当前测试使用的Entities版本为1.0.16
Unity Entities 1.0.16使用方法：
Create a component for the spawner example | Entities | 1.0.16
1. 创建SubScene
2. 在SubScene下创建挂载Authoring脚本：
Authoring是MonoBehaviour脚本，主要用来序列化配置需要创建的实体prefab资源或参数；
因为Entities目前不支持用资源名动态加载资源！没错，AssetsBundle或Addressables都不能用于Entities；也就意味着现阶段不能用Entities开发DLC或热更游戏。
Entities必须使用SubScene，而SubScene不能从资源动态加载，路被彻底封死了。
public class EntitiesAuthoring : MonoBehaviour
{
public GameObject m_Prefab;
public int m_Row;
public int m_Col;
}
3. 把步骤2的挂有Authoring脚本的GameObject转换为Entity：
SubScene中挂载的MonoBehaviour不会被执行，必须转换为Entity；
此步骤主要是把Authoring中的参数转接到自己定义的ComponentData;
class EntitiesAuthoringBaker : Baker<EntitiesAuthoring>
{
public override void Bake(EntitiesAuthoring authoring)
{
var entity = GetEntity(TransformUsageFlags.None);
AddComponent<EntitiesComponentData>(entity, new EntitiesComponentData
{
m_PrefabEntity = GetEntity(authoring.m_Prefab, TransformUsageFlags.Dynamic | TransformUsageFlags.Renderable),
m_Row = authoring.m_Row,
m_Col = authoring.m_Col
});
}
}
struct EntitiesComponentData : IComponentData
{
public Entity m_PrefabEntity;
public int m_Row;
public int m_Col;
}4. 编写创建Entity的System脚本：
由于MonoBehaviour不会在SubScene中执行，System就类似MonoBehavior，拥有OnCreate, OnUpdate, OnDestroy生命周期。Entities框架会自动执行所有已经定义的System，若不想自动执行System可以在头部添加[DisableAutoCreation]，然后使用state.World.CreateSystem<MoveEntitiesSystem>()手动创建System。
[BurstCompile]
partial struct SpawnEntitiesSystem : ISystem
{
void OnCreate(ref SystemState state)
{
//Application.targetFrameRate = 120;
state.RequireForUpdate<EntitiesComponentData>();
}
void OnDestroy(ref SystemState state)
{
}
void OnUpdate(ref SystemState state)
{
var ecbSingleton = SystemAPI.GetSingleton<BeginSimulationEntityCommandBufferSystem.Singleton>();
var ecb = ecbSingleton.CreateCommandBuffer(state.WorldUnmanaged);
foreach (var data in SystemAPI.Query<EntitiesComponentData>())
{
Unity.Mathematics.Random m_Random = new Unity.Mathematics.Random(1);
var m_RandomRange = new float4(-data.m_Row * 0.5f, data.m_Row * 0.5f, -data.m_Col * 0.5f, data.m_Col * 0.5f);
var halfSize = new float2(data.m_Col * 0.5f, data.m_Row * 0.5f);
for (int i = 0; i < data.m_Row; i++)
{
for (int j = 0; j < data.m_Col; j++)
{
var entity = state.EntityManager.Instantiate(data.m_PrefabEntity);
ecb.SetComponent(entity, LocalTransform.FromPosition(new float3(j - halfSize.x, 0, i - halfSize.y)));
ecb.AddComponent<TargetMovePointData>(entity, new TargetMovePointData() { targetPoint = new float3(m_Random.NextFloat(m_RandomRange.x, m_RandomRange.y), 0, m_Random.NextFloat(m_RandomRange.z, m_RandomRange.w)) });
}
}
state.Enabled = false;
}
}
}5. 定义一个System专门控制所有小人的移动：
使用JobSystem并行计算和设置小人的位置：
[BurstCompile]
partial struct MoveEntitiesJob : IJobParallelFor
{
[ReadOnly]
public Unity.Mathematics.Random random;
[ReadOnly]
public float4 randomRange;
[ReadOnly]
public float moveSpeed;
[ReadOnly]
public NativeArray<Entity> entities;
[NativeDisableParallelForRestriction]
public EntityManager entityManager;
[WriteOnly]
public EntityCommandBuffer.ParallelWriter entityWriter;
[BurstCompile]
public void Execute(int index)
{
var entity = entities[index];
var tPointData = entityManager.GetComponentData<TargetMovePointData>(entity);
