NPC FOV

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An NPC's Field of View or FOV is the same as the Viewcone Angle (the Viewcone Length is how far the NPC can see). Both are very important in NPC Sensing AI.

List of NPC FOVs

NPC FOV varies considerably between NPC classes.

  • This list is intended as a quick reference for level-designers positioning and angling their NPCs for effective AI behaviour. It is only a quick, crude reference and not (yet) empirically verified.
  • To do: Ultimately each NPC class's Viewcone Angle & Length should be included on their entity page, making this central list redundant.
Note: This data is culled from the various npc_*.cpp files for EP1 engine.
Static NPCs: 			m_flFieldOfView		FOV (degrees)	
npc_barnacle			0.5   			120 	down ?
npc_combinecamera		0.5   			120 	down ?
npc_missile defense		0.1			168 	up ?
npc_spotlight			VIEW_FIELD_FULL		360 
npc_turret			VIEW_FIELD_NARROW 	 90 
npc_turret_ceiling		0.0f			180 
npc_turret_floor		0.4f 			132 
npc_vehicledriver		VIEW_FIELD_FULL		360 
Moving NPCs: 			m_flFieldOfView		FOV (degrees)	
npc_antlion			-0.5f 			240 	
 ANTLION_VIEW_FIELD_NARROW	0.85f 			 64 	
npc_antlionguard		-0.4f 			228 	
npc_combine_s			-0.2  			204 	
npc_helicopter 			-1.0  			360 	
npc_basescanner			0.2   			156 
npc_npc_blob			-1.0f 			360 	
npc_bullsquid			0.2			156 
npc_combinedropship		0.5   			120 
npc_combinegunship		-0.707 			270 
npc_crow			VIEW_FIELD_FULL		360 
npc_fastzombie			0.2			156 
npc_headcrab			0.5   			120 
npc_houndeye			0.5   			120 
npc_hydra			-1.0			360 
npc_icthyosaur			-0.707 			270 
npc_manhack			VIEW_FIELD_FULL		360 
npc_metropolice			-0.2			204 
npc_playercompanion		0.02			178 
npc_poisonzombie		0.2			156 
npc_rollermine			-1.0f			360 
npc_stalker			0.1			168 
npc_strider			0.0 			180 
npc_zombie			0.2			156 
npc_zombine			0.2			156 
npc_protosniper			0.2			156 
npc_advisor			VIEW_FIELD_FULL		360 
Characters: 			m_flFieldOfView		FOV (degrees)	
npc_breen			0.5   			120 
npc_dog				0.5   			120 
npc_eli				0.5   			120 
npc_gman			0.5   			120 
npc_kleiner			0.5   			120 
npc_monk			-0.707 			270 
npc_mossman			0.5   			120 
Oddballs : 			m_flFieldOfView		
npc_bullseye  			keyvalue input ?
npc_turret_ground   		cos( ((GROUNDTURRET_VIEWCONE / 2.0f) * M_PI / 180.0f) )
npc_enemyfinder 		keyvalue input (0.5 default)


Displaying viewcones

You can display viewcones in-game through the Console Command npc_viewcone.


Source Code Variables

The NPC's ViewCone Angle or FOV can be inferred from the m_flFieldOfView value given in the relevant npc.cpp file, using the formula:

FOV = (2 * acos(m_flFieldOfView)) 

m_flFieldOfView

m_flFieldOfView indicates the width of this NPC's forward view cone (as a dotproduct result).

  • Its value must be between -1.0 and 1.0. If m_flFieldOfView is negative (ie <0) then the FOV is wider than 180 degrees.
  • To calculate the m_flFieldOfView value for a desired FOV, use:
m_flFieldOfView = (cos(0.5 * FOV))

VIEW_FIELD_FULL

Preset NPC m_flFieldOfView value defined in util.h as == 360 deg FOV.


VIEW_FIELD_WIDE

Preset NPC m_flFieldOfView value defined in util.h as == 270 deg FOV.

  • To do:  additional comment in util.h states "0.1 // +-85 degrees, used for full FOV checks" ... significant?


VIEW_FIELD_NARROW

Preset NPC m_flFieldOfView value defined in util.h as == 90 deg FOV.

  • A more narrow check used to set up ranged attacks


VIEW_FIELD_ULTRA_NARROW

Preset NPC m_flFieldOfView value defined in util.h as == 50 deg FOV.

  • A more narrow check used to set up ranged attacks.