Lecture 7 - Experience Management

AI forExperience Management

Context • We talked last week about tailoring games to speciﬁc players through content generation. • How else can we drive engagement with the player? • Talking today about ways the player engages with games. ‣ How we can use AI to aid that process.2

Monopoly • Imagine you’re winning a game of Monopoly with some friends. • You are playing the role of a successful business tycoon with a giant stack of cash. • Couldn’t you put a bounty on your opponents? • Hire arsonists to drive property value down?3

Limited Interactions • Games typically use a ﬁxed set of rules. • Limits how we can interact with the game world. • Constrained by how the designer envisaged the game be played. • Inability to step beyond the game rules. • In many cases the way to win is to think like the designer.4

Designer-Based Reasoning5

The Greatest Game Ever (...Maybe)6

What is Dungeons and Dragons? • Tabletop role playing game. • Pen and paper (and imagination) based. • Groups take the role of adventurers in a Lord of the Rings style setting. • Games may take hours to play, usually based around some sort of quest structure. ‣ E.g. Retrieve the sword of whoever from the tomb of whoever.7

The Dungeon Master • One player takes the role of the DM • In charge of running the game ‣ Narrator ‣ Arbitrator ‣ “AI” system for enemies • Responsible for ensuring that8

Interactions in D&D • Dungeons and Dragons doesn’t have rules per se • Deﬁnes a framework for interaction. • DM can interpret the framework to suit unseen / unplanned interactions. ‣ A player wants to climb the dungeon wall looking for secret passages. - This will require an athletic skill check and a dungeoneering check - Key is to let the players improvise and say “Yes and...”9

Zork • Old (oldoldold) school game from the 70s • Textbased adventure game with text input • Incorporates some language parsing systems. ‣ “Hit troll” vs “Hit the troll with the Elvish sword” ‣ Parses a variety of verbs, nouns and conjunctions • Good HCI • Still a very constrained human/game interaction10

Starship Titanic • Game from 1998 designed by Douglas Adams • Starship Titanic crashes into player’s house, player boards to try to ﬁgure out cause of disaster • Mystery game in the style of Monkey Island • Complete freedom to interact with characters using regular English. Robust parsing and response system • Tight constraints on lateral thinking11

Scribblenauts • 2009 for Nintendo DS (Scribblenauts Remix - 2011) • Casual puzzle game based around collecting stars • In order to collect the stars, solve puzzles. • Solution generally involves “summoning” an object. • Objects have distinct characteristics.12

Scribblenauts13

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Scribblenauts • 22,802* objects in the Scribblenauts database • Object characteristics ‣ Art ‣ Health ‣ AI Behaviour ‣ Animations ‣ Interactions with other objects • Adjectives give scope for lots of customisation19

Scribblenauts • Using the object database frees the player to tackle problems however they want. • In effect, the database becomes the framework for interactions. • Sufﬁcient variety that the player doesn’t perceive constraints. • Encourages lateral thinking20

Scribblenauts21

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Scribblenauts25

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Scribblenauts27

Freeform Interaction • Allows the player to solve problems in their own way. • Massive sense of satisfaction. • Moves away from “thinking like the designer” • Works in Scribblenauts primarily because of simplistic environment28

Immersive Worlds • We can engage with Scribblenauts well because, although simple, the depth of the world makes it immersive. • Limits interactions in other ways ‣ No unfolding story ‣ No characters to interact with • What if we looked at breadth of engagement rather than depth?29

Skyrim • Mentioned Skyrim last week. • Amazing breadth to the world. ‣ Talked about the option to join Thieves Guild group. - Also Companions, Dark Brotherhood, Bard’s guild, College of Magic. ‣ 18 Skill disciplines, each with ~10 individual “perks” ‣ About 300 locations within the world to explore • Massive “living” world to play in30

Skyrim - Economy • Cities in Skyrim maintain a (simplistic) economic model. • Affects availability of merchandise, amount of money NPCs have and prices of goods. • Player can affect the economy by building up (or tearing down) local business.31

