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The Pac-Man Dossier

What design and AI lessons can we learn from Namco's seminal Pac-Man? From history through behavior, Gamasutra presents a comprehensive game guide.

[What design and AI lessons can we learn from Namco's seminal Pac-Man? From history through behavior, Gamasutra presents a comprehensive Jamey Pittman-authored guide to the classic game.]

In 1999, Billy Mitchell of Hollywood, Florida became the first person to obtain a perfect score of 3,333,360 at Pac-Man, eating every possible dot, energizer, ghost, and bonus on every level without losing a single life in the process.

But perhaps what is most amazing is the fact he can play without using any memorized routines widely known as "patterns".

Instead, he relies on his familiarity with how each ghost behaves as it moves through the maze, using that knowledge to keep Pac-Man one step ahead of his enemies at all times.

Unlike Mitchell, most players are only able to rack up high scores with the aid of multiple patterns that take advantage of the game's deterministic nature.

These patterns require perfect memorization and recall to be of any real use - a single hesitation or wrong turn during execution can make the remainder of a pattern useless.

Not surprisingly, an over-reliance on these routines leaves many a player clueless as to how to effectively avoid the ghosts and finish off the remaining dots in the higher levels once a mistake occurs.

Most Pac-Man strategy guides available on the internets today are very similar in content to the books that used to be sold back in the early 80s

A summary of gameplay and scoring is provided first, followed by a list of patterns to be memorized by the reader, but very little insight is offered on how the game works or how the ghosts make decisions.

Therefore, the purpose of this guide is to give the player and game designers a better design understanding of Pac-Man by taking a closer look at gameplay, maze logic, ghost personalities, and the mysterious "split screen" level.

All information provided has been extracted from or verified with the disassembly output from the Midway Pac-Man arcade ROMs along with controlled observations of actual gameplay. As such, I have a high confidence in its accuracy.

That said, if you notice an error or omission, please contact me so it can be corrected as soon as possible. I hope you find the information just as interesting and useful as I did for gaining a better understanding of this classic game.

Special thanks to Don Hodges (www.donhodges.com) whose invaluable contributions to this guide can be found in every chapter.


Chapter 1: Welcome to the Machine

"I don't have any particular interest in [computers]. I'm interested in creating images that communicate with people. A computer is not the only medium that uses images; I could use the movies or television or any other visual medium. It just so happens I use the computer."-Toru Iwatani

It was 1977 when a self-taught, capable young man named Toru Iwatani came to work for Namco Limited, a Tokyo-based amusement manufacturer whose main product lines at the time were projection-based amusement rides and light gun shooting galleries.

He was just 22 years old with no formal training in computers, visual arts, or graphic design, but his creativity and aptitude for game design were obvious to the Namco executives that met with Iwatani. They offered to hire him-with assurances they would find a place for him in the company-and he accepted.

Iwatani eventually found his place designing titles for Namco's new video games division. His limited computer skills necessitated his being paired with a programmer who would write the actual code while Iwatani took on the role of game designer for the project.

This was a new job for the game industry in 1977 when most games were designed by the programmers who coded them. In addition to a programmer, Iwatani's team would usually include a hardware engineer to develop the various devices and components, a graphic artist to realize his visual ideas, and a music composer for any music and sound effects needed in the game.

Iwatani had initially wanted to work on pinball machines, but Namco had no interest in the pinball business. Perhaps as a concession, his first game design, called Gee Bee, was a paddle game similar to Atari's Breakout but with a decidedly pinball-inspired slant to the gameplay.

Released in 1978, it was Namco's first original video game-they had only ported existing Atari games to the Japanese market up to this point-and it enjoyed moderate success in the arcades.

But the paddle games were losing ground fast to a new genre. The unprecedented success of Taito's Space Invaders in 1978 caused an industry-wide shift toward space-themed, shoot-'em-up games (as well as a national coin shortage in Japan).

Game manufacturers scrambled to match Taito's success with space shooters of their own. Namco was quick to follow suit, assigning a team to start work on a Space Invaders clone at once. It was around this time that Toru Iwatani began thinking about designing a different kind of game. He felt the shoot-'em-up craze was destined to fade away like the paddle games before them.

Rather than make another space shooter, Toru wanted to take his game design in a completely new direction that did not focus on violence or conflict, and would appeal to both male and female audiences.

He took inspiration from a children's story about a creature that protected children from monsters by eating them. One of Iwatani's design methods included taking key words associated with a story to aid in developing his ideas. The kanji word taberu ("to eat"), became the premise for the game.

