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  • Hi. I'm Mark Brown, and this is Game Maker's Toolkit.

  • Whenever people talk about "good AI", they invariably come back to the same three examples

  • - I'm talking about the replica soldiers in the original FEAR, the various aliens in the

  • Halo series, and the marines in the first Half Life game.

  • And, yes, these games do have some really clever behaviours, and Halo 2 and FEAR actually

  • pioneered some new AI technologies that are still being used in games today.

  • But one other thing these games have in common is that they all feature particularly aggressive

  • enemies, who actively try to hunt down and kill the player, and also have a lot of health

  • points so they can stick around for longer.

  • And this is something that makes these enemies feel a lot smarter.

  • But don't take my word for it - this is something that Bungie knew, all the way back in the

  • first Halo game. During development, it set up a playtest with two versions of the game,

  • with the exact same enemy AI on both - but on one machine, the aliens didn't do much

  • damage and died quickly, and on the other they did more damage and had more hit points.

  • The number of players who thought the enemies were "very intelligent" jumped from 8 percent

  • to 43 percent, when playing against more resilient enemies.

  • But, the thing is, aggressive enemies just don't work for every type of game. This is

  • something that id software found out during the development of Doom 2016.

  • It started with enemies that would chase you down, but this made players act defensively

  • - "We’d end up in these situations where you would instantly start backing up," said

  • director Marty Stratton. Instead, the studio told the enemies to hold their ground a bit

  • more, and let the player be the one who's pushing forward.

  • So, just like everything else in game design, AI must fit the game's intended experience.

  • Which means while aggressive AI fits the Xenomorph in Alien: Isolation - it would be wildly out

  • of place in Batman: Arkham Asylum. No one gets the drop on Batman, after all.

  • And this all means there must be more to "good AI" than just "enemies who can kill the player".

  • And that's exactly what I'm going to talk about in this video - with everything from

  • good, general practices - to examples of truly ambitious and ingenious AI.

  • Good AI lets the player cheat. Just, not in ways that the player will actually notice

  • - like how you can put a bucket on a shopkeeper's head in Skyrim and rob them blind.

  • So, hopefully in more subtle ways, like how in the Uncharted games, when you pop out of cover,

  • enemies will start with a zero percent chance to hit Drake - giving you a chance to take

  • a few shots. In the Far Cry games, only a few enemies will be allowed to shoot at you

  • at once to improve your odds of winning the fight. And in the Arkham games, enemies are

  • told not to turn around during the predator sections so Batman can sneak up behind his prey.

  • These are things that the player should never really notice - but you would definitely feel

  • their absence if they weren't there. It's all about making the game feel more fair,

  • even if most games are actually biased wildly in the player's favour.

  • Good AI tells you what it's thinking. This is most often done through short vocal clips

  • - known as barks - where patrolling guards say things like... "Sounds like someone's over there..."

  • and... "Must be nothing".

  • But this can also be expressed through animation and body language, or with more gamey-elements,

  • like vision cones, light and noise sensors, and those ghostly images that show where the

  • enemy last saw you.

  • I will talk about how much of this stuff you want to surface to the player, and how much

  • you want to keep a bit fuzzy, when I talk about stealth games in a future video.

  • A different way to achieve this is to give AI characters distinct personalities, like the

  • coloured ghosts in Pac-Man, or the different leaders in Civilization's single-player modes,

  • who all have their own unique quirks.

  • Developers have actually found that this stuff makes AI characters seem smarter to players.

  • Because, if an AI has complex decision making and perception skills, like being able to

  • notice that a door along their patrol path has been opened, the player may never know

  • that the guard is capable of such a thought if they don't open their mouth and say...

  • "Did I leave that door open?"

  • But this is also critical feedback that the player can use to understand what the AI is

  • doing, or about to do - and can plan accordingly. Which brings me onto this next one...

  • Good AI is predictable. Which, sounds odd but hear me out.

  • In 2004, Halo tech lead Chris Butcher said, "The goal is not to create something that

  • is unpredictable. What you want is an artificial intelligence that is consistent so that the

  • player can do things and expect the AI will react in a certain way".

  • This allows you to play a game with intentionality - which, Far Cry 2 designer Clint Hocking

  • defined as "the ability for the player to devise his own meaningful goals through his

  • understanding of the game dynamics".

  • To break that down a bit - when you play a game you start to build up an understanding

  • of how different things work - like, you shoot a red barrel. It explodes. And now, going

  • forward, you know that every time you see a red barrel you can shoot it to create an

  • explosion - and can use this to your advantage.

  • But this applies to AI behaviour, too. If guards always return dropped guns to crates,

  • and turning off a generator will always make an enemy come check it out, you can then use

  • this information to create plans, diversions, and traps.

  • Without predictable behaviour, the player can't create satisfying plans. Halo man Butcher

  • gave the example of sneaking up behind a Grunt, and the Grunt running away - "it would be

  • bad if they only ran away half of the time, because then the player can build a plan that

  • will only work half of the time".

  • Instead, Bungie went for predictable actions but unpredictable consequences. "The Grunt

  • will always run away," said Butcher, "but you don't necessarily know where he'll run

  • away to".

  • So predicability certainly doesn't mean easy. Take a game like Spelunky where every enemy

  • acts in an almost completely scripted fashion - which would make them effortless to avoid

  • or kill, until the enemies start appearing in big groups, begin to navigate different

  • environments, and start interacting with other characters. Now it's Spelunky.

