SystemAPI.Query code with different EntityManager

[mighty wing]

I'm iterating over another world's data and this requires me to replicate the behavior of SystemAPI.Query manually. I'm not too shocked by that, however there is a performance benefit to SystemAPI.Query since it can iterate over chunks directly, whereas without it I have to use ToArchetypeChunkArray first.

When browsing the generated code, I did see EntityQueryEnumerator, which could be a good start, but it's documented with "exists only for use by code-gen".

Are there other ways to go about this?

[bitter lichen]

you can take a look into codegened code

when you use query normally

and see how it's code

codegen is nothing but a boilerplate generator in this case

ToArchetypeChunkArray this is array of actual chunks though

direct access to entity data

not copy

[mighty wing]

I mean it copies the chunk pointers to an array, of course it doesnt copy all the entity data

[mighty wing]

I did look at it, I'm just wondering if there are (or should be) other ways to iterate (or if EntityQueryEnumerator is OK to use)

[bitter lichen]

what you are doing here is not recommended alltogether so 😅

why not just have system iterate over world own data?

[mighty wing]

i have a simulation world that updates independently from the main loop; the data transfer of course needs to be in the main loop because I'm using the transferred data right after

as for not recommended, I think copying data between worlds falls perfectly in the ECS use case; netcode for entities must be doing exactly that, maybe i should take a closer look at that too

[bitter lichen]

what stops you from just prepping data in world and then simply reading it from other?

[mighty wing]

jobs that are in progress

[bitter lichen]

you can just force complete

when you need to sync

in fact

you don't care about it

if world updates are synced

you can just write to 2 containers

frame 0 you write to container 0
frame 1 you write to container 1
frame 2 you write to container 0

if 1 frame delay is tolerable you'll be able to read data without a sync point

[mighty wing]

sure, yeah, but wait a minute, we are digressing

I already have all the synchronization and chunk copies working, the point was just about accessing the chunk data and avoiding the array allocation

the data copy is properly parallelized using IJobChunk and all that

[bitter lichen]

if you already have chunks - simply use type handles

to get native arrays of component data

[mighty wing]

I'll be more specific; to iterate over the chunks on the main thread, I need to access them, and that can be done in two ways for my use case:

• EntityQuery.ToArchetypeChunkArray() -> requires iterating over chunks and allocating the array
• EntityQueryEnumerator -> "exists only for use by code-gen", but im happy to use it if there's no problem with it

[bitter lichen]

I thought you meant you already have chunks

why not just run a job?

you can't use enumerator, it's a dummy

not real code

[mighty wing]

EntityQueryEnumerator is not code-generated, it exists to be used by code-gen; you made me doubt but after testing I can assure you it works 😛

[bitter lichen]

ah, I thought you meant the other type (which is returned by SystemAPI.Query)

well yeah, all backend of it does work

[calm badge]

Just a word of caution. Those types are only intended for use by our source-generators. They likely will change in the future.

That said, Rider should show you generated code for all of the generated features we have if you F12 on the system type that contains them. This is probably a great way to see how we are doing things under the hood (and let us know if we are doing anything crazy).

[mighty wing]

Just a word of caution. Those types are only intended for use by our source-generators. They likely will change in the future.
Yes, hence this thread. I'll stick to using ToArchetypeChunkArray for now, but I think it could be nice if EntityQueryEnumerator (or equivalent) was a real part of the API.

[mighty wing]

Neat for the F12 thingy, is there an equivalent for visual studio? Right now I get there by stepping through the code. Maybe it's time to give Rider a try too.

[bitter lichen]

why not just run a job though?

should be less boilerplate overall

[mighty wing]

that will just make it slower, I need to do structural changes right after anyway

there's a reason SystemAPI uses that instead of ToArchetypeChunkArray

[bitter lichen]

but SystemAPI.Query does not let structural changes either

[mighty wing]

yeah but im doing structural changes in another world than the one im iterating on

[bitter lichen]

I'm curious if job forbids from it 🤔