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The Making Of Ms Pac-Man

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After the success of Pac-Man in 1980, it was inevitable that a sequel would appear. What many people didn’t know however is that said sequel was originally a different game entirely. Retro Gamer discovers how Crazy Otto was turned into Pac-Man’s smash hit sequel.

Classic arcade games were designed to be brutal, aiming to hook a player, end games quickly and encourage further coins to be deposited. But however tough developers made their creations, gamers mastered them, leading to hours-long sessions on single coins, angering revenue-hungry operators.

Crazy Otto - maze 3

Here’s Ms Pac-Man when it was still known as Crazy Otto.

For popular titles, after-market add-ons were sometimes used to ramp up difficulty and further challenge the best players. Most faded into obscurity, but one outshone and outsold its parent, surviving legal challenges, a publisher spat and an abrupt sex change for its main character. The title in question: Ms. Pac-Man.

The game’s origins began at MIT. Doug Macrae was operating a pinball machine in his dorm, until he took on Kevin Curran as a partner and began purchasing additional machines. 
“We quickly expanded into operating 20 arcade machines across four dorms,” recalls Macrae. Three machines were Missile Command, which initially performed well. However, the coin count dropped as people mastered or tired of the game. “We came up with the idea of creating enhancement kits to address these issues, adding new features, algorithms and difficulty levels.”

By this point, Macrae and Curran had moved out of the dorm and were renting a house in Brookline, Massachusetts, along with like-minded programmers and videogame enthusiasts Steve Golson, Mike Horowitz, John Tylko, Chris Rode and Larry Dennison.

“By April, General Computer Corporation (GCC) was incorporated, with Doug and Kevin as owners,” recalls Golson. “The kit was named Super Missile Attack, and most of us dropped out of MIT, because working on games was more interesting than going to class.” Adverts were taken out in trade magazines, and the kit was a big success.

Ms Pac-Man - blue maze

Ms Pac-Man’s getting chased. Time to grab a power pill.

With gamers and arcade owners happy with Super Missile Attack, and interest coming from manufacturers, brokers and importers within the videogames industry, the team started thinking about other games to enhance. “We started working on kits for Asteroids and Pac-Man,” says Golson. “Work on the Asteroids kit didn’t get far. For an enhancement kit to be successful, you need a large installed base, so only the most popular arcade games are good targets. Asteroids was the biggest build of any game in the USA – 77,000 cabinets – but by mid-1981 it looked like Pac-Man was going to beat that by a wide margin.”

Much of the team didn’t consider Pac-Man to be a great game, and aside from its popularity, the main reason for creating a kit was because of the game’s deficiencies. “I wasn’t a fan, but everyone else on the planet was, so we knew an after-market add-on would be popular,” explains Mike Horowitz. “And since the game was so deterministic – every game played exactly the same way – it was easy to make much, much better.”

The initial idea was to get the kit, dubbed Crazy Otto, to market in late 1981, when Pac-Man games in arcades would stop making money. Although the game’s visuals were more advanced than Pac-Man’s – bipedal characters boasted more animation frames and the maze was solid and colourful – the biggest changes were gameplay-oriented, adding randomness and more mazes. “Once players had learned Pac-Man’s maze, they could play forever, and many became bored,” says Macrae. Horowitz adds: “Adding more mazes made the game harder and acted as an incentive, because players had a reason to get to higher levels.”

“There was an idea that players would get used to a maze and then, after the first two, there would be something new. Then, after another three racks, another new maze! How many were there? Players would be eager to figure that out,” reasons Golson. “And each maze had its own quirks to learn, along with increasing the difficulty in later levels due to there being fewer escape tunnels and more corners to get trapped in.”

Ms Pac-Man - intermission 1-3

Like the original Pac-Man, Ms Pac-Man featured intermission scenes.

According to Macrae, mazes were initially sketched on graph paper, and the designers would look at various layouts to see which would be the most exciting to play. They would then get coded and tested. “Some worked very well and some did not,” he says candidly, although Golson remembers this aspect of the game “came very quickly”, with few variations and little tweaking.

Another major change focused on how the monsters moved. “Adding randomness to that aspect of the game was the most important change,” claims Horowitz. “The original algorithm for ghost movement meant that on early racks, Pac-Man could ‘hide’ in certain spots and the ghosts would never find him.” This predictability was so obvious that a book of patterns was published – How To Win At Pac-Man – and so the team realised that this was the major deficiency to attack.

