Pac-Man – Design Oriented Blog

June 30, 2015March 18, 2017

Pac-Man Design: Variables of Difficulty

POV: DESIGN. DIFFICULTY 4. LEVEL 5 – 1

With video games it’s common for levels to increase in difficulty as the game progresses. I knew this was the case for games as old as Pac-Man. But when I read through Jamey Pittman’s Pac-Man Dossier, I was surprised how many variables were tweaked to give each level its unique challenge.

Out of the 21 levels, only a few pairs of levels present an identical gameplay challenge. Otherwise, one of the game’s 13 gameplay variables is tweaked.

Pac-Man Speed
Pac-Man Dots Speed (Pac-Man slows down a bit when eating Dots)
Ghost Speed
Ghost Tunnel Speed (Ghosts slow down when traveling through the Warps on the sides)
Elroy 1 Dots Left (When there are this many Dots left, Blinkies/Red Ghosts increase in speed)
Elroy 1 Speed
Elroy 2 Dots Left (When there are this many Dots left, Blinkies/Red Ghosts increase in speed again)
Elroy 2 Speed
Fright Pac-Man Speed (after Pac-Man grabs a Power-Pellet)
Fright Pac-Man Dots Speed (speed eating Dots after Pac-Man grabs a Power-Pellet)
Fright Ghost Speed (the speed of blue vulnerable Ghosts)
Fright Time (in sec.) (the time Ghosts spend in the blue vulnerable state)
# of Flashes (the visual indication that Fright Time for Ghosts is about to expire)

Tweaking these variables across the 21 levels in Pac-Man gives players more comprehensive exposure to the design space. Players can better learn Pac-Man’s gameplay by progressing through the game and refining their strategies as the challenges get harder.

When Pac-Man eats an Energizer Power-Pellet his speed changes. In the early levels his speed increases to help players chase vulnerable Ghosts. On the other hand, during this “fright” time Pac-Man’s speed is lowered while he eats Dots. Between levels 4 and 5, the difference of Fright Pac-Man’s dot-eating speed is 4%, a change so subtle that players may not perceive it consciously, but I’m confident that players can feel the difference.

All of the variables listed above control gameplay elements that have clear feedback. Pac-Man and Ghost speed can be discerned by simply observing their sprites for a few seconds of motion. The number of times frightened Ghosts flash before becoming deadly is either 3 or 5; It would be more difficult to determine exactly when Ghosts turn deadly if the number of flashes ranged from 1-5. 1-2 flashes doesn’t give enough warning. 6 flashes is too long. Keeping it 3 and 5 gives players who anticipate a 3 flash change to react accordingly by the 5th flash.

Many variables are tuned to be easier for players to keep track of mentally. Ghosts flash an odd number of times before becoming deadly, which helps musically-inclined players who are used to musical phrases ending on an even beat. Fright times are whole numbers measured in seconds, which makes counting easier. Blinky, the red Ghost, speeds up two times in a level based on the number of Dots left in the maze. The speed values for Blinky are all divisible by 10. Pac-Man’s normal movement speed is also divisible by 10. Pac-Man’s speed matches Blinky’s, a design choice that allows Blinky to chase Pac-Man effectively and makes the tiny speed boost granted when Pac-man rounds corners more obvious. However, when there are very few Dots left in the maze and Blinky moves at his fastest, his speed is consistently 5% faster than Pac-Man’s (except on the final level of difficulty where it’s 15% faster). This consistency among all the other changing variables in Pac-Man’s difficulty design goes a long way in making the interactions easier to learn yet variable. No matter how Pac-Man’s speed changes between levels, players can rely on the ratio of speed between Pac-Man and the most aggressive Ghost, Blinky, to be the same for 20 out of 21 levels.

The most interesting piece of feedback design is the classic “waca waca” sound effect that plays when Pac-man consumes a Dot: Pac-Man’s slight speed change when rounding corners while eating Dots can be can be seen as well as heard! Listen here.

June 9, 2015March 18, 2017

Pac-Man Design: Deterministic and Random Ghosts

POV: DESIGNER. DIFFICULTY 3. LEVEL 4 – 1

My recent deep dive into Pac-Man’s design and high-level gameplay got me thinking about randomness and deterministic design elements. I’m quite a fan of randomness in game design, though it has its pros and cons. Pros include variation and unpredictability that force player improvisation. Cons include a lowered skill ceiling and a lack of player control.

