Release 0.8.0

Added

WebTransport with WASM support!

I am super excited for this: thanks to @Nul-led and @MOZGIII's help I was able the wasm webtransport working!
This means that lightyear is now available in the browser.

See here for an example running in WASM along with instructions.

PreSpawning entities

lightyear already had some support for prespawning entities on the Predicted timeline, but it was fairly awkward.
I'm introducing an easier way to do this, where the server and client can use the exact same system to spawn the entities. The only thing you need to do is add the component PreSpawnedPlayerObject on the entity, on the client and the server.

When the client receives a server entity, it will first check if that entity corresponds to one of its prespawned entities by using a hash of the Archetype and the spawn tick of the entity.

See here for an example of how to use prespawning.
You can also read more about it in the book.

Release 0.7.0

Added

• Split the Client and Server monolithic resources into a bunch of smaller independent resources to remove coupling and improve parallelism. The new resources are:

  • ConnectionManager: the main resource to use to send inputs, send messages and handle replication in general.
  • Io: for sending/receiving raw packets
  • Protocol: to access the list of channels/components/messages/inputs that make up the protocol
  • Config: access the lightyear config
  • Netcode: abstraction of a network connection on top of the raw io
  • Events: a resource that handles creating Bevy events for network-related events
  • TimeManager: keeps track of the time and when we should send network packets
  • TickManager: keeps track of the internal tick (which is incremented on each FixedUpdate run)

  I am still planning on further breaking up the remaining ConnectionManager into different parts:

  • InputManager to handle inputs

  • SyncManager for handling time-syncing between client and server

  • maybe having a different resource per channel so that you can send messages to different channels in parallel

  • Added diagnostics to print the incoming/outgoing bandwidth that is being used

You can use enable the diagnostics like so:

    app.add_plugins(LogDiagnosticsPlugin {
      filter: Some(vec![
          IoDiagnosticsPlugin::BYTES_IN,
          IoDiagnosticsPlugin::BYTES_OUT,
      ]),
      ..default()
  });

I am planning on adding more diagnostics in the future.

Fixed

• I fixed a LOT of bugs related to long-term connections after the Tick wrapped-around (after around 15 minutes); all features (input handling, replication, time-syncing) should now work correctly even for long-term sessions, up to 46 days.

• Fixed an issue where leafwing ActionStates could not be replicated correctly from client->server in some edge-cases. Now inputs are networked correctly whether the controlled Entity is Controlled, Predicted or Pre-Predicted.

Migration

• You will need to update your systems; the old 'monolithic' resources are still available as the SystemParams Client/ClientMut and Server/ServerMut. Otherwise you will mostly need to use the resources ClientConnectionManager and ServerConnectionManager.

Release 0.6.1

• Add support for bevy_xpbd 0.3.3
• Fixes some issues (overflow) for WrappedTime
• Removed some info! and warn! logs in client sync

Release 0.6.0

Summary

This release introduces the following changes:

• added an integration with leafwing_input_manager! This provides a more flexible way of handling inputs, and is now the recommended way. (gated behing the leafwing feature)
• added an integration with bevy_xpbd_2d! Some components of bevy_xpbd_2d now implement Message and can be used directly in your replication protocol. (gated behind the xpbd_2d feature)
• added the possibility to add some input delay. This lets you have a trade-off between mispredictions but responsive inputs (if the input delay is 0) or no mispredictions but delayed inputs (if the input delay is greater than the RTT)
• added the possibility to specify how to handle mispredictions: the default behaviour is to immediately snap to the Corrected state, but it is now possible to visually interpolate between the current state and the corrected state over a few ticks
• added the possibility to specify custom replication characterics per component for a given entity. The current options are:
  • whether to replicate this component or not
  • whether to replicate this component only once (but not send further updates)
  • whether to replicate this component only to a subset of Clients
• examples have been updated so that they work on real connections. I have tested all examples on a connection with a remote headless server with both UDP and WebTransport!
• Added an example showcasing most new features:
  • uses leafwing_input_manager to handle inputs
  • replicates physics via bevy_xpbd_2d
  • each client predicts every entity, and uses variable input_delay and correction_ticks to improve the handling of mispredictions
  • each client controls several entities using different keys
• Various bug fixes

Changelog

Added

Handling inputs via leafwing_input_manager (feature leafwing)

The current input_handling is quite crude and has several limitations:

• the user can only provide a single enum of possible actions
• the user must handle inputs in the FixedUpdate::Main system set

This release adds special support for networking inputs via leafwing_input_manager, so that we can get all the benefits from that crate (handling chords, having multiple entities controlled by different keys).

