The document discusses procedural content generation in video games, which utilizes AI and mathematical techniques to create assets such as buildings, trees, rocks, and weapons automatically. It explores concepts like L-systems for generating complex shapes and outlines the application of procedural generation in games like 'Borderlands' and 'Skyrim' for quests and environments. Additionally, it emphasizes the importance of controlling difficulty through procedural methods, creating a dynamic player experience.

1. Procedural Generation
of Game content

2. Procedural Content
Generation
• Procedural Content Generation is the process of
using techniques based on AI, maths and other
disciplines to automatically create game content.
• Consider a game set in a city
‣ How many unique buildings are there in a city?
‣ How frequently could you duplicate a building before
players noticed?
‣ What about trees?
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3. Trees
• Trees are complicated.
‣ Easy to get wrong
‣ The same tree over and over breaks immersion
‣ Lots of trees in a forest
• You could pay an artist to sit and come up with the
look of a whole bunch of trees, then model them,
put them into levels etc.
‣ Costly, time consuming, bloats game’s size
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4. Lindenmayer Systems
• L-Systems are recursive grammar rewriting
frameworks.
• Defined as a tuple (A, S, R)
‣ Alphabet of symbols
‣ Starting state
‣ Rules that are used to rewrite the initial state
• Great for creating fractal patterns
• Iterate n times to get interesting shapes appearing
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5. Koch Snowflakes
• A : variables - { f } constants - {+, -}
• S :f - - f - - f
• R :f > f + f - - f + f
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6. Koch Snowflakes
• Board work
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7. Koch Snowflakes
• n=0 : f -- f -- f
• n=1 : f + f -- f + f -- f + f -- f + f -- f + f -- f + f
• n=2 : f + f -- f + f + f + f + f -- f + f -- f + f -- f + f + f
+ f -- f + f -- f + f -- f + f + f + f + f -- f + f -- f + f -- f
+ f + f + f -- f + f -- f + f -- f + f + f + f + f -- f + f -- f
+ f -- f + f + f + f -- f + f
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8. Koch Snowflakes
• Assign meaning to each component of the alphabet
• f draw forwards
• + turn 60 degrees right
• - turn 60 degrees left
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9. Koch Snowflakes
N=0
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10. Koch Snowflakes
N=1
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11. Koch Snowflakes
N=2
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12. Koch Snowflakes
N=3
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13. Koch Snowflakes
N=3
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14. L-System Example
• A :Variables : {X, F} Constants : {+, -}
• S :X
• R : {X > F - [ [X] + X ] + F [ + F X ] - X, F > F F}
• Meanings :
‣ F draws forward, X is a dummy variable (no real action)
‣ - + left and right 25 degrees
‣ [ begins subtree, ] returns to start of sub tree
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15. L-System Example
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16. L-System Example
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17. Rocks
• Rocks have the same problem as trees.
• Seeing the same rock over and over has the same
issues as trees.
• Rocks can also be generated using L-Systems
‣ “SpeedRock: Procedural rocks through grammar and
evolution” Dart, Di Rossi and Togelius, Proceedings of the
FDG Workshop on Procedural Content Generation, 2011
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18. Evolving L-Systems
• It’s possible to take an L-System definition and
represent it chromosomally.
• From there we can apply all the kinds of tricks.
‣ Clustering
‣ Evolution
• We can evolve “art” based on our L-System
representation
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19. The Morph Lab
• Part of the ALife suite at http://alife.fusebox.com
• Starts from a single dot, player select the “fittest”
candidate from a selection of drawn L-Systems.
• Chromosome defines size, colour, rewrite rules and
number of iterations to rewrite for.
• Rapidly create interesting distinct patterns.
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20. The Morph Lab
• Demo
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21. Weaponry
• Procedural generation can be used for a lot more
than art.
• We can use it to generate the weapons that the
player might find in a game.
‣ Not just the models of the weapons
‣ Also the stats and effects
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22. Borderlands
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23. Borderlands
• Borderlands has over 650,000 weapons in it.
‣ Different stats
‣ Different models
‣ Different names
• In many ways, just a simple combinatorics problem
‣ Given a set of different options for these various
parameters, how many ways can we combine them?
• Beats sitting down and designing each one by hand!
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24. Galactic Arms Race
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25. Galactic Arms Race
• GAR uses the cgNEAT algorithm to evolve different
types of weaponry in the game.