The original Pac-Man arcade version strikes a delicate balance between randomization and determinism with its Ghost AI design. In Pac-Man the Ghosts change back and forth between chase and scatter AI modes. In both modes, Ghost movement is determined by a number of factors including the other Ghosts’ positions and Pac-Man’s position. Given the same positions, the Ghosts will act the same way every time.

When Pac-Man eats a power-pellet, the Ghosts run from Pac-Man in a frightened state. At every turn, they make a random decision which way to go. During this time, Pac-Man usually has zero threats on the field, so the random Ghost movement mostly affects the player’s ability to maximize score as opposed to limiting their ability to make informed decisions at times when their life is on the line. It’s a touch of randomness that that proves the skill of the designer and the potency of randomness as a design element.

On the highest difficulty levels, Ghosts don’t turn blue and don’t become vulnerable even when Pac-Man eats a Power-Pellet! Here, the exact positions of Ghosts is the result of a complex web of deterministic rules. If you play precisely the same way every time, the Ghosts will move predictably through the maze. Of course, it takes considerable planning and skill to work out a whole pathing “patterns” for these levels, but some elite players have done it and can pull them off reliably.

images from mameworld.info

If the perfectly planned pathing pattern is mistimed by even a frame or two, if Pac-Man’s movements are not in exactly the right place at the right time, the Ghost AI will react differently, starting a chain reaction of unplanned and less predictable Ghost movement. When that happens, even the best players have to improvise.

Low- and high-level players both experience the pros of randomness playing the Pac-Man arcade game. The random Ghost frighten movement creates unpredictable challenges without threatening the player in a way that creates unfair deaths. Both knowledge and adaptation (improvisation) are required to succeed. But on the final level of difficulty, expert players engage Pac-Man in a new way, using their skill to maximize score and minimize the unknown. To play at this level of skill, players need impeccable timing and incredible precision. With a microscopic misstep, even the most pre-planned gameplay turns back into the Pac-Man experience that everyone is familiar with.

June 1, 2015March 18, 2017

Pac-Man Design: Hallways and Turns Level Analysis

POV: DESIGNER. DIFFICULTY 4. LEVEL 3 – 1

A handy way to analyze Pac-Man’s maze design is to count the number of hallways, 3-way turns, and 4-way turns and then to consider their relation to each other. Turns are important to Pac-Man because every turn is the exact point in which the most meaningful decisions are made for Pac-Man and the Ghosts. In the same way players express agency with their turning and pathing choices, the Ghosts show their AI personality through the turns they take and the direction they move.

The whole gameplay experience of Pac-Man is a loop of deciding to turn or not. Figuring out the pros and cons of one turn versus another stresses knowledge about the game’s rules (complexities) and understanding of the current state of the maze, enemies, and items. Hallways (straightaways or paths with only 1-way turns) provide a nice contrast to 3-way and 4-way turns as the decision making while in a hallway is simpler (keep going forward or turn back). But keep in mind the potential to become trapped by Ghosts is higher in a hallway as there is only one entrance and one exit.

The Pac-Man Arcade maze has the following features:

4	4-way turns
22	3-way turns
26	1-way turns
15	longest hallway(measured in dots)
240	Dots
4	Power-Pellets

The relationships between the numbers described above give the original Pac-Man level its maze feel and well-tuned gameplay. Notice how most turns are 1-way and 3 way. The abundance 1-way turns makes it so that the player’s fingers are rarely idle. Though moving through a 1-way turn doesn’t involve much decision-making, it does require timing. If players don’t give a MOVE input at a 1-way turn, Pac-Man will just sit there and waste time.

The abundance of 3-way turns means players will frequently make a relatively simple choice; turn into path A, B, or turn back around for path C. Because players are typically being chased by at least one Ghost and the goal is to move forward through all the dot lined paths of the maze, a 3-way turn is mostly about choosing path A or B. While it’s easy to pick the option to avoid running into a nearby Ghost, planning ahead even a few seconds into the future is increasingly complicated. Accurately predicting Ghost movement requires understanding the AI mode timer, current level of difficulty, each Ghost’s AI personality, and a few other special rules discussed in part two of this analysis. In practice, the player chooses quickly, moves swiftly, and watches the results of their turning decisions unfold before their eyes.