IMPORTANT:

• I am not sure that all features are currently working with the current ("native") input handler (for example input delay). I might remove it in the future to only support leafwing_input_manager
• It is currently not possible to replicate inputs using a global ActionState resource. Only inputs attached to entities are supported
• Inputs that are attached to pre-Predicted entities or Confirmed entities are currently supported, but not for Predicted entities.

Bevy xpbd 2d integration (feature xpbd_2d)

It can be hard currently to directly use external components in your replication protocol, as every component must implement such custom lightyear traits such as Message or MapEntities.
I wanted to create a demo of a physics-based networked simulation so I manually implemented some good defaults for some components of bevy_xpbd_2d, so that you can use them directly in your replication protocol.

Input delay

Lightyear now supports adding some input delay: i.e. the user presses a button on tick 10 but their character only moves on tick 15.
This lets you choose a good trade-off between having a less responsive game (more input delay) vs a very responsive game but where there is more mispredictions because the client is far in the future (low input delay).
At the extreme where the input delay is higher than the RTT, the game won't have any mispredictions as both the client and server will have access to all inputs.

See more information here: https://www.snapnet.dev/docs/core-concepts/input-delay-vs-rollback/

Prediction correction

This release adds the option to visually interpolate between the current position and the corrected position when there is a misprediction rollback. This is the technique used in RocketLeague to ensure that the game still runs smoothly even when all clients are being predicted.
The two default behaviours are:

• InstantCorrector (no correction, we just perform rollback as usual)
• InterpolatedCorrector (we re-use the interpolation logic for the correction; which will happen over a few ticks)

Note that the correction still has some jittery artifacts, but that's something that I will be working on in the future.

Enable custom replication logic for specific components of an Entity

It is now possible to have some replication custom logic per component of an entity.

For instance, by default only components present in the ComponentProtocol get replicated; but there could be situations where we don't want to replicate a component of an entity even it is present in the ComponentProtocol.
This can be achieved simply by calling the following methods on the Replicate component (which defines how this entity gets replicated):

• replicate.disable_component<Component1>() to disable replication
• replicate.enable_component<Component1>() to enable replication.
  (by default, all components are enabled)

Another example is that we might want to replicate the ActionState of an entity to all players except for the player who controls the entity (since they are the ones who are updating the ActionState with their inputs). This can be done easily by calling:

replicate.add_target::<ActionState>(NetworkTarget::AllExceptSingle(client_id));

Benchmarks

I used divan to add CPU/memory benchmarks for replicating many entities to one client, or a few entities to many clients.
I still have to think about how to best interpret the results from the benchmarks. For example I suspect that I'm doing unnecessary clones:

• during serialization/deserialization in the packet/message layer
• when replicating a single object to many different clients
  Ideally the benchmarks should reflect this but I haven't been able to use them for this yet.

Improved examples

I have cleaned-up the examples and tested them all in a real connection with a remote server.
The server now has the option to run in headless mode, i.e. with all rendering-related plugins disabled. Only Bevy's MinimalPlugins are enabled, so that only the simulation is running.
All examples are working with both UDP and WebTransport!

QOL improvements

• We are now exporting the type aliases:

  type Client = Client<MyProtocol>
  type Server = Server<MyProtocol>
  type Replicate = Replicate<MyProtocol>
  

  for convenience, so that we don't have to keep mentioning the protocol as generic parameter.

• Added the AllExceptSingle and Single NetworkTargets

• The trait Message is now automatically implemented. You just need to implement the MapEntities and Named traits.

Fixed

• Fixed an issue where prediction time/interpolation time were not being computed properly when the client started, which would cause the Predicted/Interpolated entities to appear frozen

• PredictionHistory was being added even to entities that were not being Predicted. This was consuming additional CPU/memory for no reason, and has been fixed

• Removed warn loggings being emitted by mistake for pre-Predicted entities

• We are no longer getting a panic when we try to despawn the entities of a client who has disconnected

• Fixed an issue where if two entities were in the same ReplicationGroup and one of them rolled back, the other would not roll back as well. Now it is guaranteed that all components of all predicted entities will rollback if there is a mispredictions on any of them.

