npc_helicopter

Class hierarchy
CNPC_AttackHelicopter ↳CBaseHelicopter ↳CAI_BaseNPC ↳CBaseCombatCharacter ↳CBaseFlex ↳CBaseAnimatingOverlay ↳CBaseAnimating ↳CBaseEntity
npc_attackchopper.cpp

npc_helicopter is a point entity available in Half-Life 2 series, Portal, and Alien Swarm.

It is a Combine helicopter (also called a Hunter-Chopper), armed with a machine gun and capable of dropping mines. The mines are buoyant, and their timer only activates when they collide with the environment. Upon touching an NPC they detonate instantly. They can be dropped one at a time, or when triggered the helicopter can rush a target dropping a massive amount of mines.

This NPC only uses path_track for navigation: When the helicopter finds an enemy, it moves along a chain of path_tracks to the closest one to its target.

Related Entities:

• npc_heli_avoidbox is a brush entity that the helicopter will avoid.
• npc_heli_avoidsphere is an entity that keeps helicopters out of a spherical area.
• npc_heli_nobomb is an entity that suppresses helicopter bombing
• helicopter_bomb is a bomb that the helicopter can drop
• helicopter_chunk is helicopter debris created when helicopter is destroyed
• env_rotorwash_emitter is helicopter's rotor wash.
• env_rotorshooter
• npc_helicoptersensor

Tip:Use info_target_helicopter_crash entities to suggest spectacular crashing points for defeated helicopters.

Placement Tip:Hunter-Choppers are used mainly in the Half-Life 2 series as chase vehicles, hence the name.

Placement Tip:Helicopter battles require the player to be very mobile, and have some cover available to them. Just one can present a great challenge, so like striders use them sparingly.

Note:Some keyvalues, spawnflags, effect flags, inputs, or outputs might not affect an NPC, based on the functionality and coding of the NPC.

Bug:When npc_helicopter that's waiting for Activate input is killed, game crashes!  [todo tested in ?]

Destruction

When a helicopter is destroyed, three helicopter_chunks are created at its crash location along with a random number of smaller gibs.

Keyvalues

Name (targetname) <string>

The name that other entities refer to this entity by, via Inputs/Outputs or other keyvalues (e.g. parentname or target).
Also displayed in Hammer's 2D views and Entity Report.

See also:  Generic Keyvalues, Inputs and Outputs available to all entities

Initial Speed (InitialSpeed) <float>

Grace Period (GracePeriod) <float>

Time in seconds the helicopter has to see the player before it starts shooting.

Patrol Speed (PatrolSpeed) <float>

Speed at which the helicopter moves if it has no enemy.

BaseHelicopter:

Initial Speed (InitialSpeed) <string>

The speed that the entity should try to reach as soon as it spawns

Target path_track (target) <targetname>

The name of a path_track that this NPC will fly to after spawning.

BaseNPC keyvalues

CBaseCombatCharacter: Relationship (Relationship) <string> !FGD <string|targetname or classname> <string|disposition> <int|rank> Changes whether this entity likes or dislikes certain other things. Used like the ai_relationship entity, with this entity as the subject. Values for disposition are: D_HT: Hate D_FR: Fear D_LI: Like D_NU: Neutral Physics Impact Damage Scale (physdamagescale) <float> Multiplier for damage amount when this entity is hit by a physics object. With a value of 0 the entity will take no damage from physics. CAI_BaseNPC: Target Path Corner (target) <targetname> The path_corner that this NPC will move to after spawning. Squad Name (squadname) <string> NPCs that are in the same squad (i.e., have matching squad names) will share information about enemies and will take turns attacking and covering each other. Hint Group (hintgroup) <string> Hint groups are used by NPCs to restrict their hint-node searching to a subset of the map's hint nodes. Only hint nodes with matching hint group names will be considered by this NPC. Hint Limit Nav (hintlimiting) <boolean> Limits NPC to using specified hint group for navigation requests. Does not limit local navigation. Sleep State (sleepstate) <choices> Holds the NPC in stasis until specified condition. See also Wake Radius and Wake Squad. 0: None 1: Waiting for threat 2: Waiting for PVS 3: Waiting for input, ignore PVS 4: Auto PVS 5: Auto PVS after PVS Wake Radius (wakeradius) <float> Auto-wake if player comes within this distance. Wake Squad (wakesquad) <boolean> Wake all of the NPCs squadmates if the NPC is woken. Enemy Filter (enemyfilter) <targetname> Filter entity to test targets against. Ignore unseen enemies (ignoreunseenenemies) <boolean> Prefers visible enemies, regardless of distance or relationship priority. DamageFilter: Damage Filter (damagefilter) <targetname> Name of the filter_damage_type entity that controls which entities can damage us.

