View source for Hint nodes

{{lang|Hint nodes}}
{{distinguish|Hint brushes}}

'''Hints''' give specific information about their location to help [[NPC]]s 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|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 [[navigation node]]s, ''info_hint'' does not get included in the [[nodegraph]], so NPCs will not be able to navigate to it. Therefore if you set up an ''info_hint'' with 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 [[Think]]s about using it. Only use ''info_hint'' for [[AI Visually Interesting]] hint types. Otherwise use [[info_node_hint]] instead.

* '''[[info_node_hint]]''' 
: is both a [[navigation node]] and a [[hint node]], combining most 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]]''' 
: is both a [[navigation node]] and a [[hint node]], but used only by [[Flying NPCs]].

* '''[[info_node_climb]]''' 
: is both a [[navigation node]] and a [[hint node]], but used only by [[Climbing NPCs]].

{{ModernPlacementTip|Each instance of a hint node must be positioned in exactly the right location on the map - bad hint node placement will lead to dumb NPC behaviour. Each hint node can only suggest one hint, as each NPC can only use one hint at a time. Thus, sometimes you may need to position a variety of hint nodes very close to each other.}}

{{ModernPlacementTip|Ground nodes (such as ''info_node_hint'') fall to the ground when they spawn, so you can place them up to 128 units above any solid world geometry, which excludes func_brush, and they will still work. When placing ground nodes on displacements, place them slightly above the terrain to ensure nodegraph connections are properly made. By contrast, ''info_hint'' and ''info_node_air_hint'' entities will not move from their original placement positions.}}

'''[[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.

'''[[logic_navigation]]''' may also come in handy for specifying Entities which NPCs can just push out of the way (moveable phys props) or bump into (think zombies!) rather than navigating around them.

There are also a number of specialised ''hint'' entities designed to ''help'' optimise interaction of specific NPCs with the map, for example [[info_apc_missile_hint]], [[npc_heli_avoidbox]], [[npc_heli_avoidsphere]], [[npc_heli_nobomb]]. Whilst similar in effect, these entities do not use the ''AI hint system'' that this article is about.

