npc_blob

npc_blob is a point entity available in Half-Life 2. It's an experimental, unused entity that would have been a swarm of entities (probably an insect of some kind such as Snarks from Half-Life) that surrounds and consumes its prey. Its behavior is functional, with a few bugs. Visuals and sounds are not finished at all, however. In the Half-Life 2 20th Anniversary Documentary, it was revealed that this NPC was originally meant to be used for Half-Life 2: Episode 3.

Games

1. Half-Life 2

Appearance & Composition

An npc_blob emits and controls a large group of entities called blob_elements. Without an npc_blob, these blob elements will disband and drift in their last direction of travel, which is dictated by npc_blob.

The NPC computes what is called a centroid by averaging the origins of every blob_element it controls. This calculation is used for:

• Computing how far away enemies are.
• Identifying when a blob_element is stuck.
• Determining the direction blob_elements wobble in while idle.
  Confirm:Code says to do this, but blob_elements don't seem to follow it? Line 754.

It's probable that blobs would have been rendered as metaballs, similar to gel blobs in Portal 2. What blobs render as currently is a model from a list (see npc_blob_use_model below).

Abilities

1. When an enemy is found, the blob will move to it and surround it. It will even climb onto enemies, and slowly consume them.
2. Blobs prefer the ground, but will travel on walls to get somewhere, or even the player and NPCs.
3. Blobs do 5 damage every 0.025 (or 200 damage per second).

Todo: Potential method of transferring blob_elements between npc_blobs?

Notes

1. Enemies can't hurt blobs and even if they could it has over 2000000000 Health Points.
2. Blob elements don't try to stick to where they all have LOS to the centroid. This means that a wall can end up going straight through them.
3. Typically, blobs only move when they find an enemy. They do not understand assaults.
4. npc_blob appears as a combine soldier in hammer.
5. Combine soldiers will sometimes go into their "on fire" animation when being attacked by blobs.
6. It seems to copy the player regarding AI relationships, except for when antlions become allies.
7. There is some kind of crash that happens sometimes, right as an enemy is killed.
8. Blob elements have been observed going airborne on rare occasions to reach flying enemies or when going over walls.
9. Blobs seem to be invincible, but they can still be hurt by explosives. They also ignore trigger_hurts.
10. Igniting the npc_blob reveals that the NPC itself is an invisible headcrab model.
    Todo: Why...?
11. Igniting also reveals that the npc_blob never moves, only the blob_elements.

Todo: What happens when a blob element is trapped but wants to go somewhere?

History

Npc blob was first shown off at Valve Hardware Day 2006 in an interactive tech demo. Where it's blob elements appeared as a swarm of Snarks, enemies from the original Half-Life. During the tech demo, you can see npc_blob climbing over obstacles; both stationary brushes and physics objects, avoiding hazards (fires in this case), and attacking a combine soldier. This is all that we see of npc_blob in this tech demo.

In the game files for Counter Strike Global Offensive and Alien Swarm, the files for the info_node entities have context options that reference npc_blob. Looking at the data, the blob seems to have been planned to be able to "shake", "spit" and "regenerate" among other functions. These options have the prefix Ep3; suggesting that npc_blob may have been intended to appear in Half-Life 2, Episode 3 should it have been released.

Dedicated ConVars

blob_mindist <120.0> (hammer units)

Confirm:No effect?

blob_element_speed <187> (hammer units per second)

How fast blob_elements move. Higher speeds seem to cause blob elements to go airborne more frequently.

npc_blob_idle_speed_factor <0.5> (arbitrary number)

Multiplies blob_element_speed for when blobs aren't doing anything.

blob_numelements <20> (arbitrary number)

How many blob_elements a single npc_blob manages.

blob_batchpercent <100> (percentage?^[confirm])

Confirm:Looking at code, seems like it would limit the number of blobs elements processed to a certain percent. No effect observed ingame.

blob_radius <160> (hammer units)

How far blob elements like to spread out from each other. Can affect their ability to move and attack. Requires restart to take effect.

npc_blob_use_threading <1> (boolean)

Whether blobs are multithreaded or not.

npc_blob_sin_amplitude <60.0f> (arbitrary number?^[confirm])

Amplifies how much blob_elements wobble around.

Todo: Doesn't seem to go above 60? Why and how to fix.

npc_blob_show_centroid <0> (boolean)

Shows a green 3D cross indicating where the centroid mentioned above is located.

npc_blob_straggler_dist <240> (hammer units)

Defines the maximum distance a blob element would be allowed to get away from the centroid when traveling. The code for putting this ConVar to use is incomplete and commented out.

npc_blob_use_orientation <1> (boolean)

Enables blob elements rotating to face their direction of travel.

npc_blob_use_model <2> (arbitrary number)

Chooses which model to show blob_elements as. Requires restart to take effect.

0. gibs/agibs.mdl (skull)

1. props_junk/watermelon01.mdl (watermelon)

2. w_squeak.mdl (snark (not in final game, shows error model))

3. baby_headcrab.mdl (baby headcrab (not in final game, shows error model))

Note:If this is set to any other number, the map will fail to load and must be set back to a valid number.

npc_blob_think_interval <0.025> (seconds)

How often the NPC thinks.

Keyvalues

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

BaseNPC flags

Wait Till Seen : [1] Prevents this NPC from seeing (or being seen) until it enters a player's viewcone. Gag : [2] Won't make IDLE sounds until it's angry. Fall to ground (unchecked means teleport to ground) : [4] Drop Healthkit : [8] Causes this NPC to drop an item_healthvial upon dying. Efficient : [16] Don't acquire enemies or avoid obstacles Wait For Script : [128] Forces this NPC to "wait" in an idle state until it finishes playing a scripted_sequence. Long Visibility/Shoot : [256] By default, increases a NPC's sight range to 6,000 units and allows it to attack from anywhere within that distance. Fade Corpse : [512] Think outside PVS : [1024] Allows this NPC to run its regular AI outside of any player's PVS. Template NPC : [2048] Marks this NPC as a template for entities like npc_template_maker. The NPC will not spawn on its own. This is not needed for point_template. Do Alternate collision for this NPC (player avoidance) : [4096] Note:This flag is disabled in episodic for player companions, because the StartScripting input does this. Don't drop weapons : [8192] Ignore player push : [16384] (in all games since ) Entity won't give way to player.

Inputs

Todo: incomplete list

FormPathShape <string>

Tells the group to go distribute themselves along a shape defined by path corner entities

SetRadius <float>

Force the group to change the radius (density)

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

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.

See also

• Render blobs