6e918f56d8
# Objective Allow combinator and pipe systems to delay validation of the second system, while still allowing the second system to be skipped. Fixes #18796 Allow fallible systems to be used as one-shot systems, reporting errors to the error handler when used through commands. Fixes #19722 Allow fallible systems to be used as run conditions, including when used with combinators. Alternative to #19580. Always validate parameters when calling the safe `run_without_applying_deferred`, `run`, and `run_readonly` methods on a `System`. ## Solution Have `System::run_unsafe` return a `Result`. We want pipe systems to run the first system before validating the second, since the first system may affect whether the second system has valid parameters. But if the second system skips then we have no output value to return! So, pipe systems must return a `Result` that indicates whether the second system ran. But if we just make pipe systems have `Out = Result<B::Out>`, then chaining `a.pipe(b).pipe(c)` becomes difficult. `c` would need to accept the `Result` from `a.pipe(b)`, which means it would likely need to return `Result` itself, giving `Result<Result<Out>>`! Instead, we make *all* systems return a `Result`! We move the handling of fallible systems from `IntoScheduleConfigs` and `IntoObserverSystem` to `SystemParamFunction` and `ExclusiveSystemParamFunction`, so that an infallible system can be wrapped before being passed to a combinator. As a side effect, this enables fallible systems to be used as run conditions and one-shot systems. Now that the safe `run_without_applying_deferred`, `run`, and `run_readonly` methods return a `Result`, we can have them perform parameter validation themselves instead of requiring each caller to remember to call them. `run_unsafe` will continue to not validate parameters, since it is used in the multi-threaded executor when we want to validate and run in separate tasks. Note that this makes type inference a little more brittle. A function that returns `Result<T>` can be considered either a fallible system returning `T` or an infallible system returning `Result<T>` (and this is important to continue supporting `pipe`-based error handling)! So there are some cases where the output type of a system can no longer be inferred. It will work fine when directly adding to a schedule, since then the output type is fixed to `()` (or `bool` for run conditions). And it will work fine when `pipe`ing to a system with a typed input parameter. I used a dedicated `RunSystemError` for the error type instead of plain `BevyError` so that skipping a system does not box an error or capture a backtrace. |
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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.