AI: Difference between revisions

==Combat behavior part 3: "They see me shootin', they hatin'..."==

Back in 2001 Oni was highly praised for its mixture of shooting and hand to hand combat. Now what could AI designers of Oni possibly do to make AI characters aim, pull a trigger or to make them avoid being hit by enemy? In this section, [[ONWC]], together with [[ONCC]] and [[PAR3]] will tell the story.

:First let's look into [[ONCC]] file. In XML file, under <AIConstants>, there's a tag named <Flags>. In binary file it is a bitset, so more than one flag can be written into it. XML strings for flags are:

:*noStartleAnim - Disables startle animation when AI sees the enemy for the first time.

:*EnableMeleeDodge - Enables firingspread/projectile dodging when AI is in pathfinding mode or combat melee mode

:*RunAwayDodge - Enables firingspread/projectile dodging even when AI itself is shooting a gun. AI character stops shooting and tries to move away from the danger area.  

:*ShootDodge -  Enables firingspread/projectile dodging even when AI itself is shooting a gun. AI character keeps shooting its enemy while at the same time attempts to move away from the danger area.  

:*NotUsed - Some ONCC character have this bit set, however it looks like it does nothing.

[[File:Firingspread.PNG|thumb|right|alt=Example of a firingspread.|Example of a firingspread.]]

[[File:Projectile.PNG|thumb|right|alt=Example of a particle with AI projectile dodge radius.|Example of a projectile with AI dodge radius (blue sphere).]]

'''Gunfire dodging mechanics'''. Gunfire dodging mechanics is a quite interesting part of Oni AI system. Interesting because the retail version features little to no such a behavior displayed which is sad because it gives a feeling of challenge to a gunplay. In order to make AI character perform dodge mechanics, this AI must be in combat mode with some enemy. Without combat mode and some enemy, AI character won't dodge. Next, AI characters perform dodge when the character intersects with:

:*Firingspread - can be seen by '''ai2_showfiringspreads=1'''. Firing spread is an invisible prism (dimensions set in [[ONWC]]) which can be created when a weapon is fired. Not every gun has a firingspread as for some guns firingspread is useless (SCRAM cannon, SuperBall gun). If AI character can dodge gunfire and intersects with a firingspread, this AI character starts gunfire dodging mechanics.

:*Projectile - epic win of Oni modders, can be seen with '''ai2_showprojectiles=1'''. In retail version of Oni, projectile dodging '''is defunct''' due to a couple of bugs in a projectile dodging code. Since the engine hackers/modders '''fixed this issue''', AI characters can execute gunfire dodge mechanics versus [[PAR3]] particle, if these AIs are in combat mode with some enemy and the particle has set <AIDodgeRadius> to a positive non-zero value.

:Parameter of projectile dodging in particle system [[PAR3]] is AI dodge radius (AIDodgeRadius).

:[[ONWC]] parameters for targeting and prediction (xml tags in parentheses):

:*Prediction speed (PredictionSpeed) - More precisely "projectile prediction speed". This value is taken by prediction algorithm as a speed of a projectile fired with the corresponding fire mode of the [[ONWC]] weapon. Thus when actual [[PAR3]] projectile's speed is changed, prediction behavior produces misleading values (AI is unable to hit moving targets).

:*Maximal inaccuracy angle (MaxInaccuracyAngle) - Maximal allowed deviation of aim from the enemy's character pelvis in order to keep firing the weapon. If exceeded, AI ceases fire and corrects aiming, the resumes fire. Pelvis is taken as a root point of the character, so without any extra chages done to targeting origin and targeting vector (see [[ONWC]]) AI characters always target pelvis of the enemy.

:*Aim radius (AimRadius) - no idea what it does.

:*Ballistic projectile speed (ProjectileSpeed) - special prediction can be used if weapon is meant to fire relatively slow but gravity affected projectiles (grenades). AI then adjusts aiming in order to hit enemy with the projectile according to the ideal (parabolic) ballistic curve. This is a horizontal speed component.

:*Ballistic projectile gravity (ProjectileGravity) - vertical gravity attraction for the projectile.

:*Targeting direction (Direction) - Vector with three components (x, y, z) which gives orientation of a firingspread. When set to wrong values, firingspread will not cover area where the weapon shoots, but will be pointing in some other direction ( can even point backwards ^_^). Friendly advice: do not alter unless needed.

