HelloCube：ForEach

此示例演示了一个简单的ECS系统，它可以旋转一对立方体。

它显示了什么？

此示例演示了ECS中数据和功能的分离。
数据存储在组件中，如下RadiansPerSecond属性存储在RotationSpeed_ForEach组件中， 该结构体数据组件有[Serializable]修饰符，表示实例化属性。

using System;
using Unity.Entities;

// Serializable attribute is for editor support.
[Serializable]
public struct RotationSpeed_ForEach : IComponentData
{
     public float RadiansPerSecond;
}

而功能则写入系统，如下RotationSpeedSystem_ForEach 使用存储在 RotationSpeed_ForEach 组件中的data更新对象的旋转。

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

// This system updates all entities in the scene with both a RotationSpeed_ForEach and Rotation component.
public class RotationSpeedSystem_ForEach : ComponentSystem
{
     protected override void OnUpdate()
     {
         // Entities.ForEach processes each set of ComponentData on the main thread. This is not the recommended
         // method for best performance. However, we start with it here to demonstrate the clearer separation
         // between ComponentSystem Update (logic) and ComponentData (data).
         // There is no update logic on the individual ComponentData.
         Entities.ForEach((ref RotationSpeed_ForEach rotationSpeed, ref Rotation rotation) =>
         {
             var deltaTime = Time.deltaTime;
             rotation.Value = math.mul(math.normalize(rotation.Value),
                 quaternion.AxisAngle(math.up(), rotationSpeed.RadiansPerSecond * deltaTime));
         });
     }
}

ComponentSystems和Entities.ForEach

RotationSpeedSystem_ForEach是一个ComponentSystem，它使用Entities.ForEach委托来遍历实体。
此示例仅创建单个实体，但如果向场景添加了更多实体，则RotationSpeedSystem_ForEach会更新所有实体 - 只要它们具有RotationSpeed_ForEach组件（并且在将GameObject的Transform转换为ECS组件时添加了旋转组件）。
请注意，使用Entities.ForEach的ComponentSystems在主线程上运行。
要利用多个内核，可以使用JobComponentSystem（如下一个HelloCube示例所示）。

从GameObject转换为Entity

ConvertToEntity MonoBehaviour在Awake时将GameObject及其子节点转换为实体和ECS组件。
目前，ConvertToEntity可以转换的内置Unity MonoBehaviours集包括Transform和MeshRenderer。
您可以使用实体调试器（菜单：窗口> 分析> 实体调试器）来检查转换创建的ECS实体和组件。
您可以在自己的MonoBehaviours上实现IConvertGameObjectEntity接口，以提供ConvertToEntity用于将存储在MonoBehavi中的数据转换为ECS组件的转换函数。
在此示例中， RotationSpeedAuthoring_ForEach MonoBehaviour使用IConvertGameObjectEntity在转换时将RotationSpeed_ForEach组件添加到实体。

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

[RequiresEntityConversion]
public class RotationSpeedAuthoring_ForEach : MonoBehaviour, IConvertGameObjectToEntity
{
     public float DegreesPerSecond;

    // The MonoBehaviour data is converted to ComponentData on the entity.
     // We are specifically transforming from a good editor representation of the data (Represented in degrees)
     // To a good runtime representation (Represented in radians)
     public void Convert(Entity entity, EntityManager dstManager, GameObjectConversionSystem conversionSystem)
     {
         var data = new RotationSpeed_ForEach { RadiansPerSecond = math.radians(DegreesPerSecond) };
         dstManager.AddComponentData(entity, data);
     }
}

