Hint nodes

Hints give AI contextual pointers that it would not be able to work out on it’s own. They are not to be confused with compiler hints, which are used to control visibility in a map. They are point entities positioned in Hammer and interpreted by the AI when a map loads.

Hints are only semi-scripted. You cannot tell a NPC to use a hint (with the exception of actbusy routines). They are information, not orders, and are handled by a NPC's AI code.

Hint Entities

There are three entities in the hint family covering different NPC types, plus a related entity to change the hint group of a hint or NPC.

info_hint

A hint that does not add to any navigation grids. Some hint types (such as Act Busy) cannot be used with this entity.

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info_node_hint

A hint that is also an info_node. Ground NPCs only. Full range of hint types.

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info_node_air_hint

Identical to info_node_hint but used for airborne NPCs.

• Special Property: NodeHeight, unknown and possibly obsolete.

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ai_changehintgroup

Changes or adds a specific hint group to a NPC or hint.

Properties

Hint

See Hint Types, below.

Hint Activity

The activity to perform at this hint if the AI does not specify one. This might be looking around, patrolling, playing an animation, or anything.

Node FOV

NPCs can only see this hint if they are facing in this direction in relation to the hint's pitch yaw and roll. Not always applicable.

Hint Group

NPCs can filter hints to only those that match their hint groups. Useful when there are multiple NPCs in an area who should not use the same hints (for instance, two squads of fighting NPCs will only want to use hints on their side of any cover).

Minimum/Maximum State

A NPC will only look for hints that are within its state boundaries. An idle NPC will not use hints with a minimum state of alert, for example.

Hint Types

When you place a hint its type is the most important setting, defining what it is hinting at. Hints are handled by a NPC’s AI, so not all work with every character type.