The word kuchi ("mouth") has a square shape for its kanji symbol and provided the inspiration for the game's main character-the better-known legend of Iwatani receiving his inspiration from a pizza pie with a slice missing was, by his own admission, not entirely correct:

"Well, it's half true. In Japanese the character for mouth (kuchi) is a square shape. It's not circular like the pizza, but I decided to round it out. There was the temptation to make the Pac-Man shape less simple. While I was designing this game, someone suggested we add eyes. But we eventually discarded that idea because once we added eyes, we would want to add glasses and maybe a moustache. There would just be no end to it.

Food is the other part of the basic concept. In my initial design, I had put the player in the midst of food all over the screen. As I thought about it, I realized the player wouldn't know exactly what to do: the purpose of the game would be obscure. So I created a maze and put the food in it. Then whoever played the game would have some structure by moving through the maze.

The Japanese have a slang word-paku paku-they use to describe the motion of the mouth opening and closing while one eats. The name Puck-Man came from that word."

-Toru Iwatani

The monsters from the children's story were included as four ghosts that chase the player through the maze, providing an element of tension. Attacks on the player were designed to come in waves (similar to Space Invaders) as opposed to an endless assault, and each ghost was given an unique personality and character.

The children's story also included the concept of kokoro ("spirit") or a life force used by the creature that allowed him to eat the monsters. Toru incorporated this aspect of the story as four edible power pellets in the maze that turn the tables on the ghosts, making them vulnerable to being eaten by the player.

With a name and a basic design in place, Iwatani was ready to begin work. The team Namco assigned Iwatani to bring Puck-Man to life included a programmer (Shigeo Funaki), a hardware engineer, a cabinet designer, and a music composer (Toshio Kai).

Development got underway in early 1979. In the course of that year, two new pinball-themed designs from Iwatani-Bomb Bee and Cutie Q-were both released during Puck-Man's development cycle. Both games were similar to Gee Bee but with stronger gameplay and improved visuals.

The Namco team working on the Space Invaders clone for the past several months had just achieved a technological coup for Namco: the first game to use a true, multi-colored, RGB display instead of the monochrome monitors with colored cellophane tape so prevalent at the time.

Thanks to the breakthrough of the other team, Iwatani now had the new promise of color to enhance his design. Mindful that he wanted the game to appeal to women, he immediately decided to use it on the ghosts, choosing pastel shades for the bodies and adding expressive, blue eyes. Dark blue was used for the maze itself, while Puck-Man was drenched in a brilliant yellow.

The look and feel of Puck-Man continued to evolve for over a year. A large amount of time and effort was put into developing the ghosts unique movement patterns through the maze and tweaking the game difficulty variables as boards were cleared.

Bonus symbols (including the Galaxian flagship) were added into the mix at some point, and the ghosts were finally given names: Akabei, Pinky, Aosuke, and Guzuta. Sound effects and music were some of the final touches added as development neared an end along with constant tweaking of the ghosts' behavior.

Puck-Man's creation was a year and five months in the making-the longest ever for a video game to that point. Finally, on May 22nd, 1980, it was released to arcades in Japan. Initially, the game did moderately well, but was no overnight sensation.

In fact, Namco's multi-colored Space Invaders clone, called Galaxian, was much more popular with the gaming public-the predominately male, game-playing audience in Japan was unsure what to make of Puck-Man with its cartoon-like characters, maze, and pastel colors, whereas Galaxian was more immediately familiar to them with its shoot-'em-up space theme.

Midway was a distributor of coin-operated video games in the U.S. that was always looking for the next big hit from Japan to license and bring to America. They opted for both Puck-Man and Galaxian, modifying the cabinets and artwork to make them easier to manufacture as well as providing a more American look and feel.

Puck-Man went through the majority of the changes: the cabinet was modified slightly, changing the color from white to a bright yellow to make it stand out in the arcade. The detailed, multi-colored cabinet artwork was replaced with cheaper-to-produce, three-color artwork illustrating an iconic representation of Puck-Man (now drawn with eyes and feet) and one blue ghost.

English names were given to the ghosts (Blinky, Pinky, Inky, and Clyde), and the Namco title was changed to Midway. The most significant change to Puck-Man was the name. Midway feared it would be too easy for nasty-minded vandals to change the P in Puck-Man to an F, creating an unsavory epithet.

Not wanting their product associated with this word, Midway renamed the game Pac-Man before releasing it to American arcades in October 1980.

But the situation in America was reversed from Japan for these two titles. Galaxian got lost in the shuffle of the shoot-'em-up craze that blanketed America's arcades and, by the fall of 1980, it was already competing with more advanced video games like Defender.

In the end, Galaxian enjoyed moderate success in America and in Japan, but was never the smash hit the original Space Invaders was. Pac-Man was another story. There were no games to compare it to-it was in a genre all by itself. The bright yellow cabinet, visuals, and sounds drew a great deal of attention. No one had seen a game quite like this before.

