添加ASpect

Query联合查询

接上一节，我们需要应用之前创建的Speed Component，可以这样写代码

MovingSystemBase：

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using Unity.Entities;
using Unity.Transforms;
using Unity.Mathematics;

public partial class MovingSystemBase : SystemBase
{
    protected override void OnUpdate()
    {
        foreach ((TransformAspect transformAspect,Speed speed) in SystemAPI.Query<TransformAspect,Speed>())
        {
            transformAspect.LocalPosition += new float3(SystemAPI.Time.DeltaTime * speed.value, 0, 0);
            
        }
        //可选写法
        //foreach (var transformAspect in SystemAPI.Query<TransformAspect, Speed>())
        //{
        //    transformAspect.Item1.LocalPosition += new float3(SystemAPI.Time.DeltaTime * transformAspect.Item2.value, 0, 0);

        //}
    }
}

这样我们运行，在Speed Authoring的脚本上修改Speed，Entity的移动速度能就及时修改。

Unity Entities的Component大多数为struct，为此Unity提供了RefRW（reference Read Write）和RefRO（reference ReadOnly）两个工具Struct，能避免struct值在内存中总是复制而导致的一些问题。我们可以在SystemAPI.Query中直接使用：

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using Unity.Entities;
using Unity.Transforms;
using Unity.Mathematics;

public partial class MovingSystemBase : SystemBase
{
    protected override void OnUpdate()
    {
        foreach ((TransformAspect transformAspect,RefRO<Speed> speed) in SystemAPI.Query<TransformAspect,RefRO<Speed>>())
        {
            transformAspect.LocalPosition += new float3(SystemAPI.Time.DeltaTime * speed.ValueRO.value, 0, 0);
            
        }
    }
}

添加TargetPosition Component

在Scripts文件夹中新建TargetPosition脚本：

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using Unity.Entities;
using Unity.Mathematics;
public struct TargetPosition : IComponentData
{
    public float3 value;
}

在Scripts文件夹下新建TargetPositionAuthoring脚本

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

public class TargetPositionAuthoring : MonoBehaviour
{
    public float3 targetPosition;
}
public class TargetPositionBaking : Baker<TargetPositionAuthoring>
{
    public override void Bake(TargetPositionAuthoring authoring)
    {
        AddComponent(new TargetPosition() { value = authoring.targetPosition});
    }
}

将TargetPositionAuthoring脚本挂载在之前的“GameObject”上。

添加MoveToPositionAspect

Create an aspect | Entities | 1.0.0-pre.15 (unity3d.com)

我们之前说过，Aspect是Component子集的新集合，能够定义一些方法，来简化各种System里的逻辑，在这里演示一下创建方法：

在Scripts文件夹中新建MoveToPositionAspect：

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using Unity.Entities;
using Unity.Transforms;
using Unity.Mathematics;

public readonly partial struct MoveToPositionAspect : IAspect
{
    private readonly Entity entity;

    private readonly TransformAspect transformAspect;
    private readonly RefRO<Speed> speed;
    private readonly RefRW<TargetPosition> targetPosition;
    
    public void Move(float deltaTime)
    {
        float3 direction = math.normalize(targetPosition.ValueRW.value - transformAspect.WorldPosition);

        transformAspect.WorldPosition += direction * deltaTime * speed.ValueRO.value;
    }
}

创建Aspect必须是“readonly partial struct”

Aspect内部不能使用SystemAPI

在一个Aspect中可以声明一个Entity字段，用来访问对应的实体，注意，一个Aspect只能声明一个Entity字段，也就是说一个Aspect不能混合多个Entity的多个Component。

在Aspect内声明的Component必须使用RefRO、RefRW来界定，对应地，如果想在代码中引用Aspect，需要使用in关键字或ref关键字，使用in关键字会让这个aspect内部所有的引用都变成readonly，而使用ref关键字则不会

如果想让自定义的Aspect在Entity Inspector（Runtime模式）的Aspect选项卡中出现，需要编写相应的编辑器脚本

修改MovingSystemBase，在这里将SystemAPI.Time.DeltaTime传递：

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using Unity.Entities;

public partial class MovingSystemBase : SystemBase
{
    protected override void OnUpdate()
    {
        foreach (MoveToPositionAspect moveToPositionAspect in SystemAPI.Query<MoveToPositionAspect>())
        {
            moveToPositionAspect.Move(SystemAPI.Time.DeltaTime);
        }
    }
}

为MoveToPositionAspect添加Random逻辑

我们希望每个Entity靠近targetPosition时，targetPosition再随机一个新位置。我们使用Unity.Mathematics提供的random方法来进行随机。

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using Unity.Entities;
using Unity.Transforms;
using Unity.Mathematics;

public readonly partial struct MoveToPositionAspect : IAspect
{
    private readonly Entity entity;

    private readonly TransformAspect transformAspect;
    private readonly RefRO<Speed> speed;
    private readonly RefRW<TargetPosition> targetPosition;
    
    public void Move(float deltaTime)
    {
        float3 direction = math.normalize(targetPosition.ValueRW.value - transformAspect.WorldPosition);

        transformAspect.WorldPosition += direction * deltaTime * speed.ValueRO.value;

        float reachedTargetDistance = .5f;
        if( math.distance(transformAspect.WorldPosition,targetPosition.ValueRW.value) < reachedTargetDistance)
        {
            targetPosition.ValueRW.value = GetRandomPosition();//随机新位置
        }
    }

    private float3 GetRandomPosition()//添加方法
    {
        var random = new Random(1);

        return new float3(random.NextFloat(0f, 15f), 0, random.NextFloat(0f, 15f));
    }
}

