Custom entity authoring behaviour for Camera object.

CameraAuthoring.cs

using Unity.Entities;
using Unity.Transforms;
using UnityEngine;

namespace Acme.Authoring
{
    /// <summary>
    /// Custom authoring way must be used because converting Camera object to Entity in traditional way (ConvertToEntity nor SubScene) does not work.
    /// </summary>
    [DisallowMultipleComponent]
    public class CameraAuthoring : MonoBehaviour
    {
        private void Start()
        {
            var em = World.DefaultGameObjectInjectionWorld.EntityManager;
            var entity = em.CreateEntity();

            em.SetName(entity, "Main Camera");
            em.AddComponent<CopyTransformToGameObject>(entity);
            em.AddComponentData(entity, new Rotation()
            {
                Value = transform.rotation
            });
            em.AddComponentData(entity, new Translation()
            {
                Value = transform.position
            });
            em.AddComponent<LocalToWorld>(entity);

            // Taken from ConvertToEntity.InjectOriginalComponents
            foreach (var com in transform.GetComponents<Component>())
            {
                if (com is GameObjectEntity || com is ConvertToEntity ||
                    com is ComponentDataProxyBase || com is StopConvertToEntity)
                    continue;
                em.AddComponentObject(entity, com);
            }
        }
    }
}