Passing Arrays of Data to Component in ECS Baking

[rare ermine]

I'm trying to pass some data to a component through Baking and it keeps telling me that there may be a nested pointer and that this is a problem. I understand the underlying problem but I am unsure how to do what I'm trying to achieve. If you look in the code in the next comment you'll see that I try to have an assignable array of BoxColliders and through the data from those establish parameters with which I can have spawn zones by just defining 2 points of a rectangle to spawn within.

The Config is a singleton component that systems will read from to get these spawn zones.

using Unity.Collections;
using Unity.Entities;
using Unity.Mathematics;
using UnityEngine;

namespace Game.Prototype
{
    public class ConfigAuthoring : MonoBehaviour
    {
        public float MonsterSpawnDistance = 30f;
        public int NumberOfSpawns = 1000;
        public Vector3 TentSpawnPoint;
        public GameObject TentPrefab;
        public GameObject MonsterCapsulePrefab;
        public BoxCollider[] SpawnZones;

        class Baker : Baker<ConfigAuthoring>
        {
            public override void Bake(ConfigAuthoring authoring)
            {
                var entity = GetEntity(TransformUsageFlags.None);
                SpawnZone[] spawnZones = new SpawnZone[authoring.SpawnZones.Length];
                for (int i = 0; i < authoring.SpawnZones.Length; i++)
                {
                    float minX = authoring.SpawnZones[i].bounds.min.x;
                    float minZ = authoring.SpawnZones[i].bounds.min.z;
                    float maxX = authoring.SpawnZones[i].bounds.max.x;
                    float maxZ = authoring.SpawnZones[i].bounds.max.z;

                    spawnZones[i] = new SpawnZone
                    {
                        Y = 0.75f,
                        StartCorner = new float2 { x = minX, y = minZ },
                        EndCorner = new float2 { x = maxX, y = maxZ }
                    };
                }

                AddComponent(entity, new Config()
                {
                    MonsterSpawnDistance = authoring.MonsterSpawnDistance,
                    NumberOfSpawns = authoring.NumberOfSpawns,
                    TentSpawnPoint = new float3
                    {
                        x = authoring.TentSpawnPoint.x,
                        y = authoring.TentSpawnPoint.y,
                        z = authoring.TentSpawnPoint.z
                    },
                    TentEntity = GetEntity(authoring.TentPrefab, TransformUsageFlags.Dynamic),
                    MonsterCapsuleEntity = GetEntity(authoring.MonsterCapsulePrefab, TransformUsageFlags.Dynamic),
                    SpawnZones = new NativeArray<SpawnZone>(spawnZones, Allocator.Persistent)
                });
            }
        }
    }

    public struct Config : IComponentData
    {
        public float MonsterSpawnDistance;
        public int NumberOfSpawns;
        public float3 TentSpawnPoint;
        public Entity TentEntity;
        public Entity MonsterCapsuleEntity;
        public NativeArray<SpawnZone> SpawnZones;
    }

    public struct SpawnZone : IComponentData
    {
        public float Y;
        public float2 StartCorner;
        public float2 EndCorner;
    }
}

[grim depot]

You can't bake native containers

Just use a DynamicBuffer

[rare ermine]

So instead of passing a NativeArray I have to pass a dynamic buffer?

[grim depot]

if you want to do it from baking yes

but you can always just call dynamicbuffer.AsArray()

(and probably should for performance)

if you have api that takes a nativearray

[rare ermine]

I see. But can I have standard arrays in an IComponentData type?

I don't know the implementation details of NativeArrays as such, other than higher level. So I was unsure.

[grim depot]

sure, icd is just an interface it doesn't stop you storing it anywhere

and if you write an icd from an entity into an array it'll just be a copy

[rare ermine]

DynamicBuffer<SpawnZone> spawnZones = new();

public struct Config : IComponentData
{
    public float MonsterSpawnDistance;
    public int NumberOfSpawns;
    public float3 TentSpawnPoint;
    public Entity TentEntity;
    public Entity MonsterCapsuleEntity;
    public DynamicBuffer<SpawnZone> SpawnZones;
}

[grim depot]

no

that's not how dynamic buffer works

[rare ermine]

Okay. How would I go about using them?

[grim depot]

var buffer = baker.AddBuffer<SpawnZone>();

foreach(var s in spawnZones )
buffer.add(s);

[velvet glade]

https://docs.unity3d.com/Packages/com.unity.entities@1.2/manual/components-buffer.html

[grim depot]

beat me to it

[rare ermine]

Oh I see. I'll have a look at that. Thanks both of you.

[rare ermine]

I looked at that, but I can't get the EntityManager because there is none. This is happening in a Bake script.

Unless I'm just missing something

I can't get the EntityManager like they do here

[grim depot]

in baker it's just AddBuffer

you don't use entity manager in baker, that's for runtime

[rare ermine]

Ah. Right.

