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# Objective Fixes #5101 Alternative to #6511 ## Solution Corrected the behavior for ignored fields in `FromReflect`, which was previously using the incorrect field indexes. Similarly, fields marked with `#[reflect(skip_serializing)]` no longer break when using `FromReflect` after deserialization. This was done by modifying `SerializationData` to store a function pointer that can later be used to generate a default instance of the skipped field during deserialization. The function pointer points to a function generated by the derive macro using the behavior designated by `#[reflect(default)]` (or just `Default` if none provided). The entire output of the macro is now wrapped in an [unnamed constant](https://doc.rust-lang.org/stable/reference/items/constant-items.html#unnamed-constant) which keeps this behavior hygienic. #### Rationale The biggest downside to this approach is that it requires fields marked `#[reflect(skip_serializing)]` to provide the ability to create a default instance— either via a `Default` impl or by specifying a custom one. While this isn't great, I think it might be justified by the fact that we really need to create this value when using `FromReflect` on a deserialized object. And we need to do this _during_ deserialization because after that (at least for tuples and tuple structs) we lose information about which field is which: _"is the value at index 1 in this `DynamicTupleStruct` the actual value for index 1 or is it really the value for index 2 since index 1 is skippable...?"_ #### Alternatives An alternative would be to store `Option<Box<dyn Reflect>>` within `DynamicTuple` and `DynamicTupleStruct` instead of just `Box<dyn Reflect>`. This would allow us to insert "empty"/"missing" fields during deserialization, thus saving the positional information of the skipped fields. However, this may require changing the API of `Tuple` and `TupleStruct` such that they can account for their dynamic counterparts returning `None` for a skipped field. In practice this would probably mean exposing the `Option`-ness of the dynamics onto implementors via methods like `Tuple::drain` or `TupleStruct::field`. Personally, I think requiring `Default` would be better than muddying up the API to account for these special cases. But I'm open to trying out this other approach if the community feels that it's better. --- ## Changelog ### Public Changes #### Fixed - The behaviors of `#[reflect(ignore)]` and `#[reflect(skip_serializing)]` are no longer dependent on field order #### Changed - Fields marked with `#[reflect(skip_serializing)]` now need to either implement `Default` or specify a custom default function using `#[reflect(default = "path::to::some_func")]` - Deserializing a type with fields marked `#[reflect(skip_serializing)]` will now include that field initialized to its specified default value - `SerializationData::new` now takes the new `SkippedField` struct along with the skipped field index - Renamed `SerializationData::is_ignored_field` to `SerializationData::is_field_skipped` #### Added - Added `SkippedField` struct - Added methods `SerializationData::generate_default` and `SerializationData::iter_skipped` ### Internal Changes #### Changed - Replaced `members_to_serialization_denylist` and `BitSet<u32>` with `SerializationDataDef` - The `Reflect` derive is more hygienic as it now outputs within an [unnamed constant](https://doc.rust-lang.org/stable/reference/items/constant-items.html#unnamed-constant) - `StructField::index` has been split up into `StructField::declaration_index` and `StructField::reflection_index` #### Removed - Removed `bitset` dependency ## Migration Guide * Fields marked `#[reflect(skip_serializing)]` now must implement `Default` or specify a custom default function with `#[reflect(default = "path::to::some_func")]` ```rust #[derive(Reflect)] struct MyStruct { #[reflect(skip_serializing)] #[reflect(default = "get_foo_default")] foo: Foo, // <- `Foo` does not impl `Default` so requires a custom function #[reflect(skip_serializing)] bar: Bar, // <- `Bar` impls `Default` } #[derive(Reflect)] struct Foo(i32); #[derive(Reflect, Default)] struct Bar(i32); fn get_foo_default() -> Foo { Foo(123) } ``` * `SerializationData::new` has been changed to expect an iterator of `(usize, SkippedField)` rather than one of just `usize` ```rust // BEFORE SerializationData::new([0, 3].into_iter()); // AFTER SerializationData::new([ (0, SkippedField::new(field_0_default_fn)), (3, SkippedField::new(field_3_default_fn)), ].into_iter()); ``` * `Serialization::is_ignored_field` has been renamed to `Serialization::is_field_skipped` * Fields marked `#[reflect(skip_serializing)]` are now included in deserialization output. This may affect logic that expected those fields to be absent. |
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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
- The Bevy Book: Bevy's official documentation. 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 Bevy Book for a full tutorial.
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.
Libraries Used
Bevy is only possible because of the hard work put into these foundational technologies:
- wgpu: modern / low-level / cross-platform graphics library based on the WebGPU API.
- glam-rs: a simple and fast 3D math library for games and graphics
- winit: cross-platform window creation and management in Rust
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.
Third Party Plugins
Plugins are very welcome to extend Bevy's features. Guidelines are available to help integration and usage.
Thanks and Alternatives
Additionally, we would like to thank the Amethyst, macroquad, coffee, ggez, Fyrox, and Piston projects for providing solid examples of game engine development in Rust. If you are looking for a Rust game engine, it is worth considering all of your options. Each engine has different design goals, and some will likely resonate with you more than others.
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.