• Fixed some issues with rollback (including an off-by-1 error in the rollback logic)

• Fixed some issues with replication (we now compute the bevy ChangeTick correctly)

Migration

• Use Client instead of Client<Protocol>, Replicate instead of Replicate<Protocol>
• UserInput has been renamed to UserAction
• Components don't implement SyncComponent directly anymore (because this was preventing users from directly using components from external crates due to the orphan rule), instead the ComponentProtocol implements SyncMetadata<C> for each component. Use this to access the mode, interpolator, corrector of each Component

Release 0.5.0

Summary

This release introduces the following changes:

• client-side replication: entities/components spawned can now be replicated from the client to the server and to other clients!
• entity pre-spawning: it is now possible to spawn Pre-Predicted entities on the client! This means that you can spawn entities on the client timeline (i.e without any delay); as soon as you get the corresponding server entities, the pre-spawned predicted entity will update to using the server's entity as 'source of truth' for rollback
• tested most edge-cases of client-prediction (rolling back a despawned entity, rolling back a removed component); most of them are now supported correctly!

Changelog

Added

Message broadcasting

You can know send messages from client to other clients. Previously we could only send messages between a client and the server. I added the method client.send_message_to_target which allows a client to send a message to any other client (by routing via the server)

Client-side prediction

It is now possible to have replication from the client to the server!
Note that currently I do not provide any particular helper to broadcast an entity from a client to other clients; the only way to do that is to:

• replicate an entity from the client to the server
• add the Replicate component to the server entity, to specify how it will be replicated to other clients

I might add some more ergonomic way to achieve this in the future (i.e specifying directly on the client how we want the entity to be replicated to other clients).

Pre-spawning Predicted entities on the Client

Currently, the only way to spawn Predicted entities (i.e. responsive and on the client's timeline) was to spawn them on the server and wait for them to be replicated. This would introduce a delay if the entity was spawned as part of a client action. We would have to wait for:

1. the client's action to be sent to the server
2. then for the server to spawn an entity
3. and then for that entity to be replicated to the client
   to be able to spawn a Predicted entity on the client, which is at a minimum a full RTT of delay.

Instead, we can now spawn a pre-predicted entity on the client. Here is an example:

1. a client spawns a PrePredicted entity C1 by adding the component ShouldBePredicted { client_entity }
2. the client replicates that entity C1 to the server, which creates an entity S1
3. the server replicates the entity S1 back to the client, which creates a Confirmed entity C2 and re-uses the existing entity C1 as its Predicted entity

Correctly handling replication edge-cases

There are a lot of potential edge-cases with client-prediction, especially with the addition of spawning Pre-Predicted entities.

I have listed most of them in that link; for instance:

• despawning a predicted entity, but the server doesn't despawn -> need to rollback the Predicted despawn
• despawning a predicted entity, and the server accepts the despawn -> we want the server's replicated entity to be immediately despawned
• despawning the server entity -> need to replicate the despawn to Predicted entities
• ...
  etc.

I have tested most them; almost all situations are supported correctly!
The only one that has some caveats is rolling back a predicted despawn; this only happens if we receive a server update for that entity after the despawn.

Client replication example

Added a new example client_replication that show-cases the newly-added features:

• pressing M will send a message from a client to other clients
• performs client-authoritative replication by replicating the user's cursor to other clients
• pressing Space will spawn a Pre-Predicted entity. The entity is spawned immediately, and then becomes the Predicted version of a Confirmed entity once it gets replicated
• pressing Delete will delete the Predicted entity. You can use this to confirm the behavior of rollback in various edge-cases.

Updated

• Renamed the send_message methods from buffer_send ->send_message and send_to_target -> send_message_to_target for clarity.

