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  • Examining the Essentials of Stealth Game Design

    - Youssef Khatib
  • This paper will look into the inner workings of stealth centric games to find out the essential components of thistype of videogames. The paper will examine the history of such games and the design principles of stealth centric games in relation to the participating player.

    To do this, one needs to find a suitable definition of what stealth centric games are. The most common way is to define stealth games as genre.Game design books categorize stealth games as a sub-genre of actiongames. This way of categorizing is present for example in Ernest Adams and Andrew Rollings,The Fundamental of Game Design (2007)and Scott Rogers Level Up! The Guide to Great VideoGame Design(2010). However this way of categorizing games can cause some confusion due to the way the action genre is defined.

    An action game is one in which the majority of challenges presented are tests of the player's physical skills. (Adams, Rollings, pp.436, 2007)

    In the article Sorting Out the Genre Muddle, Ernest Adams explains the origin of game genre usage as symptom of the videogames industry's growth. Asmore money was being made,the cost and investments of developing new games increased rapidly. Only large publishers had access to store shelves, makingpublishers more cautious of the content being developed and less willing to use creative approaches. So videogames eventually settled into a set of genres recognized as: sports, strategy, racing, fighting, action, role-playing, and so on.(Adams, 2009)

    Stealth games arecurrently recognizedas asub-category of the action genre.Thiscauses problems because of the useof the word genre in marketing.

    The retailers began organizing their shelves along these lines. Publishers created product plans based on them. Gamers learned to prefer one genre over another, and to identify themselves as fans of shooters or platformers or real-time strategy. (Adams, 2009)

    The unregulated structure for the definition of the action genre causes problems, due to its lack of clarity. Therefore this paper will turn towards the MDA (Mechanics, Dynamics, Aesthetics) Framework (Robin Hunicke, Marc LeBlanc and Robert Zubek, 2004) as a reference point for defining stealth centric games. In the MDA framework, the design of a game can be divided into considerations of a game's mechanics, dynamics and aesthetics.Mechanics are functions that trigger actionsin the gamespace, as several mechanics interacting with each other this interaction is referred to as the dynamics of a game. These two components are often built and designed according to a desired aesthetic goal.

    Randy Smithdefines stealth centric games ashaving the following commonaesthetic goal:"[To] create the illusion of a securely guarded area that the player can sneak through by virtue of leveraging their unique abilities and tools to create and exploit security flaws" (2006).In Ernest Adams's definitions of challenge types, stealth is a sub-category for conflict challenges where the player is "avoiding being seen" (Adams and Rollings,pp.23, 2007). From the above one candevise a more precise definition of what stealth gamesare. This will be used as a base for differentiating stealth centric games from other conflict centric games.

    •1.1  Purpose

    Thepurpose of this paper is to familiarize the reader with stealth-centric games andto differentiate themfrom action games,by examining similarities between stealth games and the aesthetics they aspire to, as reflected in their mechanics.

    •1.2  Question

    What are stealth centric games, how are they designed and whatattributesare essential for adhering to their aesthetic goal?

    •1.3  Scope of work

    There are many instances where these games deviate from their stealth centric approach. This happens when they introduce combat centric scenarios for the purpose of conveying the overarching narrative of the gameworld and a prime example is when boss encounters happenin whichplayers are presented with a set of expectations unlike the default challenges present in the game. This paper will only focus on themain procedure of play for these games and not the atypical challenges found in boss battles.

    •2.    Background

    Stealth games are widely thought to have started with Metal Gear for the MSX2 home computer in 1987. However the earliest known game with stealth elements was released as early as 1981 with Castle Wolfenstein(Muse Software).Worthy of note is that many of the mechanics introduced early on, like hiding dead bodies and frisking guards for items, laterdisappeared from newer games for some time and did not resurface until decades later.

    The year 1998 saw the release of several titles that made use of stealth systems. Many of these games became commercial successes allowing this style of play to reach new audiences previously unaware of this type of game systems. During this time, many of these games evolved further, by borrowing mechanics and elements from other non-stealth centric games.

    By the turn of the millennium, stealth centric games started gaining momentum with releases like Thief II:TheMetal Age(Looking Glass Studios,2000), Metal Gear Solid 2: Sons Of Liberty (Konami, 2001) and Tom Clancy's Splinter Cell (Ubisoft, 2002). Many of the early mechanics were re-introduced and Artificial Intelligence systems became increasingly important for stealth play.

    There is anabundance of articles from game critics,from the enthusiast press, and industry professionals about this type of game. However, the information presented in such articles is often subjective in nature, since they seldom have an analytical approach in organizing information.

    The coming sections will examine the features and traits an avatar might possess to avoid detection.There are alsoobstacles that generally work against the player to create challenges. These come in the form of patrolling guards, security measures such as security cameras, alarm triggering traps and other environmental hazards.This paper derives these features from stealth centric games that have made use of them in a recurring manner through several released titles. The background is divided into two major sections; the first one representing the player and their possible actions. The second sectionpresents dynamic and static obstacles occupying the game space.

