Explains how classic video games work internally, best known for its breakdown of Pac-Man's four ghost movement algorithms.
HN links it as the focused explanation of Pac-Man ghost behavior; commenters note each ghost has its own deterministic targeting and call it surprisingly complex for 1980.
They were hard codes paths.
Not hard-coded paths, per se. It's more elegant than that. Each ghost has a distinctive deterministic movement algorithm based on Pac-Man's current position - some target the square ahead of him, some target the square behind, etc. That's why they seem so smart; it's like they're trying to surround/flank you.
(If this seems underwhelming, I assume you it was a really neat trick back then - the ghosts had a level of personality and cunning not seen before. Combined with the cute, cartoony visual design of the ghosts themselves it was quite something.)
http://gameinternals.com/understanding-pac-man-ghost-behavior
There's been a few interesting articles posted on HN about Pacman's internals and gameplay:
http://www.donhodges.com/how_high_can_you_get2.htm
http://gameinternals.com/post/2072558330/understanding-pac-man-ghost-behavior
http://home.comcast.net/~jpittman2/pacman/pacmandossier.html#Chapter_5
You can find the relevant HN discussion by searching HN algolia:
https://hn.algolia.com/?query=pacman&sort=byPopularity&prefix&page=0&dateRange=all&type=story
I wrote a post specifically about the ghost behavior almost 9 years ago: https://gameinternals.com/understanding-pac-man-ghost-behavior
There's not really anything in it that the Pac-Man Dossier doesn't cover, but it's more focused and (hopefully) easier to follow for people just interested in that aspect.
The "Retro Game Mechanics Explained" channel did a good video explanation a few months ago too: https://www.youtube.com/watch?v=ataGotQ7ir8
"This is the heart of the game. I wanted each ghostly enemy to have a specific character and its own particular movements, so they weren't all just chasing after Pac Man in single file, which would have been tiresome and flat."
— Toru Iwatani, Pac-Man creator
https://gameinternals.com/understanding-pac-man-ghost-behavior
So fun. I like the AI logic, if he wants a fun addition he should add more enemies as the score increases and implement something like the pac-man ghost logic so that they all behave differently: http://gameinternals.com/post/2072558330/understanding-pac-man-ghost-behavior
Cyan is actually much more complicated than that, it's goal is a combination of Pacman and Red's position: https://gameinternals.com/understanding-pac-man-ghost-behavior
Also all of them have "chase" and "flee" modes.