:*Targeting origin (Origin) - Vector with three components (x, y, z) which tells AI where to fire according to enemy's pelvis position. When armed AI is in combat mode with the enemy and shoots him, the AI searches for pelvis (see [[TRIA]]) as the pelvis is the only bone recognized by AI system. For AI, pelvis is a representation of a whole character. Now when AI fires at its enemy, the AI aims for pelvis. The vector described in this parameter tells AI where and how much to deviate from enemy's pelvis position.

::So when the vector is set as (0, 0, -2), AI will aim and fire at enemy's pelvis position + two units above. That means AI will fire ABOVE the pelvis position. Here is described effect of setting "x,y,z" from SHOOTER's point of view. First to positive, then to neative value:

::*x - deviate forward/backward (does not have much of an effect)

'''Miscellaneous [[ONWC]] AI setup''' - there are a few more parameters in ONWC which affect AI behavior with the weapon. They are (xml tags in parentheses):

:*Minimal shooting distance (MinShootingDistance) - defines how close can enemy be to the armed shooting AI character. If enemy comes closer than this distance, AI stops shooting and tends to move back a bit (vector type of movement, see [[#Pathfinding and movement|HERE]]) until the distance is again equal or greater than Minimal shooting distance. Then AI opens fire again. To witness the effect, see some AI operating an SBG when its enemy is close to it.

::'''IMPORTANT''' - for some unknown reason, value from this field is '''divided by 2'''. So when 100 is set, ingame AI starts backing when its enemy is 50 units close to it.

:*Maximal shooting distance (MaxShootingDistance) - contrary to the parameter described above, this limits how far can enemy be till the AI stops shooting and tends to come closer. See some AI character shooting with w2_sap at distant enemy.

:*Fight timer (FightTimer) - a bit similar to timer-based BSL command '''chr_dontaim'''. Defines in frames for how long should AI switch from a weapon varient (shooting) to a melee varient (hand to hand combat) if this firing mode was used (don't forget, weapon can has two firing modes) and certain conditions were met. See below for ''KnockdownSwitcher'' and ''StunSwitcher'' flags explanations.

:*basic parameters of a weapon (pistol or rifle type, type of ammunition etc.) can be set as a various flags in [[ONWC]] flags field (<Flags> in xml). These three flags from them affect AI behavior (xml tags in parentheses):

:**NoHolster - apart from holster disabled, this flag also makes AI character ignore this weapon on the ground. One exception is w10_ba1 when AI character has set Superammo flag (InfiniteAmmo in xml) in its [[CHAR]] profile, then this AI character can pick up WMC cannon. If AI character is given the weapon it will fire it, but if the weapon is lying on the ground and AI character does not have superammo flag, this AI character will never pick it up.

:**Stun switcher (StunSwitcher) - if the enemy is within armed AI character's shooting distance and was knockdowned, stunned or blownupped, the AI character switches to a melee for a time specified in the weapon's Fight timer (see above). The flag was designed specially for w6_vdg weapon.

:**Knockdown switcher (KnockdownSwitcher) - Similar to Stun switcher, but only knockdown or blownup makes AI switch to melee. Tailored for w4_psm, probably to avoid AI abuse of an unfair advantage the w4_psm weapon grants (enemy cannot get up as long as she/he is shot).

Modding hints: Phew, what a long section. Described material has plenty of modding possiblities. Still, modders should be aware of a few things:

:*Don't set too strong dodge vector (DodgeWeightScale) and don't overdo it with dodge timer (DodgeTimeScale, the smallest possible value is 0.4; lower is not registered). Delay before gunfire dodging (DodgeReactFrames) should be minimal, otherwise it can happen AI won't start dodging till shooter's weapon is empty.

::As a side note, there is a glitch in gunfire dodging. It is not a coding bug, but simple limitation of a "vector" type of movement. When AI starts gunfire dodge, it tries to get away from the source of danger (be it firingspread or projectile). And because vector movement works as a "desire" to go to some direction, it can happen AI will express a "desire" to go into wall. In such a case, character stops until the desire to move into a wall stops (in other words, until enemy stops shooting the AI character). When AI character is unarmed, she/he will try to switch between pathfinding movement (to go to enemy and attack him with melee) and vector projectile dodge movement, so it kind of looks like the AI still tries to dodge the gunfire. If weight of a gunfire dodge is set to be smaller than standard vector movement type weight, then AI even does not have to get stuck as it will run in zig-zag pattern towards the armed enemy.

