The AI of Horizon Zero Dawn | Part 1: Rise of the Machines | AI and Games #37

Key Takeaways

[Music] [Music] Horizon zero Dawn stands as one of the most critically acclaimed of Sony's roster of PlayStation 4 exclusives as the hunter aloy players Venture across the post-apocalyptic Landscapes of the future to uncover the mysteries of our past and how the world fell in the years before Humanity's Fall From Grace has led to the rise of the Machines robots of varying shapes and sizes that now Run free across the land these robotic animals are intelligent coordinated and lethal requiring quick thinking to survive and even greater preparation and planning to successfully destroy I'm Tommy Thompson and this is AI in games a series on research and applications of artificial intelligence in video games for the next two videos I'm exploring ing the gameplay and decision-making systems that bring these creatures to life and power the core gameplay experience I'll be looking at not only how they make decisions to scavenge to hunt and to survive but how they coordinate themselves in the wider World either individually or as part of a herd plus I explore how the game creates an ecosystem of machines that is balanced and managed across the many territories and regions of the new world [Music] the robotic wildlife of horizon zero Dawn dominate the landscape and hold control of territory throughout this open World Experience each machine carries a unique aesthetic and structure that reflects their function and purpose within The Narrative of the game as players work their way through the campaign we come to learn of the Pharaoh plague an army of Rogue war machines that rendered the world aunder alongside the race of machines constructed by the AI known as Gaia that are designed to restore the planet to its natural glory and are largely inspired by long extinct Terran species as a result the function of a given machine often holds the secrets to their weakness players can use their focus to scan local machines to ascertain not only their type but vulnerabilities as well as weak points in addition to the weak points a machines function within the narrative ultimately influences their in-game behavior this includes acquisition in scavenger robots such as the Strider and Grazer these worker class machines are typically found in open grasslands working the lands and while they're relatively doile and often flea confrontation they're nonetheless deadly when provoked Recon machines such as Watchers and long legs that Scout the region for threats and alert nearby machines such that they can fight or flee transport machines such as the Behemoth and shell Walker that gather up resources from the acquisition robots making them valuable targets for players they're slower more cumbersome and typically defended by more Nimble units and lastly Combat Machines such as sawtooths and stalkers that are primarily there to attack the player and other nearby threats there are 28 unique machines that can be found roaming the wildlands each with their own distinct passive and aggressive behaviors and players need to learn how best to approach them while the greatest threats on the path to Meridian such as the stormbird and thunderjaw roam the Wilds on their own players can still run a foul of less lethal machines that operate in herds it's common to see the smaller robots such as Watchers Striders Scrappers and Long Heads coexisting supporting one another as they achieve their base functions over time these herds increase in size and diversity as players continue to explore the world with the likes of the shell Walker convoys packs of tramplers and saws protecting nearby grazers and Lads in order to pull this off the game requires numerous AI systems that dictate the behavior of each robot how they behave within a herd the collective intelligence of the herds themselves but also balance the herds across the open world for a more varied experience the developers behind Horizon zero Dawn Guerilla games came to this project lacking many of the AI tools required in order to bring this experience to life having previously worked on their Killzone franchise their AI tool chain was largely focused to accommodate first-person shooters and none of the design challenges that faced them for a large open World experience as such during the course of development they built new Ai and gameplay systems and expanded upon existing ones within the studio to bring this world to life and over the next two videos I'm going to explore the following an agent hierarchy system that dictates how each machine behaves both individually but also as part of a pack or herd the expansion of the existing planning and execution system originally built for Killzone that allows each machine to make decisions a set of sensor systems that enables the machines to quickly and effectively detect threats and investigate when necessary a dynamic and intelligent navigation system that provides interesting movement patterns for a variety of ground-based robotss that respects the world geometry and varying machine size a completely separate navigation system that catered For Airbase machines such as glint Hawks and stormbird an animation system that respects each machine's composition and ensures they move and attack in an intelligent way and last but not least a system known as the collective that manages every single machine that is active in the game world and how they are distributed across herds so let's begin by exploring how each AI character is built to make decisions and how the game manages herd [Music] Behavior each machine is represented in the world as a separate non-player character AI called an agent but perhaps more interestingly so is each herd Horizon Z Dawn adopts a hierarchy whereby a machine can exist entirely on its own as an agent or as a child of a group agent which is used to store information about a particular herd or pack a group agent doesn't physically exist in the game world but it's responsible for coordinating all the agents within it each individual agent has its own set of sensors that enables it to hear noises close by or spot threats in proximity but in addition a group agent has a Blackboard system that stores in game information a machine might want to use this not only allows the game to keep performance costs down by storing information each individual might try to calculate on its own like safe areas to stand in or active Patrol routes but more importantly agents in a group can share information between each other hence when a Recon machine spots the player each machine can make a decision on how to respond to that information hence you might see acquisition robots in the herd such as grazers opt to run away while nearby Combat Machines move in for the kill now the actual AI system used in Horizon zero Dawn is called a hierarchical task Network planner unlike the planning systems used in games such as fear that plans one action after the other htn planning generates plans comprised of action macros each Macro contains multiple actions in a set sequence this is ideal for game development given designers can put together macros of good behavior they expect to see in game I've previously explored how htn planning was used in Transformers Fall of Cybertron but it's also used in games such as Max painan 3 Dying Light and rumor has it in Dark Souls but it's worth noting that gorilla have been using htn planning since Killzone 2 and as such this wasn't built overnight but has gradually matured over years of projects within the studio the htn planner is used in two capacities by machines individual agent agents can ask for a plan of action to resolve a specific task such as finding new areas to visit attacking a human or fleeing to safety meanwhile group agents can run plans that dictate what goals individual agents should be assigned allows for groups to actively pass information between one another within a hierarchy and potentially forms new subgroups or destroys existing ones in short each individual machine is still largely responsible for their own behavior and addressing the goals assigned to them and uses the planner to make those decisions meanwhile the groups keep individ ual coordinated regroups them based upon what's happening in the world and perhaps critically assigns roles to each machine such that they know what their job is to support the her now with all these machines operating in the world either individually or in groups how does the game know what machines to spawn in the open world and where there are designated sites across the game map where we can expect to find specific machines to appear either individually for machines like thunder jaws and storm birds or in flocks for the likes of Striders grazers and glint Hawks however the rest of the game world is full of hers comprised of different machines so how does the game know when spawning in a specific machine where to place it in the world and what groups to assign it to based on the needs of the world's Design This has achieved courtesy of a system known as the collective the collective is the supergroup all group agents and individual agents exist in the collective it manages the spawning of all machines into the world keeps track of whether they're in a group and handles their movement between groups and manages the machine ecosystem such that performance isn't impacted overall individual machines in the world can request to join an existing open world group if they're on their own this is a useful feature given many machines are left isolated after the rest of their previous grip either fled or has been destroyed so the collective can recycle isolated machines to join other groups to do this each machine has a passport their passport stores facts about that machine such as its level and machine type and the collective uses this to determine whether it will fit the requirements of another group only moving across if it satisfies the group's needs now for the remainder of this video I want to focus on how a herd operates herds are typically placed into the world in a relaxed state where they're not under threat and simply hanging out in a specific region of the map any given herd is typically a mixture of Recon acquisition and Combat Machines with acquisition robots in the center whilst Combat on the outside to defend them and Recon patrolling the region even in the earliest phases of the game we see the simplest form of this Behavior as Watchers patrol around Striders and grazers when a herd is placed into the world a number of groups will be created and at the same time each of those groups will request a role within the hierarchy this role assigns all machines it's controlling with behaviors that reflect their purpose this can include patrolling for threats searching nearby disturbances attacking enemies or simply Scavenging resources in the world these roles can shift as time passes and events Force the her to change its behavior and structure there is typically a limit on how many machines can fill a particular role within a herd such that their makeup isn't unbalanced a machine's role dictates the goals