Game Analysis of Left 4 Dead

Bachelor of Arts (Honours) in Computing
Game Programming (COMP439)
10946780T
Lau Shui Fung

Cover Pag e


Game Analysis of Left 4 Dead

Lau Shui Fung
10946780T

1

Cover Page | Game Analysis of Left 4 Dead

Conte nts Page

10946780T
Lau Shui Fung

Contents
Cover Page ....................................................................................................................................... 1
Contents .......................................................................................................................................... 2
Introduction..................................................................................................................................... 4
About the game ........................................................................................................................... 4
Game Play .................................................................................................................................... 4
Psychology of computer game players ........................................................................................... 5
Player groups and their characteristics ....................................................................................... 5
The reinforcement principle ............................................................................................................ 6
Stimulus ....................................................................................................................................... 6


Design of Computer Graphic ....................................................................................... 7



Design of Lighting and Camera .................................................................................... 8



Design of Music ........................................................................................................... 9



Design of Sound Effect................................................................................................. 9

Challenges ................................................................................................................................. 10


Common infected ...................................................................................................... 10



Special infected and boss .......................................................................................... 10

Awards ....................................................................................................................................... 11
Psychological needs ................................................................................................................... 12


The advantages of aggressive.................................................................................... 12

Cognitive dissonance principle .................................................................................................. 13


German ban ............................................................................................................... 13

The Cognitive System’s limitation ............................................................................................. 14
Social and Cultural characteristics............................................................................................. 14
The concept of Survival ............................................................................................................. 15

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10946780T
Lau Shui Fung

Design of Artificial Intelligence and Computer Interactions ......................................................... 16
Deliver robust behavior performances ..................................................................................... 16
Provide competent human player proxies ................................................................................ 17
Promote Replay ability .............................................................................................................. 17


The Navigation Mesh................................................................................................. 17



Flow Distance ............................................................................................................ 18



The Active Area Set (AAS) .......................................................................................... 18

Structured Unpredictability in Left 4 Dead ............................................................................... 19
Architectures ................................................................................................................................. 20
Game Mode ............................................................................................................................... 20


Campaign (allow single play): .................................................................................... 20



Versus: ....................................................................................................................... 20



Survival: ..................................................................................................................... 20



Scavenge: ................................................................................................................... 20

Storytelling and Game Comics ...................................................................................................... 21
Advertisements ............................................................................................................................. 22
Conclusion ..................................................................................................................................... 23
Reference ...................................................................................................................................... 24

3


Introduction

10946780T
Lau Shui Fung

About the game

Left 4 Dead 2 is a single-player and multiplayer (1-8 players) co-operative survival horror FPS game
developed by Valve Corporation and it is the sequel to Left 4 Dead. The game launched on November 17,
2009 and the support platforms of L4D2 are Microsoft Window, Mac OS X, Linux and XBOX 360.
The game focuses on four of survivors fighting against hordes of the Infected. The four survivors must
fight off infected humans while trying to escape or make their way to a safe house. It has co-operative
gameplay in epic struggle between survivors and zombies. In a campaign mode, players can play as a
survivor or be one of special Infected, each of infected possess a unique mutant ability.

Game Play
The game has 6 Plot (Campaigns). Section of each plot, the player must flee to the next place of safety
(safe room) with the other survivors.
In the last chapter, the survivors must hang on a stronghold until the advent of the rescue vehicles or
escape with the authorities successfully.
These are linear plot task, fixed start and end, but which will have several branch to increase the
playability of the game. The length of each branch, the way encountered the enemy and the number of
supplements is not the same.
In addition, players can download additional components campaign from the other pages.

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Introduction | Game Analysis of Left 4 Dead

10946780T
Lau Shui Fung

Psychology of computer game players
Player groups and their characteristics

This game’s target males and 16+ year old players, shooting game is most of male teenagers’ favorite.
Similar as counter strike, a team play shooting game, it is a famous first person shooter game of the world.
Not matter player’s race, location and culture. All the 16~26 age teenagers knew this game very well.
Players eager beat his opponent to enhance their self-value. Most of this age’s males are warlike, want to
fight and enjoy the sense of accomplishment of eliminate enemies. On the Left 4 Dead, the characters like
a hero of the world. 90% of mankind are dead and turn to zombie, but they are survived in a difficult
environment, they are strong and smart.

