Entity Component Systems

Entity-Component-System (ECS) is a distributed and compositional architectural design pattern that is mostly used in game development. Elixir is a dynamic, functional language built on top of the Erlang VM designed for building scalable and maintainable applications. In this talk, discover how we can use both ECS and Elixir in a novel approach to structure our programs beyond the traditional OO/inheritance paradigm.

1. Entity Component Systems
Yos Riady
yos.io

goo.gl/ECeFOI

2. A walkthrough of an
ECS implementation in
Elixir
A high-level overview
of Entity Component
Systems
Background
Drawbacks of
traditional OOP /
inheritance style code
ECS Examples Code Next Steps
Real life applications
and examples of ECS
in action
Further learning, future
improvements, and
conclusion

3. A walkthrough of an
ECS implementation in
Elixir
A high-level overview
of Entity Component
Systems
Background
Drawbacks of
traditional OOP /
inheritance style code
ECS Examples Code Next Steps
Real life applications
and examples of ECS
in action
Further learning, future
improvements, and
conclusion

4. Animal
hop()
Bunny
swim()
Whale
GameObject
kill()
Killer Whale

5. Animal
hop()
Bunny
swim()
Whale
hop()
kill()
Killer Bunny
GameObject
kill()
Killer Whale

6. The challenges with inheritance
The Blob Antipattern
A huge single root class
with a large amount of
functionality.
Subclasses become
overburdened with
unneeded functionality.

Deep Rigid HierarchiesThe Diamond Problem

7. A walkthrough of an
ECS implementation in
Elixir
A high-level overview
of Entity Component
Systems
Background
Drawbacks of
traditional OOP /
inheritance style code
ECS Examples Code Next Steps
Real life applications
and examples of ECS
in action
Further learning, future
improvements, and
conclusion

8. Entity Component Systems
●Originally used in game development
○Tendency to end up with very complex / monolithic classes when using inheritance
○Thief, Dungeon Siege, Caves of Qud, roguelikes
●Attempts to solve issues due to deep hierarchies
○Composition over inheritance
●Based on three key abstractions
○Entity
○Component
○System

9. Entity Component Systems

10. Component
Components are minimal, reusable
data objects that are plugged into
entities to support some behaviour.
A Component itself has no
behaviour.
A Components tags an entity with a
single quality.
Typically a struct or dictionary.
The “qualities” or “aspects”of
a thing

11. What qualities might a bunny have?

12. What components might a bunny have?
Placeable
- int x
- int y
- int z



Huggable
- int fluffiness



Consumable
- float calories


Seeing
- int sight_radius
- boolean night_vision?



Living
- float health
- float age


Hopping
- int hop_distance


Physical
- int height
- int width
- int length

13. Entities are very simple.
Entities are globally unique IDs.
Entities has no actual data or
behaviour.
Entity are solely the sum of its
components.
A Component gives an Entity its
data.
Entity
An aggregation of Components

14. The bunny entity

15. The bunny entity
Placeable
- int x
- int y
- int z



Huggable
- int fluffiness



Consumable
- float calories


Seeing
- int sight_radius
- boolean night_vision?



Living
- float health
- float age


Hopping
- int hop_distance


Physical
- int height
- int width
- int length

16. The carrot entity
Placeable
- int x
- int y
- int z



Consumable
- float calories


Physical
- int height
- int width
- int length

17. The ghost entity
Placeable
- int x
- int y
- int z



Spooky
- int spookiness



Seeing
- int sight_radius
- boolean night_vision?

18. Systems run continuously and
iterate over all Components of its
type.
Systems read and write the state of
Components, resulting in behaviour.
By transitive property, Systems give
Entities behaviour.
Could be a distributed worker pool.
System
Brings entities and components
to life

19. How does a bunny behave?



Placeable
- x 5
- y -2
- z 10



Living
- age 2.00


Placeable
- x 5
- y -2
- z 0



Living
- age 2.01


“Fall” “Age”

20. How does a bunny behave?



Placeable
- x 5
- y -2
- z 10



Living
- age 2.00


Placeable
- x 5
- y -2
- z 0



Living
- age 2.01


“Fall” “Age”
Gravity
System
Time
System

21. Data flow in ECS
Gravity
System
Placeable
- x
- y
- z



Placeable
- x
- y
- z



Placeable
- x
- y
- z



Placeable
- x
- y
- z



Placeable
- x
- y
- z



External
Event Stream
i.e. Time,
Player Input

22. Acquires behaviour
through changes in
component states.
Reads the continuously
changing state of its
components.
Listens to system
events, updates its state.
Stores data, which gets
updated in response to
events from systems.
Listens to outside
events, publishes
updates to components
Provides the logic that
manipulates the data
encapsulated in
components.

