event and apply reputation effects • Subject groups for either or both unknown • Object individual IDs different • Subject groups known and match • Object individual IDs different • Neither even has maximum magnitude

31. 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

32. Simulating Animals

33. 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

34. 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

35. 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

36. Autonomous Characters

37. 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

38. 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

39. 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

40. 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

41. Character Introspection • Suggested questions that agent should ask itself in an emergent environment • 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

42. Coordinated Behavior

43. 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

44. Getting Out Of The Way • Obstruction by ally can be resolved in 4 ways (regarding firing) • Do nothing • Fire anyway (killing ally) • Agent moves • Ally moves

45. 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

46. More Humanlike NPCs

47. 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

48. 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

49. 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

50. 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