Flags

Wait Till Seen : [1]

Gag (No IDLE sounds until angry) : [2]

Fall to ground (unchecked means *teleport* to ground) : [4]

Drop Healthkit : [8]

Efficient - Don't acquire enemies or avoid obstacles : [16]

No Rotorwash : [32]

Await Input : [64]

Wait For Script : [128]

Long Visibility/Shoot : [256]

Fade Corpse : [512]

Think outside PVS : [1024]

Template NPC (used by npc_maker, will not spawn) : [2048]

Do Alternate collision for this NPC (player avoidance) : [4096]

Don't drop weapons : [8192]

Loud rotor wash sound : [65536]

Electrical drone : [131072]

Helicopter lights : [262144]

Ignore avoid spheres+boxes : [524288]

More aggressive attacks : [1048576]

Inputs

StartBombingVehicle

Starts the chopper leading enemy vehicles and dropping bombs on them.

StartTrailingVehicle

Starts the chopper trailing enemy vehicles and shooting at them.

StartDefaultBehavior

Starts the chopper in the mode where he always stops at nav points instead of stopping anywhere in between nav points.

StartAlwaysLeadingVehicle

Starts the chopper *always* leading enemy vehicles (regardless of how they are moving w/respect to the path) and dropping bombs on them. This mode is different from StartBombingVehicle in that it never uses the machine gun.

StartSprinkleBehavior

Starts the chopper dropping bombs randomly + shooting at the player.

StartBullrushBehavior

Starts the chopper bullrushing the player.

SetHealthFraction <float>

Sets the chopper health as a percentage of max health.

EnableDeadlyShooting

Starts the chopper being deadly to on-foot players.

DisableDeadlyShooting

Stops the chopper being deadly to on-foot players.

StartNormalShooting

The chopper will fire in short bursts. Good for on-foot experiences.

StartLongCycleShooting

The chopper fires in long bursts.

StartContinuousShooting

The chopper fires continuously.

ResetIdleTime

Allows the helicopter to fire immediately if he's not in the middle of charging or firing.

SetAngles <angles>

Instantly snaps the orientation of the helicopter.

DropBomb

Immediately drops a bomb based on normal bomb dropping rules.

DropBombStraightDown

Immediately drops a bomb directly downwards.

DropBombAtTarget <targetname>

Immediately drops a bomb directly at the target destination, but only if the player isn't right there.

DropBombAtTargetAlways <targetname>

Immediately drops a bomb directly at the target destination, no matter whether it's fair or not.

DropBombDelay <float>

Add a delay before the next bomb is dropped.

BecomeIndestructible

Makes the helicopter take no more damage.

DisablePathVisibilityTests

When the helicopter moves, he will not check for visibility from the path_track to the enemy to cull out path_tracks.

EnablePathVisibilityTests

When the helicopter moves, he will only move to path_tracks that have line-of-sight to the enemy.

