How to iterate over all entities in a query during Entity.ForEach()

Unity Engine
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I’m trying to convert this Solar System simulator by Sabastian Lague to DOTS and need help when it comes to iterating over the component values for all entities in a query during Entity.ForEach().

I think I need to complete the following steps:

  • Write an EntityQuery()
  • Use the query to populate a NativeArray
  • During Entity.ForEach() iterate over the NativeArray to read the values

I’m hung up on step 2. If anyone could point me in the right direction it would be appreciated.

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I forget if Sabastian uses a compute shader here. I really think its time he tries out the job system. It is very similar in use, and burst jobs are very, very good. That would also be a good transition for you into DOTS if you decide ECS is too much.

It has been a while since I’ve looked at the logic of this, but if I recall correctly, you need to update each body based on the information from every other body.
I did something similar with a boids situation. I actually ditched the separate EntiyQuery and just used two Entities.ForEach() (this does perform a query). I make a NativeArray to contain the information I want, then I do an Entities.ForEach() to fill that array with data from every entity. I use int entityInQueryIndex as a parameter in the ForEach lambda function, before any refs or ins, to use the index of each Entity in the ForEach to assign data to a corresponding index in the NativeArray. Then I used a second ForEach() to use the data collected from every Entity to update every Entity. Again I used int entityInQueryIndex in the lambda function. This way if I was on say, Entity 7 in ForEach, I would skip using the data from index 7 in my NativeArray to update Entity 7’s components. I used ScheduleParallel() for both jobs, though I haven’t checked how parallel things actually were. Performance is very similar to a highly optimized GameObjectless MonoBehavior + Burst Jobs approach.

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//Sync
var arrayOfComponents = query.ToComponentDataArray<CustomComponent>(Allocator.TempJob);

//Async
var arrayOfComponents = query.ToComponentDataArrayAsync<CustomComponent>(Allocator.TempJob, out JobHandle jh);
Dependency = JobHandle.CombineDependencies(Dependency, jh);
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