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Pac-Man is able to
navigate the turns in the maze faster than his enemies. He does
not have to wait until he reaches the middle of a turn to change
direction as the ghosts do (see picture below). Instead, he may
start turning several pixels before he reaches the center of a
turn and for several pixels after passing it.
Turns taken one or
more pixels before reaching the center are "pre-turns";
turns taken one or more pixels after are "post-turns".
Players learn to consistently move the joystick in the direction
Pac-Man should go well before arriving at the center of a turn,
ensuring each pre-turn is started as many pixels away from center
as possible.
This technique is known as cornering and is
one of the first skills a new Pac-Man player should master.
For every successful pre-turn maneuver, Pac-Man puts a little more
distance between himself and any ghosts following close behind.
Such a small gain in distance may not seem terribly significant at
first, but cornering through a quick series of turns will shake
off even the most determined pursuer. It is a vital tool for
survival in the higher levels of the game.
Whenever Pac-Man
makes a pre-turn or post-turn, his orientation changes, and he
starts to move one pixel in his new direction for every pixel
traveled in his old direction, effectively doubling his speed as
he moves at a 45 degree angle. Once he reaches the centerline of
the new direction's path, he starts moving purely in that
direction and his speed returns to normal.
The greatest distance
advantage is thereby gained by making the earliest pre-turn
possible. The illustration below shows the layout of pre-turn
pixels (shown in green), center point pixels (shown in yellow),
and post-turn pixels (shown in red) for each of the four possible
directions a turn can be approached. Each example shows Pac-Man
entering the same four-way intersection from a different
direction.
When entering from the left, there are three pre-turn
pixels before the center of the turn, and four post-turn pixels.
Conversely, entering the same intersection from the right yields
four pre-turn pixels and three post-turn ones. Entering from the
top as opposed to the bottom exhibits the same property.
For any
turn that is made later than the earliest possible pre-turn,
Pac-Man will be one frame behind where he would be for every pixel
of "lateness" in the turn. Basically, it pays to move
the joystick well before reaching a turn to maximize your speed.
(click image for full size)
Turning at the
earliest pre-turns possible is also required to successfully
execute most any pattern. Patterns are meant to be played with
perfect cornering because it removes the human element of
uncertainty as to when Pac-Man will turn. Without cornering, it
would be nigh-impossible to reproduce the exact timing of every
turn as made by the pattern's author, thereby increasing the
possibility of unpredictable ghost behavior due to Pac-Man not
being in the exact same tile at the exact same time anymore.
Typically, the most popular patterns have been those that tend to
"hold together" well when small input timing flaws
occur (turning three pixels away from center instead of four when
approaching a turn from the right is a timing flaw, for example).
Other patterns-especially those that bring Pac-Man very
close to the ghosts late in the sequence-tend to "fall
apart" unless every turn is perfectly cornered.
During a
long Pac-Man session, even
the best players will make occasional timing mistakes during a
fast series of turns and have to deal with the possible
consequences. As such, one should aim for perfect cornering at all
times but remain alert for unexpected ghost behavior from subtle
input timing flaws creeping into the pattern.
Home Sweet Home
Commonly
referred to as the ghost house or monster pen, this
cordoned-off area in the center of the maze is the domain of the
four ghosts and off-limits to Pac-Man.
Whenever a level is
completed or a life is lost, the ghosts are returned to their
starting positions in and around the ghost house before play
continues-Blinky is always located just above and outside,
while the other three are placed inside: Inky on the left, Pinky
in the middle, and Clyde on the right.
The pink door on top is
used by the ghosts to enter or exit the house. Once a ghost
leaves, however, it cannot reenter unless it is first captured by
Pac-Man-then the disembodied eyes can return home to be
revived. Since Blinky is already on the outside after a level is
completed or a life is lost, the only time he can get inside the
ghost house is after Pac-Man captures him, and he immediately
turns around to leave once revived.
That's about all there is to
know about Blinky's behavior in terms of the ghost house, but
determining when the other three ghosts leave home is an involved
process based on several variables and conditions. The rest of
this section will deal with them exclusively. Accordingly, any
mention of "the ghosts" below refers to Pinky, Inky,
and Clyde, but not Blinky.
The first control
used to evaluate when the ghosts leave home is a personal counter
each ghost retains for tracking the number of dots Pac-Man eats.
Each ghost's "dot counter" is reset to zero when a
level begins and can only be active when inside the ghost house,
but only one ghost's counter can be active at any given time
regardless of how many ghosts are inside.
The order of preference
for choosing which ghost's counter to activate is: Pinky, then
Inky, and then Clyde. For every dot Pac-Man eats, the preferred
ghost in the house (if any) gets its dot counter increased by one.
Each ghost also has a "dot limit" associated with his
counter, per level.
