mirror of
https://github.com/bevyengine/bevy
synced 2024-11-23 05:03:47 +00:00
71f8b4a92f
# Objective
Currently for entities we serialize only `id`. But this is not very expected behavior. For example, in networking, when the server sends its state, it contains entities and components. On the client, I create new objects and map them (using `EntityMap`) to those received from the server (to know which one matches which). And if `generation` field is missing, this mapping can be broken. Example:
1. Server sends an entity `Entity{ id: 2, generation: 1}` with components.
2. Client puts the received entity in a map and create a new entity that maps to this received entity. The new entity have different `id` and `generation`. Let's call it `Entity{ id: 12, generation: 4}`.
3. Client sends a command for `Entity{ id: 12, generation: 4}`. To do so, it maps local entity to the one from server. But `generation` field is 0 because it was omitted for serialization on the server. So it maps to `Entity{ id: 2, generation: 0}`.
4. Server receives `Entity{ id: 2, generation: 0}` which is invalid.
In my game I worked around it by [writing custom serialization](https://github.com/dollisgame/dollis/blob/master/src/core/network/entity_serde.rs) and using `serde(with = "...")`. But it feels like a bad default to me.
Using `Entity` over a custom `NetworkId` also have the following advantages:
1. Re-use `MapEntities` trait to map `Entity`s in replicated components.
2. Instead of server `Entity <-> NetworkId ` and `Entity <-> NetworkId`, we map entities only on client.
3. No need to handling uniqueness. It's a rare case, but makes things simpler. For example, I don't need to query for a resource to create an unique ID.
Closes #6143.
## Solution
Use default serde impls. If anyone want to avoid wasting memory on `generation`, they can create a new type that holds `u32`. This is what Bevy do for [DynamicEntity](https://docs.rs/bevy/latest/bevy/scene/struct.DynamicEntity.html) to serialize scenes. And I don't see any use case to serialize an entity id expect this one.
---
## Changelog
### Changed
- Entity now serializes / deserializes `generation` field.
## Migration Guide
- Entity now fully serialized. If you want to serialze only `id`, as it was before, you can create a new type that wraps `u32`.
|
||
|---|---|---|
| .. | ||
| bevy_animation | ||
| bevy_app | ||
| bevy_asset | ||
| bevy_audio | ||
| bevy_core | ||
| bevy_core_pipeline | ||
| bevy_derive | ||
| bevy_diagnostic | ||
| bevy_dylib | ||
| bevy_dynamic_plugin | ||
| bevy_ecs | ||
| bevy_ecs_compile_fail_tests | ||
| bevy_encase_derive | ||
| bevy_gilrs | ||
| bevy_gltf | ||
| bevy_hierarchy | ||
| bevy_input | ||
| bevy_internal | ||
| bevy_log | ||
| bevy_macro_utils | ||
| bevy_math | ||
| bevy_mikktspace | ||
| bevy_pbr | ||
| bevy_ptr | ||
| bevy_reflect | ||
| bevy_render | ||
| bevy_scene | ||
| bevy_sprite | ||
| bevy_tasks | ||
| bevy_text | ||
| bevy_time | ||
| bevy_transform | ||
| bevy_ui | ||
| bevy_utils | ||
| bevy_window | ||
| bevy_winit | ||