Check out our community's [Code of Conduct](https://github.com/bevyengine/bevy/blob/main/CODE_OF_CONDUCT.md) and feel free to say hi on [Discord] if you'd like.
Bevy, like any general-purpose game engine, is a large project!
It can be a bit overwhelming to start, so here's the bird's-eye view.
The [Bevy Engine Organization](https://github.com/bevyengine) has 4 primary repos:
1. [**`bevy`**](https://github.com/bevyengine/bevy): This is where the engine itself lives. The bulk of development work occurs here.
2. [**`bevy-website`**](https://github.com/bevyengine/bevy-website): Where the [official website](https://bevyengine.org/), release notes, Bevy Book, and Bevy Assets are hosted. It is created using the Zola static site generator.
3. [**`bevy-assets`**](https://github.com/bevyengine/bevy-assets): A collection of community-made tutorials, plugins, crates, games, and tools! Make a PR if you want to showcase your projects there!
4. [**`rfcs`**](https://github.com/bevyengine/rfcs): A place to collaboratively build and reach consensus on designs for large or controversial features.
The `bevy` repo itself contains many smaller subcrates. Most of them can be used by themselves and many of them can be modularly replaced. This enables developers to pick and choose the parts of Bevy that they want to use.
Some crates of interest:
* [**`bevy_ecs`**](./crates/bevy_ecs): The core data model for Bevy. Most Bevy features are implemented on top of it. It is also fully functional as a stand-alone ECS, which can be very valuable if you're looking to integrate it with other game engines or use it for non-game executables.
* [**`bevy_app`**](./crates/bevy_app): The api used to define Bevy Plugins and compose them together into Bevy Apps.
* [**`bevy_tasks`**](./crates/bevy_tasks): Our light-weight async executor. This drives most async and parallel code in Bevy.
* [**`bevy_render`**](./crates/bevy_render): Our core renderer API. It handles interaction with the GPU, such as the creation of Meshes, Textures, and Shaders. It also exposes a modular Render Graph for composing render pipelines. All 2D and 3D render features are implemented on top of this crate.
## What we're trying to build
Bevy is a completely free and open source game engine built in Rust. It currently has the following design goals:
Bevy also currently has the following "development process" goals:
* **Rapid experimentation over API stability**: We need the freedom to experiment and iterate in order to build the best engine we can. This will change over time as APIs prove their staying power.
* **Consistent vision**: The engine needs to feel consistent and cohesive. This takes precedence over democratic and/or decentralized processes. See our [*Bevy Organization doc*](/docs/the_bevy_organization.md) for more details.
* **Flexibility over bureaucracy**: Developers should feel productive and unencumbered by development processes.
* **Focus**: The Bevy Org should focus on building a small number of features excellently over merging every new community-contributed feature quickly. Sometimes this means pull requests will sit unmerged for a long time. This is the price of focus and we are willing to pay it. Fortunately Bevy is modular to its core. 3rd party plugins are a great way to work around this policy.
* **User-facing API ergonomics come first**: Solid user experience should receive significant focus and investment. It should rarely be compromised in the interest of internal implementation details.
* **Modularity over deep integration**: Individual crates and features should be "pluggable" whenever possible. Don't tie crates, features, or types together that don't need to be.
* **Don't merge everything ... don't merge too early**: Every feature we add increases maintenance burden and compile times. Only merge features that are "generally" useful. Don't merge major changes or new features unless we have relative consensus that the design is correct *and* that we have the developer capacity to support it. When possible, make a 3rd party Plugin / crate first, then consider merging once the API has been tested in the wild. Bevy's modular structure means that the only difference between "official engine features" and "third party plugins" is our endorsement and the repo the code lives in. We should take advantage of that whenever possible.
* **Control and consistency over 3rd party code reuse**: Only add a dependency if it is *absolutely* necessary. Every dependency we add decreases our autonomy and consistency. Dependencies also have the potential to increase compile times and risk pulling in sub-dependencies we don't want / need.