Here are a few other details about the original Pac-Man maze:

Power Pellets are placed near the corners of the map, in hallways, away from warps, and surrounded by a combination of 4-way and 3-way turns. This placement ensures the most decision making when going for the power-pellet and the most escape options for Ghosts as they retreat in the frightened state.
There are empty areas of the map (leading into warps and around the Ghost House). This design keeps the warps optional while giving the bonus fruit an area to spawn that Pac-Man wouldn’t be incentivised to travel through otherwise.
When Ghosts switch to the scatter AI mode they move to their home corners on the map ignoring Pac-Man. This movement also means the Ghosts go on patrol in the areas around the power-pellets. So even when they’re not chasing Pac-Man, Ghosts naturally protect Pac-Man’s greatest weapon against them.

4	4-way turns
20	3-way turns
19	1-way turns
17	longest hallway (measured in dots)
270	Dots
5	Power-Pellets

The Google Doodle Version of Pac-Man (play it here) does a pretty good job creating interesting gameplay.

The biggest problems I have with the Google Doodle maze design is the concentration of turns and the placement of the Ghost House. Creating a maze out of the Google logo involves a lot of horizontal hallways. The Roman alphabet tends to create horizontally-oriented blocks of shapes. Hallways are great as a reprieve from continuous Pac-Man turning, but not as roughly half the maze paths. Basing the maze design around the Google logo also is why the Ghost House is made out of the lowercase “g” instead of the yellow “o”. The Ghost House functions best in the center of the maze so that the ghosts have the shortest distance to travel to Pac-Man once they exit. When navigating the left side of the maze in the Google Doodle Pac-Man game, consumed Ghosts are less threatening as they take more time to travel to the Ghost House and back to Pac-Man. When this happens, the gameplay experience becomes dull.

Real-life roadways, however, are not designed to challenge our brains. In fact, most streets are designed to be as simple and as straightforward as possible. This is great for modern living. It’s terrible for Pac-Man maze level design. Straight hallways in Pac-Man are death traps because they allow for very little decision-making while inside. Real-life roads are generally spaced apart from each other, further reducing the concentration of corners and turns, limiting how often Pac-Man can juke ghosts to buy more time.

It doesn’t help that the warps are unintuitive due to the lack of symmetry between entrances and exits. Sometimes entering the same warp can spit Pac-Man out of different exits. The Power-Pellets are placed randomly it seems. Sometimes they’re in a hallway; sometimes at a 3-way turn.Since the abundance of hallways means players will have less ability to out-maneuver Ghosts, grabbing the Power-Pellet becomes either necessary for survival or a boring choice–there is no expedient way to maneuver around the Power-Pellet to save it for later. Ultimately, the Power-Pellet placement algorithm results in fewer Ghost chases and fewer exciting situations where Pac-Man barely turns the table on ghosts who are rapidly cornering him.

For these reasons, most of the Google Map Pac-Man levels I’ve played have given me little fun and much frustration compared to the original Pac-Man maze. Procedurally-generated level design is harder to execute well for games that have deep and complex gameplay. With mazes designed from road maps, the algorithms Google used to generate the Ghost House, Power-Pellets, and warps don’t produce levels that support interesting gameplay.

May 29, 2015March 18, 2017

Pac-Man Design: What’s Interesting About Pac-Man’s Gameplay?

POV: DESIGNER. DIFFICULTY 2. LEVEL 2-1

Have you ever been afraid taking a closer look at a favorite and classic game might reveal that it isn’t as good as you remember? Have you wondered if your memories of a game are just a phantom, a collection of scattered thoughts you follow in an endless loop? Have you chased feelings of nostalgia trying to relive what once was? If so, then you probably can relate to the Ghosts in Pac-Man. For well-designed games, what makes them good back in the day is the same thing that makes them good today. Pac-Man’s fame is still recognized because of its polished, well-tuned gameplay. What makes Pac-Man great can be summed up like this:

Pac-Man is an action game that challenges players to move through a maze. The goal is to navigate through the twists and turns of the maze to consume each dot and Power Pellet. How you navigate is up to you: there are hundreds of ways to beat each maze. And where you need to go is easy to determine: Simply follow the trail. Playing Pac-Man would be a trivial challenge if it weren’t for the Ghosts. Avoiding, kiting, and turning the tables on the enemy Ghosts adds complexity and depth to the gameplay. The threat of running into a Ghost makes a simple pathing decision into a much more complicated one. Where you go, when you go, and why depends on the where the Ghosts are, how they’re moving, and how close Pac-Man is to Power Pellet.

A key factor in what makes Pac-Man so fun is clear feedback. With all the level and enemy elements clearly visible at a glance, the player has all the information needed to make well-informed decisions. Though Pac-Man only features a MOVE mechanic, players constantly make decisions about where and when to move by leveraging this clear feedback. Especially when players are under pressure because of the speed at which events unfold, having such good feedback keeps the Ghosts movement from feeling like frustrating ambushes from out of nowhere.

