AI: Difference between revisions

An action game like Oni needs artificial intelligence-driven characters ("AIs" or "bots") and some sort of interaction amongst these characters and between them and the world. The goal is to make an AI act at least a bit like a human being. That means giving the AI abilities such as moving in the game world believably, and seeing, hearing, and reacting to events in the game world. Different games deal with these problems in various ways, but in this article, we will take a look at Oni and its AI.

==Pathfinding and movement==

Oni has two ways to make an AI move in a game world - pathfinding, and what could be called vector-based.

'''Pathfinding''' is used when AI-driven character needs to travel from one place to another. Examples of pathfinding movement are:

:*patrol paths - AI-driven character moves in a pre-designed fashion (see [[PATR]])

:Pathfinding utilizes an [[wikipedia:A*_search_algorithm|A* (A-star)]] algorithm to design routes for AI within the game world.

==Vision and hearing==

When emulating humans with AI, senses have to be taken into an account: sight, hearing, taste, smell, touch. Unfortunately, Oni emulates only sight and hearing.

:*Peripheral: an enemy seen by peripheral vision will raise the AI's alert level to low and the AI will go into pursuit of the enemy; see [[#Pursuit|Pursuit]] section

:For more info about AI alert levels, see section [[#Reactions and awareness|Reactions and awareness]]. These sound types are used by impact effects ([[ONIE]]), and a danger sound type can be set in a particle's as part of its "danger radius".

:Modding hints: The sound system and ONIE are mighty tools if a modder knows how to use them. Even doors can have attached to them a sound sphere of one of the types listed above, so a modder can create doors which draw the attention (sound type Interesting) of nearby AIs when those doors are used.

==Reactions and awareness==

:Pursuit behavior greatly depends on the AI's level of alert. There are four parameters regarding alert levels in the CHAR profile:

:*Initial: the AI is spawned with the specified level of alert

:*JobStart: the alert level of the AI when it starts some job (typically a patrol)

:*Investigate: From the alert level specified here, and all greater alert levels, the AI will tend to pursue any suspicious sound it hears or any hostile peripheral contact it makes

Modding hints: '''Pursuit mode complications and weird glitches'''

:*The pursuit distance parameter in CMBT is important in deciding whether the character should be more of a pursuer or more of a guard.

:*Within the pursuit distance, peripheral vision pursuit follows its own rules. When an AI sees an enemy with its peripheral vision, this AI always goes into weak awareness mode and either just glances in the direction of this enemy (alert level was below Investigate level) or moves to the spot and performs weak investigation pursuit behavior (alert level was at Investigate on higher).

In order to make the AI look more human, it is a good idea to grant it the ability to interact with the world the same way that the player does. In Oni, for example, that means giving the AI the ability to use consoles.

:BSL scripting provides a command to make an AI go and use a console: [[ai2_doalarm]]. This way, an AI can be told to use any console. But there is a method to make an AI use a console completely on it own.

:In order to utilize this mechanic, there is a need for a console which has the ALARM CONSOLE flag set (see [[OBD:BINA/OBJC/CONS]]). In XML this flag is called '''IsAlarm'''. Such a console then can be used by AI characters without scripting.

:*Another way of using alarm mechanics is to create a feeling of cooperation -- in order for the player to achieve something, an AI-driven sidekick must use a console.

==Basic combat behaviors==

Of course, an action game like Oni is not complete without guns blazing and fists flying through the air. But combat in real life is usually very fickle and everything has to be considered. How can Oni's AI possibly deal with such a complex task?

::Again, the annoying "over 550" height check is present.

:*Run for alarm (RunForAlarm): see section [[#Alarm behavior|Alarm behavior]].