* **Don't re-invent every wheel**: As a counter to the previous point, don't re-invent everything at all costs. If there is a crate in the Rust ecosystem that is the "de-facto" standard (ex: wgpu, winit, cpal), we should heavily consider using it. Bevy should be a positive force in the ecosystem. We should drive the improvements we need into these core ecosystem crates.
* **Rust-first**: Engine and user-facing code should optimize and encourage Rust-only workflows. Adding additional languages increases internal complexity, fractures the Bevy ecosystem, and makes it harder for users to understand the engine. Never compromise a Rust interface in the interest of compatibility with other languages.
* **Thoughtful public interfaces over maximal configurability**: Symbols and apis should be private by default. Every public API should be thoughtfully and consistently designed. Don't expose unnecessary internal implementation details. Don't allow users to "shoot themselves in the foot". Favor one "happy path" api over multiple apis for different use cases.
* **Welcome new contributors**: Invest in new contributors. Help them fill knowledge and skill gaps. Don't ever gatekeep Bevy development according to notions of required skills or credentials. Help new developers find their niche.
* **Civil discourse**: We need to collectively discuss ideas and the best ideas *should* win. But conversations need to remain respectful at all times. Remember that we're all in this together. Always follow our [Code of Conduct](https://github.com/bevyengine/bevy/blob/main/CODE_OF_CONDUCT.md).
* **Test what you need to**: Write useful tests. Don't write tests that aren't useful. We *generally* aren't strict about unit testing every line of code. We don't want you to waste your time. But at the same time:
* Most new features should have at least one minimal [example](https://github.com/bevyengine/bevy/tree/main/examples). These also serve as simple integration tests, as they are run as part of our CI process.
* The more complex or "core" a feature is, the more strict we are about unit tests. Use your best judgement here. We will let you know if your pull request needs more tests. We use [Rust's built in testing framework](https://doc.rust-lang.org/book/ch11-01-writing-tests.html).
The Bevy Organization is the group of people responsible for stewarding the Bevy project. It handles things like merging pull requests, choosing project direction, managing bugs / issues / feature requests, running the Bevy website, controlling access to secrets, defining and enforcing best practices, etc.
Note that you *do not* need to be a member of the Bevy Organization to contribute to Bevy. Community contributors (this means you) can freely open issues, submit pull requests, and review pull requests.
* [PRs which need reviews and are not `D-Complex`](https://github.com/bevyengine/bevy/pulls?q=is%3Apr+-label%3AD-Complex+-label%3AS-Ready-For-Final-Review+-label%3AS-Blocked++).
* [`D-Complex` PRs which need reviews](https://github.com/bevyengine/bevy/pulls?q=is%3Apr+label%3AD-Complex+-label%3AS-Ready-For-Final-Review+-label%3AS-Blocked).
We use [Milestones](https://github.com/bevyengine/bevy/milestones) to track issues and PRs that:
* Need to be merged/fixed before the next release. This is generally for extremely bad bugs i.e. UB or important functionality being broken.
* Would have higher user impact and are almost ready to be merged/fixed.
There are also two priority labels: [`P-Critical`](https://github.com/bevyengine/bevy/issues?q=is%3Aopen+is%3Aissue+label%3AP-Critical) and [`P-High`](https://github.com/bevyengine/bevy/issues?q=is%3Aopen+is%3Aissue+label%3AP-High) that can be used to find issues and PRs that need to be resolved urgently.
* [GitHub Discussions]: An informal discussion with the community. This is the place to start if you want to propose a feature or specific implementation.
* [Issue](https://github.com/bevyengine/bevy/issues): A formal way for us to track a bug or feature. Please look for duplicates before opening a new issue and consider starting with a Discussion.
