The document discusses Entity system architecture with Unity using the Entitas framework. It describes common Unity pain points like testability, code sharing, and co-dependent logic that Entitas aims to address. Entitas uses components as data, entities as containers for components, and systems to define behavior. Components, entities, and systems allow for improved testability, code sharing, querying, and optimizations compared to traditional Unity scripts. The document provides examples of creating entities and systems with Entitas and demonstrates its capabilities.

1. Entity system architecture
with Unity

2. Maxim Zaks | @icex33 | github.com/mzaks
Simon Schmid | @s_schmid | github.com/sschmid

3. Wooga

5. Unity pain points
4 Testability
4 Code sharing
4 Co-dependent logic
4 Querying
4 Deleting code

6. Testability

7. Code sharing

8. Co-dependent logic

9. Co-dependent logic

10. Co-dependent logic

11. Querying

12. Deleting code

14. Entitas
Match One Demo

16. Components are just data
4 no Methods, no Start(), no Update()
4 no inheritance
+-----------+
| Component |
|-----------|
| Data |
+-----------+

17. PositionComponent
using Entitas;
public class PositionComponent : IComponent
{
public int x;
public int y;
}

18. GameBoardElementComponent
using Entitas;
public class GameBoardElementComponent : IComponent
{
}

19. Entity is a container for components
+-----------+
| Entity |
|-----------|
| Component |
| |
| Component |
| |
| Component |
+-----------+

20. Entity
4 Add Components
4 Replace Components
4 Remove Components

21. Create Blocker Entity
public static Entity CreateBlocker(this Pool pool, int x, int y)
{
return pool.CreateEntity()
.IsGameBoardElement(true)
.AddPosition(x, y)
.AddResource(Res.Blocker);
}

22. Pool contains all entities
+------------------+
| Pool |
|------------------|
| e e |
| e e |
| e e |
| e e e |
| e e |
| e e |
| e e e |
| e e e |
+------------------+

23. Pool
4 Create Entity
4 Destroy Entity
4 Get all Entities
4 Get Group

24. Groups are subsets of entities
4 Performance optimization for querying
4 Matcher is a filter description
+-------------+ Groups:
| e | Subsets of entities in the pool
| e e | for blazing fast querying
| +------------+
| e | | |
| e | e | e |
+--------|----+ e |
| e |
| e e |
+------------+

25. Get Group from pool
_pool.GetGroup(
Matcher.AllOf(
Matcher.GameBoardElement,
Matcher.Position
)
);

26. +------------------+
| Pool | Entitas in a nutshell
|------------------|
| e e | +-----------+
| e e---|----> | Entity |
| e e | |-----------|
| e e e | | Component |
| e e | | | +-----------+
| e e | | Component-|----> | Component |
| e e e | | | |-----------|
| e e e | | Component | | Data |
+------------------+ +-----------+ +-----------+
|
|
| +-------------+ Groups:
| | e | Subsets of entities in the pool
| | e e | for blazing fast querying
+---> | +------------+
| e | | |
| e | e | e |
+--------|----+ e |
| e |
| e e |
+------------+

27. Behaviour

28. System
4 Start / Execute
4 No State!!!

29. +------------------+ +-----------------------------+
| Pool | | System |
|------------------| |-----------------------------|
| e e | | - Execute |
| e e | | |
| e e | | +-------------+ |
| e e e | | | e | Groups |
| e e |+----|->| e e | |
| e e | | | +------------+ |
| e e e | | | e | | | |
| e e e | | | e | e | e | |
+------------------+ | +--------|----+ e | |
| | e | |
| | e e | |
| +------------+ |
+-----------------------------+

30. MoveSystem
public void Execute() {
var movables = _pool.GetGroup(
Matcher.AllOf(
Matcher.Move,
Matcher.Position
));
foreach (var e in movables.GetEntities()) {
var move = e.move;
var pos = e.position;
e.ReplacePosition(pos.x, pos.y + move.speed, pos.z);
}
}

31. Chain of Responsibility
| |
|-------------------------------- Game Loop --------------------------------|
| |
+------------+ +------------+ +------------+ +------------+
| | | | | | | |
| System | +---> | System | +---> | System | +---> | System |
| | | | | | | |
+------------+ +------------+ +------------+ +------------+

32. return new Systems()
.Add( pool.CreateGameBoardSystem ())
.Add( pool.CreateCreateGameBoardCacheSystem ())
.Add( pool.CreateFallSystem ())
.Add( pool.CreateFillSystem ())
.Add( pool.CreateProcessInputSystem ())
.Add( pool.CreateRemoveViewSystem ())
.Add( pool.CreateAddViewSystem ())
.Add( pool.CreateRenderPositionSystem ())
.Add( pool.CreateDestroySystem ())
.Add( pool.CreateScoreSystem ());

33. Reacting to changes in a Group
4 On Entity added
4 On Entity removed

34. ScoreLabelController
void Start() {
_pool.GetGroup(Matcher.Score).OnEntityAdded +=
(group, entity) => updateScore(entity.score.value);
updateScore(_pool.score.value);
}
void updateScore(int score) {
_label.text = "Score " + score;
}

35. Reactive System
4 Executed only when entities in a group have changed
4 Aggregate and process changes

36. Render Position System
public class RenderPositionSystem : IReactiveSystem {
public IMatcher trigger { get { return Matcher.AllOf(Matcher.Position, Matcher.View); } }
public GroupEventType eventType { get { return GroupEventType.OnEntityAdded; } }
public void Execute(Entity[] entities) {
foreach (var e in entities) {
var pos = e.position;
e.view.gameObject.transform.position = new Vector3(pos.x, pos.y);
}
}
}

37. Optimizations

38. Components
mutable vs immutable

41. Entity
Dictionary vs Array

42. Dictionary
e.AddComponent(new PositionComponent());
var component = e.GetComponent<PositionComponent>();
Array
e.AddComponent(new PositionComponent(), 5);
var component = (PositionComponent)e.GetComponent(5);

45. Code Generator

46. Before Code Generation
PositionComponent component;
if (e.HasComponent(ComponentIds.Position)) {
e.WillRemoveComponent(ComponentIds.Position);
component = (PositionComponent)e.GetComponent(ComponentIds.Position);
} else {
component = new PositionComponent();
}
component.x = 10;
component.y = 10;
e.ReplaceComponent(ComponentIds.Position, component);

47. After Code Generation
e.ReplacePosition(10, 10);

48. Code Generator Demo

49. var pool = Pools.pool;
var e = pool.CreateEntity();
e.AddPosition(1, 2, 3);
e.ReplacePosition(4, 5, 6);
e.RemovePosition();
var posX = e.position.x;
var hasPos = e.hasPosition;
e.isMovable = true;
e.isMovable = false;
var isMovable = e.isMovable;

50. Visual Debugging Demo

52. Entitas is
open sourcegithub.com/sschmid/Entitas-CSharp

53. Recap

54. Unity pain points
4 Testability
4 Code sharing
4 Co-dependent logic
4 Querying
4 Deleting code

55. Advantages
4 Straightforward to achieve Determinism and
therefore Replay
4 Simulation Speed (2x, 4x)
4 Headless Simulation, just remove systems which rely
on GameObjects (render systems)
4 Save Game (Serialization / Deserialization) send
data to backend on change

56. Q&AMaxim Zaks | @icex33 | github.com/mzaks
Simon Schmid | @s_schmid | github.com/sschmid
tinyurl.com/entitas