When creating a video game we're driven by a desire to craft a fun and interesting experiences
for players: to put them in new scenarios or retread familiar ones. Now sometimes in
order to pull that off, we have to cheat a little bit. We make tweaks gameplay systems
or concessions in how a certain feature is built to reinforce the pillars of the games
design and this applies just as much to non-player characters. Alien Isolation's Xenomorph that
has short range sensors in the back of its head and a director that always knows where
you are, the enemies in Far Cry that become less accurate the more that are fighting you,
or the demons in DOOM that patiently wait their turn to tear you to shreds. It might
sound counter-intuitive, but by limiting a characters behaviour, or giving them knowledge
and skills they shouldn't otherwise have sometimes makes sense in reinforcing the players experience.
And this brings me to Ubisoft's 'Ghost Recon Wildlands': an open-world action game released
in 2017 that has players slowly dismantle the Santa Blanca drug cartel.
I'm Tommy Thompson and this is AI and Games - a series on research and applications of
artificial intelligence in video games. In this video I'm going to talk about these guys:
Holt, Midas and Weaver - the three AI-controlled non-player characters that work alongside
the player when playing Ghost Recon Wildlands offline. This ghost squad needs to be able
to respond to player commands and react to the world around them, but also maintain the
power fantasy that the game delivers as you stealthily take down entire enemy command
posts, or roll in with an attack helicopter and blow everything to pieces. It's an interesting
design problem and it's arguably one of the most prominent examples in recent memory where
an AI frequently cheats, not because it needs to be able to do what you expect of it, but
because as players we have a low tolerance for their failure.
The AI squadmates throughout the Ghost Recon series are built to support the player and
reinforce the experience of a being a covert operative that sneaks into installations and
eliminates opposing forces. This includes being able to spot targets for the player,
synchronised kill shots of multiple enemies on your command as well as holding their own
when everything goes loud. Ghost Recon Wildlands takes this premise and blows it up with a
massive increase in scale and this presents a real problem for game designers. Unlike
more recent entries such as Ghost Recon: Future Soldier, the number of unique circumstances
that can arise has grown exponentially - and this is in part due to the systemic gameplay
systems that drive weather, patrolling enemies and rebels, civilians and more.. Players can
attack encampments from any angle they like and approach it using a variety of tools at
their disposal. So the AI systems for friendly characters need to accommodate and in some
instances relax their rules or outright cheat to support the fantasy that Ghost Recon promises.
Now all character AI in Ghost Recon Wildlands is reliant on a behaviour tree system, with
the friendly AI running a much more sophisticated system than the enemies. I'm not going to
focus on the actual behaviour tree implementation in this video, but if you're keen to learn
more about them check out my recent AI 101 on the subject. For now I'm going to explore
the design rules enforced and the supporting systems that help control your AI buddies.
The buddy-AI in Wildlands was headed up by a small team at Ubisoft Montpelier whose design
philosophy put player at the centre of all friendly AI behaviour - and dictating the
systems that were built and how they would operate. This philosophy was built atop three
core pillars.
- [DON'T STEAL THE LIMELIGHT] Teammates would support the player without stealing the limelight
- [SUPPORT WHERE NEEDED] Ghost AI must react to surroundings and help where necessary and
lastly - [FOLLOW ORDER] Do what the player tells
them to do as best as they can given the circumstances.
All of this is designed to reinforce one rule: to keep players in control of the experience
and not feel like the games systems aren't doing what they want them at a certain point
in time. In each instance the player dictates the behaviour of these AI characters either
directly or indirectly. And in an effort to reinforce the fantasy each of these circumstances
creates: either sneaking past the enemy, gunning them down or reviving us when needed, the
friendly AI repeatedly cheats to achieve it and this requires numerous gameplay systems
as well as specific concessions in both the friendly and enemy AI to pull this off.
As detailed in Mathias Rolland's 2017 GameAI North talk, teammate management is composed
of three gameplay systems that drive the ghost squad AI:
- The 'Smart Recon' system: that finds items and characters of interest within local proximity
- The 'Balance of Power' system: that influences how effective your teamates are in combat.
- And both of these tie into the biggest system known as Overlord: a suite of systems that
identifies all threats within proximity of the player and a variety of useful information
that the squadmates can use to full effect in combat.
All three systems regularly interact with the player through the companion characters
and have control over how they behave and operate within the space.
So let's do something fun: on screen up ahead now is an enemy encampment. I'm going to start
to stealthily approach this base and as I do, I'm going to explain what these systems
are doing for me. So if we look at this view on high thanks
to drone, this is a pretty busy location, there are enemies, vehicles, and no doubt
patrols and guard posts set up in the area. As we moving closer the Overlord system kicks
in and starts to identify all enemies within roughly 100m of where I'm standing. It's not
just storing how far away they are, but also whether I and the rest of the ghost squad
have line of sight on them. This comes in handy in a minute.
Now if we take a moment to check in on Holt, Midas, Weaver they're sneaking up to the base
behind me. In order to know where to go, my player character is leaving spots on the navigation
mesh like breadcrumbs for these guys to follow. Now that we've approached the camp, they're
now going to take instructions from the Overlord as to how to move through the space. Having
gathered all the information it needs about enemy characters in proximity, the Overlord
knows what areas of the map the ghost squad should not move into so as to not to be spotted.
It's at this point one of the team warns me about the chopper overhead. So I lay down
until it clears. But it doesn't matter for the squad: because while I'm in stealth mode
and not spotted, they're invisible to the enemy. The overlord is helping them appear
to look like they're being stealthy and until I either command them to move into a location
where they are then spotted or I am spotted myself, they will continue to remain invisible.