==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. 
{| cellpadding=2 class=standard-table
!align=left| Hint
!align=left| #
!align=left| Notes
!align=left| Codename
!align=left| Conditions
!align=left| NPCs affected
!align=left| Use with
|- valign="top" valign="top"
| '''None'''
| 0
| By default, no hint is provided. 
| <code></code>
| None
| All
| All
|- valign="top" valign="top"
| '''World: Window'''
| 2
| A [[npc_cscanner|scanner]] will consider inspecting whatever solid surface this hint is pointing at when idle. {{ModernPlacementTip|Consider facing this toward a brush with a window texture.}}
| <code>HINT_WORLD_WINDOW</code>
| hint is visible
| [[npc_cscanner]], [[npc_spotlight]], [[npc_clawscanner]]
| info_hint
|- valign="top"
| '''World: Act Busy Hint'''
| 12
| Used in an [[Actbusy|actbusy routine]] or [[Actbusy_Queues|queue]].
| <code>HINT_WORLD_WORK_POSITION</code>
|
*See [[Actbusy]] or [[Actbusy_Queues]]
| [[npc_citizen]]
| info_node_hint
|- valign="top"
| '''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.
| <code>HINT_WORLD_VISUALLY_INTERESTING</code>
| 
*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
|- valign="top"
| '''World: Visually Interesting (Don't aim at) '''
| 14
| Same as above, but only the head and eyes are affected.
| <code>HINT_WORLD_VISUALLY_INTERESTING_DONT_AIM</code>
| 
*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
|- valign="top"
| '''World: Inhibit Combine Mines within 15 feet'''
| 15
| Inhibits, but does not prevent, [[combine_mine|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.'''
| <code>HINT_WORLD_INHIBIT_COMBINE_MINES</code>
| valign="top" |
*The NPC is within 180 units of the hint origin
| [[combine_mine]]
| info_hint
|- valign="top"
| '''World: Visually Interesting (Stealth mode)'''
| 16
| Causes Alyx to go into stealth "readiness". This does not affect ai. She will constantly look at this point and use a slightly different posture. Causes animation glitches in combat.
| <code>HINT_WORLD_VISUALLY_INTERESTING_STEALTH</code>
| hint is visible
| [[npc_alyx]]
| [[info_hint]]
|- valign="top"
| '''Crouch Cover Medium'''
| 100
| Is calculated like normal cover (at about 64 units height), except an NPC will use ACT_COVER_LOW_RELOAD and ACT_COVER_MED when taking cover here. Due to coding issues, this only works with combine soldiers. {{ModernPlacementTip|Useful for oddly shaped cover, such as low rocks or narrow pillars.}}
| <code>HINT_TACTICAL_COVER_MED</code>
| 
* Hint is not visible to NPC's [[Threat]]
|[[npc_combine_s]], [[npc_metropolice]] {{only|{{mapbase}}}}
| [[info_node_hint]]
|- valign="top"
| '''Crouch Cover Low'''
| 101
| Tells an NPC it can find cover at this position if it crouches low (calculated at 40 units height). Can cause animation  issues with npcs other than combine soldiers; they will tend to duck down and than immediately stand up. [[ai_goal_standoff]] can fix this. {{ModernPlacementTip| This type of cover can be broken easily, which can cause ai issues. Use with caution.}}
| <code>HINT_TACTICAL_COVER_LOW</code>
| 
* Hint is not visible to NPC's [[Threat]].
| [[npc_citizen]], [[npc_combine_s]], [[npc_metropolice]]
| [[info_node_hint]]
|- valign="top"
| '''Waste Scanner Spawn'''
| 102
| {{todo|notes}}
| {{todo|codename}}
| {{todo|conditions}}
| {{todo|npcs affected}}
| {{todo|used with entity}}
|- valign="top"
|'''Entrance / Exit Pinch'''
| 103
| Obsolete. Remnant of a cut Antlion Guard behavior.
| <code>HINT_TACTICAL_PINCH</code>
| 
| npc_antlionguard
| info_node_hint
|- valign="top"
| '''Guard Point'''
| 104
| Referenced as Obsolete/Unused in code.
| <code>HINT_NOT_USED_TACTICAL_GUARD</code>
| {{todo|conditions}}
| {{todo|npcs affected}}
| {{todo|used with entity}}
|- valign="top"
| '''Enemy Disadvantage Point'''
| 105
| Obsolete. Meant to be used by the cut npc_assassin
| <code>HINT_TACTICAL_ENEMY_DISADVANTAGED</code>
| Unknown
| npc_assassin
| info_node_hint
|- valign="top"
| '''Health Kit'''
| 106
| Obsolete. Was an unfinished functionality of npc_citizen.
| <code>HINT_HEALTH_KIT</code>
| 
| npc_citizen
| info_node_hint
|- valign="top"
| '''Antlion: Burrow Point'''
| 400
| Antlions will burrow in or out out of the ground at this point.
| <code>HINT_ANTLION_BURROW_POINT</code>
| 
*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
|- valign="top"
| '''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.
| <code>HINT_ANTLION_THUMPER_FLEE_POINT</code>
| 
*The Antlion must be fleeing from a thumper
| [[npc_antlion]]
| info_node_hint
|- valign="top"
| '''Headcrab: Burrow Point'''
| 450
| Headcrabs will burrow into this point if they can't attack. They behave slightly different when spawned from canisters.
| <code>HINT_HEADCRAB_BURROW_POINT</code>
| valign="top" |
*The Headcrab must not be within leap range of a hostile
| [[npc_headcrab]]
| info_node_hint
|- valign="top"
| '''Headcrab: Exit Pod Point'''
| 451
| {{todo|notes}}
| <code>HINT_HEADCRAB_EXIT_POD_POINT</code>
| {{todo|conditions}}
| {{todo|npcs affected}}
| {{todo|used with entity}}
|- valign="top"
| '''Roller: Patrol Point'''
| 500
| Referenced as Obsolete/Unused in code.
| <code>HINT_NOT_USED_ROLLER_PATROL_POINT</code>
| {{todo|conditions}}
| {{todo|npcs affected}}
| {{todo|used with entity}}
|- valign="top"