BaseHelicopter

MoveTopSpeed The helicopter will immediately move at top speed toward its current goal, or in its current orientation if it's on top of its goal. MoveSpecifiedSpeed <float> The helicopter will immediately move at the specified speed (you provide this as parameter override in units per second) towards its current goal. ChangePathCorner <targetname> Tell the helicopter to move to a path corner on a new path. SelfDestruct Self Destruct. Activate Activate. Use to wake up a helicopter that spawned with the 'Await Input' spawnflag on. SetTrack <targetname> Set a track for the helicopter to adhere to. The helicopter will do nothing if it's on the same path, and will move to the closest point on the specified track if it's on a different path. FlyToSpecificTrackViaPath <targetname> The helicopter will first fly to the closest point on the path if it's on a different path. Then it'll fly along the path to the specified track point. FlyToPathTrack <targetname> The helicopter will fly to the given path_track. StartPatrol Start patrolling back and forth along the current track. StopPatrol Stop patrolling back and forth along the track. This will cause the helicopter to come to rest at the track which he's currently flying toward. ChooseFarthestPathPoint When tracking an enemy, choose the point on the path furthest from the enemy, but still in firing range. ChooseNearestPathPoint When tracking an enemy, choose the point on the path nearest from the enemy. StartBreakableMovement The helicopter is now allowed to disobey direct commands to go to particular points if it senses an enemy. It will move to the closest point (or farthest point, if ChooseFarthestPathPoint is used), on the path if it senses an enemy. StopBreakableMovement The helicopter can no longer disobey direct commands. It will continue to fly along it's patrol path or to it's specified target even if it senses an enemy. EnableRotorSound Starts the chopper's rotors making noise (normal behaviour) DisableRotorSound Stops the noise made by the rotors EnableRotorWash Makes the chopper exert a force on physics objects underneath its rotor, and produce a wind pattern on any water (normal behaviour) DisableRotorWash Turns off the forces and wind pattern SetAngles  !FGD InputStartLeading  !FGD InputStopLeading  !FGD GunOn Allows the chopper to use its gun (normal behaviour) GunOff Prevents the chopper from using its gun MissileOn Starts the chopper firing rockets Bug:Non-functional.  [todo tested in ?] MissileOff Stops the chopper firing rockets Bug:Non-functional.  [todo tested in ?]

BaseNPC inputs 

CAI_BaseNPC:

ActivateSpeedModifier  !FGD

DisableSpeedModifier  !FGD

Break

Smash into pieces. If this is not possible, disappear.

BecomeRagdoll  (in all games since )

Remove itself and instantly become a ragdoll with zero force (just go limp). OnDeath, etc. outputs will NOT be fired.

ForceInteractionWithNPC <string> <string>  (in all games since )

Force the NPC to use a dynamic interaction with another NPC. Syntax is <targetname> <dynamic interaction>.

ForgetEntity <targetname>

Clears out the NPC's knowledge of a named entity.

UpdateEnemyMemory  (in all games since )

Update (or create) this NPC's memory of of the given entity.

GagEnable

GagDisable

Gagged NPCs won't speak (or moan, caw, etc.) unless made to be a choreographed scene.

HolsterWeapon  (in all games since )

UnholsterWeapon  (in all games since )

Force the NPC to holster or unholster their weapon. Ignored if the NPC is scripting or if the NPC doesn't use weapons.

HolsterAndDestroyWeapon  (in all games since )

Same as HolsterWeapon, except the weapon is destroyed once it has been concealed.

IgnoreDangerSounds <float>

Ignore danger sounds for the specified number of seconds.

InsideTransition  !FGD

OutsideTransition  !FGD

SetBodyGroup <integer>

HACK: Sets this NPC's body group (from 0–n).

SetEnemyFilter <string>

SetHealth <integer>

Set the NPC's health.

SetMaxLookDistance <float> (only in )

Sets the maximum look distance for the NPC. Defaults are 2048 and 6000 for long range NPCs.

SetRelationship <string|targetname or classname> <string|disposition> <int|rank>

Changes whether this NPC likes or dislikes certain others. Used like the ai_relationship entity, with this NPC as the subject.

Values for disposition are:

• D_HT: Hate
• D_FR: Fear
• D_LI: Like
• D_NU: Neutral

SetSquad <string>

Change the name of this NPC's squad. Leaving the parameter blank will remove the NPC from any existing squad.

StartScripting

StopScripting

Enter/exit scripting state, where NPCs ignore a variety of stimulus that would make them break out of their scripts. They ignore danger sounds, ignore +Use, don't idle speak or respond to other NPCs' idle speech, and so on.

Wake

Wakes up the NPC if it is sleeping.

CBaseCombatCharacter:

KilledNPC  !FGD

Tells the entity it killed something. Despite the name, this can include a player. This input will be automatically sent by the victim when they die.

physdamagescale <float>

Scales damage energy when this character is hit by a physics object. With a value of 0 the NPC will take no damage from physics.

