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# Objective This is an alternative to #17871 and #17701 for tracking issue #18155. This thanks to @maniwani for help with this design. The goal is to enable component ids to be reserved from multiple threads concurrently and with only `&World`. This contributes to assets as entities, read-only query and system parameter initialization, etc. ## What's wrong with #17871 ? In #17871, I used my proposed staging utilities to allow *fully* registering components from any thread concurrently with only `&Components`. However, if we want to pursue components as entities (which is desirable for a great many reasons. See [here](https://discord.com/channels/691052431525675048/692572690833473578/1346499196655505534) on discord), this staging isn't going to work. After all, if registering a component requires spawning an entity, and spawning an entity requires `&mut World`, it is impossible to register a component fully with only `&World`. ## Solution But what if we don't have to register it all the way? What if it's enough to just know the `ComponentId` it will have once it is registered and to queue it to be registered at a later time? Spoiler alert: That is all we need for these features. Here's the basic design: Queue a registration: 1. Check if it has already been registered. 2. Check if it has already been queued. 3. Reserve a `ComponentId`. 4. Queue the registration at that id. Direct (normal) registration: 1. Check if this registration has been queued. 2. If it has, use the queued registration instead. 3. Otherwise, proceed like normal. Appllying the queue: 1. Pop queued items off one by one. 2. Register them directly. One other change: The whole point of this design over #17871 is to facilitate coupling component registration with the World. To ensure that this would fully work with that, I went ahead and moved the `ComponentId` generator onto the world itself. That stemmed a couple of minor organizational changes (see migration guide). As we do components as entities, we will replace this generator with `Entities`, which lives on `World` too. Doing this move early let me verify the design and will reduce migration headaches in the future. If components as entities is as close as I think it is, I don't think splitting this up into different PRs is worth it. If it is not as close as it is, it might make sense to still do #17871 in the meantime (see the risks section). I'll leave it up to y'all what we end up doing though. ## Risks and Testing The biggest downside of this compared to #17871 is that now we have to deal with correct but invalid `ComponentId`s. They are invalid because the component still isn't registered, but they are correct because, once registered, the component will have exactly that id. However, the only time this becomes a problem is if some code violates safety rules by queuing a registration and using the returned id as if it was valid. As this is a new feature though, nothing in Bevy does this, so no new tests were added for it. When we do use it, I left detailed docs to help mitigate issues here, and we can test those usages. Ex: we will want some tests on using queries initialized from queued registrations. ## Migration Guide Component registration can now be queued with only `&World`. To facilitate this, a few APIs needed to be moved around. The following functions have moved from `Components` to `ComponentsRegistrator`: - `register_component` - `register_component_with_descriptor` - `register_resource_with_descriptor` - `register_non_send` - `register_resource` - `register_required_components_manual` Accordingly, functions in `Bundle` and `Component` now take `ComponentsRegistrator` instead of `Components`. You can obtain `ComponentsRegistrator` from the new `World::components_registrator`. You can obtain `ComponentsQueuedRegistrator` from the new `World::components_queue`, and use it to stage component registration if desired. # Open Question Can we verify that it is enough to queue registration with `&World`? I don't think it would be too difficult to package this up into a `Arc<MyComponentsManager>` type thing if we need to, but keeping this on `&World` certainly simplifies things. If we do need the `Arc`, we'll need to look into partitioning `Entities` for components as entities, so we can keep most of the allocation fast on `World` and only keep a smaller partition in the `Arc`. I'd love an SME on assets as entities to shed some light on this. --------- Co-authored-by: andriyDev <andriydzikh@gmail.com> |
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What is Bevy?
Bevy is a refreshingly simple data-driven game engine built in Rust. It is free and open-source forever!
WARNING
Bevy is still in the early stages of development. Important features are missing. Documentation is sparse. A new version of Bevy containing breaking changes to the API is released approximately once every 3 months. We provide migration guides, but we can't guarantee migrations will always be easy. Use only if you are willing to work in this environment.
MSRV: Bevy relies heavily on improvements in the Rust language and compiler. As a result, the Minimum Supported Rust Version (MSRV) is generally close to "the latest stable release" of Rust.
