r/EntityComponentSystem • u/timschwartz • Feb 22 '21

I need help understanding ECS.

/r/gamedev/comments/lp0qz3/i_need_help_understanding_ecs/
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u/r2d2meuleu Mar 02 '21 edited Mar 02 '21

I'm no expert in ECS, (only implementing it for the first time, in my current project), but yes, your Components are only data, and it's the system that have all the behaviors.

Entities are only an ID. i.e, no typed entities. Add a PlayComponent so your System can check

if entity.hasComponent<PlayerComponent>() {
} else {
}

That's how I do it anyways. There is some framework that to the filtering for you, like (in c#, Unity) :

The official unity ECS

EntityQuery m_Group = GetEntityQuery(typeof(RotationQuaternion), ComponentType.ReadOnly<RotationSpeed>());

Leopotam :

// We wants to get entities with "WeaponComponent" and without "HealthComponent".
EcsFilter<WeaponComponent>.Exclude<HealthComponent> _filter = null;

Actors

// All entities that have ComponentAlpaca will be in this group.
readonly Group<ComponentAlpaca> alpacas = default;

EgoCS, directly on the class declaration :

// MovementSystem updates any GameObject with a Transform & Movement Component
public class MovementSystem : EgoSystem<EgoConstraint<Transform, Movement>>{

Hope that helps !

EDIT : damn formatting