    •2.1  Avatar Means

    •2.1.1      Avatar Characteristics

    The avatars featured in these games have a certain set of common characteristics. For example the avatarthe player inhabits in Tom Clancy'sSplinter Cell(Ubisoft, 2002) acts in a way that makes him seem dexterous and agile but also incapable of fending off multiple armed opponents in a direct confrontation. Thus the player has to learn to use the avatar'sagility attributes in order to" avoid being seen"(Adams and Rollings, 2007) and "[leverage] their abilities and tools to create and exploit security flaws" (Randy smith, 2006) in order to progress.

    The avatar'sphysical abilities can often be used to dispose of threats, overcome certain obstacles and hide behind cover. In Metal Gear Solid 3: Snake Eater (Konami, 2004) the game uses a grappling system that allows the player to quickly knock guards unconscious. In Assassin's Creed (Ubisoft, 2009) the game uses an automated navigation system that allows the avatar to transitionseamlessly between running on the ground and scaling buildings.

    •2.1.2      Movement

    How movement is designed varies greatly in these games and is dependent on how the design approaches the subject of sneaking.

    Contemporary stealth centric games require the player to manipulatethe speedat which they travel through the game-space,without alerting any threats. This type of games offers mechanics to alter the pace of movement by implementing different walk and run modes. These modes can either work as different states or in transition from one tothe other.Furthermore, these modes can alter the avatar's stance. Earlier games of stealth tended to only have one mode of movement; this meant that in early games guards generally did not have complex systems for sensory perception.(See: artificial intelligence section 6.1.2)

    Hitman: Codename 47 (Eidos ,2001) makes use of a mechanic called "Sneak mode"(Eidos,Hitman: Codename 47 Manual, 2001)This is a mode of movement, which allows the avatar to move silently without detection. The game contains several movement modes all of which emit varyinglevels of sound relative to the speed of movement. However, when the player enters "sneak mode" the avatar's sound emissions are reduced.

    Speed management in Tom Clancy'sSplinter Cell (2002, Ubisoft) functions in a particular manner, whereby the player controls the avatar's movement speed within a threshold.The function is similar to that of anaccelerator pedal in automobiles. At the highest rate ofmovement the avatar emits the highest possible sound while moving, while the opposite is true for the lowest. The avatar profile also alters this, as changing the stance of the avataralso changes the movement pattern. This means that an avatar moving in a crouch stance(i.e. lower profile)emits less sound.

    •  Cover systems

    Hiding behind cover is a way of avoiding detection. In early stealth games, the player positioning themselves behind a vision-obstructing object was enough to avoid detection. Over time, taking cover came to develop into a mechanic, which allowed theavatar to press himself against these vision-obstructing objects.These objects vary in their shapes and sizes, as long as they facilitate adequate cover from the guard's sight(Metal Gear Solid, Konami 1998).

    This further developed into a mechanic wheredesignatedobjectsacted as cover, enabling the player at a push of a button to position the avatar behind cover. Movement modes were also added to these objects, allowing players to strafe along covers for instance (Tom Clancy's Splinter Cell,Ubisoft 2002).

    •2.1.3      Visibility

    How a game communicates whether the player is visible to the guardsor not worksdifferently in everygame. This is governed through rules that are applied in the gameworld.The most common one is cover. Allowing theavatar to press himself against a wall to peek around corners, and to crouch behind smaller objects is a common way to obstruct the guard's sight of the avatar.

    In stealth games developers try to give the guards simulated sensory perceptions such as vision, hearing and sometimes smell to create a human like awareness.For further information see theArtificial Intelligencesection 6.1.2.

    •  Concealment

    Concealment,unlike cover,is a way for the avatarto blend into thesurroundings, whether it be through camouflage (Metal Gear Solid 3: Snake Eater,Konami2004), the use ofshadows for hiding (Tom Clancy's Splinter Cell, 2002) or the use of crowds to blend into. (Assassin's Creed II,Ubisoft2009)When the avatarisconcealed, special rules applyrestricting the avatar'sbehavior.For example in the situation in which a guard isfacing the avatar'sgeneral direction, while incapable of sensingthe avatar's presence due to concealment, sudden movements on the part of the avatar will cause the avatar to be detected.This serves as anabstraction of how quickly the human eye can react to movement. However while this is applicable to concealment by shadows and camouflage, sudden movements will not cause detection in the case of crowds. Crowds cycle constantly, moving around and sometimes move in groups that the avatar can move among while maintaininghisconcealment. With the potential exception of crowds, concealment generally does not protect the avatar from incoming gun fire or other attacks.

    •2.1.4      Tools

    Gadgets and firearms available to the player increase their options when they face game challenges. Traditionally stealth games rely on gadgets that help the player gauge the dangers they are about to encounter. These tools can range from radars that cover entire areas(Metal Gear Solid, Konami, 1998) to snake cameras that let the player peek around corners and under doors(Tom Clancy's Splinter Cell, Ubisoft,2002). Gadgets that create distractions are often used to divert attention from the avatar's planneddirection of entry.These tools usually work as sound causing devices, such as coin that be thrown which attracts a guard's attention to its landing spot (Hitman; Codename 47, Eidos Interactive, 2001). Firearms are often presented in these games as a last resort in case the avatar isdetected and defensive measure has to be taken and sometimes used as a way to neutralize guards standing in the avatar'spath of progression.