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Psychology of computer game players | Game Analysis of Left 4 Dead

The reinforcement principle

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Lau Shui Fung

Stimulus

In the part of stimulus, we will go through it by graphic, lighting, music and sound effect. These few parts
are the major media of game to provide a stimulus to players. We can understand how the game
designers design on the details to achieve their aims.

6

The reinforcement principle | Game Analysis of Left 4 Dead

•

Design of Computer Graphic

10946780T
Lau Shui Fung

In Left 4 Dead, the part of computing graphic aims is simulation of real world, designer try to copy
everything from real world into the game, even a detail part. Common infected have different clothing in
different scene of game. E.g.(hospital have doctors and patients)

Also, designers were using some of visual effect to achieve their aims. On the above image, it was the
screen after vomit by Boomer, player will lose most of vision and cannot to distinguish who was the
enemy or allies. This effect can made player stop shooting and try to push others away to defense their
self.

7


•

Design of Lighting and Camera

10946780T
Lau Shui Fung

In Left 4 Dead, most condition were first person shooting mode of camera except the survivor was attack
by some of special infected, the camera view will turn to a third person view and applied a special lighting
effect of the player like a movie style. On the above image, it was a survivor attack by a hunter, player was
loosed control and need a help from other survivors. The players only can watching their character die if
no others know you are under attack.

The second special part of lighting is the flashlight, most time indoor power is not available since the
background of the game is the end of the world and full of zombies. Survivors just only use their own
flashlight to searching indoor. It can provide a feeling of unease to players because they are in a
unpredictable of environment and have a limited vision.

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•

Design of Music

10946780T
Lau Shui Fung

About the music part, “left 4 dead” play unique music when a wave of large common infected coming or
boss level infected arrival. The background music designed an exciting or strong feel. One of the exception,
when survivors near the boss level infected – Witch, they can listen she is crying and a unique background
music. Since witch has very high attack force but not initiative to attack survivors only if she was got shot
or walk very close with her. Most players don’t want to disturb her and walk around her. So, the
background music of Witch provides a feeling of fear. [4]

•

Design of Sound Effect

Left 4 dead designed different sound effect of each special Infected.[5] This is a good alert for survivors
because special infected always hiding their self in game but they cannot hide the sound, survivors would
know that if and special infected are near by the team. Also, the other part of sound effects attract
players, was the dialogue of characters. Some of dialogues were trigger by the event, character will told
other characters if they find out some of supplies or saw any special infected. In other cases, if any
character was under attack by the special infected, they will call help from others. In this part of sound
effect is control by this AI system of character, player don’t need to press any key to do that, let players
can focus on shooting or search some of useful supplies or trace the special infected.

9


Challenges
•

10946780T
Lau Shui Fung

Common infected

The common infected encountered during the game are fast and agile, weak individually, but may be
overwhelming in numbers. They display a special attraction to high-pitched alarm-type sounds, such as
the beeping device attached to pipe bombs and car alarms. Common infected will often chase down the
source of these noises while ignoring lower-pitched, but much louder sounds such as gunfire. They
occasionally attack in masses referred to in-game as a "horde".
In the AI Director (a system to control the AI) created common infected at randomized intervals (90-180
seconds on Normal difficulty)

•

Special infected and boss

In addition to the common infected, there are eight "special" or "boss" infected whose mutations grant
them special attacks that make them far more dangerous. Each of the special infected, have their own
usage to hinder survivors. In versus mode, special infected can control by human player.
In the AI Director, It was created at individually randomized intervals and Use valid area in the AAS (The
Active Area Set) not visible by the Survivor team appropriate to Special’s class.