that the individual agent will seek to complete hence with a relaxed herd the acquisition machines will use the htn planner and data stored within the group to find a local area to mine meanwhile Recon and Combat Machines will generate Patrol paths to follow Patrol paths are autogenerated based on the local geometry avoiding awkward terrain and more importantly avoids passing through long grass and other vegetation the player might use to stealthily approach the herd however in order to give players a Fighting Chance many Patrol Pats will deliberately pass close to stealth vegetation such that you can place traps go in for a stealth kill or attempt to hack them more easily but of course it doesn't always stay this way as players start to attack machines their behavior will shift accordingly for machines that aren't part of herds this comes down to the specific machine class only a few will actually run away when provoked directly with the vast major of machines attacking the player with even acquisition machines often attacking the player if they're on their own however should the player attack a herd the groups within the hierarchy react in kind but only if the herd has been alerted as mentioned earlier the group agent enables data to be shared between each machine but it doesn't update instantaneously as a result the herds don't have a hive intelligence and it is possible for the player to kill a machine without alerting the rest of that group however should this be spotted or if the machine under attack surviv AV it will notify the group that it's under attack and the herd needs to respond in kind at this point the hierarchy within the herd shifts and groups of machines within the herd will request a new role in priority for execution of the corresponding Behavior as well as the htn planner rebalancing which groups exist and assigning the roles and knowledge being shared a group comprised of acquisition machines will assume a flea role and run away together while the groups comprised of combat and Recon machines will rebalance themselves prioritizing each character that is attacking the herd while in many cases this is just the player on their own this enables the system to scale for story missions where the player is part of a group or for other Dynamic events in the world where other human NPCs are attacking them while at this point things have gone horribly wrong it still gives players plenty of chances to turn the situation around as both the grouping systems and AI combat systems work to create an experience that is both fun and challenging this is achieved courtesy of an AI combat system that attempts to structure combat such that it isn't chaotic or broken taking a page out of games such as Assassin's Creed and Batman Arkham Asylum the combat groups that formed have different roles and priorities that are balanced out hence the larger machines in a herd will be spread across the groups where possible with smaller machines lined up to support them in addition groups select machines to attack the player based not just on whether the htn planner thinks it can execute a specific behavior but also whether that attack is going to be interesting if all machines simply attack the player at once then you would die a horrible death pretty quickly as such the combat systems use a similar approach to that found in games such as Halo 3 a topic I covered back in 2018 where it balances which enemy attacks you based on how interesting that attack will be in the context of combat this requires an action selection utility function that calculates how interesting it would be for that machine to attack you this is based on the current machine State whether the player is aware of that machine in their proximity how close it is to the player and the amount of damage it has received and has dished out already ready this becomes a precondition to the htn planning system and aims not only to provide some challenge but also to inject some variety into the combat perhaps more critically when the htn planner is asked to generate actions for attack groups while an attack is been selected the other machines in the group are also being given movement behaviors to circle the player and wait their turn this is done deliberately to create opportunities for the player to exploit either attacking a passive machine or countering the one that just attacked you in time you'll slowly be able to wear them down largely because the combat system is deliberately leaving itself open to attack so as we've seen throughout this video the machines of horizon zero Dawn can prove lethal either on their own or as part of a pack through hierarchical test Network planning and an intelligent agent hierarchy system machines can roam the Wilds on their own own or protect and support one another where necessary this creates a fun and exciting world to interact with that keeps players on their toes at all times thanks for watching part one of this case study on the AI of horizon zero Dawn here on AI and games in part two I'm going to dive into the tools and systems used by the individual AI characters the sensor systems used to recognize an attack nearby threats how the AI systems need to work in tandem with animation to ensure these machines look both Dynamic but realistic the navigation systems that allow Machines of different sizes to move through the same terrain plus how flying machines such as the stormbird use an entirely unique navigation system that allows them to explore the world and hunt you down as best as possible see you soon in part two [Music] [Music]