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Ms. Pac-Man step by step
05-22-2016 at 02:46 PM
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Part 4 - Ghost Behaviour - From the designer of MS. Pac-Man at GCC

From the designer of MS. Pac-Man at GCC:


“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.” - See more at:

"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.

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