Reset ECS world and jobs to start fresh again

Unity Engine
, ,
1

I’m trying to develop a physics based destruction mini-game and I’ve been stuck for a couple of days when I’m trying to reload the whole scene to start fresh again.

Here is the video of what happens:

I’m using several system using jobs to detect collision like this:

[System.Serializable]
    public partial class CollisioWallToActorDetectionSystem : SystemBase
    {
        private StepPhysicsWorld stepPhysicsWorld;
        private EndSimulationEntityCommandBufferSystem commandBufferSystem;

        protected override void OnCreate()
        {
            stepPhysicsWorld = World.GetOrCreateSystem<StepPhysicsWorld>();
            commandBufferSystem = World.GetOrCreateSystem<EndSimulationEntityCommandBufferSystem>();
        }

        protected override void OnUpdate()
        {
            var jobHandle = Dependency;
            Dependency.Complete();

            var applicationJob = new ApplicationWallToRagdollJob
            {
                actorCollider = GetComponentDataFromEntity<RagdollComponent>(),
                wallCollider = GetComponentDataFromEntity<WallColliderData>()
            };

            Dependency = applicationJob.Schedule(stepPhysicsWorld.Simulation, Dependency);
               commandBufferSystem.AddJobHandleForProducer(Dependency);
        }

        [BurstCompile]
        private struct ApplicationWallToRagdollJob : ICollisionEventsJob
        {
            public ComponentDataFromEntity<RagdollComponent> actorCollider;
            public ComponentDataFromEntity<WallColliderData> wallCollider;           

            public void Execute(CollisionEvent triggerEvent)
            {
                if (wallCollider.HasComponent(triggerEvent.EntityA))
                {
                    if (actorCollider.HasComponent(triggerEvent.EntityB))
                    {
                        WallColliderData wall = wallCollider[triggerEvent.EntityA];
                        wall.Destroy = true;
                        wallCollider[triggerEvent.EntityA] = wall;
                    }
                }

                if (wallCollider.HasComponent(triggerEvent.EntityB))
                {
                    if (actorCollider.HasComponent(triggerEvent.EntityA))
                    {
                        WallColliderData wall = wallCollider[triggerEvent.EntityB];
                        wall.Destroy = true;
                        wallCollider[triggerEvent.EntityB] = wall;
                    }
                }
            }
        }
    }

So, what should I do to start clean? I’ve tried the few things I’ve found on Internet unsuccessfully and I’ve run out of options.

2

I’ve had issues myself in the past with clearing a world and reusing it. It looked like a use case Unity had not tested properly. I did not find a solution, but here’s the workaround I use:

Create a brand new world and dispose of the previous one. This brings a couple of challenges because you have to rebind the world to the player loop, but at least it works.

3

If you destroy all entities besides prefabs, and reinstantiate them again, tha should solve the problem.

4

Thanks a lot!! It worked. The code looks like this to reset. I don’t even need to reload the scene in order to start fresh:

        public void DestroyAllEntities()
        {
            World.DefaultGameObjectInjectionWorld.EntityManager.DestroyEntity(World.DefaultGameObjectInjectionWorld.EntityManager.UniversalQuery);
            World.DisposeAllWorlds();
            DefaultWorldInitialization.Initialize("Base World", false);
            ScriptBehaviourUpdateOrder.AppendWorldToCurrentPlayerLoop(World.DefaultGameObjectInjectionWorld);
        }
5

World.DefaultGameObjectInjectionWorld.EntityManager.DestroyEntity(World.DefaultGameObjectInjectionWorld.EntityManager.UniversalQuery);

You don’t need this, you’re disposing world so it’ll clean up by itself. This will just slow it down.

6

For the future programmers who look into reseting the ECS system this is the final solution that work for me at the moment I’m posting:

        public void CleanAndRestartECS()
        {
            var defaultWorld = World.DefaultGameObjectInjectionWorld;
            defaultWorld.EntityManager.CompleteAllJobs();
            foreach (var system in defaultWorld.Systems)
            {
                system.Enabled = false;
            }
            defaultWorld.Dispose();
            DefaultWorldInitialization.Initialize("Default World", false);
            if (!ScriptBehaviourUpdateOrder.IsWorldInCurrentPlayerLoop(World.DefaultGameObjectInjectionWorld))
            {
                ScriptBehaviourUpdateOrder.AppendWorldToCurrentPlayerLoop(World.DefaultGameObjectInjectionWorld);
            }   
            SceneManager.LoadScene("Game", LoadSceneMode.Single);
        }
7

But how You destroy entities with certain tag? Like I don’t need to destroy some entities after restarting scene

8

Looks like this is indeed working (script by @Esteban-Gallardo).

I modified script a little so we no longer have this strings around.

        public void CleanAndRestartECS()
        {
            var worldName = World.DefaultGameObjectInjectionWorld.Name;
            var defaultWorld = World.DefaultGameObjectInjectionWorld;
            defaultWorld.EntityManager.CompleteAllTrackedJobs();
            foreach (var system in defaultWorld.Systems)
            {
                system.Enabled = false;
            }
            defaultWorld.Dispose();
            DefaultWorldInitialization.Initialize(worldName, false);
            if (!ScriptBehaviourUpdateOrder.IsWorldInCurrentPlayerLoop(World.DefaultGameObjectInjectionWorld))
            {
                ScriptBehaviourUpdateOrder.AppendWorldToCurrentPlayerLoop(World.DefaultGameObjectInjectionWorld);
            }

            var scene = SceneManager.GetActiveScene();
            var sceneName = scene.name;
            SceneManager.LoadScene(sceneName, LoadSceneMode.Single);
        }