10


10946780T
Lau Shui Fung

Awards

The Left 4 Dead provide many interesting awards in game. Because designers want to preserve balance of
game, all of awards were not provide any benefits or items in game to reward player. When the player
completed the requirement of awards, system will send the message to other players and players in your
friends list. Everyone knew which award you earned and provide a sense of accomplishment to the player.
In the other hand, the website of Left 4 Dead listed all of special award winners of months in the world.
Player can find out their own record on the website and show off to their friend.
Also, the game updated for new awards frequently, the awards system can provide extra of replay ability
to players.

11


Psychological needs

10946780T
Lau Shui Fung

About the cognitive system’s limitation of left 4 dead, this game increases the aggressive of player
psychological. Aggressive is the psychological needs of any males.

•

The advantages of aggressive

The aggressive help biological foraging, self-protection and courtship, that help to survive, so will be
retained in evolution. Aggressive can also protect the kinship groups against attack by outsiders, or to
help its survival. From the point of view of gene conservation, unless the environment is harsh and last
resort, bio should not attack next of kin. But human beings in addition to the reflex action of self-defense
rarely encountered external stimuli on the performance of the attack.

12


Cognitive dissonance principle

•

10946780T
Lau Shui Fung

German ban

"Left 4 Dead 2" in a large number of violent and bloody content in the Australian film and cultural
classification office decided not to give "Left 4 Dead 2" MA15 + rating. All games above MA15 + rating in
Australia, is prohibited on sale [1].
Later developers made changes to the game (including the infected in the game the Headshot and
amputation effect does not appear when killed, etc.), the modified version of the game, finally obtained
the MA15 + Rating, listed in Australia [2].
In above case, we can see Left 4 Dead was given too violent and bloody image to our society. In the
cultural classification office were not accept on sale, it means Left 4 Dead is not a best choose to their
child of parent. This is the weakness of Left 4 Dead since this game provided too reality simulation of
blood and headshot on the computer graphic.

13


The Cognitive System’s limitation

10946780T
Lau Shui Fung

Watching violent TV or playing violent video games for a while, it will increase the frequency or intensity
of aggressive behavior. At present, there are more and more research toward investigate the behavior of
the correlation of violent games and hostility.
NCTV (1990) reviewed the literature and pointed out that 75% of the study found that violent games may
encourage children or youth more violence, but they may be only a short-term relationship. (Cesarone,
1994).
Calvert and Tan (1994) study also pointed out that students playing the violent virtual reality games have
more rapid heartbeat, dizziness and nausea, and presents a more aggressive thoughts (Cesarone, 1998).

Social and Cultural characteristics

Matsushita (1997) pointed that play video games both physiological and psychological effects on the body,
physiological aspects including eye fatigue and weight gain; psychological impact of individual confusion
between real and unreal, as well as the lack of a mature social relationships.
Studies have shown that high sensation seeking individuals have a strong psychological and physiological
responses and creativity, but it is easier violate social norms, may lead to deviant behavior or crime. There
are even more than study found that young people taking psychedelic drugs, smoking, playing video
games, sexual activity, to participate in high adventure sports and crime are related to the individual
stimulation seeking.

14


The concept of Survival

10946780T
Lau Shui Fung

This game requires players stick together and have communication with each other. Players need to help
teammates who are catches by special infected. Players will lose control of their character if they are
attacked by some special infected, if no others player help them, they will die very soon. On this other
side, player will get down and cannot move until others players give a hand to help them get up again. On
the above points, it makes player must walk very close and keep a watchful eye on their teammates.

[Figure] a player is attacking by Hunter

[Figure] revived by teammate

15


10946780T
Lau Shui Fung

Design of Artificial Intelligence and Computer Interactions

Left 4 Dead's AI director system is a major feature of the game. System according to the players to choose
the difficulty, location, status, and pressure to determine the location and quantity of the props in the
map and enemies appear to accommodate players of the game technical level, and to players in each
game has a different experience (for example, when survivors team defeated by the time to start afresh,
the system will reduce the number of enemies in the scene and to increase the number of props, so that
players can have a more relaxed gaming experience). The game also director system control music, the
system will be based on the situation encountered by the players (encountered tanks survivors character
dies) to decide to play the music, so that players will not be boring game music.
About the design of Artificial Intelligence, the valve group released the document about the AI systems of
Left 4 Dead [3]. In this document, development team briefed this game have four of goals of AI. These
goals are deliver robust behavior performances, provide competent human player proxies, Promote
Replay ability and generate dramatic game pacing.

