Unity DOTS系列之Filter Baking Output与Prefab In Baking核心分析
最近DOTS发布了正式的版本, 我们来分享一下DOTS里面Baking核心机制,方便大家上手学习掌握Unity DOTS开发。今天给大家分享的Baking机制中的Filter Baking Output与Prefab In Baking。
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Filter Baking Output 机制
在默认情况下,Baking会为每个GameObject生成的Entity与Component, 这些entity都会被创建到Conversion World里面。然后在创作的时候不是所有的GameObject都需要被转换成Entity。例如: 在一个样条曲线上,一个控制点在创作的时候被用到了,但是bake成ecs数据后可能就再也没有用了,所以不需要把这个控制点Bake成entity。
为了不把这个GameObject Bake产生的Entity输出到World并保存到entity scene里面,我们可以给这个Entity添加一个BakingOnlyEntity tag Component。当你添加了这个tag component后,Baking系统就不会把你这个entity存储到entity scene里面,也不会把这个entity生成到运行的main World里面。我们可以直接在Baker函数里面添给entity 添加一个BakingOnlyEntity的组件数据,也可以在Authoring GameObject里面添加一个 BakingOnlyEntityAuthoring的组件,这两种方式都可以达到同样的效果没有区别。
你也可以给组件添加注解[BakingType],[TemporaryBakingType] attributes过滤掉掉组件component,让它不输出到entity中。
![](https://pic1.zhimg.com/80/v2-e73de8b29ebf28be91036896fec054b8_720w.webp)
[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
![](https://pic3.zhimg.com/80/v2-ef2a9e91262c4f414357f928ae83a686_720w.webp)
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<GetPrefabAuthoring>
{
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<EntityPrefabComponent>()
.WithNone<PrefabLoadResult>().Build();
state.EntityManager.AddComponent<RequestEntityPrefabLoaded>(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<RefRO<PrefabLoadResult>>().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<RequestEntityPrefabLoaded>(entity);
ecb.RemoveComponent<PrefabLoadResult>(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<RefRO<EntityPrefabComponent>>())
{
// 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<ComponentA>(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<EntityPrefabComponent>()
.WithNone<PrefabLoadResult>().Build();
state.EntityManager.AddComponent<RequestEntityPrefabLoaded>(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<RefRO<PrefabLoadResult>>().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<RequestEntityPrefabLoaded>(entity);
ecb.RemoveComponent<PrefabLoadResult>(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<BakedEntity>().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<RefRO<RotationSpeed>>().WithEntityAccess())
{
if (component.ValueRO.RadiansPerSecond <= 0)
{
ecb.DestroyEntity(entity);
}
}
ecb.Playback(state.EntityManager);
ecb.Dispose();
#endregion
今天的Baking 系列就分享到这里了,关注我学习更多的最新Unity DOTS开发技巧。