---

HelloCube_1b_ForEachWithEntityChanges

此示例演示了一个简单的ECS系统，该系统使用查询来选择要更新的正确实体集。然后它在ForEach lambda函数内部修改这些实体。

该示例定义了两个标记组件，名为MovingCube_ForEachWithEntityChanges和MoveUp_ForEachWithEntityChanges。

using System;
using Unity.Entities;

namespace Samples.HelloCube_1b
{
    // Serializable attribute is for editor support.
    [Serializable]
    public struct MoveUp_ForEachWithEntityChanges : IComponentData
    {
        // MoveUp is a "tag" component and contains no data. Tag components can be used to mark entities that a system should process.
    }
}

using System;
using Unity.Entities;

namespace Samples.HelloCube_1b
{
    // Serializable attribute is for editor support.
    [Serializable]
    public struct MovingCube_ForEachWithEntityChanges : IComponentData
    {
        // MovingCube_ForEachWithEntityChanges is a "tag" component and contains no data.
        // Tag components can be used to mark entities that a system should process.
    }
}

系统中的一个查询选择同时具有MoveUp_ForEachWithEntityChanges组件和Translation组件的所有实体。与此查询关联的ForEach lambda函数向上移动每个选定的实体，直到达到某个高度时，该函数将删除MoveUp_ForEachWithEntityChanges组件，以便下次系统更新时，将不会选择该实体，因此它不会向上移动任何更远的位置。

第二个查询选择具有Translation组件但没有MoveUp_ForEachWithEntityChanges组件的所有实体。与第二个查询关联的ForEach函数将实体向下移动到其起始位置，并添加新的MoveUp_ForEachWithEntityChanges组件。由于实体再次具有MoveUp_ForEachWithEntityChanges组件，因此下次系统更新时，实体将被第一个ForEach函数向上移动并被第二个查询跳过。

MovingCube_ForEachWithEntityChanges是一个标记组件，用于确保系统仅适用于为此示例标记的组件。示例中的两个查询都需要MovingCube_ForEachWithEntityChanges组件。

它显示了什么？

此示例演示了一个简单的ECS系统，该系统使用查询来选择要向上移动的一组实体。当它们达到一定高度时，系统会删除一个组件并使用另一个查询在较低的高度重新生成它们。它还演示了使用“标签”组件来提供选择具有待处理标记组件的特定entite组的方法。最后，此示例演示了如何在ForEach lambda函数内修改实体。

组件系统和实体.ForEach

MovementSystem_ForEachWithEntityChanges是一个ComponentSystem，它使用Entities.ForEach lambda函数迭代实体。此示例使用WithAll和WithNone约束来选择要处理的特定实体集。

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

namespace Samples.HelloCube_1b
{
     // This system updates all entities in the scene with Translation components.
     // It treats entities differently depending on whether or not they also have a MoveUp component.
     public class MovementSystem_ForEachWithEntityChanges : ComponentSystem
     {
         protected override void OnUpdate()
         {
             // If a MoveUp component is present, then the system updates the Translation component to move the entity upwards.
             // Once the entity reaches a predetermined height, the function removes the MoveUp component.
             Entities.WithAllReadOnly<MovingCube_ForEachWithEntityChanges, MoveUp_ForEachWithEntityChanges>().ForEach(
                 (Entity id, ref Translation translation) =>
                 {
                     var deltaTime = Time.deltaTime;
                     translation = new Translation()
                     {
                         Value = new float3(translation.Value.x, translation.Value.y + deltaTime, translation.Value.z)
                     };

                    if (translation.Value.y > 10.0f)
                         EntityManager.RemoveComponent<MoveUp_ForEachWithEntityChanges>(id);
                 }
             );

            // If an entity does not have a MoveUp component (but does have a Translation component),
             // then the system moves the entity down to its starting point and adds a MoveUp component.
             Entities.WithAllReadOnly<MovingCube_ForEachWithEntityChanges>().WithNone<MoveUp_ForEachWithEntityChanges>().ForEach(
                 (Entity id, ref Translation translation) =>
                 {
                     translation = new Translation()
                     {
                         Value = new float3(translation.Value.x, -10.0f, translation.Value.z)
                     };

                    EntityManager.AddComponentData(id, new MoveUp_ForEachWithEntityChanges());
                 }
             );
         }
     }
}

注意：使用Entities.ForEach的组件系统在主线程上运行。要利用多个内核，可以使用JobComponentSystem（如其他HelloCube示例所示）。这也允许更改ForEach lambda函数内的实体。