Research AI Techniques in Other Games - Alien Isolation
Alien Isolation is "one of the biggest AI driven titles of modern times" (AI and Games, 2016) that uses a technique called Psychopathic Serendipity which "indicates that the creature is guided by its own procedural intelligence rather than the canned foreknowledge of a game designer:[sic]" (Keogh and Jayemanne, 2018) this will help the alien to always find a way to disrupt and mess with the player, even the alien cannot see them, to pull this off the alien cannot be scripted and must work off events triggered by the player, such as noise while being guided by the game.
For the creation of Alien Isolation, Creative Assembly used a Two Tier System to control the alien. A Macro AI and a Micro AI.
The Macro AI is similar to a director or God-Like entity that is always watching the current situation of the game world and has a constant reference to what is happening with and the current states of the player and the alien. This means that the Macro AI will always know where the player is and what they are doing, but it cannot allow the alien to cheat and tell it where to look for the player, it will however tell the alien the general vicinity that the player is in.
Also the Macro AI's responsibility is the Menace Gauge which is used to keep track of how much the system is pressuring the player.
This is rather similar to an approach made in Left 4 Dead in which a stress gauge was used to prioritise enemy attacks. However in this case, menace would come not from attacking the player, but being in their proximity and the perceived increase in tension.The menace gauge is filled by testing certain conditions, such as;
(Thompson, 2017).
- Proximity to the player
- Time spent near the player
- Time spent in Line of Sight (LoS)
- Time visible on the motion tracker
It takes into consideration how close the alien is to the player and the ability to quickly reach the player, as the alien could be close to the player but in another room, this will cause the gauge to fill up slower. Once the gauge reaches a certain amount the Macro AI will cause the alien to back off and move to another area, this is to release some of the tension for the player and allow them to progress, as while the alien is near the player will be hiding.
While the Macro AI is managing the world around the player and directing the alien to certain locations, the alien itself is controlled by the Micro AI. Which is made up of a "series of sensors and behaviours that allow it to hunt down and find the player" (AI and Games, 2016) reacting to the player's actions as well as commands from the Macro AI.
The alien will be guided to an area that the player is in by the Macro AI and start searching around the area using its sensors and reacting to any noise created by the player, this means "you can fool it, you can surprise it and you can escape it". (AI and Games, 2016).
There is an overarching Utility AI that helps to control the aliens tasks, states and target location. The Utility AI controls the priority of which the alien should act, should the alien blend between actions and animations or should everything be dropped and the alien execute the new action immediately? Such as the player making a noise in a room next to the alien would immediately cause the alien to come and investigate.
The Utility AI keeps the alien within two main states, an active and passive state. The active state is used while the alien is actively searching for the player increasing tension, while the passive state will be activated should the menace gauge become too full and require the alien to leave the player alone for a short while.
The alien is driven by a Behaviour Tree that contains over 100 nodes, with around 30 top layer nodes that help the alien to select which behaviour to be using at that current moment. When players first start the game, certain sections of the behaviour tree are locked off from the alien. These sections will be unlocked when certain conditions are triggered by the player. This gives the alien a sense of realism as its behaviour begins to change over the course of the game, such as beginning to look inside lockers. This is to create the illusion to the player that the AI is learning from their behaviours. However, the 'learn-rate' for the alien can vary depending on how the player interacts with the world, if the player does not trigger certain specific requirements to unlock sections of the behaviour tree, there are triggers placed at certain checkpoints that will unlock these sections.
While the Macro AI is managing the world around the player and directing the alien to certain locations, the alien itself is controlled by the Micro AI. Which is made up of a "series of sensors and behaviours that allow it to hunt down and find the player" (AI and Games, 2016) reacting to the player's actions as well as commands from the Macro AI.
The alien will be guided to an area that the player is in by the Macro AI and start searching around the area using its sensors and reacting to any noise created by the player, this means "you can fool it, you can surprise it and you can escape it". (AI and Games, 2016).
There is an overarching Utility AI that helps to control the aliens tasks, states and target location. The Utility AI controls the priority of which the alien should act, should the alien blend between actions and animations or should everything be dropped and the alien execute the new action immediately? Such as the player making a noise in a room next to the alien would immediately cause the alien to come and investigate.
The Utility AI keeps the alien within two main states, an active and passive state. The active state is used while the alien is actively searching for the player increasing tension, while the passive state will be activated should the menace gauge become too full and require the alien to leave the player alone for a short while.
The alien is driven by a Behaviour Tree that contains over 100 nodes, with around 30 top layer nodes that help the alien to select which behaviour to be using at that current moment. When players first start the game, certain sections of the behaviour tree are locked off from the alien. These sections will be unlocked when certain conditions are triggered by the player. This gives the alien a sense of realism as its behaviour begins to change over the course of the game, such as beginning to look inside lockers. This is to create the illusion to the player that the AI is learning from their behaviours. However, the 'learn-rate' for the alien can vary depending on how the player interacts with the world, if the player does not trigger certain specific requirements to unlock sections of the behaviour tree, there are triggers placed at certain checkpoints that will unlock these sections.
Reference List
[1] Keogh, B. and Jayemanne, D. (2018). “Game Over, Man. Game Over”: Looking at the Alien in Film and Videogames. Arts, [online] 7(3). Available at: https://www.mdpi.com/2076-0752/7/3/43/htm [Accessed 4 Oct. 2018].
[2] Thompson, T. (2016). The AI of Alien: Isolation | AI and Games. [online] Available at: https://www.youtube.com/watch?v=Nt1XmiDwxhY [Accessed 2 Nov. 2018].
[3] Thompson, T. (2017). The Perfect Organism: The AI of Alien: Isolation. [online] Gamasutra.com. Available at: http://www.gamasutra.com/blogs/TommyThompson/20171031/308027/The_Perfect_Organism_The_AI_of_Alien_Isolation.php [Accessed 9 Oct. 2018].