Hint nodes
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.
- Unlike navigation nodes, 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 Thinks about using it. Only use info_hint for AI Visually Interesting hint types. Otherwise use info_node_hint instead.
- 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.
- is both a navigation node and a hint node, but used only by Flying NPCs.
- is both a navigation node and a hint node, but used only by Climbing NPCs.
Placement Tip: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.Placement Tip: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.
| Hint | # | Notes | Codename | Conditions | NPCs affected | Use with |
|---|---|---|---|---|---|---|
| None | 0 | By default, no hint is provided. | |
None | All | All |
| World: Window | 2 | A scanner will consider inspecting whatever solid surface this hint is pointing at when idle. Placement Tip:Consider facing this toward a brush with a window texture. |
HINT_WORLD_WINDOW
|
hint is visible | npc_cscanner, npc_spotlight, npc_clawscanner | info_hint |
| World: Act Busy Hint | 12 | Used in an actbusy routine or queue. | HINT_WORLD_WORK_POSITION
|
|
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
|
|
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
|
|
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
|
|
combine_mine | info_hint |
| 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. | HINT_WORLD_VISUALLY_INTERESTING_STEALTH
|
hint is visible | npc_alyx | info_hint |
| 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. Placement Tip:Useful for oddly shaped cover, such as low rocks or narrow pillars. |
HINT_TACTICAL_COVER_MED
|
|
npc_combine_s, npc_metropolice (only in  )
|
info_node_hint |
| 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. Placement Tip: This type of cover can be broken easily, which can cause ai issues. Use with caution. |
HINT_TACTICAL_COVER_LOW
|
|
npc_citizen, npc_combine_s, npc_metropolice | info_node_hint |
| Waste Scanner Spawn | 102 | Todo: notes
|
Todo: codename
|
Todo: conditions
|
Todo: npcs affected
|
Todo: used with entity
|
| Entrance / Exit Pinch | 103 | Obsolete. Remnant of a cut Antlion Guard behavior. | HINT_TACTICAL_PINCH
|
npc_antlionguard | info_node_hint | |
| Guard Point | 104 | Referenced as Obsolete/Unused in code. | HINT_NOT_USED_TACTICAL_GUARD
|
Todo: conditions
|
Todo: npcs affected
|
Todo: used with entity
|
| Enemy Disadvantage Point | 105 | Obsolete. Meant to be used by the cut npc_assassin | HINT_TACTICAL_ENEMY_DISADVANTAGED
|
Unknown | npc_assassin | info_node_hint |
| Health Kit | 106 | Obsolete. Was an unfinished functionality of npc_citizen. | HINT_HEALTH_KIT
|
npc_citizen | info_node_hint | |
| Antlion: Burrow Point | 400 | Antlions will burrow in or out out of the ground at this point. | HINT_ANTLION_BURROW_POINT
|
|
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
|
|
npc_antlion | info_node_hint |
| Headcrab: Burrow Point | 450 | Headcrabs will burrow into this point if they can't attack. They behave slightly different when spawned from canisters. | HINT_HEADCRAB_BURROW_POINT
|
|
npc_headcrab | info_node_hint |
| Headcrab: Exit Pod Point | 451 | Todo: notes
|
HINT_HEADCRAB_EXIT_POD_POINT
|
Todo: conditions
|
Todo: npcs affected
|
Todo: used with entity
|
| Roller: Patrol Point | 500 | Referenced as Obsolete/Unused in code. | HINT_NOT_USED_ROLLER_PATROL_POINT
|
Todo: conditions
|
Todo: npcs affected
|
Todo: used with entity
|
| Roller: Cleanup Spot | 501 | Referenced as Obsolete/Unused in code. | HINT_NOT_USED_ROLLER_CLEANUP_POINT
|
Todo: conditions
|
Todo: npcs affected
|
Todo: used with entity
|
| 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. [todo tested in?] |
HINT_CROW_FLYTO_POINT
|
npcs will pick the closest node | npc_crow npc_pigeon | info_node_air_hint, info_node_hint |
| Crow: Perch point | 701 | Obsolete, may have been used at one point, no longer functions. | HINT_CROW_PERCH_POINT
|
npc_crow | info_node_air_hint | |
| Follower: Wait point | 900 | NPCs under an ai_goal_follow will try to stand here if not in combat and near the leader. | HINT_FOLLOW_WAIT_POINT
|
|
See ai_goal_follow | info_node_hint |
| 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. | HINT_JUMP_OVERRIDE
|
|
All land-based | info_node_hint |
| 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. | HINT_PLAYER_SQUAD_TRANSITON_POINT
|
|
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_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 | |
| 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. | HINT_PLAYER_ALLY_MOVE_AWAY_DEST
|
Node must not be within 28 units, but not as far as 600 units. | npc_citizen, npc_alyx, npc_barney | info_node_hint |
| HL1 World: Machinery | 1000 | Legacy support. Used in HL1 for monster_houndeye to show curious animations at this node when IDLE. | HINT_WORLD_MACHINERY
|
The NPC is not hostile. | monster_houndeye | info_node |
| HL1 World: Blinking Light | 1001 | Legacy support. Used in HL1 for monster_houndeye to show curious animations at this node when IDLE. | HINT_WORLD_BLINKING_LIGHT
|
The NPC is not hostile. | monster_houndeye | info_node |
| HL1 World: Human Blood | 1002 | Todo: notes
|
HINT_HL1_WORLD_HUMAN_BLOOD
|
Todo: conditions
|
Todo: npcs affected
|
Todo: used with entity
|
| HL1 World: Alien Blood | 1003 | Todo: notes
|
HINT_HL1_WORLD_ALIEN_BLOOD
|
Todo: conditions
|
Todo: npcs affected
|
Todo: used with entity
|
| CS Hostage: Escape Point | 1100 | Todo: notes
|
HINT_CSTRIKE_HOSTAGE_ESCAPE
|
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; hunters will move around randomly more often and 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 mode to see when they occur.