If the preferred ghost reaches or exceeds his
dot limit, it immediately exits the house and its dot counter is
deactivated (but not reset). The most-preferred ghost still
waiting inside the house (if any) activates its timer at this
point and begins counting dots.
Pinky's dot limit
is always set to zero, causing him to leave home immediately when
every level begins. For the first level, Inky has a limit of 30
dots, and Clyde has a limit of 60. This results in Pinky exiting
immediately which, in turn, activates Inky's dot counter. His
counter must then reach or exceed 30 dots before he can leave the
house.
Once Inky starts to leave, Clyde's counter (which is still
at zero) is activated and starts counting dots. When his counter
reaches or exceeds 60, he may exit. On the second level, Inky's
dot limit is changed from 30 to zero, while Clyde's is changed
from 60 to 50. Inky will exit the house as soon as the level
begins from now on.
Starting at level three, all the ghosts have a
dot limit of zero for the remainder of the game and will leave the
ghost house immediately at the start of every level.
Whenever a life is
lost, the system disables (but does not reset) the ghosts'
individual dot counters and uses a global dot counter instead.
This counter is enabled and reset to zero after a life is lost,
counting the number of dots eaten from that point forward.
The
three ghosts inside the house must wait for this special counter
to tell them when to leave. Pinky is released when the counter
value is equal to 7 and Inky is released when it equals 17. The
only way to deactivate the counter is for Clyde to be inside the
house when the counter equals 32; otherwise, it will keep counting
dots even after the ghost house is empty.
If Clyde is
present at the appropriate time, the global counter is reset to
zero and deactivated, and the ghosts' personal dot limits are
re-enabled and used as before for determining when to leave the
house (including Clyde who is still in the house at this time).
If dot counters
were the only control, Pac-Man could simply stop eating dots early
on and keep the ghosts trapped inside the house forever.
Consequently, a separate timer control was implemented to handle
this case by tracking the amount of time elapsed since Pac-Man has
last eaten a dot. This timer is always running but gets reset to
zero each time a dot is eaten.
Anytime Pac-Man avoids eating dots
long enough for the timer to reach its limit, the most-preferred
ghost waiting in the ghost house (if any) is forced to leave
immediately, and the timer is reset to zero. The same order of
preference described above is used by this control as well. The
game begins with an initial timer limit of four seconds, but
lowers to it to three seconds starting with level five.
The more astute
reader may have already noticed there is subtle flaw in this
system resulting in a way to keep Pinky, Inky, and Clyde inside
the ghost house for a very long time after eating them. The trick
involves having to sacrifice a life in order to reset and enable
the global dot counter, and then making sure Clyde exits the house
before that counter is equal to 32.
This is accomplished by
avoiding eating dots and waiting for the timer limit to force
Clyde out. Once Clyde is moving for the exit, start eating dots
again until at least 32 dots have been consumed since the life was
lost. Now head for an energizer and gobble up some ghosts. Blinky
will leave the house immediately as usual, but the other three
ghosts will remain "stuck" inside as long as Pac-Man
continues eating dots with sufficient frequency as not to trigger
the control timer.
Why does this happen? The key lies in how the
global dot counter works-it cannot be deactivated if Clyde
is outside the house when the counter has a value of 32. By
letting the timer force Clyde out before 32 dots are eaten, the
global dot counter will keep counting dots instead of deactivating
when it reaches 32. Now when the ghosts are eaten by Pac-Man and
return home, they will still be using the global dot counter to
determine when to leave.
As previously described, however, this
counter's logic only checks for three values: 7, 17, and 32, and
once those numbers are exceeded, the counter has no way to release
the ghosts associated with them. The only control left to release
the ghosts is the timer which can be easily avoided by eating a
dot every so often to reset it. Click on the YouTube video below
to see a demonstration of this curious behavior:
The last thing to
mention about the ghost house is how to determine whether a ghost
will move right or left after exiting the home. Ghosts typically
move to the left once they get outside, but if the system changes
modes one or more times when a ghost is inside, that ghost will
move to the right instead of the left upon leaving the house.
Areas To Exploit
The illustration
above highlights four special "zones" in the maze
where ghost behavior is limited by certain conditions which can be
exploited to the player's advantage. The two red zones represent
the areas where ghosts are forbidden to make upward turns. Once a
ghost enters either of these two zones, it may only travel from
right-to-left or left-to-right until exiting the area.
Thus, only
Pac-Man has access to these four, upward-facing tunnel entrances.
It will serve the player well to remember the ghosts can still
access these tunnels from the other end! The red zone restrictions
are enforced during both scatter and chase modes, but in
frightened mode the red zones are ignored temporarily, allowing
the ghosts to turn upwards if they so choose.
The pink zones are
in the two halves of the connecting side-tunnel. As mentioned
previously, any ghost that enters the tunnel will suffer an
immediate speed penalty until leaving the zone. This slow-down
rule is always enforced and applies to ghosts only-Pac-Man
is immune.