npc_blob is a point entity available in the Half-Life 2 series. It's an experimental, unused entity that would have been a gross, sludgey monster that surrounds and consumes its prey. Its behavior is functional, with a few bugs. Visuals and sounds are not finished at all, however.
Behavior & Findings
Appearance & Composition
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
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.
When an enemy is found, the blob will move to it and surround it. It will even climb onto enemies, and slowly consume them.
Blobs prefer the ground, but will travel on walls to get somewhere, or even the player and NPCs.
To do: Potential method of transferring
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.
Typically, blobs only move when they find an enemy. They do not understand assaults.
npc_blob appears as a combine soldier in hammer.
Combine soldiers will sometimes go into their "on fire" animation when being attacked by blobs.
It seems to copy the player regarding AI relationships, except for when antlions become allies.
There is some kind of crash that happens sometimes, right as an enemy is killed.
Blob elements have been observed going airborne on rare occasions to reach flying enemies or when going over walls.
Blobs seem to be invincible, but they can still be hurt by explosives. They also ignore
npc_blob reveals that the NPC itself is an invisible headcrab model. To do: Why...?
Igniting also reveals that the
npc_blob never moves, only the
To do: What happens when a blob element is trapped but wants to go somewhere?
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)
blob_element_speedfor when blobs aren't doing anything.
blob_numelements <20> (arbitrary number)
- How many
blob_elements a single
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. To do: 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.
npc_blob_think_interval <0.025> (seconds)
- How often the NPC thinks.
- Values for
- Target Path Corner (target)
- The path_corner that this NPC will move to after spawning.
- Squad Name (squadname)
- 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)
- 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)
- Limits NPC to using specified hint group for navigation requests, but does not limit local navigation.
- Sleep State (sleepstate)
- 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)
- Auto-wake if player within this distance
- Wake Squad (wakesquad)
- Wake all of the NPCs squadmates if the NPC is woken
- Enemy Filter (enemyfilter)
- Filter entity to test targets against
- Ignore unseen enemies (ignoreunseenenemies)
- Prefer visible enemies, regardless of distance or relationship priority
- Physics Impact Damage Scale (physdamagescale)
- 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.
- Disable shadows (disableshadows)
- Prevent the entity from creating cheap render-to-texture shadows. Does not affect shadow mapping.
- Disable ShadowDepth (disableshadowdepth)
<boolean>(New with Portal 2)
- Used to disable rendering into shadow depth (for projected textures) for this entity.
- Projected Texture Cache (shadowdepthnocache)
<choices>(New with Portal 2)
- Used to hint projected texture system whether it is sufficient to cache shadow volume of this entity or to force render it every frame instead.
- 0 : Default
- 1 : No cache - render every frame
- 2 : Cache it - render only once
- Render Mode (rendermode)
- Set a non-standard rendering mode on this entity.
- Render FX / Transparency (0 - 255) (renderamt)
- Transparency amount, requires a Render Mode other than Normal. 0 is invisible, 255 is fully visible.
- Render Color (R G B) (rendercolor)
- Color tint.
- Disable Receiving Shadows (disablereceiveshadows)
- Prevent the entity from receiving shadows on itself.
- Render FX (renderfx)
- Preset pattern of appearance effects.
- Pitch Yaw Roll (Y Z X)
- This entity's orientation in the world. Pitch is rotation around the Y axis, yaw is the rotation around the Z axis, roll is the rotation around the X axis.
- Entity Scripts
<scriptlist>(New with Left 4 Dead 2)
- Space delimited list of VScript files (without file extension) that are executed after all entities have spawned. The scripts are all executed in the same script scope, later ones overwriting any identical variables and functions.
- Script think function
<string>(New with Left 4 Dead 2)
- Name of a function in this entity's script which will be called automatically every 100 milliseconds (ten times a second) for the duration of the script. It can be used to create timers or to simulate autonomous behavior. The return value (if present) will set the time until the next call. Note:Try to avoid expensive operations in this function, as it may cause performance problems.
- Allow Physics Gun (gmod_allowphysgun)
<boolean>(Only in Garry's Mod)
- If set, players cannot use Physics Gun on this entity.
- Sandbox Tool Whitelist (gmod_allowtools)
<string>(Only in Garry's Mod)
- If set, only given tools can be used on this entity. You need to supply the tool class names, the names of the .lua files of those tools. This also includes the context menu properties!
- 1: Wait Till Seen
- 2: Gag (No IDLE sounds until angry)
- 4: Fall to ground (unchecked means *teleport* to ground)
- 8: Drop Healthkit
- 16: Efficient - Don't acquire enemies or avoid obstacles
- 128: Wait For Script
- 256: Long Visibility/Shoot
- 512: Fade Corpse
- 1024: Think outside PVS
- 2048: Template NPC: This entity is a template for
npc_template_maker. It will not spawn automatically and cannot be used with
- 4096: Do Alternate collision for this NPC (player avoidance) Note:This flag is disabled in episodic for player companions because the
StartScriptinginput does this.
- 8192: Don't drop weapons
- 16384: Ignore player push (New with Half-Life 2: Episode One / Source 2006): Don't give way to player
To do: incomplete list
- Tells the group to go distribute themselves along a shape defined by path corner entities
- Force the group to change the radius (density)
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
- Set the NPC's health.