Name	Notes	Codename	Conditions	NPCs	Hint type
World: Window	A window that can be looked through. Most NPCs do not need this.	HINT_WORLD_WINDOW		npc_cscanner, npc_spotlight	info_hint
World: Act Busy Hint	Used in an actbusy routine or queue.	HINT_WORLD_WORK_POSITION	See Actbusy or Actbusy_Queues	npc_citizen	info_node_hint
World: Visually Interesting	Used to mark interesting areas that the AI would not recognise on its own. A NPC will consider aiming at this node when they next choose a new target. Depending on the call the hint is found during the NPC’s state and ability to aim may affect their decision and the node may be locked for five seconds to prevent multiple NPCs staring at it in unison. If they cannot aim they will look at the target instead.	HINT_WORLD_VISUALLY_INTERESTING	There are no hostiles in the area The hint is in the NPC’s view cone The hint is in the NPC’s range The hint is not too close	All	info_hint
World: Visually Interesting (Don't aim at)	Same as above, but only the head and eyes are affected.	HINT_WORLD_VISUALLY_INTERESTING_DONT_AIM	See above	All	info_hint
World: Inhibit Combine Mines within 15 feet	Inhibits, but does not prevent, Combine mines from clamping into the ground within a 180 unit sphere around the hint. They will instead continue to bounce themselves until they are out of the hint's influence. This hint will not always have an effect. It is ultimately up to the mine if it wants to be clamp or not.	HINT_WORLD_INHIBIT_COMBINE_MINES	The NPC is within 180 units of the hint origin	combine_mine	info_hint
Crouch Cover Medium	Tells a NPC that it can cover itself by crouching at this position. Cover itself is acquired automatically: this hint merely helps the AI efficiently determine how high said cover goes. Should provide 100 vertical units or more of cover.	HINT_TACTICAL_COVER_MED	The hint is not visible to the NPC's threat	npc_citizen, npc_combine_s, npc_metropolice	info_node_hint
Crouch Cover Low	Same as above, but tells the NPC to crouch lower.	HINT_TACTICAL_COVER_LOW	See above	See above	info_node_hint
Waste Scanner Spawn	An automated scanner factory.	HINT_TACTICAL_SPAWN	Unknown	Unknown	Unknown
Entrance / Exit Pinch	Place in tight areas such as doorways to aid navigation.	HINT_TACTICAL_PINCH	Unknown	Unknown, possibly all foot	info_node_hint
Enemy Disadvantage Point	A weak spot in your opponent's position. NPCs will try to get here to attack hostiles. Remember to use hint groups on points that are only disadvantageous to one side!	HINT_TACTICAL_ENEMY_DISADVANTAGED	Unknown	Unknown	info_node_hint
Health Kit (obsolete)	An abandoned hint. NPCs will merely look at the hint as they would a World: Visually Interesting one.	HINT_HEALTH_KIT	Unknown	npc_citizen	Unknown
Antlion: Burrow Point	Antlions will burrow in or out out of the ground at this point.	HINT_ANTLION_BURROW_POINT	To burrow out, this hint must be used in conjunction with a npc_antlion_template_maker Depending on the configuration of the npc_antlion_template_maker, the hint will not be used if the player is looking at it	npc_antlion	info_hint
Antlion: Thumper Flee Point	Antlions will use this hint to flee towards when they are forced back by a thumper. It is not required, but is useful to control precise Antlion movements.	HINT_ANTLION_THUMPER_FLEE_POINT	The Antlion must be fleeing from a thumper	npc_antlion	info_node_hint
Headcrab: Burrow Point	Headcrabs will burrow in from this point. To have them burrow out, use spawnflags.	HINT_HEADCRAB_BURROW_POINT	The Headcrab must not be within leap range of a hostile	npc_headcrab	info_node_hint
Roller: Patrol Point (obsolete)	Patrol point for one of the rollermine family of NPCs that was cut from the game.	HINT_ROLLER_PATROL_POINT	Unknown	Unknown	info_node_hint
Roller: Cleanup Spot (obsolete)	Behavioral hint for a removed NPC.	HINT_ROLLER_CLEANUP_POINT	Unknown	Unknown	Unknown
Crow: Fly to point	Crows will fly towards this point when spawning, unless a perch point is nearer.	HINT_CROW_FLYTO_POINT		npc_crow	info_node_air_hint
Crow: Perch point	Crows will attempt to land on this hint. Functional, despite having no mention in the source code.	Unknown	Unknown	npc_crow	info_node_hint
Follower: Wait point	NPCs under an ai_goal_lead will wait here for the player to catch up before continuing.	HINT_FOLLOW_WAIT_POINT	NPC must be using an ai_goal_lead	See ai_goal_lead	info_node_hint
Override jump permission	NPCs will jump from a hint of this type to another of this type, if doing so will not hurt them.	HINT_JUMP_OVERRIDE	Fall must not hurt the NPC Destination hint must be available	All land-based	info_node_hint
Player squad transition point	A NPC will teleport to one of these hints when its outsidetransition input is triggered. Locked for half a second after each use to prevent NPCs spawning inside each other.	HINT_PLAYER_SQUAD_TRANSITON_POINT	NPC is in a single-player game NPC is a player companion NPC is not marked as vital	npc_citizen	info_node_hint
NPC exit point	Part of an actbusy routine. NPCs will use this node to leave an area.	HINT_NPC_EXIT_POINT	NPC must be part of an actbusy routine	npc_citizen	info_node_hint
Strider node	Used by Striders to target their cannon weapons.	HINT_STRIDER_NODE		npc_strider
HL1 World: Machinery	HL: Source
HL1 World: Blinking Light	HL: Source
HL1 World: Human Blood	HL: Source
HL1 World: Alien Blood	HL: Source

Limitations and Bugs

• A hint can only be of one type, and only one hint can be used by a NPC at a time. You cannot have an enemy disadvantage hint that is also crouch cover.

• Sometimes AI will not use a hint when it might make sense to. This is a part of normal AI behavior.

Example

This example map contains various hints in a combat situation. Each hint's location is marked on the map with a brief description of it. Run the map several times to get a full overview of how hints are used.

Note that there are currently bugs in the map that prevent the AI from carrying out some routines. Enable developer mode to see when they occur.

Download Example (VMF)