FROM YOUTUBE VIDEO HOW TO WIN AT PAC-MAN- PROPER ARCADE VERSION BY STEVEPIERS

Perhaps the depth of Pac-Man gameplay can best be understood by considering how each aspect of the enemy Ghost elements makes the goal of eating all the dots and Power Pellet in the maze more difficult. Without Ghosts, the goal is easily obtained. Throw one Ghost in the maze, and crossing its path is generally the only thing a player would have to worry about. In fact, if the Ghost is constantly chasing the player, it stops becoming a threat as it will not be able to catch up to Pac-Man. One ghost is not enough. But throw in four Ghosts, and things get more interesting… at least initially. With a little maneuvering, the same problem exists. As long as the player can get all four Ghosts to follow in Pac-Man’s wake they will not be a threat.

The monotony of the chorale-and-run-away play strategy is shaken up by the Ghost AI personalities and AI modes.

“Ghosts’ movement patterns in the “scatter” phase once they’ve reached their home corner.” Image from the amazaing Pac-Man Dossier by Jamey Pittman See the Ghost switch from chase to scatter From youtube video How to Win at Pac-Man- Proper Arcade Version by stevepiers

Each Ghost has a personality that determines how it moves through the maze. Yes, in general all the Ghosts appear to just follow Pac-Man around, but if we look closely only the red Ghost, “Blinky”, is completely dedicated to directly hunting Pac-Man. It always tries to close in on Pac-Man’s exact position. In contrast “Pinky” prefers to move into the space that is a few squares in front of where Pac-Man is facing. What’s interesting is players generally interpret Pinky’s unique AI personality as being non-confrontational and easily spooked. Put Blinky and Pinky in the maze together and they often work together to head Pac-Man off and pin him from both sides.

Ghost AI modes shake things up in a much more obvious way. Ghosts will switch between “chase” and “scatter” modes on a timer. They’ll spend most of their time in “chase” mode and brief periods where they’ll “scatter.” Even if the Ghosts are closing in for the kill, when the timer goes off the Ghosts will ignore Pac-Man and retreat to their respective home corner. So even if a player manages to string the Ghosts along, it will only last as long as the AI mode timer allows. When Pac-Man grabs an energizer Power Pellet the Ghosts switch to a frightened AI mode, in which they will reverse direction and choose random turns as they run away. Between the automatic, timer-based modes (chase, scatter) and the player-activated mode (frightened), the apparent dominant strategy of kiting the Ghosts is minimized in effectiveness and players have to adjust to the constantly changing and partially unpredictable game state.

Here are more nuances and wrinkles to Pac-Man’s design that increase the challenge for players aiming for high scores:

Rules that determine when Ghosts leave the Ghost House
Bonus Fruit, an optional pickup out of the way of any necessary path
Blinky’s (the red Ghost) speed increase when there are fewer and fewer dots left on the field
Increasing difficulty of subsequent levels. Variables include Pac-Man Speed, Pac-Man Dots Speed, Ghost Speed, Ghost Tunnel Speed, Fright. Pac-Man Speed, Fright Pac-Man Dots Speed, Fright Ghost Speed, Fright. Time (in sec.), # of Flashes
Warp tunnels on the sides of the map that Ghosts travel through more slowly

If you take all of these aspects into account, you can see how Pac-Man’s gameplay has enough challenge and complexity for players to spend years enjoying and mastering the game.

With relatively few mechanics, elements, and rules, Pac-Man achieves gameplay that is deep, challenging, and that dynamically changes with each play. Next in this article series, we’ll look at how Pac-Man’s design and gameplay hold up in the Google Doodle and the Google Map versions.

May 18, 2015March 18, 2017

Pac-Man Design: Arcade. Doodle. Map. Mechanics

POV: DESIGNER. DIFFICULTY 2. LEVEL 1 – 1

On May 21st 2010 Google cost the world $120 million. I remember it as the day I visited google.com and found a playable version of Pac-Man in place of Google’s logo. The doodle wasn’t any larger than the normal logo, but the faithful recreation of the sights, sounds, and gameplay of Pac-Man took me from yet another Google search to a glimpse into my past. Now, about five years later, Google has outdone itself with another Pac-Man project.

On April 1st, 2015, I got to play Pac-Man through the streets around my apartment, the DFW airport, and exotic locations around the world via Google’s April Fools’ Day promotion that created Pac-Man levels out of map data.