Detour • “Raid on Bungeling Bay” (1984) involved a helicopter attacking factories in a city. • City infrastructure was intricately simulated. • Disrupting supply lines could cripple infrastructure and in turn, limit military forces counter-attacking • Level editor for this game would later be released as “Sim City”.32

Skyrim - Story • Skyrim has multiple plots that run in parallel. • Option to progress whichever you feel like. • Each group has a storyline as well as Radiant- generated side quests. • Different plots can inﬂuence each other ‣ One character appears in two plots, one as a core character, another as a guest at a party ‣ Extra interaction options at the party if you already know her33

Skyrim - Consequences • Quests and conversations have impact. • Positive and negative responses and attitudes. ‣ Characters build up a model of the player • Callbacks - the outcome of a quest will be referenced at a later date.34

Skyrim - Conclusions • The HGI here is not sophisticated. • Relies heavily on designer-led thinking. ‣ Can only interact with what has been anticipated • Few solutions to problems based on lateral thinking. ‣ Example - Can’t make a pile of brooms into a ladder • Implicitly a shallow experience. • Compensates by providing a very broad diverse world with consequences - playground of shallow.35

Immersive Worlds • Immersive worlds engage the player in a way games like Scribblenauts can’t. • We can virtually “inhabit” worlds. • Emotional attachment to characters, locations and events. • The plot’s narrative becomes secondary to the player-centric narrative of the world.36

Interactive Fiction • Iteractive Storytelling / Dynamic Narrative • The story adapts to the responses from the player • Player’s actions can shape the direction of the story • Where AI meets Storytelling37

Choose Your Own Adventure • Basic version of this is the Choose Your Own Adventure books • Page or so of text to read, then a few choices of next action. • Associated page number, reader skips to that page • Rinse and repeat through a plot til an end is reached.38

Story Beats • A “Story Beat” is a literary device. • A small piece within a scene with an exchange between the characters and an action / revelation that advances the story. • Story > Act > Scene > Beat • Smallest unit of story39

AI for Interactive Fiction • What we’re talking about with IF is : • Automating the Choose Your Own Adventure process. • Making it more subtle than “Turn to Page 14 to fall down the giant pit”. • Creating beats on the ﬂy.40

Branching Narrative • Branching narrative is most similar to choose your own adventure. • Points in the story require the player’s input • Determines the direction the story will take. • Effectively a sequence of if/else41

Branching Narrative • Combinatorial explosion is a big factor here. • If every choice has just 2 options, at the kth decision ‣ 2k possible states • We’ve seen this before in game trees, state spaces and planning.42

Branching Narrative • We can use procedural content systems to lessen the amount of work to be done. • Do we need 3 different versions of one beat which alter just one line dependent on minor actions? • Can we dynamically tweak a beat at runtime? • Effectively, this is procedural content customised based on the player’s history ingame.43

Multi-Linear Narrative • Typically media has a single linear narrative. • There may be multiple arcs at play, but a single story is being told. • Games allow us to interact. • Multiple plot lines can be set up ‣ We can explore at will • Progress (or lack of) in one can affect another. • Each one may itself be branching44

Interactive Fiction as Planning • Maria introduced Planning in the ﬁrst half of the course. • Recap ‣ Planning is the process of ﬁnding a sequence of actions that will transform a world from a given initial state into a state in which certain goals are true. • What if we don’t talk about actions?45

Planning with Beats • Let’s assume we have a pre-made set of Story Beats • We can see a narrative as a sequence of beats stitched together. • A traditional linear narrative is a standard planning problem. ‣ Characters X and Y start in this situation ‣ We want to ﬁnd a sequence of beats that puts them into this ﬁnal situation.46

Planning with Beats • We want to get the player to a speciﬁc point in the story. • We want the player to be free to choose their own path. • We always want to be guiding the player back toward the point we’re trying to get to. • This is not so straightforward.47

Plan Repair • Many assumptions related to Automated Planning ‣ When we execute a plan, it probably won’t work • We have a whole set of research ready to go on “what to do when things don’t work out” • Effectively this is the same situation as when the player doesn’t follow the path we are looking for.48