The flaw was fixed, according to Macrae, by generating a random number that could be used to determine the monsters’ behaviours, thereby stopping most pattern play, and by addressing ‘intelligence’ algorithms, making each monster a slightly smarter adversary. Golson outlined for us some specifics of how this worked. The game uses true randomness: there’s a free-running 7-bit counter in the Z80 microprocessor (the R register). It’s intended for automatic refresh of DRAM, but Golson says it “makes a great random number generator – it’s very unpredictable”. At any given time, monsters are in one of several ‘modes’ – chase, run away, take next left turn, go to the monster’s ’home’ corner. The team amended the last of those, instead sending monsters to a random corner. “It’s just enough to mess up pattern play, although in higher racks, monsters spend most time in chase mode, so randomness affects gameplay less and patterns become more useful,” explains Golson. There was also a late change to the red monster: “We found a spot in the first maze where Otto could hide and never get eaten, and so Mike changed the red monster to eventually lock into chase mode.”

Horowitz elaborates: “We thought we’d eradicated hiding spots, but late in development I found one, which caused a bit of a panic. It was too late to modify the first maze, so I made it that when the red monster went into chase mode, he stayed that way, meaning there were then no hiding places.” This resulted in a tougher game during its early levels, further magnified by the fact that, according to Golson, many players took a while to realise that the monster algorithms were no longer predictable.

Ms Pac-Man - lilac maze

Unlike Pac-Man there are a number of different mazes to navigate.

More changes added extra polish and interest. First, bonuses now roamed the mazes. “The Pac-Man hardware supports six moving objects. There’s Pac-Man, four monsters and the bonus, but in Pac-Man the bonus never moves,” says Golson. “We decided to change this. At first, the fruit was going to bounce through the maze and suddenly blow up, using an ‘explosion’ character we found in the original graphics ROM. That didn’t look good, though, so once we had the fruit coded to move into the maze, we ran it backwards if Otto didn’t grab it first.” Again, randomness was used to make the game less predictable – there are several predetermined paths, but they’re chosen at random, so you never know exactly where the bonus will go. “Also, once you get past level 7, the fruit is randomly chosen,” notes Golson. “This annoyed really serious players, because in a high level, you might get a cheap 100-point bonus instead of the maximum 5,000, making it hard to get the ‘highest possible’ score.”

Elsewhere, Horowitz worked on new intermissions: “Since these were just for fun and didn’t impact gameplay, it was an obvious choice to write new ones,” he recalls. “My inspiration was to adapt the age-old ‘girl meets boy’, ‘girl chases boy’, ‘girl gets the boy’ story.”

Aside from the first maze’s hiding-place blip, the impression given is of an almost effortless Crazy Otto development, and so how easy was the game to create from a technical standpoint? “That depends on your definition of easy,” says Horowitz, who explains that all the team had to work with were Pac-Man’s ROMs. “We had to reverse-engineer the entire game, which was a tedious process, although luckily we had a microprocessor emulator. This meant we could view the raw assembly language output from the program ROMs and map the program ROMs to writable memory, enabling us to make changes and immediately see the results.” He adds that GCC also couldn’t infringe on the copyright of the original code: “We could only add patches – jumps to the program memory on our daughter card.”

Creating new graphics and sound was also a challenge. “It was easy to find the table of byte sequences used to generate sounds, but problematic to determine what those bytes controlled,” recalls Horowitz. “Many new sounds we created came from trial and error – I’d plug in different values to different positions of the table and listen for changes.” As for graphics, Horowitz says the team had no tools for creating graphics or animation: “Someone had the great idea to use a Lite-Brite,” he grumbles. This Hasbro toy enables you to create ‘glowing’ pictures by pushing coloured pegs through black paper into a grille. On turning on the toy’s light, you see your image. “Each row is offset horizontally from its neighbour, and so can’t be used to simulate a 16×16 grid.”

“Oh, the Lite-Brite,” laughs Golson. “You’d cover the front with construction paper, to stop light leaking, but when you moved a peg you’d have a hole leaking white light!” His solution was to cover purple pegs in black marker and use them as blockers, and to use every other line in the hexagonal field to emulate the 16×16 grid that Crazy Otto characters required. “Finally, I put a sheet of white paper over the front as a diffuser – standing across the room, squinting a bit, I could test my character design!”

You can read the rest of our Making Of Ms Pac-Man in issue 81. Buy it now from GreatDigitalMags.com

Retro Gamer magazine and bookazines are available in print from Imagineshop

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