a530c07bc5
Fixes #17720 ## Objective Spawning RelationshipTargets from scenes currently fails to preserve RelationshipTarget ordering (ex: `Children` has an arbitrary order). This is because it uses the normal hook flow to set up the collection, which means we are pushing onto the collection in _spawn order_ (which is currently in archetype order, which will often produce mismatched orderings). We need to preserve the ordering in the original RelationshipTarget collection. Ideally without expensive checking / fixups. ## Solution One solution would be to spawn in hierarchy-order. However this gets complicated as there can be multiple hierarchies, and it also means we can't spawn in more cache-friendly orders (ex: the current per-archetype spawning, or future even-smarter per-table spawning). Additionally, same-world cloning has _slightly_ more nuanced needs (ex: recursively clone linked relationships, while maintaining _original_ relationships outside of the tree via normal hooks). The preferred approach is to directly spawn the remapped RelationshipTarget collection, as this trivially preserves the ordering. Unfortunately we can't _just_ do that, as when we spawn the children with their Relationships (ex: `ChildOf`), that will insert a duplicate. We could "fixup" the collection retroactively by just removing the back half of duplicates, but this requires another pass / more lookups / allocating twice as much space. Additionally, it becomes complicated because observers could insert additional children, making it harder (aka more expensive) to determine which children are dupes and which are not. The path I chose is to support "opting out" of the relationship target hook in the contexts that need that, as this allows us to just cheaply clone the mapped collection. The relationship hook can look for this configuration when it runs and skip its logic when that happens. A "simple" / small-amount-of-code way to do this would be to add a "skip relationship spawn" flag to World. Sadly, any hook / observer that runs _as the result of an insert_ would also read this flag. We really need a way to scope this setting to a _specific_ insert. Therefore I opted to add a new `RelationshipInsertHookMode` enum and an `entity.insert_with_relationship_insert_hook_mode` variant. Obviously this is verbose and ugly. And nobody wants _more_ insert variants. But sadly this was the best I could come up with from a performance and capability perspective. If you have alternatives let me know! There are three variants: 1. `RelationshipInsertHookMode::Run`: always run relationship insert hooks (this is the default) 2. `RelationshipInsertHookMode::Skip`: do not run any relationship insert hooks for this insert (this is used by spawner code) 3. `RelationshipInsertHookMode::RunIfNotLinked`: only run hooks for _unlinked_ relationships (this is used in same-world recursive entity cloning to preserve relationships outside of the deep-cloned tree) Note that I have intentionally only added "insert with relationship hook mode" variants to the cases we absolutely need (everything else uses the default `Run` mode), just to keep the code size in check. I do not think we should add more without real _very necessary_ use cases. I also made some other minor tweaks: 1. I split out `SourceComponent` from `ComponentCloneCtx`. Reading the source component no longer needlessly blocks mutable access to `ComponentCloneCtx`. 2. Thanks to (1), I've removed the `RefCell` wrapper over the cloned component queue. 3. (1) also allowed me to write to the EntityMapper while queuing up clones, meaning we can reserve entities during the component clone and write them to the mapper _before_ inserting the component, meaning cloned collections can be mapped on insert. 4. I've removed the closure from `write_target_component_ptr` to simplify the API / make it compatible with the split `SourceComponent` approach. 5. I've renamed `EntityCloner::recursive` to `EntityCloner::linked_cloning` to connect that feature more directly with `RelationshipTarget::LINKED_SPAWN` 6. I've removed `EntityCloneBehavior::RelationshipTarget`. This was always intended to be temporary, and this new behavior removes the need for it. --------- Co-authored-by: Viktor Gustavsson <villor94@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.