Setup

I know you are itching to start making games, but we need to do a small amount of setup first.

Rust Setup #

All Bevy app and engine code is written in Rust. This means that before we begin, we need to set up our Rust development environment.

Installing Rust #

Bevy relies heavily on improvements in the Rust language and compiler. As a result, the Minimum Supported Rust Version (MSRV) is "the latest stable release" of Rust.

Install Rust by following the Rust Getting Started Guide.

Once this is done, you should have the rustc compiler and the cargo build system installed in your path.

Installing OS Dependencies #

Linux #

Follow the instructions at Linux Dependencies

Windows #

• Run the Visual Studio 2019 build tools installer
• For easy setup, select the Desktop development with C++ workload in the installer.
• For a minimal setup, follow these steps:
  1. In the installer, navigate to Individual components
  2. Select the latest MSVC for your architecture and version of Windows
  3. Select the latest Windows SDK for your version of Windows
  4. Select the C++ CMake tools for Windows component
  5. Install the components

MacOS #

Install the Xcode command line tools with xcode-select --install or the Xcode app

Code Editor / IDE #

You can use any code editor you want, but we highly recommend one that has a rust-analyzer plugin. It's still in development, but it already provides top-tier autocomplete and code intelligence. Visual Studio Code has an officially supported rust-analyzer extension.

Rust Learning Resources #

The goal of this guide is to get started learning Bevy quickly, so it won't serve as a full Rust education. If you would like to learn more about the Rust language, check out the following resources:

• The Rust Book: the best place to learn Rust from scratch
• Rust by Example: learn Rust by working through live coding examples
• Rustlings: learn Rust through a series of fun and interactive exercises

Create a new Bevy Project #

Now we are ready to set up a Bevy project! Bevy is just a normal Rust dependency. You can either add it to an existing Rust project or create a new one. For completeness we will assume you are starting from scratch.

Create a new Rust executable project #

First, navigate to a folder where you want to create your new project. Then, run the following command to create a new folder containing our rust executable project:

cargo new my_bevy_game
cd my_bevy_game

Now run cargo run to build and run your project. You should see Hello, world! printed to your terminal. Open the my_bevy_game folder in your code editor of choice and take some time to look through the files.

main.rs is the entry point of your program:

fn main() {
    println!("Hello, world!");
}

Cargo.toml is your "project file". It contains metadata about your project such as its name, dependencies, and build configuration.

[package]
name = "my_bevy_game"
version = "0.1.0"
edition = "2021"

[dependencies]

Add Bevy as a dependency #

Bevy is available as a library on crates.io, the official Rust package repository.

The easiest way to add it to your project is to use cargo add:

cargo add bevy

Alternatively, you can manually add it to your project's Cargo.toml like this:

[package]
name = "my_bevy_game"
version = "0.1.0"
edition = "2021" # this needs to be 2021, or you need to set "resolver=2"

[dependencies]
bevy = "0.14" # make sure this is the latest version

Make sure to use the latest bevy crate version ().

Cargo Workspaces #

If you are using Cargo Workspaces, you will also need to add the resolver to your Cargo.toml file in the root directory:

[workspace]
resolver = "2" # Important! wgpu/Bevy needs this!

Compile with Performance Optimizations #

While it may not be an issue for simple projects, debug builds in Rust can be very slow - especially when you start using Bevy to make real games.

It's not uncommon for debug builds using the default configuration to take multiple minutes to load large 3D models, or for the framerate for simple scenes to drop to near-unplayable levels.

Fortunately, there is a simple fix, and we don't have to give up our fast iterative compiles! Add the following to your Cargo.toml:

# Enable a small amount of optimization in the dev profile.
[profile.dev]
opt-level = 1

# Enable a large amount of optimization in the dev profile for dependencies.
[profile.dev.package."*"]
opt-level = 3

You might think to simply develop in release mode instead, but we recommend against this as it can worsen the development experience by slowing down recompiles and disabling helpful debug symbols and assertions.

In fact, you may want to trade even more compile time for performance in release mode by adding the following to your Cargo.toml:

# Enable more optimization in the release profile at the cost of compile time.
[profile.release]
# Compile the entire crate as one unit.
# Slows compile times, marginal improvements.
codegen-units = 1
# Do a second optimization pass over the entire program, including dependencies.
# Slows compile times, marginal improvements.
lto = "thin"

# Optimize for size in the wasm-release profile to reduce load times and bandwidth usage on web.
[profile.wasm-release]
# Default to release profile values.
inherits = "release"
# Optimize with size in mind (also try "z", sometimes it is better).
# Slightly slows compile times, great improvements to file size and runtime performance.
opt-level = "s"
# Strip all debugging information from the binary to slightly reduce file size.
strip = "debuginfo"

When releasing for web, you can pass --profile wasm-release to cargo instead of --release.

