Enemy AI Design in Tom Clancy’s The Division (Part 1 of 2) | AI and Games

in 2016 Tom Clancy’s the division brought players together in the war-torn streets of Manhattan fighting against a variety of enemy factions as well as one another Ubisoft RPG shooter carries a diverse range of enemies to keep players on their toes but unlike other games covered on the show to date the division needs to deal with the practical issues of being an online cooperative game and how to manage all sorts of AI systems for thousands of players across the world I’m Tommy Thompson and welcome to AI in games a series on research and applications of artificial intelligence in video games over the next two videos I’m going to be looking at how developers massive entertainment sought to create a variety of interesting and challenging encounters throughout the world of the division how they designed their enemy opponents and manage their behaviors as thousands of players rushed to battle online every day in the mean streets of New York City after an outbreak of weaponized smallpox New York City breaks down into chaos and is quarantined from the outside world until the contamination is contained and order is restored players assumed the role of an agent within the strategic homeland division a sleeper government unit that’s activated in periods of national emergency in order to help first responders bring order to the region players can play individually or in groups of up to four completing a series of story missions and open-world events and a region of Manhattan that at launch spanned over six square kilometers in size ranging from 21st Street and ninth all the way to 55th and third Avenue to give players some variety in challenge regions of the map are controlled by five rival factions including the flame thrower loving cleaners escaped convicts from Rikers Island as well as the last man battalion in addition the most infected region of the city the dark zone has been cordoned off and is the game’s major PvP arena comprised of not only enemy AI but also fellow players who can go rogue any time and begin to attack you as players explored the city of New York they will interact with non player characters in one of three scenarios as rumors in the open world such as a wild dog pockets of civilians friendly GTF soldiers near safe houses or hostile mobs out on patrol placed in counters these are instances where players will find the enemy mobs out in the game world often deliberately positioned by the endgame systems with help from designers to force players into combat or making an alternative route and lastly narrative missions specific designer crafted sequences that are part of the main story of the division these are lengthy plot driven segments with an emphasis on gluing together multiple individual firefights in each instance the AI placed in the world has specific objectives that are aligned with one of two critical design goals to either add to play or immersion by enriching the in-game world in its design or to provide a puzzle to solve in combat the latter was the critical part of the game given aims to encourage players towards Scouting areas prior to combat and establishing a base level of strategy once fading break so players need to continually reevaluate their combat priorities and spatial awareness in order to come out intact this requires enemy non-player characters to ‘county interesting behavioral traits for players to recognize but also some consistency in their basic behaviors with a variety of subsystems that can handle threat detection dynamic object of handling as well as been able to react to players themselves so let’s take a look at the underlying architecture and what makes all of this tick all non player character behaviors are achieved through use of a behavior tree system where sub sections of the tree are activated to run specific behaviors that are seeded with certain objectives or variables this can include the lakes of target destinations for navigation areas to explore potential threats enemies to attack cover to move into and so on I’m going to look into the design and structure of these trees for enemy non player characters but if you want to learn more about behavior trees check out my videos on the AI of Halo 2 & 3 which cover some of this and more detail the behavior tree architecture was reliant on a richly layered system which was capable of providing multiple paths to each behavior this is because of the range of ways in which one specific action could arise and required the system to be as flexible as possible the top layer of the tree breaks down the three critical ways in which an NPC would react including direct orders from endgame systems to maintaining active combat or initiating combat if necessary if it spotted the player or their allies this moves down into the conditions layer which identifies what behaviors can be executed based on the current conditions of the world and the character itself all the way down to lower layer which handles pretty much every variation of combat that’s possible in the game what’s critical here is that the middle layer is built such that it can link to a variety of different actions on the lower layer this is to prevent behaviors being duplicated through the bottom half of the tree based on very specific conditions as such all the different NPC’s in the game which I’ll come back to in a minute as well as tools such as The Seeker Mane which is technically an AI character can have similar sub trees or behaviors to suit their purposes without having to copy them around as you can imagine this still results in a behavior tree architecture that’s rather complex and you’re a what see here is simle massive in scale and this required heavy collaboration between the programming and design teams at massive in order to get this working given the scale of the problem the challenge is faced the programming team developed numerous tools for editing and eventually debugging each of the NPCs and built these into the snowdrop engine that the division is built in these debugging tools are extensive given the ellow for the developers to identify what is going wrong with a particular character in real time in an online