  • Good AI can interact with the game's systems.

  • This is like how an enemy in Breath of the Wild doesn't just walk up to Link and start

  • wailing on him - but will run off and pick up dropped weapons, set their wooden clubs

  • alight, kick away bombs, and even throw their fellow monsters at you.

  • Oooh, that's gotta hurt!

  • Again, this has the added benefit of making an AI character seem smart. An enemy in Bioshock

  • who runs to a health dispenser midway through a fight looks like he is aware of his surroundings,

  • is interested in self preservation, and feels like he has similar abilities to the player.

  • But it also means you can screw them over by putting a trap on the health dispenser.

  • Hehehe!

  • By exposing an AI to the game's systems, we can provide loads of interesting ways to deal

  • with foes in a more roundabout fashion, like making an enemy fight for you in Prey, or

  • tricking an enemy into attacking a Cucco, so this happens...

  • By the way, I propose we call this "chicken-boning an enemy".

  • Good AI reacts to the player. This can be as simple as guards becoming more frightened

  • as you take out their buddies in the Batman games, or something as complex as Shadow of Mordor.

  • In that game, special Orc captains are randomly generated with names, abilities, and relationships

  • - and will then remember their interactions with the hero. If you run away from a battle,

  • for example, the Orc might reference this the next time they see you.

  • ZUMUG: Hey! Not letting you run this time! I's gonna finish it!

  • This is a great way to create memorable, and very personal stories for the player.

  • ORTHOG: Your death will bring me even more glory!

  • Tracking the player can also be used to adapt the way the AI works. This doesn't need to

  • be as clever as the Shadow Fighters in the new Killer Instinct, or the Drivatar system

  • in the Forza games, where Microsoft tracks the way you play and can create AI doppelgängers

  • to race or fight for you.

  • Really, it can be as simple as something like in Metal Gear Solid V, where enemies track

  • things like how often you perform headshots, take out bases without being seen, or infiltrate

  • during the dark - and then change to different behaviours like wearing helmets, laying traps,

  • or using night-vision goggles.

  • These are all things that the AI has been told how to do - it's not actually "learning"

  • - but it just won't do them until the player hits a certain threshold. And the intended

  • effect is stopping the player from using the same boring strategy for every base in Afghanistan.

  • A similar system is used in Alien Isolation where the Alien unlocks new abilities as the

  • game goes on, to make it look like the Xenomorph is learning from the player, and to keep the

  • game interesting as the hours tick by.

  • Adapting the AI to the player is also used to build a good mood, or drive the game's

  • pacing. The most famous implementation of this is certainly the AI director in Left 4

  • Dead. This clever system tracks the wellbeing of each player, based on their health and

  • run-ins with special infected, and if the team is cruising along, the intensity of the

  • zombie horde is increased - before the AI director eases off to give the team a chance to relax.

  • But this tech isn't as new as you might think and something similar was actually used in

  • Pac-Man. Designer Toru Iwatani said "I felt it would be too stressful for Pac Man to be

  • continually surrounded and hunted down. So I created the monsters' invasions to come

  • in waves".

  • So, in the game, ghosts swap between chasing the player and just wandering off into the four

  • corners of the maze.

  • Good AI has its own goals. Beyond, "kill the player", I mean. This game is Rainworld, by the way,

  • where other animals in the game are hunting for food and will end up in territorial scraps

  • with rivals. Sometimes, it's best to just let them get on with it.

  • That's also how STALKER: Shadow of Chernobyl works. Or is supposed to work. Bandits make

  • plans, and then wander about the wasteland alone or in groups to enact those plans. Meaning

  • you could come across a raging battle that only occurred because two rival factions happened

  • to accidentally run into one another.

  • The AI is a bit buggy though, and you will need to install mods if you want the AI to

  • be doing stuff outside of your immediate location. But STALKER's A-Life system sure was ambitious

  • and we certainly need more games like it.

  • Or maybe more games like Waking Mars - a captivating sci-fi indie game about increasing biodiversity

  • in the belly of the red planet. When you figure out how different plants and animals react

  • to one another, you can forge self-sufficient ecosystems where AI critters can live and

  • breed - even while you're exploring a completely different part of Mars.

  • Finally, good AI isn't just about enemies, and we need better friendlies. Because even in games with

  • great combat encounters, the good buys can be as dumb as dirt.

  • SCIENTIST: Hello!

  • Now, some developers just cheat, and make their AI companions invincible - like Elizabeth

  • in Bioshock Infinite who can't get hurt during combat. Probably a wise decision, given the

  • tumultuous history of escort missions in games.

  • But there are other uses for friendly characters than just defenceless girls who follow the

  • male hero around.

  • In The Last Guardian, you work with a giant beast called Trico who can take care of enemies.

  • But Trico is nervous around stained glass windows that you can smash. This means the

  • player and the AI must work together - something which can get a bit frustrating when Trico

  • has been specifically told to ignore the player's instructions about half the time, in an attempt

  • to make it seem more like an animal.

  • In Event[0], developer Ocelot Society was inspired by internet chatbots

  • to make a game where you can talk with an artificial intelligence, and work with it

  • to solve puzzles on a derelict space ship. I've got much more on that game in an earlier video.