Hi I'm Tommy Thompson and this is AI and Games: a series on research and applications of artificial
intelligence in video games. If you've watched the case studies series on this channel, you'll
know that I explore how AI is built in commercial video games long after the projects completion.
I've never had the opportunity to talk to a studio more candidly about their experiences
and the path their work has taken from initial concept to being on store shelves and surviving
in the modern gaming ecosystem. And this is what brought me here, on the outskirts of
the sleepy town of Twycross in the English midlands as I was invited to the offices of
Rare - one of the most revered and seasoned studios in the British games industry. In
March of 2018 Rare released Sea of Thieves: an online pirate adventure game that not only
brought a unique experience to the Xbox platform, but also helped redefine the studios identity.
Join me as I go behind the scenes with some of the programming team responsible for Sea
of Thieves and learn first-hand not only how the game was built, but the ongoing dedication
and craft as it sees continued updates and improvements today.
[THE MAKING OF SEA OF THIEVES PART 1: BUILDING A PIRATES PARADISE]
Rare is one of the longest-serving companies in the British games industry and has survived
for over 30 years by evolving and adapting to the changes in the market: first developing
titles on the ZX Spectrum, to forging a strong partnership with Nintendo in the 1990's and
now as one of Microsoft's internal studios supporting the Xbox brand. In 2015 - following
the release of three titles in the Kinect Sports series and the anniversary collection
Rare Replay, the studio had focussed its efforts on something completely different - a project
that would challenge not just the *types* of games they made at the studio, but *how*
they were going to make them as well.
Sea of Thieves is derived from a desire to do something unique. Whilst Rare sought to
move towards creating a live service game - something they had never done before - its
design was intended to be player centric. Players can tackle missions from different
quest-givers at their own pace, allowing you to prioritise the experiences you enjoy the
most and keep the game as accessible as possible. In return, players not only increase their
standing with different factions, but earn currency to acquire a variety of new cosmetics:
a cool new hat or peg leg, a nice top sail for your ship, or a gold trimmed water bucket.
Through this approach, players can derive their own satisfaction from achieving tasks
in the game, from attacking skeleton forts to sailing through storms and playing sea
shanties with strangers - along with a tankard of grogg or two. But it all started from more
humble beginnings.
Over time, Sea of Thieves has developed a dedicated fan base that continues to sail
the seas for adventures that can challenge even the most ardent of Pirate Legends. Much
of this is thanks to Rare's continued development of the game, with four major updates within
eight months after the games release. Meanwhile April's anniversary update kickstarts the
2019 content drops as Rare supports the game for the foreseeable future, with the introduction
of PvP mode The Arena, the new Tall Tales storyline as well as new gameplay mechanics.
These new features, combined with continued refinement of existing ones, seeks to mix
things up in new and interesting ways that adds new layers of complexity to the core
gameplay.
The game has a variety of AI systems under the hood that continues to increase with each
update. While the game launched with traditional humanoid enemies such as the skeletons as
well as ambient AI on islands such as snakes and pigs the game has focussed on the expanding
its roster of sea-based threats that can threaten you and your ship. Not content with sharks
at launch, 2018 saw the addition of the kraken, the megalodon and haunted galleons with each
continuing to change and evolve with each new expansion. All of this requires systems
that balance that experience: ensuring this online world with hundreds of AI characters
is stable and manageable as pirate crews sail the seas and get up to all sorts of shenanigans
on each server. Plus by virtue of it being a live service game, the project needs to
be maintained in a manner that it can be iterated upon quickly, allowing for new content to
be released frequently and ensures the game continues to be stable for players. All the
while achieving this without overworking the development team - and AI even has a part
to play there too. But before any of that can come into play, let's consider it's earliest
beginnings and how Sea of Thieves was built.
Having been invited to Rare's offices by Andy Bastable - the principal gameplay engineer
on Sea of Thieves - I was keen to learn as much as I could not just about the AI behind
the game, but how it all came to be in the first place. Sea of Thieves is built in Epic's
Unreal Engine 4, which is of course not just one of the most popular commercial video game
engines, but one that has a strong reputation within the AAA industry.
Unreal is known for being a reliable engine both for networked gameplay and cross-platform
development - which was critical given the intention to launch the game on both Xbox
One and PC and connected into the Xbox Live ecosystem. In addition, UE4 arguably has the
most robust set of AI tools available in a commercial engine for developers to work with.
Not only does it provide a suite of navigation mesh tools - which ensures characters can
move across surfaces and recognise changes in terrain - it also has the behaviour tree
system for creating versatile behaviours that are responsive to in-game events. Plus whilst
still in an experimental stage when Sea of Thieves started production, the environmental
query system (or EQS) can simulate sensory inputs and minimise performance overheads
for checking whether characters can be seen or heard in proximity. However, that still
wasn't enough for what Rare had in mind. Given, as we'll see throughout these videos, only
the skeletons and other land-based AI such as pigs and chickens are built entirely using
the original AI frameworks - with a bit of Rare's own special spices of course.