The addictive gameplay and challenge of increasing levels of difficulty kept the die-hard gamers more than happy, while the simplicity of the game appealed to younger children. The lack of war-like motifs and violence did as Iwatani had hoped and attracted a sizable female audience-a first for a video game. Even the parents wary of the violence-themed arcade games had no problem with their kids playing as cute and innocuous a game as Pac-Man.

Pac-Man went on to capture the world's imagination like nothing before or since. It was a genuine phenomenon on a global scale, selling over 100,000 machines in its first year alone. Easy to learn but notoriously difficult to master, everyone from school children to Wall Street executives dropped quarter after quarter into an ever-increasing number of waiting Pac-Man machines.

By 1982, Pac-Man merchandise was literally everywhere: t-shirts, hats, keychains, wrist bands, bedsheets, air fresheners, wall clocks, drinking glasses, trading cards, stickers, cereal boxes, comic books-even a Saturday morning cartoon.

A novelty song called "Pac-Man Fever" received significant radio play, reaching number nine on the U.S. Billboard charts. Many books were written offering tips and tricks used by the best players to achieve high scores-the first-ever strategy guides published for a video game.

Fast-forward to nearly thirty years later: Pac-Man remains the best-selling coin-operated video game in history. Still considered the most widely-recognized video game character in the U.S., his likeness has been licensed to over 250 companies for over 400 products.

His namesake has been adopted by the business world to describe a way to defend against a hostile takeover (the defending company swallows up the larger company instead in a move known as the "Pac-Man defense"). There is even an upright Pac-Man machine on display at the Smithsonian Institution in Washington, D.C.

Unlike the majority of his early-80s contemporaries, new Pac-Man games are still in development today. Most recently, Pac-Man Championship Edition was released in 2007 for the X-Box 360 console with the aid of Namco game designer Toru Iwatani.

Interest in the original coin-op title has never completely faded, thankfully. Thanks to Namco's re-release of Pac-Man and other arcade classics for modern home consoles, new generations of Pac-addicts have worn their hands out playing a game often older than themselves.

Many classic titles are also kept alive thanks to the advent of high-quality arcade emulators available for the home computer (like MAME) that use a software copy of the arcade ROM chips to recreate the game with 100% accuracy. Several web pages with information about the original Pac-Man arcade game can be found online including Wikipedia and the Killer List Of Video Games.


Chapter 2: Gameplay Details

"As Pac-Man was originally conceived to appeal to women players, it is a very easy and approachable game. I believe that is an ingredient in the longevity of the game."-Toru Iwatani, creator of Pac-Man

The Basics

The premise of Pac-Man is delightfully simple: using a four-way joystick, the player guides Pac-Man-up, down, left, and right-through a maze filled with dots for him to gobble up. Four ghost monsters are also in the maze and chase after our hero, trying to capture and kill him.

The goal is to clear the maze of dots while avoiding the deadly ghosts. Each round starts with the ghosts in the "monster pen" at the center of the maze, emerging from it to join in the chase.

If Pac-Man is captured by a ghost, a life is lost, the ghosts are returned to their pen, and a new Pac-Man is placed at the starting position before play continues. When the maze is cleared of all dots, the board is reset, and a new round begins. If Pac-Man gets caught by a ghost when he has no extra lives, the game is over.

There are 244 dots in the maze, and Pac-Man must eat them all in order to proceed to the next round. The 240 small dots are worth ten points each, and the four large, flashing dots - best known as energizers - are worth 50 points each.

This yields a total of 2,600 points for clearing the maze of dots each round. Players have two ways to increase their score beyond what is earned from eating dots:

The first way to increase your score each round is by turning the tables on your enemies by making them your prey. Whenever Pac-Man eats one of the four energizer dots located in the corners of the maze, the ghosts reverse their direction and, in early levels, turn the same shade of blue for a short period of time before returning to normal.

While blue, they are vulnerable to Pac-Man and can be gobbled up for extra points providing they are caught before the time expires. After being eaten, a ghost's eyes will return to the monster pen where it is resurrected, exiting to chase Pac-Man once again.

The first ghost captured after an energizer has been eaten is always worth 200 points. Each additional ghost captured from the same energizer will then be worth twice as many points as the one before it-400, 800, and 1,600 points, respectively. If all four ghosts are captured at all four energizers, an additional 12,000 points can be earned on these earlier levels. This should not prove too terribly difficult to achieve for the first few rounds as the ghosts initially remain blue for several seconds.

Soon after, however, the ghosts' "blue time" will get reduced to one or two seconds at the most, making it much more problematic to capture all four before time runs out on these boards. By level 19, the ghosts stop turning blue altogether and can no longer be eaten for additional points.

The second way to increase your score each round is by eating the bonus symbols (commonly known as fruit) that appear directly below the monster pen twice each round for additional points. The first bonus fruit appears after 70 dots have been cleared from the maze; the second one appears after 170 dots are cleared.

