design fundamentals of stealth gameplay in the thief series, rsmith@ionstorm.com design fundamentals...

Design Fundamentals of Stealth Gameplay in the Thief Series, rsmith@ionstorm.com

Design FundamentalsDesign Fundamentalsof Stealth Gameplayof Stealth Gameplayin the in the Thief Thief seriesseries

Randy Smith

rsmith@ionstorm.com

DisclaimersDisclaimers

• I didn’t design Thief’s gameplay» Doug Church» Marc LeBlanc» Tom Leonard» Paul Neurath

• This is about open-ended stealth gameplay. Other games mentioned are being evaluated by this standard only.

» Tim Stellmach» Greg LoPicollo» Dorian Hart» etc.

What is stealth in What is stealth in Thief Thief ??

• Goal = move through space» Steal» Blackjack» etc.

• Failure = AI state becomes “alert”» Combat» Fleeing

» Pick lock» Pick pocket

How does the AI become How does the AI become alert?alert?

• The player has detectability» Visibility (light gem = feedback)» Audibility

• The AI has senses» Seeing» Hearing

• The overlap between player detectability and AI senses…» …is where the AI becomes alert or

not» …is where stealth happens

What is this lecture about?What is this lecture about?

• It is about stealth gameplay» Player movement through space» Player detectability» AI Senses» AI State

• It is not about:» Goals (such as stealing)» Consequences (such as combat)

Let’s design a stealth Let’s design a stealth game!game!

You are a thief in a medieval city. There is a mansion in the distance, full of loot. A wall separates you from the mansion, and a guard patrols in front of the gate. A torch nearby spills light across the area.

Do you:A) Wait until the guard has his back

turned and run through the gate.B) Put out the torch with a water arrow.C) Sneak up on the guard through the

shadows and blackjack him.

More stuff this lecture is More stuff this lecture is about:about:

• It is not about:» Stealth flavored gameplay» How gameplay is qualified (what

makes stealth gameplay stealth gameplay??)

» What is the definition of “open-ended” gameplay?

» Discrete interaction

• It is about:» Player expression» Analog interaction

Major concepts for this Major concepts for this lecturelecture

• Discrete Interaction Structures» Exemplified by Choose-Your-Own-

Adventure books

• Analog Interaction Structures» Exemplified (for the sake of this

presentation) by Quake or other FPS

Qualities of Discrete Qualities of Discrete Interaction StructuresInteraction Structures

• Finite, enumerable choices offered to the player.

• Player must choose one of the available options, not something in-between, not invent their own thing.

• Designer must explicitly create all interaction for the player.

• Should be called “Choose Someone Else’s Adventure”

What are Analog What are Analog Interaction Structures?Interaction Structures?

• Rough Definition: A collection of player-influenced, interacting game systems

• An abstract design tool for (de)constructing open-ended gameplay and analyzing relevant data

• A “unified theory” of existing thought:» Simulation vs. Emulation» Player Tools» Partial Failure

» Feedback» etc.

What are analog What are analog interaction structures interaction structures

NOT NOT ??• The only way to think about,

construct, or deconstruct any type of gameplay

• Necessarily the most useful tool for the job

• A ton of brand new thought

A Useful MetricA Useful Metric

• To what extent can the designer predict the player’s experiences?» A lot, the player can not take any

action the designer did not explicitly implement and intent Discrete Interaction

» Not much, really, the player has near-infinite ways to overcome the game’s challenges Analog Interaction

Analog Expression: Player Analog Expression: Player Movement in QuakeMovement in Quake

• Data relating to player movement:» Player location (X,Y,Z)» Player orientation (H, P)» Player velocity vector» Player acceleration vector

• Player expression:» Accelerate in various directions» Look right, left, up, down, or combo» Some fancy movement (jump, duck, etc.)

What makes it “analog”?What makes it “analog”?• Hey, yea! There aren’t analog

variables – so theoretically, all possible states are enumerable.

• ...but the player cannot “choose” their movement data. There is no “choice”.

• Instead, the player uses movement tools to set or “express” their desired movement data.

Player movement is Player movement is relevant to Quake’s core relevant to Quake’s core

gameplaygameplay• Player movement data is

critical to resolving combat from moment to moment:» Orientation is how you aim weapons» Movement is how you dodge, take

cover, charge, etc.» These are examples of the player

expressing “higher order concepts”

What else does Quake What else does Quake have?have?

• For both Player and Enemies:» Movement» Weapons that fire projectiles» Damage model (hit points)

• Projectiles

• A game world with physics simulation.» Collisions between player, terrain,

projectiles.

Components to Analog Components to Analog Interaction StructuresInteraction Structures

• A game world that hosts interactions dictated by simulations (in Quake, physics in the 3D world)

• Analog player expression (in Quake, player movement)

• Analog/partial failure (in Quake, hit points)

• Player tools to take arbitrary actions (in Quake, weapons that fire projectiles)

Let’s talk about Thief Let’s talk about Thief alreadyalready

• Game world that hosts interactions dictated by simulations = 3D world, similar to Quake» Physics » Line-of-sight (LOS)» Lighting, light sources» Sound propagation, noisy surfaces

Analog Expression in Analog Expression in ThiefThief

• Player movement» Player location (X,Y,Z)» Player orientation (H, P)» Player velocity vector» Player acceleration vector

• Player movement expression » Accelerate in various directions» Look right, left, up, down, combo» Some fancy movement (jump, climb,

Higher Order Concepts in Higher Order Concepts in Expressing StealthExpressing Stealth

• Hide in shadows = move into a dark part of the world

• Move silently = avoid moving over loud surfaces, move slowly

Quake with only 1 hit Quake with only 1 hit pointpoint

• No partial / analog failure

• A lot of the data becomes much less relevant to resolving combat:» How damaging weapons are» Player’s emergent combat tactics

when they are weak versus when they are healthy

Stealth-related tools in Stealth-related tools in ThiefThief

• Potions» Invisibility» Speed

• Thrown tools» Flashbomb

• Arrows» Water arrow» Moss arrow» Noisemaker arrow

Analog Interaction Analog Interaction Structure chart = a data Structure chart = a data

analysis toolanalysis tool• Useful for thinking about data:

» What data the player has input into» How data flows from system to

system and eventually leads to success or failure

• Drawing the chart is as much art as science» Which data boxes?» How many arrows?» Draw the chart differently to analyze

the data differently

Feedback in ThiefFeedback in Thief

• AI State and AI Senses» Broadcast speech» Animations» Behavior

• Player Visibility / Audibility» Light gem» Listening

• AI Movement» Player senses

Level-building for Analog Level-building for Analog InteractionInteraction

• Don’t create “scripts”» Don’t plan the player’s experiences

for them.

• Create “possibility spaces”» Populate the world with challenges

» Populate the world with things that interact with the player’s tools, the simulations, manipulate the data flow

» Avoid absolutes, embrace gradients

Design new types of Design new types of analog gameplay!analog gameplay!

• A game world that hosts interactions dictated by simulations

• Analog player expression

• Analog failure

• Player tools to take arbitrary actions

design fundamentals of stealth gameplay in the thief series, rsmith@ionstorm.com design fundamentals...

collection of player

openended stealth gameplay

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player location x

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