ECS concepts

If you are familiar with Entity-component-system (ECS) concepts, you might see the potential for naming conflicts with Unity's existing GameObject/Component setup.

The purpose of this page is:

  1. Clarify and disambiguate the concepts as used in the ECS.
  2. Provide a brief introduction to each concept as an entry point to a new user.

EntityManager

Manages memory and structural changes.

ComponentData

Parallel streams of concrete, blittable data.

e.g.

Position HitPoints
64,30 69
58,55 70
95,81 81

See: General purpose components

Entity

An ID which can be used for indirect component lookups for the purposes of graph traversal.

e.g.

Entity Position HitPoints
0 64,30 69
1 58,55 70
2 95,81 81

See: Entities

SharedComponentData

Type of ComponentData where each unique value is only stored once. ComponentData streams are divided into subsets by each value of all SharedComponentData.

e.g. (Mesh SharedComponentData)

Mesh = RocketShip

Position HitPoints
64,30 69
58,55 70
95,81 81

Mesh = Bullet

Position HitPoints
10,50 19
36,24 38
67,33 40

See: Shared components

Dynamic Buffers

This is a type of component data that allows a variable-sized, "stretchy" buffer to be associated with an entity. Behaves as a component type that carries an internal capacity of a certain number of elements, but can allocate a heap memory block if the internal capacity is exhausted.

See: Dynamic Buffers

EntityArchetype

Specific set of ComponentData types and SharedComponentData values which define the subsets of ComponentData streams stored in the EntityManager.

e.g. In the above, there are two EntityArchetypes:

  1. Position, HitPoints, Mesh = RocketShip
  2. Position, HitPoints, Mesh = Bullet

See: EntityArchetype in detail

ComponentSystem

Where gameplay/system logic/behavior occurs.

See: ComponentSystem in detail

World

A unique EntityManager with specific instances of defined ComponentSystems. Multiple Worlds may exist and work on independent data sets.

See: World in detail

SystemStateComponentData

A specific type of ComponentData which is not serialized or removed by default when an entity ID is deleted. Used for internal state and resource management inside a system. Allows you to manage construction and destruction of resources.

See: SystemStateComponentData in detail

JobComponentSystem

A type of ComponentSystem where jobs are queued independently of the JobComponentSystem's update, in the background. Those jobs are guaranteed to be completed in the same order as the systems.

See: JobComponentSystem in detail

EntityCommandBuffer

A list of structural changes to the data in an EntityManager for later completion. Structural changes are:

  1. Adding Component
  2. Removing Component
  3. Changing SharedComponent value

See: EntityCommandBuffer in detail

EntityCommandBufferSystem

A type of ComponentSystem, which provides an EntityCommandBuffer. i.e. A specific (synchronization) point in the frame where that EntityCommandBuffer will be resolved.