unity ecs的备忘录

关于parent和LinkedEntityGroup

• parent 涉及到localtoworld, 以及一些物理和其他的转换规则

  • parent和位置有关系..所以父实体需要添加Translation和LocalToWorld.否则会删除该parent和LocalToParent组件

  • 添加了parent组件且添加了Translation,LocalToWorld,LocalToParent组件,会自动给父实体添加child组件,四个组件缺一不可

  • 如果使用了LocalToParent,这个时候Translation代表的是相对于父对象的坐标..相当于传统的localTranslation
    这个时候如果获取世界坐标..可以使用LocalToWorld.pos

• linkedEntityGroup 和 Instantiate SetEnabled DestroyEntity 有关

关于转换

在Conversion World中，仅仅是复制生成了来自Classic World的、保留原有Hierarchy关系的GameObject Entity，这些Entity拥有的组件仍然是我们熟知的传统Unity组件，例如Transform、MeshFilter。接下来，将调用DOTS预置的或我们自定义的Convert接口，完成向IComponentData组件的转换。自然而然的，可能没有实现对某Component Object的转换接口，那么在转换过程中将被丢弃，所以该转换不一定是“一对一”，所以Unity称呼其为”Primary Entity”。下图呈现了转换全过程。

转换过程都是在Conversion World中完成的,DOTS在内部为转换过程创建了一个World。作为独立World，它拥有自己的EntityManager和ComponentSystem，进而拥有并管理自己的Entity和ComponentData。

1. 使用ConvertToEntity组件,添加IConvertGameObjectToEntity接口,或者在组件上添加[GenerateAuthoringComponent]

   

2. 同一,但是使用代码控制转换的时机,继承ConvertToSingleEntity,并覆盖awake,然后在手动调用.

   public class ConvertToSingleEntity : ConvertToEntity
   {
       void Awake()
       {
       }
   }
   
   //实际上就是ConvertToEntity中的代码
   public static void ConvertGameObejct(World dstWorld, GameObject gameObject)
   {
       var system = World.DefaultGameObjectInjectionWorld.GetOrCreateSystem<ConvertToEntitySystem>();
   
       var convert = gameObject.GetComponent<ConvertToEntity>();
   
       if (convert == null)
       {
           return ;
       }
       system.AddToBeConverted(dstWorld, convert);
   }

3. 使用IDeclareReferencedPrefabs.声明实体的prefab,然后进行存储,以便进行之后的实例化

   对于转换世界中的每个游戏对象，在任何转换系统运行之前，都会在目标世界中自动创建一个主要实体。随后可以通过 GameObjectConversionSystem.GetPrimaryEntity 访问与 GameObject 关联的实体。

   /*
      *    
      *    
          if (m_Prefab == Entity.Null)
                {
                    var prefabEntity = GetSingletonEntity<GamePrefabCollectionComponent>();
                    var prefabs = GetBuffer<GamePrefabBuffer>(prefabEntity);
                    for (int i = 0; i < prefabs.Length; ++i)
                    {
                        if (HasComponent<Player.State>(prefabs[i].Value))
                            m_Prefab = prefabs[i].Value;
                    }
                }
      * 
      * 
      * 添加进来的prefab不需要添加convert to entity
      * 可以用单例获取GamePrefabCollectionComponent,然后获取想要的entity
      * 
      */
     public class GameDeclareReferencedPrefabs : MonoBehaviour, IConvertGameObjectToEntity, IDeclareReferencedPrefabs
     {
    
         public List<GameObject> Prefabs = new List<GameObject>();
      
         public void Convert(Entity entity, EntityManager dstManager, GameObjectConversionSystem conversionSystem)
         {
             dstManager.AddComponentData(entity, default(GamePrefabCollectionComponent));
             var prefabs = dstManager.AddBuffer<GamePrefabBuffer>(entity);
      
             foreach (var prefab in Prefabs)
             { 
                 var prefabEnt = conversionSystem.GetPrimaryEntity(prefab);
                 if (dstManager.Exists(prefabEnt))
                     prefabs.Add(new GamePrefabBuffer { Value = prefabEnt });
                 else
                     Debug.LogError($"The prefab {prefab.name} in the ghost collection was no converted to an entity, skipping it");
             }
         }
      
         public void DeclareReferencedPrefabs(List<GameObject> referencedPrefabs)
         {
             foreach (var prefab in Prefabs)
             {
                 if(prefab == null)
                 {
                     continue;
                 }
                 referencedPrefabs.Add(prefab);
             }
         }
     }

   4.从转换系统中根据component获取实体,和上面类似..因为转换子物体的时候,转换系统中会生成实体,这个时候可以使用组件从conversionSystem中获取,

   public static void AddAbilityComponents(Entity entity, EntityManager dstManager, GameObjectConversionSystem conversionSystem, AbilityAuthoring[] abilities)
      {
          dstManager.AddComponentData(entity, new AbilityCollection.State());
      
          // Create ability entities
          var abilityEntities = new List<Entity>(abilities.Length);
          for (int i = 0; i < abilities.Length; i++)
          {
              var e = conversionSystem.GetEntities(abilities[i]);
              e.MoveNext();
              var abilityEntity = e.Current;
      
              if (abilityEntities.Contains(abilityEntity))
              {
                  GameDebug.LogError("Ability " + abilities[i] + " registered multiple times in abilities list");
              }
      
              abilityEntities.Add(abilityEntity);
          }
      
          // Add abilities to ability buffer
          dstManager.AddBuffer<AbilityCollection.AbilityEntry>(entity);
          var abilityBuffer = dstManager.GetBuffer<AbilityCollection.AbilityEntry>(entity);
          for (int i = 0; i < abilities.Length; i++)
          {
              abilityBuffer.Add(new AbilityCollection.AbilityEntry
              {
                  entity = abilityEntities[i],
                  abilityType = abilities[i].abilityTypeFlags,
                  canRunWith = abilities[i].canRunWithFlags,
                  canInterrupt = abilities[i].canInterruptFlags,
              });
          }
      }

   5.手动转换gameobject,他的代码和ConvertToEntitySystem的代码差不多.会创建一个ConversionWorld,然后进行转换,都是使用了GameObjectConversionUtility.Convert工作

   public static Entity ConvertGameObjectPrefab(GameObject go,World dstWorld,out BlobAssetStore blob)
   {
       Entity returnEntity = Entity.Null;
   
       blob = new BlobAssetStore();
      
       returnEntity =
           GameObjectConversionUtility.ConvertGameObjectHierarchy(go,GameObjectConversionSettings.FromWorld(dstWorld, blob));
      
       return returnEntity;
   }