Struct GhostSendSystem
System present only for servers worlds, and responsible to replicate ghost entities to the clients. The GhostSendSystem is one of the most complex system of the whole package and heavily rely on multi-thread jobs to dispatch ghosts to all connection as much as possible in parallel.
Ghosts entities are replicated by sending a 'snapshot' of their state to the clients, at NetworkTickRate frequency. Snaphosts are streamed to the client when their connection is tagged with a NetworkStreamInGame component (we usually refere a connection with that tag as "in-game"), and transmitted using an unrealiable channel. To save bandwith, snapshosts are delta-compressed against the latest reported ones received by the client. By default, up to 3 baseline are used to delta-compress the data, by using a predictive compression scheme (see GhostDeltaPredictor). It is possible to reduce the number of baseline used (and CPU cycles) using the GhostSendSystemData settings.
The GhostSendSystem is designed to send to each connection one single packet per network update. By default, the system will try to replicate to the clients all the existing ghost present in the world. When all ghosts cannot be serialized into the same packet, the enties are prioritized by their importance.
The base ghost importance can be set at authoring time on the prefab (Unity.NetCode.GhostAuthoringComponent); At runtime the ghost importance is scaled based on:
- age (the last time the entities has been sent)
- scaled by distance, (see GhostConnectionPosition, GhostDistanceImportance
- scaled by custom scaling (see GhostImportance
Ghost entities are replicated on "per-chunk" basis; all ghosts for the same chunk, are replicated together. The importance, as well as the importance scaling, apply to whole chunk.
The send system can also be configured to send multiple ghost packets per frame and to to use snaphost larger than the MaxMessageSize. In that case, the snapshot packet is sent using another unreliable channel, setup with a Unity.Networking.Transport.FragmentationPipelineStage.
Implements
Inherited Members
Namespace: Unity.NetCode
Assembly: Unity.NetCode.dll
Syntax
[WorldSystemFilter(WorldSystemFilterFlags.ServerSimulation, WorldSystemFilterFlags.Default)]
[UpdateInGroup(typeof(SimulationSystemGroup), OrderLast = true)]
[UpdateAfter(typeof(EndSimulationEntityCommandBufferSystem))]
[BurstCompile]
public struct GhostSendSystem : ISystem, ISystemCompilerGeneratedMethods
OnCreate(ref SystemState)
Called when this system is created.
Declaration
public void OnCreate(ref SystemState state)Parameters
| Type | Name | Description |
|---|---|---|
| SystemState | state | The Unity.Entities.SystemState backing this system instance |
Remarks
Implement an OnCreate function to set up system resources when it is created.
OnCreate is invoked before the the first time Unity.Entities.ISystemStartStop.OnStartRunning(ref Unity.Entities.SystemState)
and Unity.Entities.ISystem.OnUpdate(ref Unity.Entities.SystemState) are invoked.
OnCreateForCompiler(ref SystemState)
Generated by compilation pipeline and used internally.
Declaration
public void OnCreateForCompiler(ref SystemState state)Parameters
| Type | Name | Description |
|---|---|---|
| SystemState | state | The Unity.Entities.SystemState backing this system instance |
OnDestroy(ref SystemState)
Called when this system is destroyed.
Declaration
[BurstCompile]
public void OnDestroy(ref SystemState state)Parameters
| Type | Name | Description |
|---|---|---|
| SystemState | state | The Unity.Entities.SystemState backing this system instance |
Remarks
Systems are destroyed when the application shuts down, the World is destroyed, or you call Unity.Entities.World.DestroySystem(Unity.Entities.SystemHandle). In the Unity Editor, system destruction occurs when you exit Play Mode and when scripts are reloaded.
OnUpdate(ref SystemState)
Implement OnUpdate to perform the major work of this system.
Declaration
[BurstCompile]
public void OnUpdate(ref SystemState state)Parameters
| Type | Name | Description |
|---|---|---|
| SystemState | state | The Unity.Entities.SystemState backing this system instance |
Remarks
By default, the system invokes `OnUpdate` once every frame on the main thread. To skip OnUpdate if all of the system's [EntityQueries] are empty, use the [RequireMatchingQueriesForUpdateAttribute]. To limit when OnUpdate is invoked, you can specify components that must exist, or queries that match specific Entities. To do this, call Unity.Entities.SystemState.RequireForUpdate<T>() or Unity.Entities.SystemState.RequireForUpdate(Unity.Entities.EntityQuery) in the system's OnCreate method. For more information, see Unity.Entities.SystemState.ShouldRunSystem().
You can instantiate and schedule an Unity.Entities.IJobChunk instance; you can use the [C# Job System] or you can perform work on the main thread. If you call Unity.Entities.EntityManager methods that perform structural changes on the main thread, be sure to arrange the system order to minimize the performance impact of the resulting [sync points].
[sync points]: xref:concepts-structural-changes
[C# Job System]: https://docs.unity3d.com/Manual/JobSystem.html
[EntityQueries]: xref:Unity.Entities.EntityQuery
[RequireMatchingQueriesForUpdateAttribute]: xref:Unity.Entities.RequireMatchingQueriesForUpdateAttribute