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The Pac-Man Dossier


February 23, 2009 Article Start Previous Page 3 of 10 Next
 

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

indefinite

Frightening Behavior

Anytime Pac-Man eats one of the four energizers on the level, the ghosts reverse direction and, on earlier levels, go into frightened mode. Frightened ghosts turn dark blue and wander about the maze for a few moments, flashing briefly as a warning before returning to normal. Ghosts use a pseudo-random number generator (PRNG) to pick a way to turn at each intersection when frightened.

The PRNG generates an pseudo-random memory address to read the last few bits from. These bits are translated into the direction a frightened ghost must first try. If a wall blocks the chosen direction, the ghost then attempts the remaining directions in this order: up, left, down, and right, until a passable direction is found. The PRNG gets reset with an identical seed value every new level and every new life, causing predictable results.

This is why the frightened ghosts' movements are repeatable in the context of a memorized pattern or sequence. As the levels progress, the time ghosts spend in frightened mode grows shorter until eventually they no longer turn blue at all (they still reverse direction). Refer to Table A.1 in the appendices for the frightened time in seconds and number of flashes, per level.

Speed

The game starts with Pac-Man at 80% of his maximum speed. By the fifth level, Pac-Man is moving at full speed and will continue to do so until the 21st level. At that point, he slows back down to 90% and holds this speed for the remainder of the game. Every time Pac-Man eats a regular dot, he stops moving for one frame (1/60th of a second), slowing his progress by roughly ten percent-just enough for a following ghost to overtake him.

Eating an energizer dot causes Pac-Man to stop moving for three frames. The normal speed maintained by the ghosts is a little slower than Pac-Man's until the 21st level when they start moving faster than he does. If a ghost enters a side tunnel, however, its speed is cut nearly in half.

When frightened, ghosts move at a much slower rate of speed than normal and, for levels one through four, Pac-Man also speeds up. The table below summarizes the speed data for both Pac-Man and the ghosts, per level. This information is also contained in Table A.1 in the appendices.

 


PAC-MAN SPEED

GHOST SPEED

LEVEL

NORM

NORM DOTS

FRIGHT

FRIGHT DOTS

NORM

FRIGHT

TUNNEL

1

80%

71%

90%

79%

75%

50%

40%

2 - 4

90%

79%

95%

83%

85%

55%

45%

5 - 20

100%

87%

100%

87%

95%

60%

50%

21+

90%

79%

-

-

95%

-

50%


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