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The AI Systems of "Left 4 Dead" [pdf]
- TillE 14y agoscribd 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_l4d_mike_booth.pdf http://www.valvesoftware.com/publications/2009/ai_systems_of...
- DanBC 14y agoPDF submissions are automatically substituted for scribd links.
- jfb 14y agoI had wondered why everybody else at HN seemed to love that garbage. What a terrible misfeature.
- alexatkeplar 14y agoScribd is a Y Combinator investment.
- jfb 14y agoYeah, I figured.
- fafner 14y agoThe link is to the original. The scribd link is to the side and is automatically added by HN. (I never really liked scribd and with pdf.js it's clearly obsolete)
- jfb 14y agoFor PDFs at least, scribd seems purely parasitic.
- zdw 14y agoI believe the intention of having the scribd links is to mirror the content if the original source goes down under the HN reader load, which has happened at times.
- jfb 14y agoIME, HN readers will almost always post either a Google cache link or cache the original content. The scribd thing just slows everybody down.
- alexatkeplar 14y agoOr, the intention of having Scribd links is to boost SEO for and awareness of Scribd, thus increasing the value of Y Combinator's equity stake.
- regularfry 14y agoThis is news.ycombinator.com. I don't begrudge that.
- jfb 14y agoIt wouldn't bug me if it didn't decrease the utility of the PDF links. EDIT: as pointed out below, it doesn't. Belay this comment.
- corin_ 14y agoIt doesn't. If you don't want to see Scribd then don't click on the "[Scribd]" - the rest of the title takes you straight to the PDF itself.
- 14y ago
- lazyjones 14y agoThat's a very interesting read, even though in practice, the ingame AI still feels lackluster. Survivor bots often ignore nearby players attacked by special infected to move (slowly) towards some far away target (another attacked/incapacitated player) and special infected bots could really use some cooperation (as do many human players ...).
- manmal 14y agoI always wished that I could tell the bot teammates "stick together", "fan out" or "help me" via the chat. That would give them an actual sense of social intelligence, and bring them closer to real players (to be 100% realistic they would then have to ask "where r u??" :)).
- Extigy 14y agoOh man that would be so cool. I suppose if text based adventure games can "understand" meaning within text, there's no reason it couldn't be remodelled into a chat setting.
- freehunter 14y agoThere are plenty of FPS games with AI that you can control with commands. The Rainbow Six games all have this, and if I'm not mistaken, I believe Counter Strike's bots can be controlled with commands as well.
- Fargren 14y agoQuake III's AI not only receives but also gives commands by chat. If you enter a team full of bots, you can see them talk to each other and "plan" to a certain extent.
- qznc 14y ago"Daemia patrol from quad to bfg for 3 minutes" ;) http://www.angelfire.com/linux/vmerchand/quake.htm http://www.angelfire.com/linux/vmerchand/quake.htm
- cateye 14y agoThis 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.
- ddorian43 14y agoplay multiplayer?
- arethuza 14y agoI 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.
- robotmay 14y agoYeah, it's not anything amazing from my experience. I've heard the FEAR games had decent AI, as well as Far Cry. If we're not talking FPS then I've been impressed by the AI in XCOM. God damn those bastards are hard work.
- alan_cx 14y agoI have heard that about Far Cry too, but even as a fan of all of the FC games, I really cant see why people say that. I'm not saying the AI is bad or sub par, just that I'm ignorant!!! To be fair though, I don't play that many games, so I don't really have much to compare to.
- arocks 14y agoIt 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.
- vy8vWJlco 14y agoGoogle's PDF viewer works for reading in the browser (scribd isn't working on this one): https://docs.google.com/viewer?embedded=true&url=http://www.valvesoftware.com/publications/2009/ai_systems_of_l4d_mike_booth.pdf https://docs.google.com/viewer?embedded=true&url=http://...
- fafner 14y agopdf.js works as well.
- adriancooney 14y agoThe climbing sequence is particularly impressive but maybe a tad excessive in my opinion but. I count six operations, two of which seem to computationally intensive due to their trial-and-error approach. I can see the reasoning behind it if the AI is climbing a physics props but surely map data could be retrieved relative to position and save all that ray tracing (if that's the correct term)?
- supar 14y agoNot sure what you mean by "map data". You can certainly have a list of props that are in the way and have them as a mesh. It's certainly easier if you have only one prop, but you have to account for that they may stack together in any way- and suddently the geometry configuration becomes non-trivial again.
- kriro 14y agoQuestion 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)
- NickPollard 14y agoNavigation meshes are commonly generated from actual collision geometry, i.e. as created by the art and design team.