<integer>(New with Half-Life 2: Episode Two / Source 2007)
<integer>(New with Half-Life 2: Episode Two / Source 2007)
- Add to or remove from the NPC's health.
- HACK: Sets this NPC's body group (from 0 - n).
- Scales the damage taken when this character is hit by a physics object. 0 means this feature is disabled for backwards compatibility.
- Burst into flames.
- Ignite for the given number of seconds.
- Ignite with the given number of hitbox fires.
- Ignite with the given hitbox fire scale.
- Smash into pieces. If this is not possible, disappear.
BecomeRagdoll(New with Half-Life 2: Episode Two / Source 2007)
- Remove itself and instantly become a ragdoll with zero force (just go limp). OnDeath, etc. Outputs will NOT be fired.
- 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 NPC's idle speech, and so on.
- Start an assault at the given rally point.
- Change the name of this NPC's squad. Leaving the parameter blank will remove the NPC from any existing squad.
- Wakes up the NPC if it is sleeping.
- Clears out the NPC's knowledge of a named entity.
- Gagged NPCs won't speak (or moan, caw, etc.) unless made to be a choreographed scene.
- Ignore danger sounds for the specified number of seconds.
HolsterWeapon(New with Half-Life 2: Episode One / Source 2006)
UnholsterWeapon(New with Half-Life 2: Episode One / Source 2006)
- Force the NPC to holster or unholster their weapon. Ignored if the NPC is scripting or if the NPC doesn't use weapons.
HolsterAndDestroyWeapon(New with Half-Life 2: Episode One / Source 2006)
- Same as
HolsterWeapon, except the weapon is destroyed once it has been concealed.
ForceInteractionWithNPC <string> <string>(New with Half-Life 2: Episode One / Source 2006)
- Force the NPC to use a dynamic interaction with another NPC. Syntax is
<targetname> <dynamic interaction>
UpdateEnemyMemory(New with Half-Life 2: Episode One / Source 2006)
- Update (or create) this NPC's memory of of the given entity.
<float>(Only in Garry's Mod)
- Sets the maximum look distance for the NPC. Defaults are 2048 and 6000 for long range NPCs.
- Sets the entity's transparency to a number from 0 (invisible) to 255 (fully visible). Requires the entity to have its Render Mode (rendermode) set to a number other than
- Sets an RGB color for the entity.
- Removes this entity and any entities parented to it from the world.
- Functions the same as
Kill, although this entity and any entities parented to it are killed on the same frame, being marginally faster than
- Evaluates a keyvalue/output on this entity. It can be potentially very dangerous, use with care.
<output name> <targetname>:<inputname>:<parameter>:<delay>:<max times to fire, -1 means infinite>
- Fire the
OnUseroutputs; see User Inputs and Outputs.
- Same as a player invoking +use; may not do anything. Can also be invoked by creating an output that does not specify an input.
This input is not included in Valve's FGDs.
<script>(New with Left 4 Dead 2)
- Execute a VScript file from disk, without file extension. The script contents are merged with the script scope of the receiving entity.
<string>(New with Left 4 Dead 2)
- Execute a string of VScript source code in the scope of the entity receiving the input. String quotation may be needed when fired via console. Bug: In , the code is executed in the script scope of the entity that fires the output, not the one receiving the input.Warning: Never try to pass string parameters to a script function with this input. It will corrupt the VMF structure because of the nested quotation marks, which then must be removed manually with a text editor.
<string>(New with Left 4 Dead 2) !FGD
- Execute a VScript function in the scope of the receiving entity.
<coordinates>(New with Alien Swarm) !FGD
- Send this entity to a spot in the map. If the entity is parented to something, it will be offset from the parent by this amount.
<angles>(New with Alien Swarm) !FGD
- Set this entity's angles.
- Fired when this NPC takes damage (activator is the damage inflictor)
- Fired when this NPC is killed (activator is the killer)
- Fired when this NPC reaches half of its maximum health
- Fired when this NPC hears a sound (other than combat or the player)
- Fired when this NPC hears the player
- Fired when this NPC hears combat sounds
- Fired when this NPC establishes line of sight to its enemy
- Fired when this NPC loses line of sight to its enemy
- 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
- Fired when this NPC establishes line of sight to its enemy, and that enemy is a player
- Fired when this NPC loses line of sight to its enemy, and that enemy is a player
- 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
- Fired when this NPC is hurt by a player (activator is the attacker or vehicle driver (if friendly fire))
- 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))
- Fired when this NPC has refused to join the player's squad
- Fired when this NPC enters a sleep state
- Fired when this NPC comes out of a sleep state
- Fired when the NPC starts a forced interaction.
- Fired when the NPC aborts a forced interaction for some reason (target NPC died, couldn't be pathed to, etc)
- "NPCs in actbusies can no longer perform dynamic interactions." To do: What does this mean?
- These Outputs each fire in response to the firing of the like-numbered
FireUser4Input; see User Inputs and Outputs.
OnKilled(Only in the Left 4 Dead series)
- This Output fires when the entity is killed and removed from the game.