So I do this then, from what I understand:

DynamicBuffer<SpawnZoneBuffer> spawnZoneBuffers = AddBuffer<SpawnZoneBuffer>(entity);
for (int i = 0; i < authoring.SpawnZones.Length; i++)
{
    float minX = authoring.SpawnZones[i].bounds.min.x;
    float minZ = authoring.SpawnZones[i].bounds.min.z;
    float maxX = authoring.SpawnZones[i].bounds.max.x;
    float maxZ = authoring.SpawnZones[i].bounds.max.z;

    spawnZoneBuffers.Add(new SpawnZoneBuffer
    {
        Y = 0.75f,
        StartCorner = new float2 { x = minX, y = minZ },
        EndCorner = new float2 { x = maxX, y = maxZ }
    });
}

[grim depot]

looks good

[rare ermine]

But how would I get the buffer from my component later?
It's not assigned to anything in a field.
So would I do something like GetBuffer<MyBufferType> and it returns the buffer that I can iterate?

[grim depot]

it's not on your component

it's a separate component

[rare ermine]

Sorry, I meant on my entity

[grim depot]

the same way you get your component

except instead of getcomponent

you use getbuffer

(or getsingleton vs getsingletonbuffer etc)

[rare ermine]

What happens if you want multiple buffers of the same type on the same entity?
Is that not allowed then?

[grim depot]

of the same type? no

[rare ermine]

Alright. Good to know.

Thank you.

@grim depot and just for completeness sake, I made my buffer type like this:

[InternalBufferCapacity(20)]
public struct SpawnZoneBuffer : IBufferElementData
{
    public float Y;
    public float2 StartCorner;
    public float2 EndCorner;
}

Far as I understand the capacity was about the space for the types stored, and so if my math is correct that would be 5*4 bytes so 20.

[grim depot]

contrary to its name capacity, InternalBufferCapacity is number of elements so this would take 100 bytes

        /// <summary>
        /// The number of elements stored inside the chunk.
        /// </summary>
        public readonly int Capacity;```

i nearly always set this to 0 except on singletons

[rare ermine]

I was going by this explanation here from the documentation:

The initial capacity of a dynamic buffer is defined by the type that the buffer stores. By default, the capacity defaults to the number of elements that fit within 128 bytes. For more information, see DefaultBufferCapacityNumerator. You can specify a custom capacity using the InternalBufferCapacity attribute. For information on how to create a dynamic buffer component type, see Create a dynamic buffer component type.

[grim depot]

yeah the initial capacity is always 128

[rare ermine]

So I was under the impression that 5*4, due to 5 floats, would be right.

So how come it's 100?

[grim depot]

beacuse 20 elements * 5 [sizeof(SpawnZoneBuffer)] == 100

[rare ermine]

20 elements?

Where do you get that from?

[grim depot]

thats what 20 means

because you wrote 20 ^_^'

it's number of elements

not capacity

[rare ermine]

Aah

[grim depot]

even though it's called capacity

[rare ermine]

Right, sorry. That is..confusing.

[grim depot]

if you want proof

                var capacityAttribute = (InternalBufferCapacityAttribute)type.GetCustomAttribute(typeof(InternalBufferCapacityAttribute));
                if (capacityAttribute != null)
                    bufferCapacity = capacityAttribute.Capacity;
                else
                    bufferCapacity = DefaultBufferCapacityNumerator / elementSize; // Rather than 2*cachelinesize, to make it cross platform deterministic

                sizeInChunk = sizeof(BufferHeader) + bufferCapacity * elementSize;```

[rare ermine]

So you say setting it to 0 is what you typically do?

Regardless of number of elements?

[grim depot]

yeah i don't store in the chunk

i like to keep my archetype size as small as possible

[rare ermine]

Sure, smaller is better.

[grim depot]

to fit as many entities per chunk as i can

[rare ermine]

But that is quite a misleading name, perhaps. Or I don't know.
Odd.

[grim depot]

a chunk is 16kb

and can have 128 entities max

which gives them 128bytes per entity

[rare ermine]

Right

[grim depot]

to have max capacity in a chunk

at 100 bytes you've used up 80% of your per entity capacity if you wanted max entiites

now it's unlikely for most entities you'll ever get 128 in a chunk except for small utility entities you've broken off

but it's still beneficial to fit as much as possible

but if i'm a singleton entity, capacity no longer matters

[rare ermine]

It is a singleton, yes.

Readonly singleton buffer in this case I suppose

[grim depot]

if it's a singleton then yeah just fit as much as you need in the chunk

if you know an upper limit that isn't ridiculous

[rare ermine]

Following the Unity samples I've made a config object with some prefabs and data in it that I want systems to use for instantiation and informing decisions for spawnpoints and whatnot.

The Config is a singleton.

Every prefab of course has Authoring scripts to bake

[grim depot]

that's totally fine