【Unity3D】ECS入门学习（十一）ComponentSystem、JobComponentSystem

 ComponentSystem：仅支持主线程执行，不支持多线程，并且无法使用SystemBase介绍的扩展方法。

using Unity.Entities;
using Unity.Transforms;
using Unity.Mathematics;/// <summary>
/// 仅主线程执行，不支持多线程
/// </summary>
public class MyComponentSystem : ComponentSystem
{protected override void OnUpdate(){Entities.ForEach((ref Translation trans) =>{trans.Value = new float3(0, 1, 1);});//无法使用SystemBase的其他扩展功能}
}

JobComponentSystem：仅支持多线程，不支持主线程，可以使用扩展方法，并且重写的方法与其他都不同，它需要一个JobHandle返回值 

using Unity.Entities;
using Unity.Jobs;
using Unity.Transforms;
/// <summary>
/// 支持多线程 但不支持主线程执行
/// </summary>
public class MyJobComponentSystem : JobComponentSystem
{protected override JobHandle OnUpdate(JobHandle inputDeps){return Entities.ForEach((ref Translation trans) =>{trans.Value = new Unity.Mathematics.float3(0, 0, 1);}).WithName("MyName").Schedule(inputDeps);//可以使用SystemBase扩展方法}
}

具体文档：Using Entities.ForEach | Entities | 0.50.1-preview.2

如下图是三个执行筛选的方法限制，简单理解就是：
Run：非Burst编译下 可访问所有成员，可修改实体。【主线程执行】
Schedule：仅能获取局部成员，可修改实体。【新开一个后台线程执行】
ScheduleParallel：仅能获取局部成员，可以读取实体，但不能修改实体，并且可读数据只允许存储到WithReadOnly(xxx)方法标记的只读变量内。【多线程并行执行】

Supported Feature	Run	Schedule	ScheduleParallel
Capture local value type	x	x	x
Capture local reference type	x (only WithoutBurst and not in ISystem)
Writing to captured variables	x
Use field on the system class	x (only WithoutBurst)
Methods on reference types	x (only WithoutBurst and not in ISystem)
Shared Components	x (only WithoutBurst and not in ISystem)
Managed Components	x (only WithoutBurst and not in ISystem)
Structural changes	x (only WithStructuralChanges and not in ISystem)
SystemBase.GetComponent	x	x	x
SystemBase.SetComponent	x	x
GetComponentDataFromEntity	x	x	x (only as ReadOnly)
HasComponent	x	x	x
WithDisposeOnCompletion	x	x	x
WithScheduleGranularity			x