Design Goals
- Capable: Offer a complete 2D and 3D feature set
- Simple: Easy for newbies to pick up, but infinitely flexible for power users
- Data Focused: Data-oriented architecture using the Entity Component System paradigm
- Modular: Use only what you need. Replace what you don't like
- Fast: App logic should run quickly, and when possible, in parallel
- Productive: Changes should compile quickly ... waiting isn't fun
About
- Features: A quick overview of Bevy's features.
- News: A development blog that covers our progress, plans and shiny new features.
Docs
- Quick Start Guide: Bevy's official Quick Start Guide. The best place to start learning Bevy.
- Bevy Rust API Docs: Bevy's Rust API docs, which are automatically generated from the doc comments in this repo.
- Official Examples: Bevy's dedicated, runnable examples, which are great for digging into specific concepts.
- Community-Made Learning Resources: More tutorials, documentation, and examples made by the Bevy community.
Community
Before contributing or participating in discussions with the community, you should familiarize yourself with our Code of Conduct.
- Discord: Bevy's official discord server.
- Reddit: Bevy's official subreddit.
- GitHub Discussions: The best place for questions about Bevy, answered right here!
- Bevy Assets: A collection of awesome Bevy projects, tools, plugins and learning materials.
Contributing
If you'd like to help build Bevy, check out the Contributor's Guide. For simple problems, feel free to open an issue or PR and tackle it yourself!
For more complex architecture decisions and experimental mad science, please open an RFC (Request For Comments) so we can brainstorm together effectively!
Getting Started
We recommend checking out the Quick Start Guide for a brief introduction.
Follow the Setup guide to ensure your development environment is set up correctly. Once set up, you can quickly try out the examples by cloning this repo and running the following commands:
# Switch to the correct version (latest release, default is main development branch)
git checkout latest
# Runs the "breakout" example
cargo run --example breakout
To draw a window with standard functionality enabled, use:
use bevy::prelude::*;
fn main(){
App::new()
.add_plugins(DefaultPlugins)
.run();
}
Fast Compiles
Bevy can be built just fine using default configuration on stable Rust. However for really fast iterative compiles, you should enable the "fast compiles" setup by following the instructions here.
Bevy Cargo Features
This list outlines the different cargo features supported by Bevy. These allow you to customize the Bevy feature set for your use-case.
Thanks
Bevy is the result of the hard work of many people. A huge thanks to all Bevy contributors, the many open source projects that have come before us, the Rust gamedev ecosystem, and the many libraries we build on.
A huge thanks to Bevy's generous sponsors. Bevy will always be free and open source, but it isn't free to make. Please consider sponsoring our work if you like what we're building.
This project is tested with BrowserStack.
License
Bevy is free, open source and permissively licensed! Except where noted (below and/or in individual files), all code in this repository is dual-licensed under either:
- MIT License (LICENSE-MIT or http://opensource.org/licenses/MIT)
- Apache License, Version 2.0 (LICENSE-APACHE or http://www.apache.org/licenses/LICENSE-2.0)
at your option. This means you can select the license you prefer! This dual-licensing approach is the de-facto standard in the Rust ecosystem and there are very good reasons to include both.
Some of the engine's code carries additional copyright notices and license terms due to their external origins.
These are generally BSD-like, but exact details vary by crate:
If the README of a crate contains a 'License' header (or similar), the additional copyright notices and license terms applicable to that crate will be listed.
The above licensing requirement still applies to contributions to those crates, and sections of those crates will carry those license terms.
The license field of each crate will also reflect this.
For example, bevy_mikktspace has code under the Zlib license (as well as a copyright notice when choosing the MIT license).
The assets included in this repository (for our examples) typically fall under different open licenses. These will not be included in your game (unless copied in by you), and they are not distributed in the published bevy crates. See CREDITS.md for the details of the licenses of those files.
Your contributions
Unless you explicitly state otherwise, any contribution intentionally submitted for inclusion in the work by you, as defined in the Apache-2.0 license, shall be dual licensed as above, without any additional terms or conditions.