A viewcone is a representation of the spatial geometry of an NPC's current visual field. A target has to be within this cone for the NPC to recognize/react to its presence. (Even if it's being shot at, it cannot chase or flee from something it cannot see.)
- The angle or scope of the cone represents the NPC's Angular Field of View (FOV) (as determined by its m_flFieldOfView value).
- The edges or boundaries of the cone represents the NPC's periphery of vision.
- The length or depth of the cone's long axis represents the NPC's maximum sight range. (It appears to be the same for all NPCs: 2048 units, or seemingly unlimited if their Long Visibility flag is set. The Think Outside PVS flag does not effect this range.)
- The direction of the cone is determined by the NPCs current orientation, or Angles.
- npc_viewcone - A partial representation of viewcones.