Each fruit is worth anywhere from 100 to 5,000 points, depending on what level the player is currently on. Whenever a fruit appears, the amount of time it stays on the screen before disappearing is always between nine and ten seconds. The exact duration (i.e., 9.3333 seconds, 10.0 seconds, 9.75 seconds, etc.) is variable and does not become predictable with the use of patterns. In other words, executing the same pattern on the same level twice is no guarantee for how long the bonus fruit will stay onscreen each time.

This usually goes unnoticed given that the majority of patterns are designed to eat the bonus fruit as quickly as possible after it has been triggered to appear. The symbols used for the last six rounds completed, plus the current round are also shown along the bottom edge of the screen (often called the fruit counter or level counter). See Table A.1 in the appendices for all bonus fruit and scoring values, per level.

Ghosts have three mutually-exclusive modes of behavior they can be in during play: chase, scatter, and frightened. Each mode has a different objective/goal to be carried out:

  1. CHASE - A ghost's objective in chase mode is to find and capture Pac-Man by hunting him down through the maze. Each ghost exhibits unique behavior when chasing Pac-Man, giving them their different personalities: Blinky (red) is very aggressive and hard to shake once he gets behind you, Pinky (pink) tends to get in front of you and cut you off, Inky (light blue) is the least predictable of the bunch, and Clyde (orange) seems to do his own thing and stay out of the way.

  2. SCATTER - In scatter mode, the ghosts give up the chase for a few seconds and head for their respective home corners. It is a welcome but brief rest-soon enough, they will revert to chase mode and be after Pac-Man again.

  3. FRIGHTENED - Ghosts enter frightened mode whenever Pac-Man eats one of the four energizers located in the far corners of the maze. During the early levels, the ghosts will all turn dark blue (meaning they are vulnerable) and aimlessly wander the maze for a few seconds. They will flash moments before returning to their previous mode of behavior.

Reversal Of Fortune

In all three modes of behavior, the ghosts are prohibited from reversing their direction of travel. As such, they can only choose between continuing on their current course or turning off to one side or the other at the next intersection. Thus, once a ghost chooses which way to go at a maze intersection, it has no option but to continue forward on that path until the next intersection is reached.

Of course, if you've spent any time playing Pac-Man, you already know the ghosts will reverse direction at certain times. But how can this be if they are expressly prohibited from doing so on their own? The answer is: when changing modes, the system can override the ghosts' normal behavior, forcing them to go the opposite way. Whenever this happens, it is a visual indicator of their behavior changing from one mode to another.

Ghosts are forced to reverse direction by the system anytime the mode changes from: chase-to-scatter, chase-to-frightened, scatter-to-chase, and scatter-to-frightened. Ghosts do not reverse direction when changing back from frightened to chase or scatter modes.

When the system forces the ghosts to reverse course, they do not necessarily change direction simultaneously; some ghosts may continue forward for a fraction of a second before turning around.

The delay between when the system signals a reversal and when a ghost actually responds depends on how long it takes the ghost to enter the next game tile along its present course after the reversal signal is given (more on tiles in Chapter 3). Once the ghost enters a new tile, it will obey the reversal signal and turn around.

Scatter, Chase, Repeat...

Ghosts alternate between scatter and chase modes during gameplay at predetermined intervals. These mode changes are easy to spot as the ghosts simultaneously reverse direction when they occur. Scatter modes happen four times per level before the ghosts stay in chase mode indefinitely.

Good players will take full advantage of the scatter periods by using the brief moment when the ghosts are not chasing Pac-Man to clear dots from the more dangerous areas of the maze. The scatter/chase timer gets reset whenever a life is lost or a level is completed. At the start of a level or after losing a life, ghosts emerge from the ghost pen already in the first of the four scatter modes.

For the first four levels, the first two scatter periods last for seven seconds each. They change to five seconds each for level five and beyond. The third scatter mode is always set to five seconds. The fourth scatter period lasts for five seconds on level one, but then is only 1/60th of a second for the rest of play. When this occurs, it appears as a simple reversal of direction by the ghosts.

The first and second chase periods last for 20 seconds each. The third chase period is 20 seconds on level one but then balloons to 1,033 seconds for levels two through four, and 1,037 seconds for all levels beyond-lasting over 17 minutes! If the ghosts enter frightened mode, the scatter/chase timer is paused.

When time runs out, they return to the mode they were in before being frightened and the scatter/chase timer resumes. This information is summarized in the following table (all values are in seconds):

Mode

Level 1

Levels 2-4

Levels 5+

Scatter

7

7

5

Chase

20

20

20

Scatter

7

7

5

Chase

20

20

20

Scatter

5

5

5

Chase

20

1033

1037

Scatter

5

1/60

1/60

Chase

indefinite

indefinite

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