* [Pull Request](https://github.com/bevyengine/bevy/pulls) (or PR for short): A request to merge code changes. This starts our "review process". You are welcome to start with a pull request, but consider starting with an Issue or Discussion for larger changes (or if you aren't certain about a design). We don't want anyone to waste their time on code that didn't have a chance to be merged! But conversely, sometimes PRs are the most efficient way to propose a change. Just use your own judgement here.
2. Other community members review and comment in an ad-hoc fashion. Active subject matter experts may be pulled into a thread using `@mentions`. If your PR has been quiet for a while and is ready for review, feel free to leave a message to "bump" the thread, or bring it up on [Discord](https://discord.gg/bevy) in an appropriate engine development channel.
3. Once they're content with the pull request (design, code quality, documentation, tests), individual reviewers leave "Approved" reviews.
4. After consensus has been reached (typically two approvals from the community or one for extremely simple changes) and CI passes, the [S-Ready-For-Final-Review](https://github.com/bevyengine/bevy/issues?q=is%3Aopen+is%3Aissue+label%3AS-Ready-For-Final-Review) label is added.
Individual contributors often lead major new features and reworks. However these changes require more design work and scrutiny. Complex changes like this tend to go through the following lifecycle:
1. A need or opportunity is identified and an issue is made, laying out the general problem.
2. As needed, this is discussed further on that issue thread, in cross-linked [GitHub Discussion] threads, or on [Discord] in the Engine Development channels.
3. Either a Draft Pull Request or an RFC is made. As discussed in the [RFC repo](https://github.com/bevyengine/rfcs), complex features need RFCs, but these can be submitted before or after prototyping work has been started.
4. If feasible, parts that work on their own (even if they're only useful once the full complex change is merged) get split out into individual PRs to make them easier to review.
5. The community as a whole helps improve the Draft PR and/or RFC, leaving comments, making suggestions, and submitting pull requests to the original branch.
6. Once the RFC is merged and/or the Draft Pull Request is transitioned out of draft mode, the [normal change process outlined in the previous section](#making-changes-to-bevy) can begin.
If you ever find yourself at a loss for what to do, or in need of mentorship or advice on how to contribute to Bevy, feel free to ask in [Discord] and one of our more experienced community members will be happy to help.
If you need help, don't hesitate to ask for help on [GitHub Discussions], [Discord], or [reddit](https://www.reddit.com/r/bevy). Generally you should prefer asking questions as [GitHub Discussions] as they are more searchable.
When you think you've found a bug, missing documentation, or a feature that would help you make better games, please [file an issue](https://github.com/bevyengine/bevy/issues/new/choose) on the main `bevy` repo.
Do your best to search for duplicate issues, but if you're unsure, open a new issue and link to other related issues on the thread you make.
By helping others with their issues, and teaching them about Bevy, you will naturally learn the engine and codebase in greater depth while also making our community better!
Bugs in Bevy (or the associated website / book) are filed on the issue tracker using the [`C-Bug`](https://github.com/bevyengine/bevy/issues?q=is%3Aissue+is%3Aopen+label%3AC-Bug) label.
If you're looking for an easy place to start, take a look at the [`D-Good-First-Issue`](https://github.com/bevyengine/bevy/issues?q=is%3Aopen+is%3Aissue+label%3AD-Good-First-Issue) label, and feel free to ask questions on that issue's thread in question or on [Discord].
You don't need anyone's permission to try fixing a bug or adding a simple feature, but stating that you'd like to tackle an issue can be helpful to avoid duplicated work.
When you make a pull request that fixes an issue, include a line that says `Fixes #X` (or "Closes"), where `X` is the issue number.
This will cause the issue in question to be closed when your PR is merged.
General improvements to code quality are also welcome!
Bevy can always be safer, better tested, and more idiomatic.
### Writing docs
Like every other large, rapidly developing open source library you've ever used, Bevy's documentation can always use improvement.
This is incredibly valuable, easily distributed work, but requires a bit of guidance:
* Inaccurate documentation is worse than no documentation: prioritize fixing broken docs.