Migration guide 0.4.0 -> 0.5.0

• server.send_to_target has been renamed to server.send_message_to_target
• server.buffer_send has been renamed to server.send_message
• client.buffer_send has been renamed to client.send_message
• Adding Replicate on the server to re-replicate client entities to other clients must be done in the newly added MainSet::ClientReplication SystemSet
• Correctly despawning Predicted entities requires to use EntityCommands::prediction_despawn instead of EntityCommands::despawn

Release 0.4.0

Summary

This release:

• enables the replication of Messages and Components that contain Entities
• greatly improves the stability of client-prediction and snapshot-interpolation
• adds a more involved example showing how to use custom interpolation logic, and components that contain Entities

Changelog

Added

• Added an example ReplicationGroups that showcases:
  • the concept of ReplicationGroups: where multiple entities are guaranteed to be replicated in a single message, so will always be in sync with each other
  • how replicating components that refer to other entities works (via the MapEntities trait)
  • how to execute a complex custom snapshot interpolation logic: the interpolation is not a simple linear interpolation. The interpolated will stay on the "path" of the snake, and never do any diagonal movement
  • showcases how prediction/interpolation performs with bad connections; the example default settings are with 400ms RTT, 40ms jitter and 10% packet loss

Updated

• Handle entity mappings more rigorourously now! By Entity Mapping I mean Messages or Components that contain references to other entities, such as HasParent(Entity). The entity in the message is from the server's World, and it needs to be mapped to the client's World.

  • refactored the MapEntities trait to be more flexible
  • introduced also entity mapping between the Confirmed entities and the Predicted/Interpolated entities (i.e. a component with HasParent(Entity) on the Confirmed entity will be synced with the correct mapping on the Predicted/Interpolated entities)
  • A Replication Group will be guaranteed to be replicated with an entity order that respects any dependencies between the entities: for example if you have two entities A and B and B depends on A (maybe because it contains a component HasParent(A), B will be replicated after A has finished replicating.

• Updated the Input handling logic to get rid of some jitter around client prediction:

  • clients now must send inputs every tick (even if there are no inputs), so that the server can distinguish between "no input" and "lost input"
  • For a lost input, the server uses the last received input as a fallback estimate
  • this helps reduce prediction errors by a huge amount; client prediction should be more robust now!

• Refactored some of the interpolation logic:

  • a Component only needs to implement Add and Mul if it uses LinearInterpolation, not if it uses a custom interpolation function
  • added an option to give the user complete freedom to implement their interpolation logic

Fixed

• Fixed an issue that was causing some instability during client-prediction: the client inputs were not buffered for long enough, so the input buffer was sometimes empty during rollback
• Fixed some issues that were causing instability/jitter during snapshot-interpolation: the interpolation start and end ticks were sometimes not computed correctly, which would cause the interpolation to 'jitter'. Snapshot interpolation should be much smoother now
• Fixed an issue where the ping buffer was sometimes too small and would panic, especially if the ping send_interval was short

Migration guide

• Clients must now send inputs every tick, even if the user isn't doing any action. Practically, this means that you need to add a None variant in your Input enum, like so:

pub enum Inputs {
    Direction(Direction),
    Delete,
    Spawn,
    // *new*: inputs must be sent every tick, even if there is no action
    NoAction,
}

• The MapEntities trait has been modified; all old implementors must be updated to match the new trait:

/// Trait that Messages or Components must implement to be able to map entities
pub trait MapEntities<'a> {
    /// Map the entities inside the message or component from the remote World to the local World
    fn map_entities(&mut self, entity_mapper: Box<dyn EntityMapper + 'a>);

    /// Get all the entities that are present in that message or component
    fn entities(&self) -> EntityHashSet<Entity>;
}

Release 0.3.0

Release 0.3.0

Added

• Added interest management via the concept of Room, to be able to replicate only a subset entities to a certain client to save bandwidth and prevent cheating. See more information here
• Updated the replication manager to be much more robust. The new manager:
  • makes sure that an entity or a group of entities (via ReplicationGroup) are replicated with a consistent state. See more information here
  • inspired by what bevy_replicon is doing
  • this fixes some edge cases with prediction/interpolation; in particular when send_interval is small compared with jitter
• Added a new UnreliableSenderWithAck channel where senders can get notified when a given message has been ACK-ed
• Some common bevy structs (Transform, Color, Visibility) now implement the Message trait and can be used for replication

Updated

• the ComponentProtocol now derives Debug directly (which shows the type of the replicated Component, but not the value)

Fixed

• the existing world state is now replicated properly to newly connected clients (whether they use Room or not for replication)