var tPoint = tPointData.targetPoint;
var transform = entityManager.GetComponentData<LocalTransform>(entity);
float3 curPoint = transform.Position;
var offset = tPoint - curPoint;
if (math.lengthsq(offset) < 0.4f)
{
tPointData.targetPoint = new float3(random.NextFloat(randomRange.x, randomRange.y), 0, random.NextFloat(randomRange.z, randomRange.w));
entityWriter.SetComponent(index, entity, tPointData);
}
float3 moveDir = math.normalize(tPointData.targetPoint - curPoint);
transform.Rotation = Quaternion.LookRotation(moveDir);
transform.Position += moveDir * moveSpeed;
entityWriter.SetComponent(index, entity, transform);
}
}Entities测试结果：
10万个移动的小人，140多帧，同等数量级比自定义BatchRendererGroup帧数高出20+，那是因为Entities Graphics内部实现了BatchRendererGroup的剔除Culling，相机视口外的物体会被Culling。自定义BatchRendererGroup只要在OnPerformCulling回调方法中实现Culling也能达到相同的性能：
其实到这里测试已经没有意义了，GPU端Entities Graphics结局已经注定，所谓Entities ECS结构也只是对CPU的性能提升，但海量物体的渲染GPU是最大的瓶颈。
使用Entities 1.0.16安卓端性能：
1万个小人，12帧；
查了查URP的渲染实现，其实内部也是Batch Renderer Group, 所以这也注定了无论是自定义Batch Renderer Group还是使用Entities，在移动端都是一样的性能。
扩展讨论：
Unity是支持配置Android端多线程策略的，Android CPU大小核性能差距巨大，大核性能强劲但耗电量大，小核弱鸡但省电，如果Jobs分配到小核执行会比主线程还慢，就会导致负优化。
既然万人同屏延迟主要在渲染线程，那么能否通过配置只允许渲染线程用大核心呢？(或者Unity默认策略就是这样的)；
可以参考：Unity - Manual: Android thread configuration对Android线程策略进行配置。
结论：
目前为止(Entities 1.0.16)有太多致命局限性，也只是对PC平台做了性能优化，并且有开挂般的大幅提升；
但是对于移动平台收效甚微，JobSystem在移动平台并行线程数迷之变少，并且暂无开放接口设置。图形库必须为OpenGLES3及以上或Vulkan，与使用限制和开发门槛相比，ECS结构微弱的性能提升不值一提。
移动平台万人同屏方案尝试失败，弃坑。不过苍蝇再小也是肉，单线程的Unity编程方式早已跟不上如今的硬件发展，虽然HybridCLR不支持Burst加速，只能以解释方式执行JobSystem，但是安全的多线程对大量数据的计算仍然有很大的意义。
期待Entities的资源系统早日面世...
最后附上Entities万人同屏测试代码：
using Unity.Burst;
using Unity.Collections;
using Unity.Entities;
using Unity.Jobs;
using Unity.Mathematics;
using Unity.Transforms;
using UnityEngine;
using UnityEngine.Jobs;
public class EntitiesAuthoring : MonoBehaviour
{
public GameObject m_Prefab;
public int m_Row;
public int m_Col;
}
class EntitiesAuthoringBaker : Baker<EntitiesAuthoring>
{
public override void Bake(EntitiesAuthoring authoring)
{
var entity = GetEntity(TransformUsageFlags.None);
AddComponent<EntitiesComponentData>(entity, new EntitiesComponentData
{
m_PrefabEntity = GetEntity(authoring.m_Prefab, TransformUsageFlags.Dynamic | TransformUsageFlags.Renderable),
m_Row = authoring.m_Row,
m_Col = authoring.m_Col
});
}
}
struct EntitiesComponentData : IComponentData
{
public Entity m_PrefabEntity;
public int m_Row;
public int m_Col;
}
[BurstCompile]
partial struct SpawnEntitiesSystem : ISystem
{
void OnCreate(ref SystemState state)
{
//Application.targetFrameRate = 120;
state.RequireForUpdate<EntitiesComponentData>();
}
void OnDestroy(ref SystemState state)
{
}
void OnUpdate(ref SystemState state)
{
var ecbSingleton = SystemAPI.GetSingleton<BeginSimulationEntityCommandBufferSystem.Singleton>();
var ecb = ecbSingleton.CreateCommandBuffer(state.WorldUnmanaged);
foreach (var data in SystemAPI.Query<EntitiesComponentData>())
{
Unity.Mathematics.Random m_Random = new Unity.Mathematics.Random(1);
var m_RandomRange = new float4(-data.m_Row * 0.5f, data.m_Row * 0.5f, -data.m_Col * 0.5f, data.m_Col * 0.5f);
var halfSize = new float2(data.m_Col * 0.5f, data.m_Row * 0.5f);