Drop-In Drop-Out Narrative • A big goal for narrative is the ability to drop-in and drop-out and still have the story make sense. • Consider games that offer co-operative story lines. ‣ Halo 3, Gears of War • Typically require a constant companion that is controlled by the computer in single player. • Another person can assume control.49

Drop-In Drop-Out Narrative • Consider an online game such as WoW. • Large raids involve up to 40. • What happens when a sub-group is late? • What happens when a group has to leave early?50

Drop-In Drop-Out Narrative • Technique that allows for customisation of the plot. • In many ways similar to Planning. • Finding explanations for why extra players arrive. ‣ Alternate routes into a level. • Explaining why players leave within the context of the narrative. ‣ E.g. Banished, teleported etc.51

Interactive Fiction • IF allows us to generate worlds that feel more engaging to players. • The world can react to the player’s actions. • The AI can direct the player’s attention to ensure target “gates” are passed through in the narrative. • Makes the world “come alive”52

AI for Scenario Control • We’ve looked at ways we can adapt the plot of the world to match what the player is doing. • Can we adapt the pace of the world too? ‣ Alter the ﬂow of enemies.53

Left 4 Dead • Survival shooter game from Valve (2008) • Everyone turned into zombies except four survivors • Cooperative game for 1-4 players ‣ Take the role of the survivors ‣ Escape the city and ﬁnd safety • If playing short-handed, AI players will ﬁll the team54

Horror Movie Pacing • The core thing Valve were aiming for was replicate the dramatic pacing of a horror movie. • This is a standard device for building suspense. • “Emotional Intensity” ‣ Starts low, gradually builds, peaks at a high level. ‣ Tapers off to a relaxation level. ‣ Cycle repeats.55

Measuring Intensity • In order to model intensity need a range of metrics. • Problem of feature selection we discussed earlier in section on Dimensionality Reduction. • Selected features for this include : ‣ Damage being dealt ‣ Damage being taken ‣ Distance to nearest zombie • Decays over time.56

Delta(Intensity) • The desired emotional intensity matches the current progression through the dramatic cycle. • The current actual intensity will be different. • This gives rise to a difference between them. • The AI Director modulates the game world to compensate for this difference.57

The AI Director in Action58

Altering the Game • In Left 4 Dead, the principle method of altering the game is changing the number of enemies. ‣ For peak intensity, hordes of enemies come from all sides - Spawned by the Director ‣ At low intensity, during relaxation periods, enemies are removed. • Pretty basic approach - ﬁrst pass at the technology59

Enhanced AI Directors • More subtle methods can be used to manage the player’s experience. ‣ Weather - varying intensity of storms and lightning to build intensity. ‣ Items - during intense times, reduce the amount of ammo available. ‣ Enemy types - keep the player on their toes60

Hierarchical Concurrent State Machines • The HCSM is the driving force behind the AI Director. • 1998 technique developed for scenario management in a driving simulator.61

Hierarchical Concurrent State Machines • Building block of an HCSM is itself an HCSM ‣ Recursive by nature • Analogue input wire • Conﬁguration parameters • Output wire62

Hierarchical Concurrent State Machines63

Hierarchical Concurrent State Machines • Input - Delta(Intensity) • Conﬁguration - current parameters of level • Objective - Minimise Delta(Intensity) • Child HCSMs - Spawn new enemies, alter level etc.64

Further Reading • HCSMs were ﬁrst introduced in ‣ “HCSM: A Framework for Behaviour and Scenario Control in Virtual Environments” Cremer, Kearney and Papelis • Discussed in some detail on AIGameDev.com ‣ http://aigamedev.com/open/reviews/hcsm-concurrent- state-machine/ (me)65

Summary • Covered “Experience Management” • Interaction Design for Immersive Worlds • Interactive Fiction • Scenario Control ‣ HCSMs66

Next (Final) Lecture • What is Game AI? • Traditional AI vs Game AI • Emergence • Debugging • Software Engineering in AI ‣ Scrum • Your AI Toolbox67

Lecture 7 - Experience Management

by Luke Dicken on Dec 04, 2011

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Lecture 7 - Experience Management — Presentation Transcript

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