While I've been moving towards the camp, the Smart Recon System has been registering nearby
props such as anti air defences and power generators, but also nearby enemies. It grades
them based on a perceived relevance as well as the potential of my being able to take
them out. It's at this point I'm notified that there's a soldier nearby, but also given
some contextual information about where he is and he's placed both on my HUD and in the
minimap.
While it might not fit the reality - given sometimes they call out things they might
not actually be able to see - it provides a supporting mechanism that prevents me screwing
up early on and identify targets and points of interest I might otherwise have missed.
However, that isn't what I'm after, given I've noted the sniper towers nearby. So having
spotted the snipers myself, we're going to take them out quietly. To do this, we use
the sync shot command, where I select up to three enemies to be taken out by the ghosts.
With the go signal triggered either by my holding A when aimed down sight or in a drone
or by shooting another target. Now what makes this interesting is that these sync shots
rely on the player being able to mark the target, then the friendly AI being able to
take the shot. But sometimes the shot is not actually possible for the AI and there's a
degree to which it will bend the rules to make the shot happen. So perhaps it has to
shoot around a corner at times, but if the enemy is in a bunker and there's no way there
could be a line of sight from that angle, the squad mate will tell me they can't get
the shot.
So as we watch them go down there is a slight delay and that's in part to ensure I see it
happen. But also, you might be wondering about whether the ghost squad can miss. Well, it's
impossible for them to miss, because they don't actually shoot them. This is what the
AI team refer to as the MAGIC SHOT: where the squad pretend to shoot the enemy on your
command and all the enemy AI just mysteriously drop dead. It ensures they don't miss and
as a result don't screw up the mission for you in the simplest way possible.
So as I move into the base, this process continues. The squad continue to follow the Overlords
rules about where they scan stand and we take out more enemies within the base using MAGIC
SHOTS. Plus the smart recon system points out to me the power generator that I had failed
to spot during my recon. Having snuck into the base, the teammates slowly begin to follow
me inside, with the Overlord ensuring they only go through the safer areas that I have
established. Not that it matters anyway, because they're invisible.
But I decide once inside the base to go loud and make a mess. It's at this point not only
will the buddy-AI aim to rally on me and start attacking enemies. The Overlord system switches
modes into combat and as such the information it's passing about target prioritisation as
well as where to move in the world changes accordingly. On top of this, the Balance of
Power system kicks in. This system is effectively a realtime balancing tool that makes the ghost
squad more or less effective in combat the longer a battle continues: influencing their
shot damage, attack frequency and their overall resilience. The better I perform in avoiding
damage and eliminating enemies, so do the squad. Plus the squads gets an initial boost
on the start of a fight so as to help me avoid getting slaughtered once it all gets a bit
messy.
Plus once again returning to the core design pillars, they'll not only frequently aim to
support me, but also make sure they're within close proximity when they do it so that I
know they're doing it. While the firefight has kicked off, the Smart Recon system is
still in effect, they're still spotting targets such as that one sniper I forgot about as
well as more attack helicopters.
Now it all gets a bit much and I wind up getting shot down and needing revived. As you can
see there are quite a few enemies surrounding me as this is when another system known as
the Revive Manager kicks in. The Revive Manager selects one of the ghost squad to revive me
and tells them to activate the corresponding behaviour tree. Given as players we'll be
super pissed off if the AI fails to revive me, it won't fail to do so. If the player
is surrounded by enemies, it will use magic shots on the nearest ones to clear the space.
Did you get downed on a rooftop or awkward piece of geometry? Then the companion will
teleport onto the surface or in the worst case literally on top of your body to ensure
the revive goes through. This same system is also used to have allies revive each other
whenever necessary.
And so this process continues until either we end conflict or are killed in action. In
any case, the squad continues to provide information, become more effective as I turn the tide of
battle and revive me until it's no longer possible. But despite all this, it doesn't
make me invincible: otherwise it would remove all of the challenge. So in time, if I don't
find a way to end the conflict I'll eventually get wiped out.
Now outside of this example there are still numerous instances where the squad act in
very specific ways or cheat in order to assist my experience. The most obvious one for players
is driving around in vehicles. If I get in a vehicle, the team will attempt to get in
with me. However, if I drive off without them, they'll simply teleport into the vehicle so
as to provide assistance. In the event it's a vehicle that can't carry all four of us,
they'll simply teleport to me once I stop and get out on foot again.
One thing I did briefly mention earlier, is how AI are invisible when I don't tell them
what to do. They cannot be seen and will not attack enemies until you give the go either
by giving a sync shot command, telling them to attack using the command wheel or just
start attacking the enemy yourself. The only time their invisibility is disabled is when
the player issues a movement order in the command wheel and they're then spotted by
the enemy. If in that moment they're spotted, that's on you. You made that mistake and not
the AI. So as far as the game is concerned, the AI cannot be told off for making a stupid
decision, because really it was you that was the idiot, how do you like them apples?
Building supporting characters for games such as Ghost Recon Wildlands is never an easy
proposition. Players are... fickle shall we say, at the best of times. And as a result,
we need to provide systems that can behave as expected in stealth incursions, big gun
battles and just mucking around on the highway. As a game developer myself, I find it refreshing
to see a AAA game such as this one makes such dramatic concessions to reinforce the experience.
I use the word 'cheat' frequently in this video, but it doesn't deny the player of the
experience the designers intended. It just irons out many of the larger implementation
hiccups that can easily drag down a game of this scale. Making smart AI for open world
games is a lot harder than many would give credit and if it keeps you engaged than sure,
let's cut the corners. Even if it means your AI can teleport into a moving helicopter.
Thanks for watching this video on Ghost Recon Wildlands and be sure to subscribe to AI and
Games for more of my case study series. My next topic is brought to you by my wonderful
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