* Bevy is remarkably unstable: before tackling a new major documentation project, check in with the community on Discord or GitHub (making an issue about specific missing docs is a great way to plan) about the stability of that feature and upcoming plans to save yourself heartache.
* Code documentation (doc examples and in the examples folder) is easier to maintain because the compiler will tell us when it breaks.
* Inline documentation should be technical and to the point. Link relevant examples or other explanations if broader context is useful.
* The Bevy book is hosted on the `bevy-website` repo and targeted towards beginners who are just getting to know Bevy (and perhaps Rust!).
* Accepted RFCs are not documentation: they serve only as a record of accepted decisions.
[docs.rs](https://docs.rs/bevy) is built from out of the last release's documentation, which is written right in-line directly above the code it documents.
To view the current docs on `main` before you contribute, clone the `bevy` repo, and run `cargo doc --open` or go to [dev-docs.bevyengine.org](https://dev-docs.bevyengine.org/),
Most [examples in Bevy](https://github.com/bevyengine/bevy/tree/main/examples) aim to clearly demonstrate a single feature, group of closely related small features, or show how to accomplish a particular task (such as asset loading, creating a custom shader or testing your app).
In rare cases, creating new "game" examples is justified in order to demonstrate new features that open a complex class of functionality in a way that's hard to demonstrate in isolation or requires additional integration testing.
1.**Working:** They must compile and run, and any introduced errors in them should be obvious (through tests, simple results or clearly displayed behavior).
2.**Clear:** They must use descriptive variable names, be formatted, and be appropriately commented. Try your best to showcase best practices when it doesn't obscure the point of the example.
3.**Relevant:** They should explain, through comments or variable names, what they do and how this can be useful to a game developer.
4.**Minimal:** They should be no larger or complex than is needed to meet the goals of the example.
Use a generous sprinkling of keywords in your description: these are commonly used to search for a specific example.
See the [example style guide](.github/contributing/example_style_guide.md) to help make sure the style of your example matches what we're already using.
More complex demonstrations of functionality are also welcome, but these should be submitted to [bevy-assets](https://github.com/bevyengine/bevy-assets).
With the sheer volume of activity in Bevy's community, reviewing others work with the aim of improving it is one of the most valuable things you can do.
You don't need to be an Elder Rustacean to be useful here: anyone can catch missing tests, unclear docs, logic errors, and so on.
If you have specific skills (e.g. advanced familiarity with `unsafe` code, rendering knowledge or web development experience) or personal experience with a problem, try to prioritize those areas to ensure we can get appropriate expertise where we need it.
Focus on giving constructive, actionable feedback that results in real improvements to code quality or end-user experience.
If you don't understand why an approach was taken, please ask!
Provide actual code suggestions when that is helpful. Small changes work well as comments or in-line suggestions on specific lines of codes.
Larger changes deserve a comment in the main thread, or a pull request to the original author's branch (but please mention that you've made one).
When in doubt about a matter of architectural philosophy, refer back to [*What we're trying to build*](#what-were-trying-to-build) for guidance.
Once you're happy with the work and feel you're reasonably qualified to assess quality in this particular area, leave your `Approved` review on the PR.
If you're new to GitHub, check out the [Pull Request Review documentation](https://docs.github.com/en/github/collaborating-with-pull-requests/reviewing-changes-in-pull-requests/about-pull-request-reviews).
**Anyone** can and should leave reviews ... no special permissions are required!
It's okay to leave an approval even if you aren't 100% confident on all areas of the PR: just be sure to note your limitations.
When maintainers are evaluating the PR to be merged, they'll make sure that there's good coverage on all of the critical areas.
If you can only check that the math is correct, and another reviewer can check everything *but* the math, we're in good shape!
Similarly, if there are areas that would be *good* to fix but aren't severe, please consider leaving an approval.
The author can address them immediately, or spin it out into follow-up issues or PRs.
Large PRs are much more draining for both reviewers and authors, so try to push for a smaller scope with clearly tracked follow-ups.