::In case AI is armed with a loaded weapon, there is no point in AI running towards enemy. That means if the AI character starts dodging and meets a wall, this AI character gets "stuck" until enemy's gunfire stops. In case this character has set "ShootDodge" in [[ONCC]], it will at least fire back at the enemy shooter. But in case the character has set "RunAwayDodge", then it simply stands near the wall and stares and waits till enemy's gunfire ceases.

::From the text above it can be seen that gunfire dodge parameters should be set to make AI dodge but to not make dodge vector outweight the vector for moving towards the enemy.

:*AI's skills with weapons (in [[ONCC]]) can be used greatly to create sharpshooters or rookies who cannot hold a gun properly. For example by setting "ShootGroupError = 10.0" for w1_tap, we create a total amateur who's hand shakes all over the place when he fires Campbell equalizer.

:*Unless really needed, do NOT alter [[ONCC]] prediction parameters. Bungie set them quite reasonably and if they are messed, AI character loses the ability of prediction.

:*In [[ONWC]], Prediction speed is used for a calculation of AI's aim. The value should be exactly the same as the value of this weapon's projectile. Projectile's velocity is usually set in a emitter of a projectile particle ([[PAR3]]). That means Prediction speed and actual speed of a particle used as weapon's projectile may differ, the most significant case being w3_phr (plasma balls accelerate rapidly).

::If Prediction speed is set lower than the speed of a projectile is, AI will tend to shoot too much in front of the moving enemy since it will assume projectile is slower than it really is. On the other side, setting this value higher means AI will shoot more directly at the moving enemy (and probably miss) as the AI will assume projectiles are fast enough to hit the target.  

:*Similar to Prediction speed, there are Ballistic projectile speed and Ballistic projectile gravity. When these two are set non-zero, AI assumes ballistic projectiles (grenades) and tries to shoot projectiles according to an ideal parabole (the solution with shorter fly time is always chosen). In order to make AI sucesfully hit enemy's pelvis, these two must again corespond with [[PAR3]] particles's speed and particles's gravity attraction, but they can be used for modding purposes as well. For example if projectiles's gravity attaction is 0.5 but in [[ONWC]] Ballistic projectile gravity is set as 0.3, AI will shoot projectiles at enemy's feet as it will assume that gravity attraction of the projectile is lower thus it does not have to aim so high in order to hit the pelvis (credits to [[user:Gumby|Gumby]]). Remember: for AI system, pelvis is a representation of a whole character.

:*Targeting origin vector ([[ONWC]]) can be utilized to make AI fire not directly at pelvis, but for example higher (negative "z" component), so AI can score headshots. So far such a change does not have any purpose as characters don't have damage multipliers for bodyparts. But maybe in future...or with Paradox's headshot mod / material dependent damage mod ideas (see [[XML:BINA/ONIE#Extra_damage_for_head_hits|HERE]]).

:*One thing purposefully left out in main talk about weapons is that there is an option for AI chracters to make "startle" misses - when startled, AI fires at some random direction. Parameters for this behavior are in [[ONCC]] and [[ONWC]], but overall this feature is so subtle it does not need any special modding attention.

:*Remember: in [[ONWC]], Minimal shooting distance is '''divided by 2'''. Reason is unknown, maybe some bug in a code.

:*Through modification of Minimal shooting distance in conjunction with BSL scripting, a modder can achieve pseudo-dynamic holster behavior. If enemy gets too close, AI start moving away, facing the enemy. Since simply backing away is almost never used by armed AI (it usually move to the side), it can be detected via BSL function '''chr_wait_animation''' and subsequent script makes AI character holster held weapon. To unholster, different animation check has to be used, for example a check for a taunt animation. In [[MELE]], modder can set up approppriate melee profile which makes AI character taunt only at safe distance.  

::Drawback of this modification is is that enemy ''will not fire the weapon at point blank range'' and also it limits Melee override in [[CMBT]] to be only None or IfPunched, otherwise instead of backing away, AI character goes directly into melee.