Data flow in ECS
System Component Entity

23. The spreadsheet analogy for ECS

24. The spreadsheet analogy for ECS

25. ●Good decoupling, helps divide your monolithic classes
●Clear separation of responsibility
○Encourages small interfaces
○Entity.build([PlayerInputComponent])
●Easy reuse and composability
○Entity.build([FlyingComponent])
○Entity.build([FlyingComponent, SeeingComponent])
●Straightforward unit testing and mocking
○Substitute components with mocked components at runtime
●Separates data from functions that act on it
●Runtime object definition
●Parallelizable

Advantages of ECS

26. ●Most people have never even heard of this pattern
●Handling interprocess communication introduces complexity
●Inter-Component communication
○What happens when a system needs to access multiple components?
●Inter-System communication
○What happens when two systems need to access the same component?
●Not as concretely defined as other patterns such as MVC
○There are a multitude of ways to implement ECS
●Instantiation of entities is more involved
○Who wires up the components?
○Does the entity itself creates its own components?
○Does outside code provides the components?
Challenges of ECS

27. A walkthrough of an
ECS implementation in
Elixir
A high-level overview
of Entity Component
Systems
Background
Drawbacks of
traditional OOP /
inheritance style code
ECS Examples Code Next Steps
Real life applications
and examples of ECS
in action
Further learning, future
improvements, and
conclusion

28. ECS in the Real World

30. A walkthrough of an
ECS implementation in
Elixir
A high-level overview
of Entity Component
Systems
Background
Drawbacks of
traditional OOP /
inheritance style code
ECS Examples Code Next Steps
Real life applications
and examples of ECS
in action
Further learning, future
improvements, and
conclusion

31. Entity Component Systems
in Elixir

32. What is Elixir?
●Language that compiles to Erlang
●Built on top of the famed Erlang VM (“nine 9s of reliability”)
○Traditionally used for telecommunications by Ericsson
○WhatsApp, Facebook Messenger, RabbitMQ, Riak
●Built-in concurrency abstractions (Actor model and OTP)
●A pleasant, modern syntax similar to Ruby
●Immutable and Functional
●Gradual types
●Pattern Matching
●Interop with Erlang
●Metaprogramming through Macros

33. The Actor Model
●Actors are computational entities that can:
○Send messages
○Receive messages
○Create other actors
●Elixir processes
○The key abstraction of Elixir’s concurrency model (Demo)
●Erlang OTP
○Battle-tested patterns for building distributed, fault-tolerance
applications
○GenServer

34. Component
A struct containing state attributes

System
A GenServer

Entity
A struct with string id and a collection of
Component PIDs

An ECS implementation in Elixir

35. Demo

36. A walkthrough of an
ECS implementation in
Elixir
A high-level overview
of Entity Component
Systems
Background
Drawbacks of
traditional OOP /
inheritance style code
ECS Examples Code Next Steps
Real life applications
and examples of ECS
in action
Further learning, future
improvements, and
conclusion

37. Next Steps
ECS is an overlooked architectural pattern that overcomes some of the drawbacks
of OOP-style inheritance, and is a great fit for distributed systems.

Branching out into unfamiliar domains is a fruitful source of new ideas and
patterns to write better software.

39. “
The worst case:
The next generation of programmers grows up only being shown one way of thinking about programming.
So they kind of work on that way of programming—they flesh out all the details, they, you know, kind of solve that particular
model of programming. They’ve figured it all out. And then they teach that to the next generation. So that second generation
then grows up thinking: “Oh, it’s all been figured out. We know what programming is. We know what we’re doing.”

So the most dangerous thought that you can have as a creative person is to think that you know what you’re doing. Because
once you think you know what you’re doing, you stop looking around for other ways of doing things.

If you want to be open or receptive to new ways of thinking, to invent new ways of thinking, I think the first step is you have
to say to yourself, “I don’t know what I’m doing. We as a field don’t know what we’re doing.”
”

Bret Victor, on the Future of Programming
https://vimeo.com/71278954
Next Steps

40. Thanks
Yos Riady
yos.io