Feedback EntityCommandBuffer.CreateEntity reference in IComponentData

I just have to say, the automatic fixup of Entity references inside IComponentData when calling Add/SetComponent on EntityCommandBuffer is nothing short of brilliant. Well done.

I would however highly recommend adding a note about this in the EntityCommandBuffer documentation. It is not immediately obvious that the Entity returned by CreateEntity is something you should not store a reference to unless you do so via Add/SetComponentData on the *same* EntityCommandBuffer.

 

Huh, since when is this happening? I have worked around that issue and made 2 threads about it.

Direct references are still not possible, right? But if I put the new entity in a component it gets automatically updated from Id values like -1 that we are seeing in the debugger?

This is great info! I need to utilize this.

 

If you call EntityCommandBuffer.CreateEntity and then store that immediately in a ref IComponentData in say, an IJobForEach job -- yes your reference will be bad (it'll have a command buffer relative value like Entity{Version=0, Index=-1...}). If you set that same IComponentData via a call to EntityCommandBuffer.SetComponent, any Entity references in your IComponentData get fixed-up when the commands are played back.

 

Yes, it works! Thanks so much!

My spawner system now puts a SpawnComplete tag with the new instanced entity on the SpawnCommand so PostProcessing_ comps know what to work on.
Before I had to put a SpawnComplete with the parent on the instance and it was a pain to get all the data back or even knowing what data was there in the first place.

Now it's all good. Finally! Haha

 

Glad my somewhat accidental discovery was useful. If you are curious on implementation details at all, look in EntityCommandBufferData.AddEntityComponentCommand -- you can see how they explicitly check if an IComponentData needs Entity fixups. Clever stuff.

 

Thank you. Here is a code (line 30) reference showing the working code (and a single-threaded version for comparison)

Code (CSharp):

1.             ////single threaded
2.             //{
3.             //    Entities.ForEach((int entityInQueryIndex, ref Spawner spawner, in Translation trans, in Rotation rot) =>
4.             //    {
5.             //        if (!EntityManager.Exists(spawner.spawnObject))
6.             //        {
7.             //            //doesn't exist, so spawn a copy of the prefab, using transform details from the spawner
8.             //            spawner.spawnObject = EntityManager.Instantiate(spawner.spawnPrefab);
9.             //            EntityManager.SetComponentData(spawner.spawnObject, trans);
10.             //            EntityManager.SetComponentData(spawner.spawnObject, rot);
11.             //        }
12.             //    })
13.             //    .WithStructuralChanges().Run();
14.             //}
15.  
16.             //parallel
17.             {
18.                 var ecbSystem = World.GetOrCreateSystem<EndSimulationEntityCommandBufferSystem>();
19.                 var ecb = ecbSystem.CreateCommandBuffer().AsParallelWriter();
20.                 Entities
21.                 .ForEach((Entity spawnerEnt, int entityInQueryIndex, ref Spawner spawner, in Translation trans, in Rotation rot) =>
22.                 {
23.                     if (!HasComponent<Translation>(spawner.spawnObject))  //works in a Parallel ForEach(), makes sure that Entity and Translation component exist
24.                     {
25.                         //doesn't exist, so spawn a copy of the prefab, using transform details from the spawner
26.                         spawner.spawnObject = ecb.Instantiate(entityInQueryIndex, spawner.spawnPrefab); //creates a TEMPORARY entity reference.   needs to be fixed up (see below)
27.                         ecb.SetComponent(entityInQueryIndex, spawner.spawnObject, trans);
28.                         ecb.SetComponent(entityInQueryIndex, spawner.spawnObject, rot);
29.  
30.                         ecb.SetComponent(entityInQueryIndex, spawnerEnt, spawner); //need re-copy the spawner component back onto itself, to fix up the spawner.spawnObject reference.
31.                     }
32.                 })
33.                 .ScheduleParallel();
34.                 ecbSystem.AddJobHandleForProducer(this.Dependency);
35.             }