Between the original Arcade version of Pac-Man and the two Google Pac-Man projects, we have the perfect case study to examine the design of this classic. Because Pac-Man is a relatively simple game, we can dig deep into its entire design and highlight how the small differences between Google’s recreations and the original game make a big difference in the player experience. In this article, I’ll cover the basic mechanic of Pac-Man and build from there in future posts.

There is only one mechanic in Pac-Man; MOVE. No jumping, punching, or shooting. Just moving up, down, left, and right with no momentum or acceleration to worry about. In fact, You don’t even have to hold a particular direction since Pac-Man continues to move in the direction he’s going until stopped by a wall or a Ghost. What’s great about Pac-Man, and what creates gameplay of interesting choices, isn’t deciding how to move, but deciding where to move and when. Still, with controls so simple, there are a few subtle details in the tuning of Pac-Man’s MOVE mechanic we should cover.

In the original Pac-Man arcade, the entire game is designed to fit onto a grid. Pac-Man and the Ghosts are one square large. The walls and lanes are also mapped to this grid so that all movement through the maze is both clear in how it communicates travelable spaces, and clean in that there are no sprite edges to get hung up on as Pac-Man rounds corners.

To make movement even smoother, players can input the direction they want Pac-Man to move before Pac-Man reaches a turn. Doing so allows Pac-Man to turn the corner as quickly and efficiently as possible. This leaning into turns due to the buffered input helps reduce the skill needed to make efficient turns thus freeing up the player’s attention to focus on the strategy of surviving the maze.

The Google doodle nails the controls of Pac-Man. It’s free and you should play it right now to remind yourself how smooth controls lay the foundation for smooth gameplay. Treasure the finely tuned controls while you have them because the controls in the Google map Pac-Man are frustratingly bad.

The core creative conceit of Google Maps Pac-Man (GMPM) is obvious: play Pac-Man out on the roads of the world. The organic geometry of roads, with curves and many-way intersections at odd angles, significantly complicates the control design of Pac-Man.

There are two facets of controller design to focus on here: directness and intuitiveness. Controls are direct when mechanics (player actions) are designed in a way that matches the input method. For Pac-Man arcade version Pac-man can only ever move in a cardinal direction, and an arcade stick allows only cardinal directions, thus forming a perfect mapping. In other words, the player cannot manipulate the input in a way that can’t be reflected in the game. Pressing up moves Pac-Man up always. This design also makes the controls intuitive.

In GMPM, even the controls are not as direct or intuitive as the Pac-Man arcade version, and I blame the curves. When you press up on the Google Maps version, Pac-Man’s path can eventually curve so that Pac-Man moves left, right, down, or any angle in between. Pac-Man will keep traveling down even a curved path automatically. But it’s when I attempt to buy time by moving back and forth along a single curved road that the lack of directness becomes troublesome. On a curved road do I press left-right-left, up-right-up, or some combination of diagonals?

Diagonal road intersections are especially frustrating in GMPM. It’s hard to tell if you should press one or two directions to make a diagonal turn. Because the turns can branch off at any angle, even adding diagonals through 8-way movement controls won’t eliminate ambiguous turns. Since you often can’t tell where Pac-Man will go at an intersection if you hit a certain direction, playing Google Map Pac-Man becomes more about how to move instead of just when and where.

D-pads are the best input device for instantaneous movement at constant speeds and quick, repeatable discrete movements along 4 axes. Curved movement in games necessitates the use of more complex rules to govern movement that tend to benefit from more complex control input devices like analog sticks. Fortunately, the Google map Pac-Man offers mouse control. With a small yellow arrow indicating the direction Pac-Man will move if possible, the mouse helps players navigate curved paths and angled turns with greater accuracy than the digital arrow controls. Unfortunately, because the mouse is a relative pointing device, Pac-Man will attempt to move toward the mouse cursor at all times. This means you can’t simply move down roads by tapping a direction and taking your hand off the controls. If you aren’t constantly adjusting where the mouse points, Pac-Man may take turns or even reverse direction when unintended. The worst case of this is happens when Pac-Man moves off the edge of the screen–where he ends up is often asymmetrical to where he came from and unpredictable. Keeping control over Pac-Man via mouse position tends to require quick and precise mouse movements. During these brief moments, I feel like I’m playing a first person shooter, not a maze runner.

For the Google Map Pac-Man I like the arrow keys for their simplicity, but I end up using the mouse controls for their accuracy.

Controls and mechanics are the first step to understanding a game. In part 2, we’ll look at what makes Pac-Man gameplay so interesting