/** Work in progress **/
decs
decs is my attempt to build a @nogc D language Entity Component System. I'm not really a game dev, im trying to learn how an ECS works so some portions of this code can be inefficients or bug prone.
It's inspired by the following projects :
- https://github.com/miguelmartin75/anax => C++ ECS
- https://github.com/jzhu98/star-entity => D ECS
- https://github.com/claudemr/entitysysd => D ECS
How to build
You have to use dub to build the project.
Add this project as a dependency to your dub.json:
"dependencies": {
"decs": "~>1.0.3"
}How to use
Entity Manager
import decs;
void main()
{
auto em = new EntityManager();
while(game)
{
em.update(dt);
}
// !important!
em.dispose();
}
Entities
You can create an entity, kill it, invalidate it or activate it (still need some work here).
auto entity = em.createEntity();
// Notifies all systems that a new entity is alive
entity.activate();
// Entity is still alive but will be invalid in current scope
entity.invalidate();
// Poor entity :<
entity.kill();Components
A component must be represented as a struct.
struct PositionComponent
{
float x, y, z;
}You can add a component to an entity :
// add
entity.add!PositionComponent(1, 2, 3);
// update (its handled as a pointer)
entity.get!PositionComponent().y = 50;
// check
if(entity.has!PositionComponent())
{
// ...
}Systems
A system must be a class that inherits decs.System.
class MovementSystem : System
{
public void update(in float delta)
{
}
}There is 2 ways to query entities from your system :
- 1 => Using entity manager entities!(components...) method
- 2 => Using the mixin template mixin ComponentsFilter!(components...);
If you provide a components filter, when an entity is activated, it will be automatically added to the systems whose filters match her components.
class MovementSystem : System
{
// option 2
mixin ComponentsFilter!(PositionComponent);
public void update(in float deltaTime)
{
// option 1
auto entities = this.m_entityManager.entities!(PositionComponent);
// option 2 (should be more efficient)
foreach(entity; this.m_entities)
{
}
}
}System's update method will be called automatically by the entity manager in the main loop. If you want to handle the update manually, you can set the System.UpdatePolicy to manual :
class MovementSystem : System
{
public this()
{
super(System.UpdatePolicy.Manual);
}
}
// ...
while(game)
{
em.update(dt);
// you have to call it manually (before or after the em.update call)
myMovementSystem.update(dt);
}Events
A receiver is a class that implements Receiver(EventType) interface.
// An event must be a struct
struct MovementEvent
{
Entity target;
}
// The receiver
class CameraSystem : Receiver!MovementEvent
{
/**
* Movement event received from a system
*/
public void receive(ref MovementEvent event)
{
// follow event.entity...
}
}
// Subscribe to events
void main()
{
auto cameraSys = new CameraSystem();
auto em = new EntityManager();
em.subscribeToEvent!MovementEvent(cameraSys);
}You can send events from systems by using the m_eventManager.emit method.
// Sending an event from the MovementSystem
class MovementSystem : Receiver!MovementEvent
{
public void update(in float deltaTime)
{
foreach(entity; this.m_entities)
{
this.m_eventManager.emit(MovementEvent(entity));
}
}
}TODOs
- Add @Component and @Event UDAs
- Add an example project
- Improve this readme
- DOCS !
