ECS + Jobs - pass Entity array to job

Hi, Im wanted to try new ECS and C# Jobs features and want to code simple collision system. I want to write job which will check Collider with all other Colliders and I dont know how to pass/inject array of all Colliders to job. Here is what I have so far

Code (CSharp):

1. namespace ECSGame
2. {
3.     [UsedImplicitly]
4.     [UpdateAfter(typeof(RigidBodySystem))]
5.     public class CollisionSystem : JobComponentSystem
6.     {
7.         [BurstCompile]
8.         private struct UpdateBoundsJob : IJobProcessComponentData<Position, Collider>
9.         {
10.             public void Execute([ReadOnly] ref Position position, ref Collider collider)
11.             {
12.                 collider.Bounds.Center = position.Value + collider.Center;
13.                 collider.Bounds.HalfWidth = collider.Size;
14.             }
15.         }
16.  
17.         [BurstCompile]
18.         private struct CollisionJob : IJobProcessComponentData<Collider>
19.         {
20.             public void Execute([ReadOnly] ref Collider collider)
21.             {
22.                 foreach (var c in Colliders)
23.                 {
24.                     Check(collider.Bounds, c.Collider.Bounds);
25.                 }
26.             }
27.  
28.             private static bool Check(AABB a, AABB b)
29.             {
30.                 var x = math.abs(a.Center.x - b.Center.x) <= (a.HalfWidth.x + b.HalfWidth.x);
31.                 var y = math.abs(a.Center.y - b.Center.y) <= (a.HalfWidth.y + b.HalfWidth.y);
32.                 var z = math.abs(a.Center.z - b.Center.z) <= (a.HalfWidth.z + b.HalfWidth.z);
33.  
34.                 return x && y && z;
35.             }
36.         }
37.  
38.         protected override JobHandle OnUpdate(JobHandle inputDependencies)
39.         {
40.             var updateBoundsJob = new UpdateBoundsJob();
41.             var updateBoundsJobHandle = updateBoundsJob.Schedule(this, inputDependencies);
42.  
43.             var collisionJob = new CollisionJob();
44.             return collisionJob.Schedule(this, updateBoundsJobHandle);
45.         }
46.     }
47. }

 

Colliders allowed only on main thread yet. Or it your own?

 

It is my own entity. Im going pure ECS

 

Ok I came up with this

Code (CSharp):

1. using JetBrains.Annotations;
2. using Unity.Burst;
3. using Unity.Collections;
4. using Unity.Entities;
5. using Unity.Jobs;
6. using Unity.Mathematics;
7. using Unity.Transforms;
8.  
9. namespace ECSGame
10. {
11.     [UsedImplicitly]
12.     [UpdateAfter(typeof(RigidBodySystem))]
13.     public class CollisionSystem : JobComponentSystem
14.     {
15.         private struct Group
16.         {
17.             public readonly int Length;
18.             public ComponentDataArray<Collider> Colliders;
19.         }
20.  
21.         [BurstCompile]
22.         private struct UpdateBoundsJob : IJobProcessComponentData<Position, Collider>
23.         {
24.             public void Execute([ReadOnly] ref Position position, ref Collider collider)
25.             {
26.                 collider.Bounds.Center = position.Value + collider.Center;
27.                 collider.Bounds.HalfWidth = collider.Size;
28.             }
29.         }
30.  
31.         [BurstCompile]
32.         private struct CollisionJob : IJobParallelFor
33.         {
34.             [ReadOnly] public ComponentDataArray<Collider> colliders;
35.  
36.             private static bool Check(AABB a, AABB b)
37.             {
38.                 var x = math.abs(a.Center.x - b.Center.x) <= (a.HalfWidth.x + b.HalfWidth.x);
39.                 var y = math.abs(a.Center.y - b.Center.y) <= (a.HalfWidth.y + b.HalfWidth.y);
40.                 var z = math.abs(a.Center.z - b.Center.z) <= (a.HalfWidth.z + b.HalfWidth.z);
41.  
42.                 return x && y && z;
43.             }
44.  
45.             public void Execute(int index)
46.             {
47.                 for (var i = index + 1; i < colliders.Length; i++)
48.                 {
49.                     Check(colliders[index].Bounds, colliders[i].Bounds);
50.                 }
51.             }
52.         }
53.  
54.         [Inject]
55.         private Group group;
56.  
57.         protected override JobHandle OnUpdate(JobHandle inputDependencies)
58.         {
59.             var updateBoundsJob = new UpdateBoundsJob();
60.             var updateBoundsJobHandle = updateBoundsJob.Schedule(this, inputDependencies);
61.  
62.             var collisionJob = new CollisionJob
63.             {
64.                 colliders = group.Colliders
65.             };
66.             return collisionJob.Schedule(group.Length, 100, updateBoundsJobHandle);
67.         }
68.     }
69. }

and it seems work. But checking collisions between 2000 entities costs 16ms and with 20000 entities editor freezes I think I will need another solution for such scale.

 

Just a heads up, injection like that will be removed soon~

Also you need a broadphase to limit the number of checks you need to perform. Some type of spatial map etc.

Usually you should only need to perform a couple of dozen checks at most for collisions.

 

By removing method call in job i was able to get 50ms for 20000 entities and few second freez at hit play in editor. For sure will need some thing to reduce checks count.

 

Octree or spatial map, direct check All<->All not use no one

 

Ye, i know it's not the best solution. I just wanted to try simple solution and check how it will work with burst and c# jobs.

 

Oh noes! I'm building on that. Do we know what will be the replacement and what is suggested to be used in meantime?

 

Chunk Iteration and Component Groups.

 

Component groups look cleaner,I'll stick with them.However you are more experienced than me,what do you suggest for performance?

 

The general approach now is to turn the component group into chunk iteration

var chunks = this.chunkGroup.CreateArchetypeChunkArray(Allocator.TempJob);

The alternative to chunk iteration, which is very clean and ideally should be used where possible is

IJobProcessComponentData

IJobProcessComponentDataWithEntity

This does chunk iteration behind the scenes but hides it. Ever since the added the WithEntity version you should be able to do the majority of your work with it.

The only thing that is currently limited with these 2 approaches seems to be hybrid/legacy objects.

 

+ IJobChunk

 

Both.

 

I was a bit slacking in ECS area recently. Missed important news.
What is current alternative for injection?
Keywords, or reference to the related topic would be sufficient.

 

Ok, in meantime. found partial answer.