• Fitness is based on the amount a weapon is used
• Parameters evolved include
‣ Colour
‣ Effects
‣ Trajectory
‣ Bullet lifetime
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26. Galactic Arms Race
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27. Galactic Arms Race
• Important - none of the behaviour the GAR
weapons exhibit is defined by the developer
• Completely emergent
• Randomised weapons guided by player preference
• Interesting effects appear quickly
• Balance could be difficult
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28. Quests
• Typically Role Playing Games (RPG) involve “quests”
• A mechanic for giving the player tasks and goals.
• Two different types
‣ Storyline - part of the narrative of the game
‣ Side-quest - time-wasting stuff that has no impact other
than giving the player things to do.
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29. Skyrim
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30. Skyrim - Radiant
• Skyrim is the debut for Bethesda’s Radiant quest
generator.
• Various quest-givers across the world are
generating quests procedurally.
• Not part of the core story arcs.
• Can have an effect on the world.
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31. Example - Thieves Guild
• The Thieves Guild is a group that the player can join
• Major quest arc related to the group
• Range of side quests
‣ Burglary, pickpocket, “shill” jobs
• Each type of quest has standard objectives
• The location of the objective changes each time, as
do the details e.g. what to steal.
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32. Mechanics
• In order to adequately execute this kind of system
‣ Need a rich selection of potential locations
‣ More immersive when we can talk about specific people
rather than generic villagers
• What does the player get from this diversion?
‣ Reward
‣ Experience and reputation
‣ Perhaps affects the world more broadly
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33. Levels
• It’s possible not only to generate components of the
game such as scenery and objective procedurally.
• Also entire environments for the player to
experience.
• Keeps the game fresh
• Enhances replayability
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34. Tiny Wings
• iPhone game based around a bird
• Touch the screen to fold wings, untouch to flap
wings
• Landscape features valleys
‣ Slide down the valley to gain speed
‣ Flip up the other side to fly through the air
• Aim is to get as far as possible in a given time
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35. Tiny Wings
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36. Tiny Wings
• Landscape is broken into discrete islands
• Each island has a general character
‣ 1st island has gentle rolling hills
‣ 4th island has sharp, deep valleys
• The level changes every day, but the overall tone of
it doesn’t.
• How can this be achieved?
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37. Parametric Definitions
• Landscape in Tiny Wings is effectively defined by a
single function for each island.
‣ Sinosoidal function.
‣ (More likely a unification of several sinosoidals)
• We can define the function with parameters
‣ The non-parameterised components define the character
‣ The parameters define the specific shape for today’s level
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38. Parametric Definitions
Sin(x) - note the characteristic roll
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39. Parametric Definitions
Contrast with 2sin(2x) - totally different “character”
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40. Parametric Definitions
2sin(2x) with 2.3sin(1.8x+15)
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41. Levels
• We can specify the level design in Tiny Wings as a
parameterised function.
• We can update the parameters on a regular basis to
alter the experience the player gets.
• We can control the way the experience changes by
how the parameters are applied.
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42. Difficulty
• Lots of games give players options of what difficulty
they want.
• There are obvious (naive) ways we can alter
difficulty.
‣ Give bad guys more health / make player weapons deal
less damage.
‣ More bad guys.
‣ Fewer items, less ammo
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43. Difficulty
• We can also do stuff that’s way more subtle.
‣ Alter timings
‣ Decrease visibility of “signposts” (markers within the
level that cue the player - often subconsciously - where
to go)
‣ Mess around with the design of the level in more detail
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44. Difficulty of Levels
• We can make the same kind of manipulations to the
functions generating a Tiny Wings level dependent
on what difficulty the player has selected
‣ Easy level gives the functions a more gentle curve
‣ Hard level gives the functions a harsher minima
• Even within the different islands characters, we can
generate “easy” versions and “hard” versions.
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45. Difficulty in a
Mario-style game
• Consider a game like Mario
• Side scrolling
‣ Lots of jumping over obstacles
‣ Gaps to jump between
• How can we modify the difficulty of the level?
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46. Summary
• Procedurally Generated Content
‣ In-game assets
‣ Levels
‣ Quests
• Introduced concept of difficulty in games
• Talked about the difference between obvious and
subtle changes in difficulty
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47. Next Lecture
• Talking about how we can use the player models we
created last week to understand video games better
• Using these models to build better content
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