这样写是不对的，因为每次调用时都会用相同的seed创建random，这会导致每次返回的位置都相同。

我们需要想个办法，每次调用Random时，返回不同的数值。这里介绍一个使用SystemAPI.GetSingleton来制作全局Random生成器的方法，这样能够还原UnityEngine.Random那样的体验。

创建RandomComponent

在Scripts文件夹中新建RandomComponent文件

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using Unity.Mathematics;
using Unity.Entities;

public struct RandomComponent : IComponentData
{
    public Random random;
}

在Scripts文件夹中新建RandomComponentAuthoring文件

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using Unity.Entities;
using UnityEngine;

public class RandomComponentAuthoring : MonoBehaviour
{
    
}
public class RandomComponentBaker : Baker<RandomComponentAuthoring>
{
    public override void Bake(RandomComponentAuthoring authoring)
    {
        AddComponent(new RandomComponent { random = new Unity.Mathematics.Random(1) });
    }
}

在“TestUnitySubScene”内新建一个空对象，命名为“Random”，并挂载RandomComponentAuthoring

获取RandomComponent单例

我们先修改MoveToPositionAspect：

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using Unity.Entities;
using Unity.Transforms;
using Unity.Mathematics;

public readonly partial struct MoveToPositionAspect : IAspect
{
    private readonly Entity entity;

    private readonly TransformAspect transformAspect;
    private readonly RefRO<Speed> speed;
    private readonly RefRW<TargetPosition> targetPosition;
    
    public void Move(float deltaTime,Random random)//添加Random引用
    {
        float3 direction = math.normalize(targetPosition.ValueRW.value - transformAspect.WorldPosition);

        transformAspect.WorldPosition += direction * deltaTime * speed.ValueRO.value;

        float reachedTargetDistance = .5f;
        if( math.distance(transformAspect.WorldPosition,targetPosition.ValueRW.value) < reachedTargetDistance)
        {
            targetPosition.ValueRW.value = GetRandomPosition(random);
        }
    }

    private float3 GetRandomPosition(Random random)//添加Random引用
    {
        return new float3(random.NextFloat(0f, 15f), 0, random.NextFloat(0f, 15f));
    }
}

我们再修改MovingSystemBase：

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using Unity.Entities;

public partial class MovingSystemBase : SystemBase
{
    protected override void OnUpdate()
    {
        var random = SystemAPI.GetSingleton<RandomComponent>().random;//使用SystemAPI.GetSingleton
        foreach (MoveToPositionAspect moveToPositionAspect in SystemAPI.Query<MoveToPositionAspect>())
        {
            moveToPositionAspect.Move(SystemAPI.Time.DeltaTime,random);
        }
    }
}

我们运行一下，会发现物体移动到第二次之后就不会随机一个新位置了。

修改出现的问题

Unity.Mathematics.Random是一个struct，如果我们不做一些界定，每次引用它都会复制一个Random：

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var random = SystemAPI.GetSingleton<RandomComponent>().random;//复制一次
public void Move(float deltaTime,Random random)//又复制了一次
private float3 GetRandomPosition(Random random)//又复制了一次

如果我们不做界定，第二次调用SystemAPI.GetSingleton这个方法时，它会使用复制的Random struct，也就是说每次一都会new 一个相同的Random。

要解决这个问题，我们需要换个思路，首先，我们使用SystemAPI.GetSingletonRW这个API替换之前的SystemAPI.GetSingleton，来保证RandomComponent的唯一性

修改MovingSystemBase：

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using Unity.Entities;

public partial class MovingSystemBase : SystemBase
{
    protected override void OnUpdate()
    {
        var randomComponent = SystemAPI.GetSingletonRW<RandomComponent>();//使用SystemAPI.GetSingletonRW
        foreach (MoveToPositionAspect moveToPositionAspect in SystemAPI.Query<MoveToPositionAspect>())
        {
            moveToPositionAspect.Move(SystemAPI.Time.DeltaTime,randomComponent);
        }
    }
}

修改MoveToPositionAspect：

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using Unity.Entities;
using Unity.Transforms;
using Unity.Mathematics;

public readonly partial struct MoveToPositionAspect : IAspect
{
    private readonly Entity entity;

    private readonly TransformAspect transformAspect;
    private readonly RefRO<Speed> speed;
    private readonly RefRW<TargetPosition> targetPosition;
    
    public void Move(float deltaTime,RefRW<RandomComponent> randomComponent)
    {
        float3 direction = math.normalize(targetPosition.ValueRW.value - transformAspect.WorldPosition);

        transformAspect.WorldPosition += direction * deltaTime * speed.ValueRO.value;

        float reachedTargetDistance = .5f;
        if( math.distance(transformAspect.WorldPosition,targetPosition.ValueRW.value) < reachedTargetDistance)
        {
            targetPosition.ValueRW.value = GetRandomPosition(randomComponent);
        }
    }

    private float3 GetRandomPosition(RefRW<RandomComponent> randomComponent)
    {
        return new float3(
            randomComponent.ValueRW.random.NextFloat(0f, 15f), 
            0, 
            randomComponent.ValueRW.random.NextFloat(0f, 15f)
            );
    }
}

我们全部都在引用RefRW<RandomComponent>，这样就能保证唯一性，问题就能得到解决了。