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The AI Systems of "Left 4 Dead" [pdf]

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Re: The AI Systems of "Left 4 Dead" [pdf]

#11

Post by arocks »

cateye wrote: post #4

This is exactly the reason why I don't like playing computer games. The games feel really scripted. Enemy character that wait until I cross a line before they attack me etc. I wished that instead of investing in graphics, the AI got more attention.

It is not fully scripted. The game has enough random elements that it might result in an unplayably hard scenario e.g. key portal blocked by dozens of mobs. Hence the AI must be smart enough to reduce the intensity of the generated content to a sufficiently playable level.

This is a challenge in every randomly generated game content and the AI Director solution seems to be a fair one.

Re: The AI Systems of "Left 4 Dead" [pdf]

#12

Post by arethuza »

ddorian43 wrote: post #7
cateye wrote: post #4

This is exactly the reason why I don't like playing computer games. The games feel really scripted. Enemy character that wait until I cross a line before they attack me etc. I wished that instead of investing in graphics, the AI got more attention.

play multiplayer?

I only ever play multiplayer (mostly Halo 4 these days) - any time I try Campaign I find the AI rather boring and predictable. I don't know if the Halo series are bad for this or not.

Re: The AI Systems of "Left 4 Dead" [pdf]

#13

Post by NickPollard »

kriro wrote: post #9

Question about the navigation mesh. I'm assuming that represents an entire open area (otherwise the path optimization makes no sense) and the dark stuff are the obstacles. In that case I'm wondering how the arrive at the actual grids and arrows (slide 12)

Navigation meshes are commonly generated from actual collision geometry, i.e. as created by the art and design team.

Re: The AI Systems of "Left 4 Dead" [pdf]

#14

Post by gmaslov »

kriro wrote: post #9

Question about the navigation mesh. I'm assuming that represents an entire open area (otherwise the path optimization makes no sense) and the dark stuff are the obstacles. In that case I'm wondering how the arrive at the actual grids and arrows (slide 12)

This link explains fairly well how a navigation mesh may be automatically generated from the level geometry: http://udn.epicgames.com/Three/NavigationMeshReference.html . I believe it's also a good practice for the level designer to examine it manually and make any necessary corrections for sharp corners, narrow corridors, etc.

As for the path, A* search is usually the name of the game for any kind of 2D pathfinding. With the usual Euclidean distance heuristic it always returns the shortest path, but it's possible to use an "inadmissible" heuristic to make it run faster (and produce sub-optimal paths). The arrows shown on the slides are a little baffling; I can't imagine why those four vertically stacked boxes on the right-hand side would create a jagged path, for instance. It may just be exaggerated for effect.

Re: The AI Systems of "Left 4 Dead" [pdf]

#15

Post by jfb »

DanBC wrote: post #8
TillE wrote: post #2

scribd is "unable to display this document", and the download button doesn't even work. Just link the original. http://www.valvesoftware.com/publications/2009/ai_systems_of...

PDF submissions are automatically substituted for scribd links.

I had wondered why everybody else at HN seemed to love that garbage. What a terrible misfeature.

Re: The AI Systems of "Left 4 Dead" [pdf]

#16

Post by akx »

kriro wrote: post #9

Question about the navigation mesh. I'm assuming that represents an entire open area (otherwise the path optimization makes no sense) and the dark stuff are the obstacles. In that case I'm wondering how the arrive at the actual grids and arrows (slide 12)

You might be interested in checking out https://code.google.com/p/recastnavigation/ (which, coincidentally, is what UDK/UE3 also uses nowadays (as a reference to the sibling comment))

Re: The AI Systems of "Left 4 Dead" [pdf]

#17

Post by ccozan »

That's hardly AI. It's just algorithms. Parametrized, using a probability distribution to randomize the environment, user programmed algorithms.

EDIT: Well, if this AI in game development, then so be it. But it's still not AI in the generic way, IMHO. To downvoters: I didn't contest the fact that they don't work. I do enjoy this games a lot and I praise the programmers that make such games work.

Re: The AI Systems of "Left 4 Dead" [pdf]

#18

Post by gmaslov »

ccozan wrote: post #17

That's hardly AI. It's just algorithms. Parametrized, using a probability distribution to randomize the environment, user programmed algorithms. EDIT: Well, if this AI in game development, then so be it. But it's still not AI in the generic way, IMHO. To downvoters: I didn't contest the fact that they don't work. I do enjoy this games a lot and I praise the programmers that make such games work.

Ah, yes. The perennial curse of AI: as soon as it works, it's not called AI anymore ;-)

Re: The AI Systems of "Left 4 Dead" [pdf]

#19

Post by setrofim_ »

ccozan wrote: post #17

That's hardly AI. It's just algorithms. Parametrized, using a probability distribution to randomize the environment, user programmed algorithms. EDIT: Well, if this AI in game development, then so be it. But it's still not AI in the generic way, IMHO. To downvoters: I didn't contest the fact that they don't work. I do enjoy this games a lot and I praise the programmers that make such games work.

That's what "AI" usually means in the context of game development.

Re: The AI Systems of "Left 4 Dead" [pdf]

#20

Post by setrofim_ »

gmaslov wrote: post #18
ccozan wrote: post #17

That's hardly AI. It's just algorithms. Parametrized, using a probability distribution to randomize the environment, user programmed algorithms. EDIT: Well, if this AI in game development, then so be it. But it's still not AI in the generic way, IMHO. To downvoters: I didn't contest the fact that they don't work. I do enjoy this games a lot and I praise the programmers that make such games work.

Ah, yes. The perennial curse of AI: as soon as it works, it's not called AI anymore ;-)

Reminds me of this passage from Douglas Hofstadter's GEB:

Loocas the Thinker comes across an unknown object--a woman. ... "Behold! I can look upon her face, which is something she cannot do--therefore women can never be like me!"

And thus he proves man's superiority over women, much to his relief ... The woman argues back: "Yes, you can see my face, which is something I can't do--but I can see your face, which is something you can't do! We're even."

"I'm sorry, you're deluded if you think you can see my face. What you women do is not the same as what we men do--it is, as I have already pointed out, of an inferior caliber, and does not deserve to be called by the same name. You may call it 'womanseeing'. Now the fact that you can womansee my face is of no import, because the situation is not symmetric. You see?"

"I woman-see," womanreplies the woman, and womanwalks away . . .

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