User login

A Complete Guide to Fort AI Mechanics

5 replies [Last post]
InTehVaria's picture
InTehVaria
Offline
Citizen
Joined: 02/21/2013

http://www.youtube.com/watch?v=POuIUCyeqa8

Assassin's Creed III - A Complete Guide to Fort AI Mechanics

This is my attempt at a definitive document for AC3's AI systems in "stealth" paradigms. This should hopefully clarify for many exactly how they work, and set a stronger foundation for criticism of the game and the series in general going forward. Much of this may be old news to the people on this site, but this compiles everything, and it definitely includes things I didn't fully understand until recently. I hope you enjoy, and find it useful.

Here are my full comments:

This is the accompaniment to a special demo video showing a group of mechanics that operate in Forts that I, as well as many others I'm sure, have wondered about. If you've watched my other videos you've noticed that enemies inside of Forts will have behavioral changes after certain events, most prominently starting to repeat a single phrase over and over. In my Perfect Stealth and Perfect Stealth Barehanded series this behavior was unavoidable because it's triggered by powder reserve explosions, which of course are a prerequisite for completing the run using those rulesets, but those are optional in Silent Exterminations. As I've progressed in this latest series I've noticed other strange things about enemy behavior in Forts, and I felt compelled to figure out how it all works.

The observation that kicked this all off was that after a certain event enemies would not only start repeating a single sound bite, but some would also change the routes they patrolled. This baffled me at first, since I'd never seen enemies change patrol routes before doing Silent Exterminations. Then I found out what exactly triggered this change: the discovery of a corpse. Ironically, it took me a while to realize this because my previous runs had a focus on pacifism. When a corpse is discovered, the entire Fort goes on "high alert;" enemies will start their repeating sound bites and patrol routes will change (not all patrolling enemies have more than one patrol route, the ones that don't will stay the same).

Corpse discovery often works the way you'd expect it to. An corpse comes into an enemy's field of vision and the enemy goes to investigate it. However, the full scope of this mechanism is surprising, and quite unintuitive. An enemy is completely "dead" when they go limp after collapsing, their bodies "ragdolling." At the moment this happens any enemy that would have an unobstructed view of the corpse if they were to look in its direction will know it is there and investigate, even if they were looking in a completely different direction at the time. You can visualize an enemy's corpse detection zone like a huge halo extending around their head in every direction. This bizarre bit of design has big consequences. Since some enemies are constantly within the corpse detection zone of others unless they are lured away, it's impossible to clear some Forts without triggering "high alert" without tool use or whistling. I've used the strange mechanics of corpse detection to my advantage many times already in my Silent Exterminations at Fort Washington, Fort Independence and Fort St-Mathieu, and I realize that there were times in those runs where corpses were discovered that could have been hidden. I'm considering redoing those runs to correct this.

Corpse discovery isn't the only trigger for "high alert." There are three other triggers that I know of: gunpowder barrels exploding, trip wire mines exploding, and being seen by the soldiers guarding the entrances (this only happens at Fort Independence, Fort Duquesne and Fort Hill). You've probably noticed the trend of explosions as a cause, and powder reserve explosions are no exception. However, they have a strange additional quirk: as soon as the bells stop ringing, the Fort goes back to its default state. The shift back to default happens no matter what, so if you put a Fort on "high alert" then blow up the reserve the enemies will revert to their original patrol routes once the bells end!

Add to all this the "cowards" who become harmless and run around randomly if their Captain is killed within a certain distance of them (this only happens at Fort Independence and Fort St-Mathieu) and you've got a good summary of AC3's Fort specific AI mechanisms. Corpse detection works the same way outside of Forts of course. I'm glad I finally have a solid grasp of them, they explain so much that I was confused about before. I hope this video and guide can help others as well!

Double McStab with Cheese's picture
Double McStab w...
Offline
Citizen
male
San Diego, CA
Joined: 03/29/2012

Even though I have nothing to add to this thread, I wanted to let you know that I fully appreciate the time and energy you (and others) put in to fully understanding the internal workings of these games. You are then able to push them to their limits (silent exterminations, exploits, etc) and play the games like few others on the planet can. I don't have the dedication to do it, but this sort of effort into understanding the game gets a big thumbs up from me. Rob's applause

“Force has no place where there is need of skill." Herodotus

Calvar The Blade's picture
Calvar The Blade
Offline
Citizen
male
Joined: 11/21/2010

The forts were some of my favorite parts of the game, but they definitely had some jankiness to them.

I hope they reworked the player and corpse detection mechanics as well as patrol pathing, for AC4.

I'm completely sure they know about the flaws of the current system, the only question is if back in 2011 they decided that reworking it in a major way would be a priority for Black Flag.

AC3 introduced a lot of new tools and abilities and potential for interesting design, but while your toolbox was massively changed, the sandbox was a variation of the same one we've had since 2007. I think at this point, modern stealth and open-world games have advanced in a number of ways, and the AC series has, in a lot of cases, not taken some important cues from them.

Both fictionally, technically, and design-wise, I hope that Black Flag can be a fresh start for the series. I know that's what they're aiming for, I just hope they go far enough to make that a reality.

the posts a bit guy

gerund's picture
gerund
Offline
Citizen
male
The Netherlands
Joined: 10/29/2012

Did you ever think about doing Sequence 11- Memory 2 again? The New York military district is basically one big fort. Since you are really good at stealthily taking down forts, I think you will find this challenging as well.

"...and if I had no self-awareness, I think I'd know."

Double McStab with Cheese's picture
Double McStab w...
Offline
Citizen
male
San Diego, CA
Joined: 03/29/2012
gerund wrote:
Did you ever think about doing Sequence 11- Memory 2 again? The New York military district is basically one big fort. Since you are really good at stealthily taking down forts, I think you will find this challenging as well.

FANTASTIC IDEA... don't worry about the time limit... I want to see someone get to the top of the tower after a silent extermination of everyone in the restricted area... (should be easy to note when you're seen, as the mission fails).

You now have your mission. Tongue

“Force has no place where there is need of skill." Herodotus

InTehVaria's picture
InTehVaria
Offline
Citizen
Joined: 02/21/2013

A Silent Extermination there is probably possible, bit it would require copious amounts of tool use because guards are in such large groups on the streets. There's hardly anyone on the rooftops either, and those are flat and uninteresting to traverse. It'd be no fun. It's just a very poorly designed mission, which is sadly the norm in this game. The Forts are among the wonderful exceptions.