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 an NPC to use a hint. They are information, not orders, and are handled by an 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
Obsolete? They do not seem to be recognised by NPCs.
info_node_hint
The basic hint type. Used by ground-based NPCs.
info_node_air_hint
Identical to info_node_hint but used for airborne NPCs.
- Special Property: NodeHeight, unknown and possibly obsolete.
ai_changehintgroup
Changes or adds a specific hint group to an 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.
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
An 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.
World: Window
A window that can be looked out of to find or engage other NPCs.
World: Act Bust Hint
If you aren’t doing anything useful, perform an interesting action here.
World: Visually Interesting
This hint marks an interesting area: pay attention to it.
World: Visually Interesting (Don't aim at)
Same as above, but only the head will turn.
World: Inhibit Combine Mines within 15 feet
Unknown. Could stop mines from setting themselves, or from triggering, or both.
Crouch Cover Medium
This hint gives you cover while crouching.
Crouch Cover Low
This hint gives you some cover while crouching.
Waste Scanner Spawn
An automated scanner factory.
Entrance / Exit Pinch
Place at bottlenecks like doorways to aid navigation.
Enemy Disadvantage Point
A weak spot in your opponent's position. NPCs will try to get here to attack hostiles.
Health Kit
Marks a health kit. Seems obsolete – NPCs don't need it.
Antlion: Burrow Point
Antlions will burrow out from this point. See npc_antlion
Antlion: Thumper Flee Point
When fleeing from a thumper, head to this position? See npc_antlion
Headcrab: Burrow Point
Headcrabs will burrow out from this point. See npc_headcrab
Roller: Patrol Point
Obsolete?
Roller: Cleanup Spot
Obsolete?
Crow: Fly to point
See npc_crow
Crow: Perch point
See npc_crow
Follower: Wait point
Wait here for the player to catch up if you are guiding him?
Override jump permission
It is safe to jump from this spot.
Player squad transition point
Unknown.
NPC exit point
Unknown.
Strider node
Fire cannon here? See 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 an 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.
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.