How to access GameObject and it's components from an ECS Systems?

[Zedikus]

Hi!
In my project I have multiple cameras with different values of Field Of View which can also be dynamically changed. Also I need to switch active camera (deactivate one and activate another during the runtime). All of this makes me access these authoring Camera components so I can manipulate their values.

Is there ways to access authoring components of specific GameObjects from ECS Systems?

P.S. Obviously I can’t just use Singleton link because cameras more than one

[andrew-lukasik]

@Zedikus

Is there ways to access authoring components of specific GameObjects from ECS Systems?

I answered very similar question here:

Access regular transform from ECS

You can use entityManager.AddComponentObject(obj) to create an Entity that references any object, Transform included. It’s good idea to reference a “tag” type object (Camera or Light component in this case) alongside it as well so this Entity will be easier to distinguish (EntityQuery) from other similar entities. https://docs.unity3d.com/Packages/com.unity.entities@1.2/api/Unity.Entities.EntityManager.AddComponentObject.html This ObjectsToEntity will create you an Entity that will host refe…

ObjectsToEntity.cs is your authoring-like component that maintains an Entity with references to any UnityEngine.Object you want.

ObjectsToEntity.cs

@andrew-lukasik

using UnityEngine;
using Unity.Entities;

public class ObjectsToEntity : MonoBehaviour
{
    [SerializeField] Object[] _objects;
    Entity _entity;
    void Awake ()
    {
        var em = World.DefaultGameObjectInjectionWorld.EntityManager;
        _entity = em.CreateEntity();
        foreach( var obj in _objects )
        {
            em.AddComponentObject( _entity , obj );
        }
    }
    void OnDestroy ()
    {
        var em = World.DefaultGameObjectInjectionWorld.EntityManager;
        if( em.Exists(_entity) ) em.DestroyEntity( _entity );
    }
}

In short, this is how accessing Camera component would look like on ECS side:

Camera cam = EntityManager.GetComponentObject<Camera>(entity);

ISystem example

@andrew-lukasik

using UnityEngine;
using Unity.Entities;
using Unity.Collections;

public partial struct MerrySystem : ISystem
{
    EntityQuery _query;
    public void OnCreate ( ref SystemState state )
    {
        _query = state.EntityManager.CreateEntityQuery( typeof(Camera) , typeof(Transform) );
        state.RequireForUpdate( _query );
    }
    public void OnDestroy ( ref SystemState state )
    {
        _query.Dispose();
    }
    public void OnUpdate ( ref SystemState state )
    {
        var em = state.EntityManager;
        foreach( Entity entity in _query.ToEntityArray(Allocator.Temp) )
        {
            Vector3 pos = em.GetComponentObject<Transform>(entity).position;
            Debug.DrawLine( pos , new Vector3(pos.x,0,pos.z) , Color.magenta );
        }
    }
}

→ More details in the linked thread.