- gmaslov 14y agoThis link explains fairly well how a navigation mesh may be automatically generated from the level geometry: http://udn.epicgames.com/Three/NavigationMeshReference.html 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.
- deleted 14y ago[deleted]
- kriro 14y agoYeah I couldn't make sense of the arrows but I only know AI from 2d and have 0 clue about 3d game development. Most toy examples I know use an even square grid so I was wondering if I might be missing something there. Either way thanks for the answer (same goes for the other posters who provided links)
- akx 14y agoYou might be interested in checking out https://code.google.com/p/recastnavigation/ https://code.google.com/p/recastnavigation/ (which, coincidentally, is what UDK/UE3 also uses nowadays (as a reference to the sibling comment))
- ccozan 14y agoThat'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.
- gmaslov 14y agoAh, yes. The perennial curse of AI: as soon as it works, it's not called AI anymore ;-)
- setrofim_ 14y agoReminds 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 . . .
- xhrpost 14y agoIf I remember correctly, people used to criticize IBM's Deep Blue for not being "real" AI because it just basically brute-forced a ton of possible play paths in the chess game. Someone then said: "Saying that Deep Blue doesn't really think is like saying an airplane doesn't really fly because it doesn't flap its wings."
- setrofim_ 14y agoThat's what "AI" usually means in the context of game development.
- johnyzee 14y agoAdjusting enemy spawn and behavior by a calculated 'emotional intensity' of the player - very nice.
- TheMakeA 14y agoValve is (was) very open with their publications. There are more available on their website[1]. I definitely recommend taking a little time to look through them. [1] http://www.valvesoftware.com/publications.html http://www.valvesoftware.com/publications.html
- Brashman 14y agoAny idea why there hasn't been anything since 2009? Have they stopped publishing/presenting or just not updated the site?
- solnyshok 14y agoIf a SurvivorBot ever gets far out of place for any reason, it is teleported near the team when no human is looking at it (AI cheating algoritm!!! Really enjoyed that)
- illicium 14y agoThis works as long as the player doesn't notice. Counterexample: the Watson NPC in the Sherlock Holmes Nemesis game, http://youtu.be/13YlEPwOfmk http://youtu.be/13YlEPwOfmk
- lotharbot 14y agoOne of the reasons for this is SurvivorBots, despite their relatively solid behavior overall, can occasionally get stuck on an obstacle or trying to decide between divergent priorities (follow the others or grab a powerup? They can get stuck in a "dancing loop" where they shuffle a couple steps one way and then the other.) It's important in L4D to require players to pay attention to their teammates, but it's also important to maintain the "fun" aspects of the game. It's one thing if the AI gets behind because they're being attacked and the player is doing a bad job of protecting them; it's entirely different if the AI gets behind because its algorithm sometimes gets hung up (and it's not fun for the player to have to try to solve pathing glitches!)
- Robadob 13y agoThere is a similar exploit people have used in survival maps. If you were are able to get your player physically stuck (usually by moving up and down an angled area which goes below your player height, e.g. stair rail with ceiling above) you would teleport to the nearest teammate. http://www.youtube.com/watch?v=m_TzVMFRO-c http://www.youtube.com/watch?v=m_TzVMFRO-c
- danso 14y agoI love this game, one of the last FPSes I still play other than Team Fortress 2...unfortunately, like TF2, it's not very playable unless everyone in the round is amenable to being a team player. The multiplayer deathmatch allows one team to take the role of monsters, who have the backing of the zombie horde to make up for lack of guns. Playing it really provides some interesting insights to how the AI effectively functions, by slowly getting the human players to come unglued, either by targeting stragglers or letting the best players get too overconfident and move ahead of the team. Of course, all deathmatch games have this dynamic but it's very explicit in L4D, mostly because it's impossible for one human or monster player to singlehandedly own the opposing team in the way that an ace player can miraculously wipe out a team in Counter-Strike. edit: The AI controlled human players is extremely competent, maybe the best bot players yet created. But they do show their limitations in multiplayer...among their weaknesses: they're too willing to sacrifice their healthpacks for an injured teammate, and will almost always try to help an incapacitated player no matter how hopeless his/her cause. Real humans can be total assholes, but in some situations its best for the team to leave a straggler behind, especially if the enemy has set up an ambush for the rescuers.
- afreak 14y ago> like TF2, it's not very playable unless everyone in the round is amenable to being a team player Amen. TF2 and L4D are two games that I consistently play years after the fact which is unlike other games I have. Unless you're playing with people you know, both games are equally frustrating. Specifically in TF2, it's those who go and play support classes when there are already enough of those in play on the map on your team that makes it frustrating.