Deliver robust behavior performances
The first goal was deliver robust behavior performances, the development team want to create jagged
path and move fluidly through navigation mesh. Based on the needs, there have two methods to
implement the idea; its Path Optimization and Reactive Path Following. In the document [3], they have
explained the methods of execution in details.
About the concept of Reactive Path Following, bots move towards “look ahead” point farther down path
and use local obstacle avoidance. The benefits are repathing cost is low, the local avoidance handles small
physics prop/corners/other bots.

[Figure] Reactive Path Following

16

Design of Artificial Intelligence and Computer Interactions | Game Analysis of Left 4 Dead

Provide competent human player proxies

10946780T
Lau Shui Fung

The second goal is provide competent human player proxies, development team created the behavior
system built to reproduce decisions and actions players make while playing the game. The system
replicated human performance based on actual gameplay experience. On the major idea is players need
to believe bot since this is cooperative nature game and need close collaboration of Survivor team and
implicit trust in teammate’s action choices. Based on this objective, have a few rules it must be observe by
the bot. These included survivor Bots prioritize human teammates over bots, Survivor Bots cannot deal
friendly fire damage and Survivor Bots never use Molotov.

Promote Replay ability
The second goal is about Promote Replay ability. To achieve this goal, development team needs to design
an unpredictable experience created by interactions between teams of players drives replay ability. In Left
4 Dead, Procedural Population of enemies and loot strongly promotes replay ability. It made game session
is viewed as a skill challenge instead of a Memorization exercise. Based on this objective, development
team given up the static placement of enemies and loot because it will hinders replay ability. Players are
good at memorizing all static locations and removes suspense of not knowing what will happen next;
Results in “optimal strategy” that works every time, These are weakness of static placement. The final
solution to achieve the replay ability is using structured unpredictability. This is a part of the system of “AI
Director”.
Development team created four of methods to implement this solution.

•

The Navigation Mesh

Major concept of this method is to divide space to Represents “walkable space”. It is originally created for
Counter-Strike Bot of path finding. It is useful for general spatial.

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10946780T
Lau Shui Fung

•

Flow Distance

About this concept, mainly is travel distance from the starting safe room to each area in the navigation
mesh. And then following increasing flow gradient always takes you to the exit room. About the escape
route, it is the shortest path from start safe room to exit.

•

The Active Area Set (AAS)

The active area set means a set of Navigation Areas. The AI Director creates/destroys population as the
AAS moves through the environment. These sets allows for hundreds of enemies using a small set of
reused entities.

18


Structured Unpredictability in Left 4 Dead

10946780T
Lau Shui Fung



Wanderers (high frequency)
Common Infected that wander around in a daze until alerted by a survivor. It was stored as a
simple count (N) in each area, Counts are randomly determined at map start based on Escape
Route length and desired density.



Mobs (medium frequency)
A large group (20-30) of enraged common infected that periodically rushes the survivors. It was
created at randomized intervals (90-180 seconds on Normal difficulty) or boomer Vomit forces
Mob spawn. Mob size grows from minimum just after spawn to maximum after duration to
balance difficulty of successive, frequent Mobs.



Special Infected (medium frequency)
Individual Infected with special abilities that harass the Survivor team. The AI Director created at
individually randomized intervals. And use valid area in the AAS not visible by the Survivor team
appropriate to Special’s class.



Bosses (low frequency)
Powerful Infected that force the Survivors to change their strategy. The boss positioned every N
units along random on“escape route”. Three Boss events are shuffled and dealt out: Tank,
Witch, and Nothing. And the successive repeats are not allowed.