| '''Roller: Cleanup Spot
| 501
| Referenced as Obsolete/Unused in code.
|<code>HINT_NOT_USED_ROLLER_CLEANUP_POINT</code>
| {{todo|conditions}}
| {{todo|npcs affected}}
| {{todo|used with entity}}
|- valign="top"
| '''Crow: Fly to point'''
| 700
| Crows will fly to this point when they detect an enemy or hear combat sounds. {{bug| Crows tend to "stick" to the node they pick.}}
| <code>HINT_CROW_FLYTO_POINT</code>
| npcs will pick the closest node
| [[npc_crow]] [[npc_pigeon]]
| [[info_node_air_hint]], [[info_node_hint]]
|- valign="top"
| '''Crow: Perch point'''
| 701
| Obsolete, may have been used at one point, no longer functions.
| <code>HINT_CROW_PERCH_POINT</code>
| 
| [[npc_crow]]
| info_node_air_hint
|- valign="top"
| '''Follower: Wait point'''
| 900
| NPCs under an [[ai_goal_follow]] will try to stand here if not in combat and near the leader.
| <code>HINT_FOLLOW_WAIT_POINT</code>
| valign="top" |
*NPC must be using an [[ai_goal_follow]]
*The distance NPCs will look for these depends on [[ai_goal_follow]] formations
*This can use the Hint Activity
| See [[ai_goal_follow]]
| info_node_hint
|- valign="top"
| '''Override jump permission'''
| 901
| NPCs will jump from a hint of this type to another of this type, if it's within their jump parameters.
| <code>HINT_JUMP_OVERRIDE</code>
| valign="top" |
*Check [[AI Metrics]] for jump parameter information
*Destination hint must be available
| All land-based
| info_node_hint
|- valign="top"
| '''Player squad transition point'''
| 902
| An 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.
| <code>HINT_PLAYER_SQUAD_TRANSITON_POINT</code>
| 
* NPC is in a single-player game
* NPC is a player companion
* NPC is not marked as vital
| [[npc_citizen]]
| info_node_hint
|- valign="top"
| '''NPC exit point'''
| 903
| Part of an [[actbusy]] routine. NPCs will use this node to leave an area.
| <code>HINT_NPC_EXIT_POINT</code>
| valign="top" |
*NPC must be part of an actbusy routine
| [[npc_citizen]]
| info_node_hint
|- valign="top"
| '''Strider node'''
| 904
| Used by Striders to navigate and target their cannon weapons.
| <code>HINT_STRIDER_NODE</code>
| 
| [[npc_strider]]
| info_node_hint
|- valign="top"
| '''Player Ally: Push away destination'''
| 950
| Player allies will prefer these points when moving out of the player's way. Having multiple allies with multiple nodes will cause them to pick different points.
| <code>HINT_PLAYER_ALLY_MOVE_AWAY_DEST</code>
| Node must not be within 28 units, but not as far as 600 units.
| [[npc_citizen]], [[npc_alyx]], [[npc_barney]]
| [[info_node_hint]]
|- valign="top"
| '''HL1 World: Machinery'''
| 1000
| Legacy support. Used in HL1 for [[monster_houndeye]] to show curious animations at this node when IDLE.
| <code>HINT_WORLD_MACHINERY</code>
| The NPC is not hostile.
| [[monster_houndeye]]
| info_node
|- valign="top"
| '''HL1 World: Blinking Light'''
| 1001
| Legacy support. Used in HL1 for monster_houndeye to show curious animations at this node when IDLE.
| <code>HINT_WORLD_BLINKING_LIGHT</code>
| The NPC is not hostile.
| [[monster_houndeye]]
| info_node
|- valign="top"
| '''HL1 World: Human Blood'''
| 1002
| {{todo|notes}}
| <code>HINT_HL1_WORLD_HUMAN_BLOOD</code>
| {{todo|conditions}}
| {{todo|npcs affected}}
| {{todo|used with entity}}
|- valign="top"
| '''HL1 World: Alien Blood'''
| 1003
| {{todo|notes}}
| <code>HINT_HL1_WORLD_ALIEN_BLOOD</code>
| {{todo|conditions}}
| {{todo|npcs affected}}
| {{todo|used with entity}}
|- valign="top"
| '''CS Hostage: Escape Point'''
| 1100
| {{todo|notes}}
| <code>HINT_CSTRIKE_HOSTAGE_ESCAPE</code>
| {{todo|conditions}}
| {{todo|npcs affected}}
| 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).
* An NPC's '''hintgroup [[keyvalue]]''' is used to restrict the NPC's hint-node searching to a subset of the map's hint nodes. Only hint nodes with matching hintgroup names will be considered by the NPC. 
* An NPC's '''hintlimiting keyvalue''' limits the NPC to using the specified hintgroup for navigation requests, but does not limit local navigation. 
* Both or either of and NPC's ''hintgroup name'' and ''hintlimiting status'' can be changed dynamically by an [[ai_changehintgroup]] entity.
* Some NPCs react differently when in a hintgroup; [[npc_hunter|hunters]] will move around randomly more often and [[npc_combine_s|soldiers]] will take cover against NPCs that lack a range attack.

=== 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 ===
{{note|This enables/disables only the ''hint type'' effect of the hint node, not the ''[[nodegraph]]'' effect (use [[info_node_link_controller]] to dynamically enable/disable areas of the nodegraph).}}

By default the '''StartHintDisabled keyvalue''' is set to 0 (No), which means that the hint is ''active'' when the game begins. Set this value to 1 (Yes) to disable the hint until it is triggered by another event, via the [[Inputs and Outputs]] system. Hint Nodes can accept as many '''EnableHint''' and '''DisableHint''' inputs as you like.

==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 Console|developer mode]] to see when they occur.

:'''[http://www.steamreview.org/external/vdc/info_hint/info_hint.zip Download Example (VMF)]'''

[[Category:AI]]
[[Category:Entities]]
[[Category:Level Design]]
[[Category:Theory]]