- ahelwer 14y agoThat only matters if you care about winning. TF2 also has a huge accessibility problem which contributes to an overabundance of support class players, but also makes it a brilliant game. As opposed to the Battlefield series, where seeing the enemy first is most of the battle, it's actually difficult to inflict any damage at all in TF2. For instance, I'm at about the 200 hour mark and when I play demo I can only hit ground-based targets with pipes maybe 20-30% of the time - and that's quite good! For beginners, the only playable frontline classes are pyro and heavy. Spy and sniper are also popular because it's easier to survive when playing them, and maybe sneak a few insta-kills. Medic is easy to play, but can be very boring. tl;dr: Don't hate the player, hate the game. And don't hate the game, because you'd be hating what makes TF2 such a wonderful game to play. Even at professional levels getting an airshot is a remarkable feat.
- jnazario 14y agoin the past few months i started to learn a little bit about AI, including algorithms in planning (like PDDL) and logic engines. the more i learned the more i saw what the gaming companies, and that entire community, are doing and how they are some of the biggest consumers of these technologies. i have to say that it's impressed me, and it seems like the gaming companies are on the forefront of multiple areas of technologies, not just graphics and specialized CPUs. no if only i could hire from that talent pool :)
- kaoD 14y agoWoah, I've been doing the same thing for the past few months because I took an AI branch for my last year in college. Unfortunately I feel they've been teaching us mostly outdated and useless algorithms (with all due respect). I wish I was taught more about neural networks, machine learning, data mining techniques... and less about classic (and failed) AI algorithms. The most I learnt about these techniques was from teaching myself, even for the last year. Perhaps we attend the same classes? [sorry for the OT guys, no PMs in Hacker News!]
- jnazario 14y agono, i'm not a student. presentations and papers like this are what i'm referring to: https://skatgame.net/mburo/icaps2010-pg/ICAPS-PG.2010.1.bartheye.pdf https://skatgame.net/mburo/icaps2010-pg/ICAPS-PG.2010.1.bart... http://www.plg.inf.uc3m.es/icaps-pg2007/papers/Symbolic%20Exploration%20for%20Generalized%20Game%20Playing%20in%20PDDL.pdf http://www.plg.inf.uc3m.es/icaps-pg2007/papers/Symbolic%20Ex... http://www.slideshare.net/StavrosVassos/the-simplefps-planning-domain-a-pddl-benchmark-for-proactive-npcs http://www.slideshare.net/StavrosVassos/the-simplefps-planni... http://abotea.rsise.anu.edu.au/data/offline-htn-planning.pdf http://abotea.rsise.anu.edu.au/data/offline-htn-planning.pdf http://www.guerrilla-games.com/presentations/VUA07_Verweij_Hierarchically-Layered-MP-Bot_System.pdf http://www.guerrilla-games.com/presentations/VUA07_Verweij_H... etc etc etc. turns out a lot of these ideas people thought were failures are getting a new lease on life in games, and they're working pretty well. curious what classic AI algorithms you think are failing. from where i sit i'm seeing them get a new lease on life. maybe it's just the natural cycle of things: they get hot and invested in, they then fail to live up to their assumed potential, they fall out of favor for a while, and when everyone who was familiar with them - and their shortcomings - is gone a new generation finds it again and starts the cycle over.
- lucb1e 14y agoI never felt like playing this game until now. The AI sounds very interesting to try for myself! Game producers should release such documents upon launching the game, it makes it that much more interesting.
- mwctahoe 13y agobut then some people will look through the docs, find the exploits and become the top players. Wouldnt really be fair from a game play standpoint but I agree this was one of the most interesting things i have read in weeks.
- lucb1e 13y agoI don't think it's all that hard for many students (or others with no life) to play the game enough to find flaws in the AI without releasing technical documentation. You're right though, this is a concern... Perhaps if they release the docs a few weeks delayed?
- krsunny 13y agoIts hard to find a good match these days, people will either kill you or themselves at the beginning of a PVP match.
- iam 13y agoGreat stuff, have to disagree on the "replayability" section though. There were only 2-3 tier 2 weapon spawns on the entire map, the crescendos were pretty much always in the same spot (this was a bit better in L4D2), and so on. After the first 10 times every map felt the exact same.
- hpcorona 13y agoAs a 3+ years of playing every night, i will have to disagree. The weapon spots are not important... The replayability comes with everything it provides. I have over 1 tb of dem files because i record every single match since start, and i still enjoy it.
- iam 13y agoOh, I don't think the game is not replayable, I had a lot of fun playing it and L4D2. I just don't think it was at all obvious accomplished their goals with the director AI that they set out to. Hence "replayability section" (directly referring to the PDF)