Fireblade ECS (Entity-Component System)

This is a dependency free, lightweight, fast and easy to use Entity-Component System implementation in Swift. It is developed and maintained as part of the Fireblade Game Engine project.

See the Fireblade ECS Demo App or have a look at documentation in the wiki to get started.

🚀 Getting Started

These instructions will get you a copy of the project up and running on your local machine and provide a code example.

📋 Prerequisites

• Swift Package Manager (SPM)
• Swiftlint for linting - (optional)
• SwiftEnv for Swift version management - (optional)

💻 Installing

Fireblade ECS is available for all platforms that support Swift 5.1 and higher and the Swift Package Manager (SPM).

Extend the following lines in your Package.swift file or use it to create a new project.

// swift-tools-version:5.1

import PackageDescription

let package = Package(
    name: "YourPackageName",
    dependencies: [
        .package(url: "https://github.com/fireblade-engine/ecs.git", from: "0.14.0")
    ],
    targets: [
        .target(
            name: "YourTargetName",
            dependencies: ["FirebladeECS"])
    ]
)

📝 Code Example

🏛️ Nexus

The core element in the Fireblade-ECS is the Nexus. It acts as a centralized way to store, access and manage entities and their components. A single Nexus may (theoretically) hold up to 4294967295 Entities at a time.
You may use more than one Nexus at a time.

Initialize a Nexus with

let nexus = Nexus()

👤 Entities

then create entities by letting the Nexus generate them.

// an entity without components
let newEntity = nexus.createEntity()

To define components conform your class to the Component protocol

final class Position: Component {
	var x: Int = 0
	var y: Int = 0
}

and assign instances of it to an Entity with

let position = Position(x: 1, y: 2)
entity.assign(position)

You can be more efficient by assigning components while creating an entity.

// an entity with two components assigned.
nexus.createEntity {
	Position(x: 1, y: 2)
	Color(.red)
}

// bulk create entities with multiple components assigned.
nexus.createEntities(count: 100) { _ in
	Position()
	Color()
}

👪 Families

This ECS uses a grouping approach for entities with the same component types to optimize cache locality and ease up access to them.
Entities with the same component types may belong to one Family. A Family has entities as members and component types as family traits.

Create a family by calling .family with a set of traits on the nexus. A family that contains only entities with a Movement and PlayerInput component, but no Texture component is created by

let family = nexus.family(requiresAll: Movement.self, PlayerInput.self,
                          excludesAll: Texture.self)

These entities are cached in the nexus for efficient access and iteration. Families conform to the Sequence protocol so that members (components) may be iterated and accessed like any other sequence in Swift.
Access a family's components directly on the family instance. To get family entities and access components at the same time call family.entityAndComponents. If you are only interested in a family's entities call family.entities.

class PlayerMovementSystem {
	let family = nexus.family(requiresAll: Movement.self, PlayerInput.self,
                              excludesAll: Texture.self)

	func update() {
		family
			.forEach { (mov: Movement, input: PlayerInput) in
			
			// position & velocity component for the current entity
			
			// get properties
			_ = mov.position
			_ = mov.velocity
			
			// set properties
			mov.position.x = mov.position.x + 3.0
			...
			
			// current input command for the given entity
			_ = input.command
			...
			
		}
	}

	func update2() {
		family
			.entityAndComponents
			.forEach { (entity: Entity, mov: Movement, input: PlayerInput) in
			
			// the current entity instance
			_ = entity

			// position & velocity component for the current entity
			
			// get properties
			_ = mov.position
			_ = mov.velocity
			
			
		}
	}

	func update3() {
		family
			.entities
			.forEach { (entity: Entity) in
			
			// the current entity instance
			_ = entity
		}
	}
}

🧑 Singles

A Single on the other hand is a special kind of family that holds exactly one entity with exactly one component for the entire lifetime of the Nexus. This may come in handy if you have components that have a Singleton character. Single components must conform to the SingleComponent protocol and will not be available through regular family iteration.

final class GameState: SingleComponent {
    var quitGame: Bool = false
}
class GameLogicSystem {
    let gameState: Single<GameState>
    
    init(nexus: Nexus) {
        gameState = nexus.single(GameState.self)
    }
    
    func update() {
        // update your game sate here
        gameState.component.quitGame = true
        
        // entity access is provided as well
        _ = gameState.entity
    }
}

👫 Relatives (deprecated)

This ECS implementation provides an integrated way of creating a directed acyclic graph (DAG) hierarchy of entities by forming parent-child relationships. Entities can become children of a parent entity. In family terms they become relatives. Families provide iteration over these relationships.
The entity hierarchy implementation does not use an additional component therefore keeping the hierarchy intact over different component-families. This feature is especially useful for implementing a scene graph.

// create entities with 0 to n components
let parent: Entity = nexus.createEntity(with: Position(x: 1, y: 1), SomeOtherComponent(...))
let child: Entity  = nexus.createEntity(with: Position(x: 2, y: 2))
let child2: Entity = nexus.createEntity(with: Position(x: 3, y: 3), MySpecialComponent(...))

// create relationships between entities
parent.addChild(child)
child.addChild(child2)
// or remove them
// parent.removeChild(child)

// iterate over component families descending the graph
nexus.family(requires: Position.self)
     .descendRelatives(from: parent) // provide the start entity (aka root "node")
     .forEach { (parent: Position, child: Position) in
        // parent: the current parent component
        // child: the current child component
        
        // update your components hierarchically
        child.x += parent.x
        child.y += parent.y
     }

🔗 Serialization

To serialize/deserialize entities you must conform their assigned components to the Codable protocol.
Conforming components can then be serialized per family like this:

// MyComponent and YourComponent both conform to Component and Codable protocols.
let nexus = Nexus()
let family = nexus.family(requiresAll: MyComponent.self, YourComponent.self)

// JSON encode entities from given family.
var jsonEncoder = JSONEncoder()
let encodedData = try family.encodeMembers(using: &jsonEncoder)

// Decode entities into given family from JSON. 
// The decoded entities will be added to the nexus.
var jsonDecoder = JSONDecoder()
let newEntities = try family.decodeMembers(from: jsonData, using: &jsonDecoder)

🧪 Demo

See the Fireblade ECS Demo App to get started.

📖 Documentation

Consult the wiki for in-depth documentation.

🏷️ Versioning

We use SemVer for versioning. For the versions available, see the tags on this repository.

✍️ Authors

• Christian Treffs - Initial work
• Manuel Weidmann

See also the list of contributors who participated in this project.

🔏 License

This project is licensed under the MIT License - see the LICENSE file for details

🙏 Acknowledgments

Inspired by

• Ashley
• Entitas
• EntitasKit