NPC movement

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January 2024

This is a list of important components of an NPC movement schedule and task. One day it may end up as a full tutorial.

Schedule tasks

All of these tasks can be found in CAI_BaseNPC::StartTask(). Their TASK_ prefixes have been removed for readability.

Find targets

GET_PATH_TO_PLAYER

Sets the NPC's goal to the player's location at the time of calculation.

WANDER <int|min_dist * 10000 + int|max_dist>

Pick a random location for a goal. The parameter is complex because it is actually two values forced into one.

GET_PATH_TO_ENEMY_LOS

GET_FLANK_RADIUS_PATH_TO_ENEMY_LOS

GET_FLANK_ARC_PATH_TO_ENEMY_LOS

GET_PATH_TO_ENEMY_LKP_LOS

Various hostile-related goal selection tasks.

FIND_COVER_FROM_BEST_SOUND

FIND_HINTNODE

FIND_LOCK_HINTNODE

Walk/Run

WALK_PATH

RUN_PATH

WALK_PATH_FOR_UNITS <units>

RUN_PATH_FOR_UNITS <units>

WALK_PATH_WITHIN_DIST <units>

RUN_PATH_WITHIN_DIST <units>

Basic movement tasks. WITHIN_DIST are useful when the target itself isn't accessible, e.g. is an entity's origin.

RUN_PATH_FLEE <units>

Run this many units. Won't set a goal though, so use it in conjunction with another task.

WALK_PATH_TIMED <float|seconds>

RUN_PATH_TIMED <float|seconds>

Wait this many seconds, then move.

Bug:Seems to be broken.

WEAPON_RUN_PATH

ITEM_RUN_PATH

Move to pick up a weapon or item; fail if it is picked up or otherwise removed.

SCRIPT_RUN_TO_TARGET

SCRIPT_WALK_TO_TARGET

SCRIPT_CUSTOM_MOVE_TO_TARGET

For scripted movement.

MOVE_TO_TARGET_RANGE

MOVE_TO_GOAL_RANGE

Move within weapons range. Identical, except that one uses a goal while the other uses a target entity.

GET_PATH_AWAY_FROM_BEST_SOUND

MOVE_AWAY_PATH

Turning/Facing

TURN_RIGHT

TURN_LEFT

FACE_ENEMY

FACE_PLAYER

FACE_HINTNODE

FACE_LASTPOSITION

FACE_SAVEPOSITION

FACE_AWAY_FROM_SAVEPOSITION

FACE_TARGET

FACE_IDEAL

FACE_SCRIPT

FACE_PATH

FACE_REASONABLE

SavePosition

STORE_POSITION_IN_SAVEPOSITION

STORE_BESTSOUND_IN_SAVEPOSITION

CLEAR_LASTPOSITION

STORE_LASTPOSITION

TASK_STORE_BESTSOUND_REACTORIGIN_IN_SAVEPOSITION

TASK_STORE_ENEMY_POSITION_IN_SAVEPOSITION

TASK_FIND_BACKAWAY_FROM_SAVEPOSITION

Utility

WAIT_FOR_MOVEMENT <float|seconds>

Wait this long for any ongoing movement to complete (pass 0 to wait forever if necessary). A very common task.

WAIT_FOR_MOVEMENT_STEP <float|seconds>

Same as above, but fails if the goal is a cover location which a hostile has LOS to.

Tip: Given the name, Valve presumably intended this task to handle all sorts of "mid-stride" fails that didn't make good interrupts. This makes it a good place to add your own!

SET_ROUTE_SEARCH_TIME <seconds>

Maximum time to spend building a route. The schedule will fail if it is overrun. Remember that different CPU speeds will give different results - don't use it except as a fail-safe.

STOP_MOVING

Like, duh.

Task functions

General

SetTarget( CBaseEntity )

The NPC's target is the entity it is acting upon - moving towards, looking at, shooting at, etc. Theoretically, multiple targets can be acted upon in the same frame by changing this value over the course of execution.

GetNavigator()->

The NPC's CAI_Navigator instance, which defines the core movement functions.

SetGoal(const AI_NavGoal_t &goal, unsigned int flags = 0)

The standard function for telling an NPC where it should head to when next given the command to move. Can be called with only a vector thanks to an AI_NavGoal_t overload.

SetDirectGoal( vector &goalPos, Navigation_t navType = <npc default> )

Bypasses much of SetGoal's code. Purpose is unclear.

SetArrivalDirection( vector || qangle || CBaseEntity )

The direction to face on arrival at the task goal. The NPC will probably begin turning shortly before arrival.

Tip: If a CBaseEntity is passed the NPC will turn to look at it. To use an entity's angles themselves, call GetAbsAngles().

StopMoving( bool bImmediate )

bImmediate doesn't seem to have any effect on walking NPCs - they stop immediately either way.

GetTacticalServices()->

Combat movement functions.