for (int i = 0; i < data.m_Row; i++)
{
for (int j = 0; j < data.m_Col; j++)
{
var entity = state.EntityManager.Instantiate(data.m_PrefabEntity);
ecb.SetComponent(entity, LocalTransform.FromPosition(new float3(j - halfSize.x, 0, i - halfSize.y)));
ecb.AddComponent<TargetMovePointData>(entity, new TargetMovePointData() { targetPoint = new float3(m_Random.NextFloat(m_RandomRange.x, m_RandomRange.y), 0, m_Random.NextFloat(m_RandomRange.z, m_RandomRange.w)) });
}
}
state.Enabled = false;
}
}
[BurstCompile]
partial struct MoveEntitiesSystem : ISystem
{
Unity.Mathematics.Random m_Random;
float4 m_RandomRange;
void OnCreate(ref SystemState state)
{
state.RequireForUpdate<TargetMovePointData>();
}
void OnStartRunning(ref SystemState state)
{
if (SystemAPI.TryGetSingleton<EntitiesComponentData>(out var dt))
{
m_RandomRange = new float4(-dt.m_Row * 0.5f, dt.m_Row * 0.5f, -dt.m_Col * 0.5f, dt.m_Col * 0.5f);
}
else
{
m_RandomRange = new float4(-50, 50, -50, 50);
}
}
void OnDestroy(ref SystemState state)
{
}
void OnUpdate(ref SystemState state)
{
EntityCommandBuffer.ParallelWriter ecb = GetEntityCommandBuffer(ref state);
m_Random = new Unity.Mathematics.Random((uint)Time.frameCount);
var entityQuery = SystemAPI.QueryBuilder().WithAll<TargetMovePointData>().Build();
var tempEntities = entityQuery.ToEntityArray(Allocator.TempJob);
var moveJob = new MoveEntitiesJob
{
random = m_Random,
moveSpeed = SystemAPI.Time.DeltaTime * 4,
randomRange = m_RandomRange,
entities = tempEntities,
entityManager = state.EntityManager,
entityWriter = ecb
};
var moveJobHandle = moveJob.Schedule(tempEntities.Length, 64);
moveJobHandle.Complete();
}
private EntityCommandBuffer.ParallelWriter GetEntityCommandBuffer(ref SystemState state)
{
var ecbSingleton = SystemAPI.GetSingleton<BeginSimulationEntityCommandBufferSystem.Singleton>();
var ecb = ecbSingleton.CreateCommandBuffer(state.WorldUnmanaged);
return ecb.AsParallelWriter();
}
}
struct TargetMovePointData : IComponentData
{
public float3 targetPoint;
}
[BurstCompile]
partial struct MoveEntitiesJob : IJobParallelFor
{
[ReadOnly]
public Unity.Mathematics.Random random;
[ReadOnly]
public float4 randomRange;
[ReadOnly]
public float moveSpeed;
[ReadOnly]
public NativeArray<Entity> entities;
[NativeDisableParallelForRestriction]
public EntityManager entityManager;
[WriteOnly]
public EntityCommandBuffer.ParallelWriter entityWriter;
[BurstCompile]
public void Execute(int index)
{
var entity = entities[index];
var tPointData = entityManager.GetComponentData<TargetMovePointData>(entity);
var tPoint = tPointData.targetPoint;
var transform = entityManager.GetComponentData<LocalTransform>(entity);
float3 curPoint = transform.Position;
var offset = tPoint - curPoint;
if (math.lengthsq(offset) < 0.4f)
{
tPointData.targetPoint = new float3(random.NextFloat(randomRange.x, randomRange.y), 0, random.NextFloat(randomRange.z, randomRange.w));
entityWriter.SetComponent(index, entity, tPointData);
}
float3 moveDir = math.normalize(tPointData.targetPoint - curPoint);
transform.Rotation = Quaternion.LookRotation(moveDir);
transform.Position += moveDir * moveSpeed;
entityWriter.SetComponent(index, entity, transform);
}
}
}