A big reason for this is that the game largely takes place in-water, either swimming around
or in rowboats and ships, and navigation meshes don't support that - a point I'll come back
to later. Fortunately, UE4 provides access to the engines source code. This enabled the
developers to build their own custom water navigation system and then hook it into the
existing navigation framework of the engine, a point I'll return to in part 2 when we look
at the shark AI. Plus as we'll see in part 3, enemies such as the kraken and haunted
ships required bespoke tools that would enable the AI to behave in a way that simply isn't
possible in UE4 by default. So once again Rare were able to create unique systems that
fit into the existing Unreal Engine AI workflow, and ensure the toolchain doesn't become too
unwieldy to manage.
As mentioned, I'm going to explore how all of these AI threats are designed throughout
the series. However in the meantime if you're watching and don't understand what either
a behaviour tree or navigation mesh is, be sure to check out my AI 101 episodes on each
topic, where I explain what these things are and why they're so important for making AI
in games.
As the time of this video, Sea of Thieves is now one year old - having been released
on March 20th 2018 - and during this first year, the game carried three main activities
for players to participate in. Each of these activities have their own requirements and
dependencies in terms of gameplay, mission construction and AI behaviours where necessary.
Non-player characters based at outputs allowed for you to collect missions from one of the
tree main trading companies:
- The Gold Hoarders: Where you travel to specific islands and dig up buried treasure.
- The Merchant Alliance: that asks players to acquire specific items - be it animals
such as pigs and chickens or cargo runs of rum and plants - and deliver them to islands
across the open world. - And lastly there is The Order of Souls:
where you need to go one or more tropical locales, find undead skeleton warriors, kill
them all over again and then sell their skulls for gold - which isn't creepy at all.
In each instance, these missions require gameplay systems to generate AI characters at runtime
to facilitate the missions requirements. For example Order of Souls missions require skeletons
to spawn onto specific islands for the player to fight against, but also the specific high-value
targets you need to take out. Meanwhile in Gold Hoarders and Merchant Alliance quests,
skeleton warriors will still appear on islands at specific times in order to present a challenge
and get in the way between and your loot. Plus in Merchant Alliance quests where animals
need to be captured, the game needs to make sure animals are going to spawn in for you
on certain regions of a given island for you to capture them. This has since been embellished
with the recent anniversary update which introduced a fourth trading company - Hunter's Call - that
introduced fishing mechanics - and new fish AI to go along with it.
With a mission in play, the game not only needs to ensure these characters are spawning
in, but they're balanced in terms of number and difficulty based on the size of the players
crew, the location the mission will take place in, the ranking of the player who acquired
the mission from the Trading Company, as well as the mission type itself. That's where a
little bit of procedural generation comes into play as Rob Massella and Stuart Holland
explained
to me.
Over time, each of these mission types scale in their own unique ways, providing an ever
increasing challenge not just for players but designers too!
Each of these mission strands scale independently from one another, allowing players to prioritise
quest lines they prefer and not to be punished or left confused when picking up missions
from other Trading Companies. Hence you can decide after hours of playing through the
Order of Souls to do a quick run for the Merchant Alliance but the scale and difficulty of that
subsequent mission won't be influenced by your preceding hours of play.
But this presents a much bigger problem for AI performance and networking: given your
crew isn't the only one on a given server. This is similar to the challenges raised when
I looked at the AI of Tom Clancy's The Division, where the game had to balance all the AI behaviours
happening out in the active world. How do you maintain the performance of the game world
with all these AI characters running around? It was a big topic that we discussed at length
in the studio and while the exact maths involved is still a secret, what I did learn is that
the AI characters for each mission are only spawning in when necessary and not wasting
CPU and memory resource by running around on an island that is miles away from the nearest
player, or sailing the seas where nobody is going to notice them.
This process helps ensure that while one crew might be busy hunting a Megalodon, it doesn't
impact another the crew on an island completing an Order of Souls mission. AI characters such
as pigs and chickens don't spawn on islands until crews are close enough that they might
actually see them. But in addition, pigs, snakes and skeletons on the same island as
players often go dormant when not in combat and beyond the line of sight of any human
player. It's a safe tactic to employ that minimises unnecessary computation on server-side,
given nobody is going to notice what happens to these characters anyway, freeing up server
resources that could be put to better use elsewhere.
As we'll see in the upcoming episodes, this philosophy holds true for the likes of the
skeleton galleons, the megalodon and the kraken. However, the rules of these systems are unique
in each instance and run on completely separate services and behaviour systems.
Bringing this swash-buckling adventure to players already sounds likes a daunting task,
but this is just the beginning and I still have a lot of exciting topics to cover. Here's
just a taste of what's still to come...
The behaviour tree architecture of the skeletons AI and how they're built to use the same controls
as humans.
How sharks required a completely different navigation system at launch.
The deadliest threats looming deep under the sea: Megan and Karen!
Plus the looming threat of Skevin! Or is it Skelly?
And finally we're going to look at the automated testing framework that enable Rare to extensively
test the game during development, minimise errors and enable faster and more streamlined
deployment of the game both before and after launch.
Thanks for watching part 1 of the AI of Sea of Thieves here on AI and Games: a series
brought to you by its supporters on Patreon.