a312170749
# Objective Currently, `bevy_ecs`'s `children!` macro only supports spawning up to twelve children at once. Ideally there would be no limit. ## Solution `children!` is limited because `SpawnableList`, [the primary trait bound here](https://docs.rs/bevy/0.16.0-rc.5/bevy/ecs/hierarchy/struct.Children.html#method.spawn), uses the fake variadics pattern on tuples of up to twelve elements. However, since a tuple itself implements `SpawnableList`, we can simply nest tuples of entities when we run out of room. This PR achieves this using `macro_rules` macros with a bit of brute force, following [some discussion on Discord](https://discord.com/channels/691052431525675048/692572690833473578/1362174415458013314). If we create patterns for lists of up to eleven bundles, then use a repetition pattern to handle the rest, we can "special-case" the recursion into a nested tuple. In principle, this would permit an arbitrary number of children, but Rust's recursion limits will cut things short at around 1400 elements by default. Of course, it's generally not a good idea to stick that many bundles in a single invocation, but it might be worth mentioning in the docs. ## Implementation notes ### Why are cases 0-11 expanded by hand? We could make use of a tertiary macro: ```rs macro_rules! recursive_spawn { // so that this... ($a:expr, $b:expr) => { ( $crate::spawn::Spawn($a), $crate::spawn::Spawn($b), ) }; // becomes this... ($a:expr, $b:expr) => { $crate::spawn_tuple!($a, $b) }; } ``` But I already feel a little bad exporting `recursive_spawn`. I'd really like to avoid exposing more internals, even if they are annotated with `#[doc(hidden)]`. If I had to guess, I'd say it'll also make the expansion a tiny bit slower. ### Do we really need to handle up to twelve elements in the macro? The macro is a little long, but doing it this way maximizes the "flatness" of the types to be spawned. This should improve the codegen a bit and makes the macro output a little bit easier to look at. ## Future work The `related!` macro is essentially the same as `children!`, so if this direction is accepted, `related!` should receive the same treatment. I imagine we'd want to extract out the `recursive_spawn` macro into its own file since it can be used for both. If this should be tackled in this PR, let me know! ## Testing This change is fairly trivial, but I added a single test to verify that it compiles and nothing goes wrong once recursion starts happening. It's pretty easy to verify that the change works in practice -- just spawn over twelve entities as children at once! |
||
|---|---|---|
| .cargo | ||
| .github | ||
| assets | ||
| benches | ||
| crates | ||
| docs | ||
| docs-rs | ||
| docs-template | ||
| errors | ||
| examples | ||
| release-content | ||
| src | ||
| tests | ||
| tests-integration/simple-ecs-test | ||
| tools | ||
| .gitattributes | ||
| .gitignore | ||
| Cargo.toml | ||
| clippy.toml | ||
| CODE_OF_CONDUCT.md | ||
| CONTRIBUTING.md | ||
| CREDITS.md | ||
| deny.toml | ||
| LICENSE-APACHE | ||
| LICENSE-MIT | ||
| README.md | ||
| rustfmt.toml | ||
| typos.toml | ||
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.