TemporaryBakingType\]:被这个attributes注记的Component会在Baking Output的时候不会输出到entity。这个Component只会存活在Baker过程中,Baker结束以后就会销毁。
我们有时候需要在Baking System里面批量处理一些组件数据，处理完后这些组件就没有用了。例如,baker 把一个bounding box 转换成了ecs component 数据，接下来我们定义了一个Baking System批量处理所有的entity,来计算entity的凸包。计算完成后原来的bounding box组件就可以删除了，这种情况下就可以使用上面的Filter Component Bake output机制。
Prefab In Baking机制
生成entity prefab到entity scene以后，我们就可以像使用普通的Prefab创建GameObject一样来创建entity到世界。但是使用enity prefab之前一定要确保它已经被Baker到了entity scene。当预制体实例化到Authoring Scene中的时候，Baking把它当作普通的GameObject来进行转换，不会把它当作预制体。
生成一个entity prefab你需要注册一个Baker,在Bake函数里面添加一个依赖关系，让这个依赖于Authoring GameObject Prefab。然后Prefab将会被bake出来。我们搞一个组件保存了entity prefab的一个引用，那么unity就会把这个entity prefab 序列化到subscene中。当需要使用这个entity prefab的时候就能获取到。代码如下:
public struct EntityPrefabComponent : IComponentData
{
public Entity Value;
}
public class GetPrefabAuthoring : MonoBehaviour
{
public GameObject Prefab;
}
public class GetPrefabBaker : Baker
{
public override void Bake(GetPrefabAuthoring authoring)
{
// Register the Prefab in the Baker
var entityPrefab = GetEntity(authoring.Prefab, TransformUsageFlags.Dynamic);
// Add the Entity reference to a component for instantiation later
var entity = GetEntity(TransformUsageFlags.Dynamic);
AddComponent(entity, new EntityPrefabComponent() {Value = entityPrefab});
}
}
#endregion
在Baking的时候，当我们需要引用一个entity prefab, 可以使用EntityPrefabReference。这个会把它序列化到entity scene文件里面去。运行的时候直接load进来，就可以使用了。这样可以防止多个subscene不用重复拷贝生成同一个Prefab。
#region InstantiateLoadedPrefabs
public partial struct InstantiatePrefabReferenceSystem : ISystem
{
public void OnStartRunning(ref SystemState state)
{
// Add the RequestEntityPrefabLoaded component to the Entities that have an
// EntityPrefabReference but not yet have the PrefabLoadResult
// (the PrefabLoadResult is added when the prefab is loaded)
// Note: it might take a few frames for the prefab to be loaded
var query = SystemAPI.QueryBuilder()
.WithAll()
.WithNone().Build();
state.EntityManager.AddComponent(query);
}
public void OnUpdate(ref SystemState state)
{
var ecb = new EntityCommandBuffer(Allocator.Temp);
// For the Entities that have a PrefabLoadResult component (Unity has loaded
// the prefabs) get the loaded prefab from PrefabLoadResult and instantiate it
foreach (var (prefab, entity) in
SystemAPI.Query>().WithEntityAccess())
{
var instance = ecb.Instantiate(prefab.ValueRO.PrefabRoot);
// Remove both RequestEntityPrefabLoaded and PrefabLoadResult to prevent
// the prefab being loaded and instantiated multiple times, respectively
ecb.RemoveComponent(entity);
ecb.RemoveComponent(entity);
}
ecb.Playback(state.EntityManager);
ecb.Dispose();
}
}
#endregion
实例化entity prefab可以使用EntityManager与entity command buffer。
#region InstantiateEmbeddedPrefabs
public partial struct InstantiatePrefabSystem : ISystem
{
public void OnUpdate(ref SystemState state)
{
var ecb = new EntityCommandBuffer(Allocator.Temp);
// Get all Entities that have the component with the Entity reference
foreach (var prefab in
SystemAPI.Query>())
{
// Instantiate the prefab Entity
var instance = ecb.Instantiate(prefab.ValueRO.Value);
// Note: the returned instance is only relevant when used in the ECB
// as the entity is not created in the EntityManager until ECB.Playback
ecb.AddComponent(instance);
}
ecb.Playback(state.EntityManager);
ecb.Dispose();
}
}
#endregion
实例化EntityPrefabReference,可以使用如下代码:
#region InstantiateLoadedPrefabs
public partial struct InstantiatePrefabReferenceSystem : ISystem
{
public void OnStartRunning(ref SystemState state)
{
// Add the RequestEntityPrefabLoaded component to the Entities that have an
// EntityPrefabReference but not yet have the PrefabLoadResult
// (the PrefabLoadResult is added when the prefab is loaded)
// Note: it might take a few frames for the prefab to be loaded
var query = SystemAPI.QueryBuilder()
.WithAll()
.WithNone().Build();
state.EntityManager.AddComponent(query);
}
public void OnUpdate(ref SystemState state)
{
var ecb = new EntityCommandBuffer(Allocator.Temp);
// For the Entities that have a PrefabLoadResult component (Unity has loaded
// the prefabs) get the loaded prefab from PrefabLoadResult and instantiate it
foreach (var (prefab, entity) in
SystemAPI.Query>().WithEntityAccess())
{
var instance = ecb.Instantiate(prefab.ValueRO.PrefabRoot);
// Remove both RequestEntityPrefabLoaded and PrefabLoadResult to prevent
// the prefab being loaded and instantiated multiple times, respectively
ecb.RemoveComponent(entity);
ecb.RemoveComponent(entity);
}
ecb.Playback(state.EntityManager);
ecb.Dispose();
}
}
#endregion
在实例化EntityPrefabReference之前，Unity必须要先加载对应的entity prefab,然后才能使用它，添加RequestEntityPrefabLoaded组件能确保entity prefab被加载。Unity会PrefabLoadResult加载到带有RequestEntityPrefabLoaded同一个entity上。
预制体也是entity,也可以被查询到，如果需要把一个预制体被查询到,可以在查询条件上添加IncludePrefab。
#region PrefabsInQueries
// This query will return all baked entities, including the prefab entities
var prefabQuery = SystemAPI.QueryBuilder()
.WithAll().WithOptions(EntityQueryOptions.IncludePrefab).Build();
#endregion
使用EntityManager与entity command buffer也可以销毁一个预制体节点,代码如下:
#region DestroyPrefabs
var ecb = new EntityCommandBuffer(Allocator.Temp);
foreach (var (component, entity) in
SystemAPI.Query>().WithEntityAccess())
{
if (component.ValueRO.RadiansPerSecond <= 0)
{
ecb.DestroyEntity(entity);
}
}
ecb.Playback(state.EntityManager);
ecb.Dispose();
#endregion
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