Weapon Caches (low frequency)
It is collections of more powerful weapons. Map designer creates several possible weapon
caches in each map; the AI Director chooses which will actually exist



Scavenge Items (medium frequency)
Scavenge items means Pipe bombs, Molotovs, Pain Pills, Extra Pistols. Map designer creates
many possible item groups throughout the map. The AI Director chooses which groups actually
exist.

19


Architectures

10946780T
Lau Shui Fung

Game Mode
In Left 4 Dead 2, it is includes four of the game modes. On the different game mode can give extra
experience of players. The brief of each game mode is showed on below.

•

Campaign (allow single play):

Up to four human players fight against the Infected to make their way through Campaign stages; any
Survivor not controlled by a human player is controlled by the computer. A Single player mode allows
players to play without intrusion from human players.

•

Versus:

Up to four other human players take control of various Special Infected to try and prevent the Survivors
from completing a stage. Special Infected are randomly assigned to Infected players

•

Survival:

A timed challenge where the Survivors are trapped in a section of the campaign maps, and try to survive
as long as possible against an unending onslaught of Infected.

•

Scavenge:

A new 4-on-4 mode that requires the Survivor players to collect and use as many fuel cans scattered
about a level to fill up a power generator, while the Infected players attempt to stop them.
On the above game modes, it’s provided a standard mode of campaign, player can resistance to infected
with others 3 player or AI player.

20

Architectures | Game Analysis of Left 4 Dead

10946780T
Lau Shui Fung

Storytelling and Game Comics

In the comic of left 4 dead, VALVE released comic of official story telling the background of game. About
the background story in videogame, the game had not told it to player directly by animation or text since
it is a shooting game. But, the game designer leave many clues in the game scene, like the other survivors
will leave messages in the safe room, player can guest the virus source and develop of the story. And a
Left 4 Dead comic on web are helps players fill in the narrative blanks left empty by the videogame. [6]

The game takes place in Pennsylvania, the game in the disaster is caused by a variant of the rabies virus in
game four survivors immunity against this virus. This virus is transmitted by bodily fluids.

21

Storytelling and Game Comics | Game Analysis of Left 4 Dead

Advertisements

10946780T
Lau Shui Fung

About the advertisements of this game, most is based on game magazine and the branding of valve
(vendor of counter-strike). In other hand, Left 4 dead has a lot of flat-screen advertising on street, almost
is the poster or title only, haven’t show any screen of the game content. The advertising is not very affect
the sales of this game since most hard core players who are targeted by this game are known Masterpiece
before it release.

22

Advertisements | Game Analysis of Left 4 Dead

Conclusion

10946780T
Lau Shui Fung

The summary of this game, this is a very successful works attracted many players to buy, at the same time
become one of the world-renowned game.
The success of the game from the game designers make improvements based on the psychology of
players on the AI Director. Further strengthen the gameplay and variability.
In the design of the game, the background story design and the design of the scene is very delicate. The
designers left many clues to the story in the scene, increasing the engagement of the players.
Because of the delicate 3D animation, as well as a wide range of sound enhance the player into a sense of
tension. Addicted to this game for many players, the future launch of the second generation version is
also very popular.
Even if the publisher does not put too much money on marketing, sales still ideal, at the same time
become the winner of numerous awards.
On the other hand, violence and excessive bloody make this game at an early stage by the European ban
the sale. The developers immediately change the picture of the game, reducing the bloody part.

23

Conclusion | Game Analysis of Left 4 Dead

Reference

10946780T
Lau Shui Fung

[1]太過血腥？！《惡靈勢力 2》遭禁止在澳洲上市
http://gnn.gamer.com.tw/9/39409.html
[2] Injunction
http://technolex-anwaelte.de/?id=43&news_id=360
[3] The AI Systems of Left 4 Dead
http://www.valvesoftware.com/publications/2009/ai_systems_of_l4d_mike_booth.pdf
[4] Music of witch cry
https://www.youtube.com/watch?v=cBeaLwGYg08
[5] Sound effect of different special infected
https://www.youtube.com/watch?v=_npS_-NfxWk
[6] Game comics
http://www.l4d.com/comic/

24

Reference | Game Analysis of Left 4 Dead

Game Analysis of Left 4 Dead

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