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Pac-Man's Ghost Behavior Algorithms
An anonymous reader writes "This article has a very interesting description of the algorithms behind the ghosts in Pac-Man. I had no idea about most of this information, but that's probably because it's difficult to study the ghosts when I die every 30 seconds. Quoting: 'The ghosts are always in one of three possible modes: Chase, Scatter, or Frightened. The "normal" mode with the ghosts pursuing Pac-Man is Chase, and this is the one that they spend most of their time in. While in Chase mode, all of the ghosts use Pac-Man's position as a factor in selecting their target tile, though it is more significant to some ghosts than others. In Scatter mode, each ghost has a fixed target tile, each of which is located just outside a different corner of the maze. This causes the four ghosts to disperse to the corners whenever they are in this mode. Frightened mode is unique because the ghosts do not have a specific target tile while in this mode. Instead, they pseudorandomly decide which turns to make at every intersection.'"
Or half of the class writes ghost algorithms while the other half writes an algorithm controlling pac-man himself, and then the algorithms are pitted against each other!
based on being really good at the original pacman, achieving a high score was simply a matter of learning patterns, so they must not really be referring to the original pacman here because I think that algorithm must have been pretty simple. To be a great player on the original pacmac you run pacman through the same pattern every time in every level you've learned, hitting the energizer pellets precisely when you know you can always run the same pattern and eat the four ghosts as the flee. Always the exact same pattern for each level until you finally reach a level where you have to learn the pattern. It was really crazy playing because you could do all the levels you'd memorized pretty much with your eyes closed, so when you got really good; it took a frigging long time to get to a level you did not know.
Did you ever wake up in the morning, with a Zombie Woof behind your eyes? -- FZ
Take note CS professors: writing a Pac Man ghost algorithm would be an awesome exercise.
I wrote a PacMan in GWBasic when I was around 13 or so.
The Ghost algorithm was one of the more interesting problems. The chase rules were simple... at each intersection the ghost chose to move towards pac-man, with the one caveat that it wasn't allowed to simply reverse direction. There was also a smallish random chance that the ghost would go a different direction if available.
This made them mostly but not entirely predictable, and also helped break them up when multiple ghosts ended up in the same place behind pac-man. And was the only way they used the left-right 'teleporter'
It worked well enough and by fine tuning the random chance of going in a random direction I was able to get a pretty satisfactory game.
The algorithm was actually based more on my observations of lode-runner than of PacMan. (I desperately wanted to be able to write a lode-runner type game, but I was self-taught... and didnt' under stand data modelling. My pacman sprites navigated the maze by acutually looking a the pixel colors around them... white was a wall.
My next project was tetris a couple years later, in pascal, with the same sort of inspect the pixels to see if a row was complete, and to stop falling, see if rotations were allowed, etc.
I remember having the data model epipaphany when I was trying to write a variable width font word processing thing (again in basic), and I couldn't for the life of me figure out how to support 'backspace'; looking backwards at the screen and comparing the pixels with the bitmaps for the different letters was simply a mess...hmmm... instead of simply drawing the letters as I type and moving the cursor forwards what if I put the letters I typed into a string as well... ooooooooooh.
A real personal Eureka moment there.