Advanced Wasm optimizations #

Binaryen is a Wasm compiler toolchain that provides a wasm-opt CLI tool for making .wasm files smaller and faster:

wasm-opt -Os --output output.wasm input.wasm

Note that wasm-opt runs very slowly, but it can make a big difference, especially in combination with the optimizations from the previous section.

See the following for more information on optimizing Wasm:

• https://rustwasm.github.io/book/reference/code-size.html
• https://rustwasm.github.io/docs/wasm-bindgen/reference/optimize-size.html
• https://rustwasm.github.io/book/game-of-life/code-size.html

Enable Fast Compiles (Optional) #

Bevy can be built just fine using default configuration on stable Rust. Unfortunately, the compile times are rather long. This section explains how to speed up iterative compiles: the amount of time it takes to rebuild your project after changing a single file.

Dynamic Linking #

This is the most impactful compilation time decrease! You can compile bevy as dynamic library, preventing it from having to be statically linked each time you rebuild your project. You can enable this with the dynamic_linking feature flag.

cargo run --features bevy/dynamic_linking

If you don't want to add the --features bevy/dynamic_linking to each run, this flag can permanently be set with this command (edits Cargo.toml for you):

cargo add bevy -F dynamic_linking

Alternative Linkers #

The Rust compiler spends a lot of time in the final "link" step, especially with a massive library like Bevy. lld is much faster at linking than the default Rust linker. To install LLD, find your OS below and run the given command.

Then, add one of the following to your Cargo config at /path/to/project/.cargo/config.toml (where /path/to/project is the directory which contains Cargo.toml) depending on your OS:

# for Linux
[target.x86_64-unknown-linux-gnu]
linker = "clang"
rustflags = ["-C", "link-arg=-fuse-ld=lld"]

# for Windows
[target.x86_64-pc-windows-msvc]
linker = "rust-lld.exe"

[target.x86_64-unknown-linux-gnu]
linker = "clang"
rustflags = ["-C", "link-arg=-fuse-ld=/usr/bin/mold"]

Nightly Rust Compiler #

This gives access to the latest performance improvements and "unstable" optimizations, including generic sharing below.

Create a rust-toolchain.toml file in the root of your project, next to Cargo.toml.

[toolchain]
channel = "nightly"

For more information, see The rustup book: Overrides.

Cranelift #

This uses a new nightly-only codegen that is about 30% faster at compiling than LLVM. It currently works best on Linux.

To install cranelift, run the following.

rustup component add rustc-codegen-cranelift-preview --toolchain nightly

To activate it for your project, add the following to your .cargo/config.toml.

[unstable]
codegen-backend = true

[profile.dev]
codegen-backend = "cranelift"

[profile.dev.package."*"]
codegen-backend = "llvm"

This enables faster compiles for your binary, but builds Bevy and other dependencies with the more-optimized LLVM backend. See the cranelift setup guide for details on other ways in which cranelift can be enabled. The installation process for Windows is a bit more involved. Consult the linked documentation for help. MacOS builds can currently crash on Bevy applications, so you should still wait a bit before using cranelift on that system.

While cranelift is very fast to compile, the generated binaries are not optimized for speed. Additionally, it is generally still immature, so you may run into issues with it. Notably, Wasm builds do not work yet.

When shipping your game, you should still compile it with LLVM.

Generic Sharing #

Allows crates to share monomorphized generic code instead of duplicating it. In some cases this allows us to "precompile" generic code so it doesn't affect iterative compiles. This is currently only available on nightly Rust (see above).

# /path/to/project/.cargo/config.toml
[target.x86_64-unknown-linux-gnu]
rustflags = [
  # (Nightly) Make the current crate share its generic instantiations
  "-Zshare-generics=y",
]

Improve Runtime Performance (Optional) #

Bevy's dependencies do a lot of trace logging that is not relevant for an end user. To improve your runtime performance, you can add the following to the [dependencies] section of your Cargo.toml. It will disable detailed log levels on compile time so that they do not need to be filtered out while your app is running.

log = { version = "*", features = ["max_level_debug", "release_max_level_warn"] }

Build Bevy #

Now run cargo run again. The Bevy dependencies should start building. This will take some time as you are essentially building an engine from scratch. You will only need to do a full rebuild once. Every build after this one will be fast!

Now that we have our Bevy project set up, we're ready to start making our first Bevy app!