Design Fundamentals of Stealth Gameplay in the Thief series

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Design Fundamentalsof Stealth Gameplayin the
Thief series

• Randy Smith
• rsmith_at_ionstorm.com

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Disclaimers

• I didnt design Thiefs 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.

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What is stealth in Thief ?

• Goal move through space
• Steal
• Blackjack
• etc.
• Failure AI state becomes alert
• Combat
• Fleeing

• Pick lock
• Pick pocket

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How does the AI become 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

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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)

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Lets design a stealth 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.

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More stuff this lecture is 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

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Major concepts for this lecture

• 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

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Qualities of Discrete Interaction 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 Elses Adventure

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What are Analog 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.

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What are analog interaction structures 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

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A Useful Metric

• To what extent can the designer predict the
  players 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 games challenges ? Analog
  Interaction

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Analog Expression Player Movement 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.)

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What makes it analog?

• Hey, yea! There arent 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.

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Player movement is relevant to Quakes core
gameplay

• 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

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What else does Quake 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.

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Components to Analog Interaction 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)

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Lets talk about Thief already

• 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

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Analog Expression in Thief

• 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, etc.)

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Higher Order Concepts in Expressing Stealth

• Hide in shadows move into a dark part of the
  world
• Move silently avoid moving over loud surfaces,
  move slowly

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Quake with only 1 hit point

• No partial / analog failure
• A lot of the data becomes much less relevant to
  resolving combat
• How damaging weapons are
• Players emergent combat tactics when they are
  weak versus when they are healthy

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Stealth-related tools in Thief

• Potions
• Invisibility
• Speed
• Thrown tools
• Flashbomb
• Arrows
• Water arrow
• Moss arrow
• Noisemaker arrow

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Analog Interaction Structure chart a data
analysis 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

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Feedback in Thief

• AI State and AI Senses
• Broadcast speech
• Animations
• Behavior
• Player Visibility / Audibility
• Light gem
• Listening
• AI Movement
• Player senses

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Level-building for Analog Interaction

• Dont create scripts
• Dont plan the players experiences for them.
• Create possibility spaces
• Populate the world with challenges
• Populate the world with things that interact with
  the players tools, the simulations, manipulate
  the data flow
• Avoid absolutes, embrace gradients

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Design new types of analog gameplay!

• A game world that hosts interactions dictated by
  simulations
• Analog player expression
• Analog failure
• Player tools to take arbitrary actions