1. Design Fundamentals of Stealth Gameplay in the Thief series
Randy Smith
Design Fundamentals of Stealth Gameplay in the Thief Series,

2. Disclaimers 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.
Design Fundamentals of Stealth Gameplay in the Thief Series,

3. What is stealth in Thief ?
Goal = move through space
Steal
Blackjack
etc.
Failure = AI state becomes “alert”
Combat
Fleeing
Pick lock
Pick pocket
Design Fundamentals of Stealth Gameplay in the Thief Series,

4. 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
Design Fundamentals of Stealth Gameplay in the Thief Series,

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

6. 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)
Design Fundamentals of Stealth Gameplay in the Thief Series,

7. Let’s 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.
Design Fundamentals of Stealth Gameplay in the Thief Series,

8. 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
Design Fundamentals of Stealth Gameplay in the Thief Series,

9. 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
Design Fundamentals of Stealth Gameplay in the Thief Series,

10. A choose-your-own adventure book.
Design Fundamentals of Stealth Gameplay in the Thief Series,

11. 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 Else’s Adventure”
Design Fundamentals of Stealth Gameplay in the Thief Series,

12. WHOA!! Don’t worry, we’re going to build this step by step as we go.
It’s an example analog interaction chart.
Design Fundamentals of Stealth Gameplay in the Thief Series,

13. 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.
Design Fundamentals of Stealth Gameplay in the Thief Series,

14. 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
Design Fundamentals of Stealth Gameplay in the Thief Series,

15. A 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
Design Fundamentals of Stealth Gameplay in the Thief Series,

16. 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.)
Design Fundamentals of Stealth Gameplay in the Thief Series,

17. 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.
Design Fundamentals of Stealth Gameplay in the Thief Series,

18. Player movement is relevant to Quake’s 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”
Design Fundamentals of Stealth Gameplay in the Thief Series,

19. To win a single-player level in quake, the player must eventually move to the exit. So, they express “success” via movement.
Design Fundamentals of Stealth Gameplay in the Thief Series,

20. An example of a theoretical stealth game in which moving to the exit is the goal and moving into the view cones is failure – the player uses movement in this game to express “success” or “failure”.
Design Fundamentals of Stealth Gameplay in the Thief Series,

21. 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.
Design Fundamentals of Stealth Gameplay in the Thief Series,

22. 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)
Design Fundamentals of Stealth Gameplay in the Thief Series,

23. This chart shows design elements in a simulated world
This chart shows design elements in a simulated world. The nodes are design elements. The arrows represent data flowing from element to element.
Design Fundamentals of Stealth Gameplay in the Thief Series,

24. Let’s 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
Design Fundamentals of Stealth Gameplay in the Thief Series,

25. Here’s the simulated world of Thief – world systems include physics, line of sight, light sources, noisy surfaces / sound propagation
Design Fundamentals of Stealth Gameplay in the Thief Series,

26. AI State = failure (when AI state = “I see the player”, the player has failed at stealth)
Player Goal = success (get to the end of the level to succeed)
Design Fundamentals of Stealth Gameplay in the Thief Series,

27. 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.)
Design Fundamentals of Stealth Gameplay in the Thief Series,

28. Player must use the expressive tool of movement to succeed.
Design Fundamentals of Stealth Gameplay in the Thief Series,

29. But player movement is what makes them visible and audible.
Design Fundamentals of Stealth Gameplay in the Thief Series,

30. AI’s can see and hear, and that’s what changes their state to the failure condition.
Design Fundamentals of Stealth Gameplay in the Thief Series,

31. Player visibility and audibility is what the AI senses detect.
So we now see the very basics of a stealth game, complete with success, failure, and the fundamental tension:
- the player must move to succeed, but moving makes them detectable, and the AI senses pick up on that, possibly eventually leading to the failure state.
- this is a pretty technical analysis (for design, anyway) in as much as it runs highly parallel to the underlying game systems
- therefore, it can help keep us honest as designers. If under-the-hood data isn’t flowing from one design concept to another, then there is no chance that the design concept is contributing to success/failure, and thus isn’t really a part of gameplay (in the sense of analog interaction)
Design Fundamentals of Stealth Gameplay in the Thief Series,

32. 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
Design Fundamentals of Stealth Gameplay in the Thief Series,

33. AI Senses (eg – where their vision cone is located and oriented) is dependant on AI movement (eg – where the AI is located and oriented).
Again, an example of how underlying data is being passed from design component to design component. In this example, it shows us that AI movement data is crucial to resolving success/failure of analog stealth gameplay.
This suggests that if you give the player a tool to manipulate AI Movement data, then that tool can be used by the player (possibly improvisationally) to form a goal to succeed. We’ll see examples of this later.
Design Fundamentals of Stealth Gameplay in the Thief Series,

34. AI State -> AI Movement/Senses - when AIs become suspicious, they “search” by perking up their senses and moving around.
Design Fundamentals of Stealth Gameplay in the Thief Series,

35. 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
Player’s emergent combat tactics when they are weak versus when they are healthy
Design Fundamentals of Stealth Gameplay in the Thief Series,

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

37. This is an all-too-common example of a stealth game with no analog failure. As soon as the player steps into a view cone, they have failed at stealth. Therefore, the only way to succeed here is exactly how the designer intended.
Design Fundamentals of Stealth Gameplay in the Thief Series,

38. Thief’s analog failure model
Design Fundamentals of Stealth Gameplay in the Thief Series,

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

40. Stealth-related tools in Thief
Potions
Invisibility
Speed
Thrown tools
Flashbomb
Arrows
Water arrow
Moss arrow
Noisemaker arrow
Design Fundamentals of Stealth Gameplay in the Thief Series,

41. Potions change player visibility data, player movement data.
- With this example as with the next few, we’re demonstrating that since these tools effect data crucial to resolving analog gameplay, they play a meaningful role in player expression / gameplay.
Design Fundamentals of Stealth Gameplay in the Thief Series,

42. Flashbombs change AI senses and movement.
Design Fundamentals of Stealth Gameplay in the Thief Series,

43. Water arrows and moss arrows impact the underlying simulation.
Design Fundamentals of Stealth Gameplay in the Thief Series,

44. Noisemaker arrows introduce a new element into the underlying world simulation
Design Fundamentals of Stealth Gameplay in the Thief Series,

45. An important side-effect to note: using projectiles can impact player visibility and audibility data (eg – AIs can see/hear you better when you shoot a fire arrow), which may lead to unexpected gameplay consequences.
Design Fundamentals of Stealth Gameplay in the Thief Series,

46. 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
You could probably be really rigorous in setting up the chart, but if it helps you analyze your game design, then it’s useful.
Design Fundamentals of Stealth Gameplay in the Thief Series,

47. Feedback in Thief AI State and AI Senses
Broadcast speech
Animations
Behavior
Player Visibility / Audibility
Light gem
Listening
AI Movement
Player senses
Design Fundamentals of Stealth Gameplay in the Thief Series,

48. In other words, the player needs to see/hear the AI in order to know how well they’re doing at stealth. In order to see/hear the AI, the player has to be in the right place. This is an analysis that explains the concept of “scouting”, which is a major emergent player dynamic in the game.
Design Fundamentals of Stealth Gameplay in the Thief Series,

49. Level-building for Analog Interaction
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 Fundamentals of Stealth Gameplay in the Thief Series,

50. 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
One of the really useful applications of this tool is that it can be used to explore new types of interaction – you can use it to prove to yourself that your gameplay is meaningful and involves player expression, and isn’t just discrete and flavored.
Design Fundamentals of Stealth Gameplay in the Thief Series,