    •2.2  Avatar Challenges

    •2.2.1      Guards

    Guards are generally the main dynamic obstacles in a stealth centric game; they can patrol certain routesor have static placements.Sometimes they also march in groups (Assassin's Creed II,2009,Ubisoft). Upon the detection of the avatar they usually react with hostility, often attacking the avatar while alerting fellow guards to the avatar'slocation. If the avatar manages to escape their sight, they initiate a search for the avatar, using the senses and intelligence they have been given.

    •2.2.2      Environmental Hazards

    These hazards exist as a threat that can give away the avatar'slocation to a guard'ssenses,for example loud flooring(Thief: The Dark Project, Looking Glass Studios 1998) or water puddles (Metal Gear Solid, Konami, 1998) that emit sounds when trod upon. Other hazards can serve to break the concealment such as motion sensitive lights reacting to the avatar's movementsby lighting updarkenedareas.(Tom Clancy's Splinter Cell: Pandora Tomorrow, Ubisoft, 2004) There are also life-threatening hazards such as land mines or floor traps (Metal Gear Solid, Konami, 1998) .

    •2.2.3      Security Measures

    Security cameras are often used to detect intruders in stealth games (Metal Gear Solid, Konami 1998).Other measures also include laser beams(Tom Clancy's Splinter Cell: Pandora Tomorrow, Ubisoft, 2004), motion sensors (Mark Of The Ninja, Klei Entertainment, 2012) or a trip alarmdevice that gives out a loud sound. These threats are designed to trigger the alarm state upon their activation.

    •2.2.4      Alarmstate

    The alarmstate is usually triggered upon the avatar's detection by patrolling guards. This phase generally causes an increase in difficulty bychanging the guard's idle patrolling, to a more hostile behavior. In early stealth games, once the player had been detected, only the guards patrolling in the area were aware of the avatar's location. As technology advanced, guards can trigger general alarms, alerting guards outside the present area.

    Many stealth centric games employ alarmstates differently. Some have implemented multiple steps that need to be performed by a guard before the alarm can be raised. InMetal Gear Solid 2: Sons of Liberty (Konami, 2002) a guard has to first spot the avatar, call his commander on the radio and ask for backup. During this sequence, the player has time to react in order neutralize the guard or destroy the radio to hinder the alarm from being triggered.

    Tom Clancy's Splinter Cell (2002, Ubisoft) populatessomelevelswith alarm switches on various walls that the guard has to interact with in order to trigger the alarm. However whether this is the first course of action or to shoot at the player first can vary depending on how the artificial intelligencesystem works.

    Alarm states tend to take on different stages. In Metal Gear Solid(Konami,1998) alarms have multiple stages. The first stage (Alert Phase) directs all guardsat the avatar's location. The second stage (Evasion Phase) is where guards lose track of the avatar's location and start actively searching, until a certain time threshold has been reached, which causes the guards to abandon their search.

    •3.    Method

    The paper will go throughdesign principles presented by industry professionals. This is done by examining stealth centric game design principles and the design ofartificial intelligence in videogames. One can develop a general perception of what stealth centric design isby also examining the dynamic relationship of guard and avatar. Level design will then be considered examining thearchitecturebehind level design for stealth games in ordertograsp why stealth based levels need to functionin a specific way. From this we can extract a set of common design requirementswhich stealthcentric games need to achievetheir aesthetic goal, butalso the technical requirement that has to be present for stealth play to work.

    Games and level designer Randy Smith has held two Game Developers' Conference (GDC) talks.The firsttalk,in which he discussed the open-endedness of stealth gameplay, is called "Design Fundamentals of Stealth Gameplay in the Thiefseries"(2002). The second talk was held in 2006and goes by the title"Level Building for Stealth Gameplay".It discusses requirements of stealth levels.

    Additionally Christopher W. Tottenhas a thought-provoking approachto level design, in which he breaks down rooms into spaces which trigger different human emotions depending on certain conditions. While Totten writes about level design in general, his work touches on the relevance of game space to establishing an approach to stealth centric level design.

    Tom Leonard and Donald Kehoe both write about Artificial Intelligence design for games. Leonard goes into how an Artificial Intelligence Sensory system works. He worked on artificial intelligence sensory systemforThief: The Dark Project (Looking Glass Studios,1998).Kehoe writes in a more general manner on Artificial Intelligence design for videogames.However the article also goes through the consequence of using AI state machines that work to shift the guard's behaviorinrelation to theavatar'sactions in the game-space.

    These people's work will be used in analyzing and organizing the information needed to establish the building blocks of stealth centric games.The paper will also look at camera models as an information gathering tool that the player makes use of during play.


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