Survey of Procedural Content

Procedural Content Generation

• Procedural generation refers to content generated algorithmically rather than manually.– numbers, strings, movies, games, pictures,

simulation, programs, natural language, etc.• Why have procedural content?– Replayability

• Scene variety• Infinite levels

– Development time and costs

Development costs – facts and figures

• Gran Turismo 5 budget: $60 Million [source]• Average AAA game development cost:

$28 Million [source]

• For comparison:– Movie budgets• Kick-Ass (2012) : budget of $28 Million

– Television• Game of Thrones : budget approx. $60 Million [source]

Development costs – facts and figures

• How the Wii was born

• Cost and Sales breakdowns

• $60 price point – inflation and cost breakdown

Procedural content in games

Procedural generation algorithms

Examples in commercial games

Additional reading and resources

• Procedural Content Generation for Games: A Survey– Direct Link to author’s preprint– ACM Digital Library Link

• Essential facts about the computer and video game industry: Sales, demographics, and usage data– 2012 infographic

Examples

Adapted from material by James Grisetti and Luke Aust

Contemporary GeneratorsPerlin Noise

• Mathematical interpolation of floating point numbers

• Creates fractional Brownian Motion• Used to make CGI textures look more realistic

Contemporary GeneratorsL-Systems

• Lindenmayer systems• Defined as a 3-tuple

V, the alphabet of the system (variables and constants)ω, initial string of the system (axiom, start, or initiator)P, set of production rules (one for each variable in V)

Contemporary GeneratorsL-Systems Continued

• At each iteration, each variable in the current string is replaced with its corresponding production to produce the next string

• State is the string after a given number of iterations

• The state is usually used to direct a “turtle graphic”

• One of the most commonly used PCGs

Contemporary GeneratorsL-Systems Continued

ExampleV = {A,B}ω = AP = {A→AB,

B →A}

Iteration• A• AB• ABA• ABAAB• ABAABABA

Contemporary GeneratorsL-Systems Demonstration 1

V = {F,+,-}F means “draw forward”‘+’ and ‘-’ are used to change angle

ω = F--F--F--P = {F→F+F--F+F}

Contemporary GeneratorsL-Systems Demonstration 2

V = {X,F,[,],+,-}F means “draw forward”‘[‘ and ‘]’ are used to save and restore position‘+’ and ‘-’ are used to change angleX has no meaning outside of the L-System

ω = XP = { X → F-[[X]+X]+F[+FX]-X,

F → FF }

Contemporary GeneratorsExpert Systems

• Departure from previous approaches• Use statistical methods to determine world

shape and item placement• First notably used in Procedural Content

Generation in Valve’s Left4Dead

Future Work

• Most contemporary PCGs are involved in generating terrain artifacts (landscape)

• Some use in animations, textures, and lighting

The next generation of Procedural Content Generation will be involved in creating entire maps

Future Work

Going to the extreme:Programming programs that program programs

In a paper published this year, Mahlmann, Togelius, Yannakakis at the IT University of Denmark suggest the use of Procedural Content Generation for entire games, including rule sets, unit hierarchies, game maps, etc.

Future Work

Another paper by Dimovska, Jarnfelt, Selvig, Yannakakis from the same university explores the use of procedural techniques to aid in physical rehabilitation using the Wii platform

Example ApplicationsMinecraft

• Terrain is generated procedurally• “Mobs” are placed procedurally

Example ApplicationsCityEngine

• Middleware intended for simulation and use in motion pictures

• Requires map data for input• Creates road layouts, building shapes, and

textures based on user parameters

Example ApplicationsSubversion

• Independently developed game• Goal is for the entire world to be procedurally

generated

Example Applications.kkrieger

• Created circa 2004 for the then state-of-the-art hardware

• Uses PCG techniques to create maps, play music, and place items and enemies all at runtime

• Executable is 97,280 bytes

ReferencesKnowledge• The omniscient www.wikipedia.org• Mahlmann, et al. “Towards Procedural Strategy Game Generation:

Evolving Complementary Unit Types” (link)• Dimovska, et al. “Towards Procedural Level Generation for Rehabilitation”

(link)• Müller and Parish. “Procedural Modeling of Cities” SIGGRAPH 2001 (link)

Example Applications:• http://www.theprodukkt.com/kkrieger• http://www.introversion.co.uk/subversion• http://www.procedural.com• http://www.minecraft.net

Software

• .kkreiger (2004 .theprodukkt)• .debris (2009 .theprodukkt)• .werkkzeug 1 (2002 .theprodukkt)• .werkkzeug 3 TE (2007 .theprodukkt)• Dwarf Fortress (2006 Bay 12 Games)• Vega Strike (2008 TVST) All above content is Open Source and Freeware that

can not be resold or redistributed for any price, all credit is given to original publishers and contributors who have allowed me to distribute this content.

Bibliography

• http://pcg.wikidot.com• http://vegastrike.sourceforge.net• http://www.theprodukkt.com/• http://www.bay12games.com/dwarves/• http://df.magmawiki.com/