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# Objective There are currently too many disparate ways to handle entity mapping, especially after #17687. We now have MapEntities, VisitEntities, VisitEntitiesMut, Component::visit_entities, Component::visit_entities_mut. Our only known use case at the moment for these is entity mapping. This means we have significant consolidation potential. Additionally, VisitEntitiesMut cannot be implemented for map-style collections like HashSets, as you cant "just" mutate a `&mut Entity`. Our current approach to Component mapping requires VisitEntitiesMut, meaning this category of entity collection isn't mappable. `MapEntities` is more generally applicable. Additionally, the _existence_ of the blanket From impl on VisitEntitiesMut blocks us from implementing MapEntities for HashSets (or any types we don't own), because the owner could always add a conflicting impl in the future. ## Solution Use `MapEntities` everywhere and remove all "visit entities" usages. * Add `Component::map_entities` * Remove `Component::visit_entities`, `Component::visit_entities_mut`, `VisitEntities`, and `VisitEntitiesMut` * Support deriving `Component::map_entities` in `#[derive(Coomponent)]` * Add `#[derive(MapEntities)]`, and share logic with the `Component::map_entities` derive. * Add `ComponentCloneCtx::queue_deferred`, which is command-like logic that runs immediately after normal clones. Reframe `FromWorld` fallback logic in the "reflect clone" impl to use it. This cuts out a lot of unnecessary work and I think justifies the existence of a pseudo-command interface (given how niche, yet performance sensitive this is). Note that we no longer auto-impl entity mapping for ` IntoIterator<Item = &'a Entity>` types, as this would block our ability to implement cases like `HashMap`. This means the onus is on us (or type authors) to add explicit support for types that should be mappable. Also note that the Component-related changes do not require a migration guide as there hasn't been a release with them yet. ## Migration Guide If you were previously implementing `VisitEntities` or `VisitEntitiesMut` (likely via a derive), instead use `MapEntities`. Those were almost certainly used in the context of Bevy Scenes or reflection via `ReflectMapEntities`. If you have a case that uses `VisitEntities` or `VisitEntitiesMut` directly, where `MapEntities` is not a viable replacement, please let us know! ```rust // before #[derive(VisitEntities, VisitEntitiesMut)] struct Inventory { items: Vec<Entity>, #[visit_entities(ignore)] label: String, } // after #[derive(MapEntities)] struct Inventory { #[entities] items: Vec<Entity>, label: String, } ``` |
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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.