DamageFilter:

SetDamageFilter <string>

Sets the entity to use as damage filter. Pass in an empty string (no parameter) to clear the damage filter.

Outputs

OnHealthChanged <integer>

Fires when the helicopter health changes. The integer is the percentage of health the chopper has from 0-100.

OnShotDown

Fires when the helicopter is killed. When an info_target_helicopter_crash entity is present, this output should be used instead of OnDeath.

BaseNPC Outputs

OnDamaged Fired when this NPC takes damage (!activator is the damage inflictor). OnDamagedByPlayer Fired when this NPC is hurt by a player (!activator is the attacker or vehicle driver [if friendly fire]). OnDamagedByPlayerSquad Fired when this NPC is hurt by a player OR by one of the player's squadmates (!activator is the attacker or vehicle driver [if friendly fire]). OnDeath Fired when this NPC is killed (!activator is the killer). OnDenyCommanderUse Fired when this NPC has refused to join the player's squad. OnForcedInteractionAborted Fired when the NPC aborts a forced interaction for some reason (target NPC died, couldn't be pathed to, etc.). OnForcedInteractionStarted Fired when the NPC starts a forced interaction. OnForcedInteractionFinished "NPCs in actbusies can no longer perform dynamic interactions." Todo: What does this mean? OnHalfHealth Fired when this NPC reaches half of its maximum health. OnHearCombat Fired when this NPC hears combat sounds. OnHearPlayer Fired when this NPC hears the player. OnHearWorld Fired when this NPC hears a sound (other than combat or the player). OnFoundEnemy <targetname> Fired when this NPC establishes line of sight to its enemy. OnLostEnemy Fired when this NPC loses its enemy. Usually due to the enemy being killed/removed, or because this NPC has selected a newer, more dangerous enemy. OnLostEnemyLOS Fired when this NPC loses line of sight to its enemy. OnFoundPlayer <targetname> Fired when this NPC establishes line of sight to its enemy, and that enemy is a player. OnLostPlayer Fired when this NPC loses its enemy, and that enemy was a player. Usually due to the enemy being killed/removed, or because this NPC has selected a newer, more dangerous enemy. OnLostPlayerLOS Fired when this NPC loses line of sight to its enemy, and that enemy is a player. OnSleep Fired when this NPC enters a sleep state. OnWake Fired when this NPC comes out of a sleep state.

Dedicated Console Variables

Cvar/Command	Parameters or default value	Descriptor	Effect
sk_helicopter_health	5600	int	Helicopter Spawn Health.
sk_helicopter_firingcone		float	The angle in degrees of the cone in which the shots will be fired.
sk_helicopter_burstcount		int	How many shot bursts to fire after charging up. Bigger number = longer firing.
sk_helicopter_roundsperburst		int	How many shots to fire in a single burst.
sk_helicopter_grenadedamage		float	The amount of damage the helicopter grenade deals.
sk_helicopter_grenaderadius		float	The damage radius of the helicopter grenade.
sk_helicopter_grenadeforce		float	The physics force that the helicopter grenade exerts.
sk_npc_dmg_helicopter_to_plr		float	Damage helicopter shots deal to the player. Used in ammotype "HelicopterGun".
sk_npc_dmg_helicopter		float	Damage helicopter shots deal to everything but the player.Used in ammotype "HelicopterGun".
sk_helicopter_drone_speed		float	How fast does the zapper drone move?
g_helicopter_chargetime		float	How much time we have to wait (on average) between the time we start hearing the charging sound + the chopper fires.
g_helicopter_bullrush_distance		float	Todo: Effect description.
g_helicopter_bullrush_bomb_enemy_distance		float	Todo: Effect description.
g_helicopter_bullrush_bomb_time		float	Todo: Effect description.
g_helicopter_idletime		float	Todo: Effect description.
g_helicopter_maxfiringdist		float	Todo: Effect description.
g_helicopter_bullrush_bomb_speed		float	Todo: Effect description.
g_helicopter_bullrush_shoot_height		float	Todo: Effect description.
g_helicopter_bullrush_mega_bomb_health		float	Todo: Effect description.