1. Pull requests which are ready and in need of more reviews on [bevy](https://github.com/bevyengine/bevy/pulls?q=is%3Aopen+is%3Apr+-label%3AS-Ready-For-Final-Review+-draft%3A%3Atrue+-label%3AS-Needs-RFC+-reviewed-by%3A%40me+-author%3A%40me).
Finally, if nothing brings you more satisfaction than seeing every last issue labeled and all resolved issues closed, feel free to message the Project Lead (currently @cart) for a Bevy org role to help us keep things tidy.
As discussed in our [*Bevy Organization doc*](/docs/the_bevy_organization.md), this role only requires good faith and a basic understanding of our development process.
Bevy is actively open to code contributions from community members.
If you're new to Bevy, here's the workflow we use:
1. Fork the `bevyengine/bevy` repository on GitHub. You'll need to create a GitHub account if you don't have one already.
2. Make your changes in a local clone of your fork, typically in its own new branch.
1. Try to split your work into separate commits, each with a distinct purpose. Be particularly mindful of this when responding to reviews so it's easy to see what's changed.
2. Tip: [You can set up a global `.gitignore` file](https://docs.github.com/en/get-started/getting-started-with-git/ignoring-files#configuring-ignored-files-for-all-repositories-on-your-computer) to exclude your operating system/text editor's special/temporary files. (e.g. `.DS_Store`, `thumbs.db`, `*~`, `*.swp` or `*.swo`) This allows us to keep the `.gitignore` file in the repo uncluttered.
3. To test CI validations locally, run the `cargo run -p ci` command. This will run most checks that happen in CI, but can take some time. You can also run sub-commands to iterate faster depending on what you're contributing:
*`cargo run -p ci -- lints` - to run formatting and clippy.
*`cargo run -p ci -- test` - to run tests.
*`cargo run -p ci -- doc` - to run doc tests and doc checks.
*`cargo run -p ci -- compile` - to check that everything that must compile still does (examples and benches), and that some that shouldn't still don't ([`crates/bevy_ecs_compile_fail_tests`](./crates/bevy_ecs_compile_fail_tests)).
* to get more information on commands available and what is run, check the [tools/ci crate](./tools/ci).
4. When working with Markdown (`.md`) files, Bevy's CI will check markdown files (like this one) using [markdownlint](https://github.com/DavidAnson/markdownlint).
To locally lint your files using the same workflow as our CI:
5. When working with Toml (`.toml`) files, Bevy's CI will check toml files using [taplo](https://taplo.tamasfe.dev/): `taplo fmt --check --diff`
1. If you use VSCode, install [Even better toml](https://marketplace.visualstudio.com/items?itemName=tamasfe.even-better-toml) and format your files.
2. If you want to use the cli tool, install [taplo-cli](https://taplo.tamasfe.dev/cli/installation/cargo.html) and run `taplo fmt --check --diff` to check for the formatting. Fix any issues by running `taplo fmt` in the root directory of the Bevy project.
6. Check for typos. Bevy's CI will check for them using [typos](https://github.com/crate-ci/typos).
1. If you use VSCode, install [Typos Spell Checker](https://marketplace.visualstudio.com/items?itemName=tekumara.typos-vscode).
2. You can also use the cli tool. Install [typos-cli](https://github.com/crate-ci/typos?tab=readme-ov-file#install) and run `typos` to check for typos, and fix them by running `typos -w`.
7. Push your changes to your fork on Github and open a Pull Request.
8. Respond to any CI failures or review feedback. While CI failures must be fixed before we can merge your PR, you do not need to *agree* with all feedback from your reviews, merely acknowledge that it was given. If you cannot come to an agreement, leave the thread open and defer to a Maintainer or Project Lead's final judgement.
9. When your PR is ready to merge, a Maintainer or Project Lead will review it and suggest final changes. If those changes are minimal they may even apply them directly to speed up merging.
