Entity
A object defined within the Source Engine as having characteristics which differentiate it from "the world" (world brushes).
There are three main types of entities:
Brush entities
These entities are built from brushes and covers its area of effect. They include things such as triggers, conveyor belts, and rain.
How to create a brush entity
- Create a new worldbrush.
- Select it.
- Right-click on it.
- Choose Tie to Entity from the right-click menu.
- Select the type of brush entity to create from the Class list.
- Clicking Apply.
Point Entities
These entities are created at a position point in the grid, and has no area of effect of its own, unless it is given a model.
Logic entities
These entities are invisible entities that affect the game, including AI managers, lights, and choreography.
Prop entities
These entities are mostly non-living objects that uses a model for its appearance and function. They can be static, dynamic, or physics. Some props can have AI, such as npc_rollermine, and some props can have functionality, such as prop_vehicle.
NPC entities
NPC entities are "Non-Player Characters"; they refers to all of the bots (living/robotic opponents and allies beside the player(s)). They have predefined behavior AI of their own; visible NPCs have their own models too.
Nodes
These entities are created like point entities, and will together create a network that will aid the NPCs (See below.) to gain knowledge about their surroundings, making them smarter than their basic programming.