Hint nodes

Note:Do not confuse Hint nodes with Hint brushes, which are used to control visibility in a map.

Hints give specific information about their location to help NPCs decide how to react to, or make best use of, that specific locus. Hints are only semi-scripted. You cannot force an NPC to use a hint (with the exception of actbusy routines). Hints are only suggestions, to be weighed by an NPC's AI code during gameplay.

Hint Entities

There are only four point-based classes of entity that provide hints to NPCs.

• info_hint

Unlike the hybrid hint nodes, info_hint does not get included in the nodegraph, so NPCs will not be able to navigate to it. Therefore if you set an info_hint to a hint type that tells the NPC to do something when they arrive at that locus (eg "Crouch Cover Low"), it will never get used but may well confuse an NPC who Thinks about using it. Only use info_hint for 'remote target' hint types such as "World: Visually Interesting". Otherwise use info_node_hint instead.

• info_node_hint

A Nodegraph and Hint System entity, combining all the features of both info_hint and info_node. It is a ground node, used by all NPCs that walk or crawl upon the earth.

• info_node_air_hint

A Nodegraph and Hint System entity, but used only by Flying NPCs.

• info_node_climb

A Nodegraph and Hint System entity, but used only by Climbing NPCs.

Each instance of a hint node must be positioned in exactly the right location on the map - dumb hint node placement will lead to dumb NPC behaviour. (As always, there's an exception and in this case it's ground nodes : if you position an info_node_hint in space above ground level it will always 'fall' to ground level. By contrast, info_node_air_hint, info_hint, etc will maintain their position in space.)

Each hint node can only suggest one hint, as an NPC can only use one hint at a time. Thus you may need to position an "enemy disadvantage hint" very close to a "crouch cover".

ai_changehintgroup also deserves an honourable mention: it is an event-logic entity that can be used to change the hint group of hint nodes and NPCs. It does not actually provide hints itself.

Hint Entity Properties

Hint

The most important property of a hint node is its hint type, which defines what information is being given to the NPC.

Please note that some NPC classes have special AI features, so not all hints will work with every NPC type.

Hint	#	Notes	Codename	Conditions	NPCs	Use with
None	0	By default, no hint is provided. This allows you to use an info_node_hint as an info_node, or an info_node_air_hint instead of info_node_air. Arguably it makes the basic info_node entities redundant. Obviously an info_hint without a hint is rather pointless.		None	All	info_node_hint info_node_air_hint
World: Window	2	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	12	Used in an actbusy routine or queue.	HINT_WORLD_WORK_POSITION	See Actbusy or Actbusy_Queues	npc_citizen	info_node_hint
World: Visually Interesting	13	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)	14	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	15	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 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	100	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	101	Same as above, but tells the NPC to crouch lower.	HINT_TACTICAL_COVER_LOW	See above	See above	info_node_hint
Entrance / Exit Pinch	103	A node representing a small area through which NPCs should file one at a time, such as a doorway.	HINT_TACTICAL_PINCH	Hint must be between the NPC and its destination node.	All?	info_node_hint
Enemy Disadvantage Point	105	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
Antlion: Burrow Point	400	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	401	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	450	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
Crow: Fly to point	700	Crows will fly towards this point when spawning, unless a perch point is nearer.	HINT_CROW_FLYTO_POINT		npc_crow	info_node_air_hint
Follower: Wait point	900	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	901	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	902	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	903	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	904	Used by Striders to navigate and target their cannon weapons.	HINT_STRIDER_NODE		npc_strider	info_node_hint

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

Imagine this node requires that an NPC be in the node's field of view in order to use this hint. 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).

TargetNode

The node ID of an associated target node, if any.

IgnoreFacing

Don't pay attention to the facing of the node. May not apply to a given hint type.

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.

Enable/Disable Hint

Hint Nodes can accept both EnableHint and DisableHint inputs via the Inputs and Outputs system. This enables/disables only the hint type function of the hint node, not the nodegraph function (useinfo_node_link_controller to dynamically enable/disable areas of the nodegraph).

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)