:*Mutant Muro thunderbolt (MuroThunderbolt): Upon initial contact, the AI turns on chenille mode and runs toward the enemy. If chenille mode is turned off then, until definite awareness of the enemy is lost, this behavior will not cast chenille mode again. This behavior also allows the AI to use a special long range attack: the character turns off chenille, goes into AnimState 69 - Thunderbolt, and loops a special TRAM animation of AnimState 69 - Thunderbolt and AnimType 231 - Muro_Thunderbolt. That lasts for 10 seconds. Then the AI stops the animation for 5 seconds and runs toward the enemy. If, after those 5 seconds, the AI is still executing Mutant Muro thunderbolt behavior, the AI resumes the looping TRAM between AnimType 231 and 69.

::This behavior's special looping animation continues even when an enemy enters some another combat range, with the exception of Short range. If the enemy enters Short range while the looped animation is running, the loop is forced to stop and the AI starts using Short range behavior.

:*Barabbas Shoot and Barabbas Melee behaviors have access to a healing ability which can be a great asset for introducing mutants or stronger enemy units. However, remember that Barabbas Shoot limits rate of fire to one shot per three seconds.

:*Barabbas Advance is the only behavior which allows an AI to fire a weapon in its secondary fire mode. However the behavior is quite glitchy (the AI often looks away and fires stray shots). Still, with the proper gun and proper setup it can be useable for boss fights.

::One other important thing about these behaviors: if the AI does not have required the TRAMs in its [[TRAC]], the AI can get stuck if it uses these behaviors.

:*If there is no console with the ALARM CONSOLE flag within the Alarm search distance, then the behavior "Run For Alarm" will make an AI just stand and stare. Choose this behavior with caution, and consider using a workaround where Medium and Short combat ranges have very close radii, with Run For Alarm being the MediumRetreat behavior, so that the Run For Alarm behavior is executed only for a brief amount of time as the AI almost immediately switches to LongRetreat. Even one frame is enough, because if an alarm is found, the AI is requested to perform an alarm run which can override combat (see section [[#Alarm behavior|Alarm behavior]] for more info).

:*Alarm running: It is actually required if an alarm run is called via the no-gun alarm run behavior, otherwise glitches will appear.

:*Retreating behavior - When the no-gun behavior is set as "Retreat", an unarmed AI will try to run away from its enemy. However, if enemy meets the Melee override parameter (for example getting into the Short range while the melee override is set to ShortRange), then this AI stops running away and starts attacking the enemy.

:*Weapon pickup: if the AI is trying to pick up a weapon and an enemy crosses the range specified in MeleeOverride, then the weapon pickup behavior is overridden by melee.

:*Maybe some other aspects of AI behavior?

'''Weapon pickup behavior ([[ONCC]] file)''': When in combat mode, an unarmed AI can be told to move to a loaded weapon and pick it up or to swap a held, empty gun for a loaded gun which is lying on the floor. Overall, AIs can only register pickup-able weapons up to a distance of 60 world units (hardcoded). In the ONCC file, these parameters can be set to alter the gun pickup behavior (XML tags in parentheses):

:*Chance for pickup (GoForGunChance): percent chance of AI deciding to go and pick up a weapon. It seems that the weapon closest to the AI character is always chosen to be picked up.

'''Getting up after being knocked down (ONCC file)''': If an AI is knocked to the ground, it stays on the ground for a while (a simulation of being stunned), then gets up. In the ONCC file there are two parameters regarding getting up (XML tags in parentheses):

:If a knocked-down AI gets hit by melee, it gets up immediately after the hit. Being hit by weapons does not make AI character instantly get up. Standard get-ups are simple ones (the same result as if the knocked-down player hits a directional key). If the AI is in melee combat mode, its [[MELE]] profile has get-up attacks listed, and the enemy is within the required range, there is a chance that this AI will use a get-up attack instead of a simple get-up animation.

::Nevertheless, BSL does provide a function to make a character holster or unholster a weapon: [[chr_forceholster]]. In order to make a character holster a held weapon, this character has to be using a pistol or rifle animation variant (see [[TRAM]]). Since AI can use "walk_noaim" and "run_noaim" movement modes (which disable weapon variants, i.e., aiming with weapons), the weapon variant should be explicitly forced on via the BSL function [[chr_dontaim]]. Unholstering is easier: the character simply has to be be executing some aiming overlay-compatible animation at the moment when chr_forceholster is executed. That means standing, running, crouching, walking, and jumping are OK -- the function will succeed -- but attack animations or animations of getting hit are not OK and the function will fail.