instance and I’ll come back to talking about this later so know that we know a little bit more about the AI architecture let’s take a look at the design of the npcs themselves launch the division had 36 enemy non-player character types spread across five factions archetypes help establish the type of behavior of a given character while factions govern attributes that are specific to all NPC’s within them to enable a bit of gameplay diversity there are a large number of archetypes in the division namely assault which has basic shooting and cover capabilities Russia who rushed directly towards targets tanks that take and deal large amounts of damage snipers who act long range with accurate assault capabilities throwers who throw grenades and area-of-effect items support who assist team mates in combat typically through healing items heavies who can suppress players leaders who provide buffs to nearby non player characters and controllers who typically fight via proxy using something like a turret there is also the special NPC that doesn’t actually adhere to the archetypes but that is only used in endgame and boss battles each of these archetypes is designed to give clear feedback of the immediate dangers to the player and how to strategize their attack patterns in addition many of these archetypes complement one another such that one can exploit each other’s attributes in order to achieve their goals for example while snipers maintain their distance from players to deal large amounts of damage rushers deal damage up close and immediately try and close the distance between themselves and the player meanwhile tanks and heavies force players to stay in cover while throwers will attempt to flush players out as such this forces players to use tactics throw a given battle beast on the enemy unit composition this is driven by our desire to force players to continually evaluate three key gameplay attributes target prioritization and ordering who should I be attacking right now positioning and exposure am I in the best cover given the current scenario and that often results in players moving to obey our tactical positions and keeping them from coming our cover and lastly rewarding endurance the division provides long protracted battles that test a player’s ability to maintain their posture at a given level of intensity there was mentioned earlier the 36 MPC types were spread across the major NPC factions rioters cleaners Rikers and the last man battalion the split into tiers one and two depending on where you are within the New York map you’ll encounter one or more of these factions in combat each faction is designed to scale difficulty as you progress through the game progressing in the order I listed them but given there are so many individual NPC types how do you manage the difficulty progression and a manner that’s easy for designers to iterate upon but also effective enough to be pervasive across entire groups of non player characters to achieve this massive bill an AI profile system that modifies a large number of exposed attributes for each of the non player characters this enables them to become more or less of a threat to the player accordingly and there are eight different attributes that are influenced reaction time to player actions movement speed group behavior cover usage skill usage stagger resistance suppression resistance health and damage accuracy the profiles are built to be consistent across either a specific non-player character archetype or a faction that those NPCs will exist within so for example the rioters who are the first faction in the game players will encounter are restricted to using a dumb profile where all of these attributes are fairly low however all heavies supports and turrets have dedicated profiles for those archetypes that are consistent across all factions meanwhile the last man battalion have their own elite profile which makes them far more threatening to players than all others the last and final modifier that has an influence on an AI s– behavior as its role and rank within the itself characters range from regular grunts to veterans Elise and finally the named MPC rank which is reserved for only the most high priority targets as a NPC’s role increases this has an influence on the base stats such as weapon damage armor and shot accuracy with elite and named NPCs having access to unique weapons and mods they even get custom laser sights that have absolutely zero effect on their game playability put it puts players on edge as a result the suite of gameplay and AI systems and Knievel’s Tom Clancy’s the division to build up a rigorous and diverse collection of non player characters that helped bring Manhattan to life whilst these systems fundamentally use the same core a high architecture the use of archetypes factions profiles and ranks enables for a lot of diversity and not just the behaviors executed but also the level of challenge of these characters present for thousands of players across the world but therein lies the bigger problem how do you maintain performance for these kinds of systems in a game designed to run online the division has hosted over 10 million players since launch with a peak of over 1 million concurrent players that’s a lot of non player characters that need to be created maintained and controlled over thousands of individual game instances in part 2 of my case study and the division we’re going to look at how massive entertainment pulled this off and explore the online integration the design decisions that were made to ensure the game runs as smoothly as possible and the problems and limitations as presented for the AI systems in addition we’ll also look at the tools that were built to enable testing of the AI behaviors in online instances as well as how a AI players were used to test the consistency and stability of story missions on test servers in the meantime don’t forget the AI in games as a crowdfunded show on patreon and is supported thanks to the people whose names are on screen now you can support the continued development of this series via the links on screen now and in the description thanks for watching and I’ll be back soon with part 2

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