::*IMPORTANT NOTE: The AI must be "active" all the time in order to perform BSL animation checks ([[chr_wait_animation]]/[[chr_wait_animtype|animtype]]/[[chr_wait_animstate|animstate]] checks). Remember that Oni was developed mostly in the '90s, so various tricks were used to save memory and enhance performance. One technique was to make unseen characters (behind a wall, closed doors, etc.) go into an "inactive" mode, which means they are only stored in RAM as a structure, but no physics, collision checks, or drawing functions are performed on them in order to save system resources (and yes, that means inactive characters can [https://www.youtube.com/watch?v=GC4HLDekxQI walk in mid-air and pass through walls]). On the other hand, when a character is active, it is fully operational, with physics working, collisions being checked, and character being ready in graphics memory to be drawn any time. To make sure a character stays active requires either applying [[chr_lock_active]] to each AI, or (since computers have a lot more memory these days) simply setting [[chr_all_active]] to 1 to force all characters active.

   #Setup of AI - gets spawned, forced to be always active, weapon gets holstered.

:*A melee override can be used together with the "Go For Gun" behavior and a properly-set Short combat range to create AIs who go for a gun any time they have a chance, yet they are not allowing an enemy to land free hits in the process (if the enemy gets too close, the Short range melee override kicks in).

:*Setting short get-up times is a good way to make an AI-driven character a formidable opponent in hand-to-hand combat. However, too-short get-up times can introduce problems. It is a good idea to experiment with get-up parameters till the character feels "natural".

:*NotUsed: Some characters have this bit turned on, however it looks like it does nothing.

'''Gunfire dodging mechanics'''. Gunfire dodging mechanics are quite an interesting part of Oni's AI system -- interesting because the retail version displays little to no such behavior, which is sad because it adds challenge to the gunplay. In order to make an AI perform gunfire dodging, this AI must be in combat mode with an enemy. Without combat mode and some enemy, AI character won't dodge. Additionally, an AI will only perform a dodge when the character senses one of these two things:

:*Firing spread. This can be seen by using [[ai2_showfiringspreads]]. The firing spread has the shape of a prism (its dimensions set in ONWC) which can be created when a weapon is fired. Not every gun has a firing spread, as for some guns a firing spread is useless (e.g. the Scram Cannon and Super Ball Gun). If an AI can dodge gunfire and intersects with a firing spread, this AI character starts its gunfire dodging behavior.

:*Shoot group decay (ShotGroupDecay): the random deviation of the target spot itself. The target spot is naturally based on the enemy's position. Can be set higher than 1.0.

:*Shooting inaccuracy multiplier (ShootingInaccuracyMultiplier): also controls the degree that the AI's aim strays from the target, but it's not clear how much it really affects aiming.

:*The basic parameters of a weapon (pistol or rifle, type of ammunition, etc.) can be set using various flags in the ONWC (<Flags> in XML). These three flags from among those affect AI behavior (XML tags in parentheses):

:**NoHolster: apart from disabling the ability to holster the weapon, this flag also makes the AI ignore this weapon when lying on the ground. One exception is w10_ba1 when the AI has the Superammo flag (InfiniteAmmo in XML) set in its CHAR profile; then this AI character can pick up the WMC cannon. If an AI is given the weapon, it will still fire it.

::From this explanation, it can be seen that the gunfire dodge parameters should be set to make the AI dodge, but to not make the dodge vector outweigh the vector for moving towards the enemy.

:*Unless really necessary, do NOT alter the ONCC prediction parameters. Bungie set them quite reasonably, and if they are messed with, the AI loses accurate predictive abilities.

Structure of a melee technique:

Modding hints: Creating custom MELE profiles can be fun, but beware of a few pitfalls: