# Examples These examples demonstrate the main features of Bevy and how to use them. To run an example, use the command `cargo run --example `, and add the option `--features x11` or `--features wayland` to force the example to run on a specific window compositor, e.g. ```sh cargo run --features wayland --example hello_world ``` **⚠️ Note: for users of releases on crates.io!** There are often large differences and incompatible API changes between the latest [crates.io](https://crates.io/crates/bevy) release and the development version of Bevy in the git main branch! If you are using a released version of bevy, you need to make sure you are viewing the correct version of the examples! - Latest release: [https://github.com/bevyengine/bevy/tree/latest/examples](https://github.com/bevyengine/bevy/tree/latest/examples) - Specific version, such as `0.4`: [https://github.com/bevyengine/bevy/tree/v0.4.0/examples](https://github.com/bevyengine/bevy/tree/v0.4.0/examples) When you clone the repo locally to run the examples, use `git checkout` to get the correct version: ```bash # `latest` always points to the newest release git checkout latest # or use a specific version git checkout v0.4.0 ``` --- ## Table of Contents - [Examples](#examples) - [Table of Contents](#table-of-contents) - [The Bare Minimum](#the-bare-minimum) - [Hello, World!](#hello-world) - [Cross-Platform Examples](#cross-platform-examples) {% for category, _ in all_examples %} - [{{ category }}](#{{ category | slugify }}) {% endfor %} - [Tests](#tests) - [Platform-Specific Examples](#platform-specific-examples) - [Android](#android) - [Setup](#setup) - [Build & Run](#build--run) - [Old phones](#old-phones) - [iOS](#ios) - [Setup](#setup-1) - [Build & Run](#build--run-1) - [WASM](#wasm) - [Setup](#setup-2) - [Build & Run](#build--run-2) - [WebGL2 and WebGPU](#webgl2-and-webgpu) - [Audio in the browsers](#audio-in-the-browsers) - [Optimizing](#optimizing) - [Loading Assets](#loading-assets) # The Bare Minimum ## Hello, World! Example | Description --- | --- [`hello_world.rs`](./hello_world.rs) | Runs a minimal example that outputs "hello world" # Cross-Platform Examples {% for category, details in all_examples %} ## {{ category }} {% if details.description is string %}{{ details.description }} {% endif %}Example | Description --- | --- {% for example in details.examples %}[{{ example.name }}](../{{ example.path }}) | {{ example.description }} {% endfor %}{% endfor %} # Tests Example | Description --- | --- [How to Test Systems](../tests/how_to_test_systems.rs) | How to test systems with commands, queries or resources # Platform-Specific Examples ## Android ### Setup ```sh rustup target add aarch64-linux-android armv7-linux-androideabi cargo install cargo-apk ``` The Android SDK must be installed, and the environment variable `ANDROID_SDK_ROOT` set to the root Android `sdk` folder. When using `NDK (Side by side)`, the environment variable `ANDROID_NDK_ROOT` must also be set to one of the NDKs in `sdk\ndk\[NDK number]`. ### Build & Run To run on a device setup for Android development, run: ```sh cargo apk run -p bevy_mobile_example ``` When using Bevy as a library, the following fields must be added to `Cargo.toml`: ```toml [package.metadata.android] build_targets = ["aarch64-linux-android", "armv7-linux-androideabi"] [package.metadata.android.sdk] target_sdk_version = 31 ``` Please reference `cargo-apk` [README](https://crates.io/crates/cargo-apk) for other Android Manifest fields. ### Debugging You can view the logs with the following command: ```sh adb logcat | grep 'RustStdoutStderr\|bevy\|wgpu' ``` In case of an error getting a GPU or setting it up, you can try settings logs of `wgpu_hal` to `DEBUG` to get more information. Sometimes, running the app complains about an unknown activity. This may be fixed by uninstalling the application: ```sh adb uninstall org.bevyengine.example ``` ### Old phones Bevy by default targets Android API level 31 in its examples which is the [Play Store's minimum API to upload or update apps](https://developer.android.com/distribute/best-practices/develop/target-sdk). Users of older phones may want to use an older API when testing. To use a different API, the following fields must be updated in Cargo.toml: ```toml [package.metadata.android.sdk] target_sdk_version = >>API<< min_sdk_version = >>API or less<< ``` Example | File | Description --- | --- | --- `android` | [`mobile/src/lib.rs`](./mobile/src/lib.rs) | A 3d Scene with a button and playing sound ## iOS ### Setup You need to install the correct rust targets: - `aarch64-apple-ios`: iOS devices - `x86_64-apple-ios`: iOS simulator on x86 processors - `aarch64-apple-ios-sim`: iOS simulator on Apple processors ```sh rustup target add aarch64-apple-ios x86_64-apple-ios aarch64-apple-ios-sim ``` ### Build & Run Using bash: ```sh cd examples/mobile make run ``` In an ideal world, this will boot up, install and run the app for the first iOS simulator in your `xcrun simctl devices list`. If this fails, you can specify the simulator device UUID via: ```sh DEVICE_ID=${YOUR_DEVICE_ID} make run ``` If you'd like to see xcode do stuff, you can run ```sh open bevy_mobile_example.xcodeproj/ ``` which will open xcode. You then must push the zoom zoom play button and wait for the magic. Example | File | Description --- | --- | --- `ios` | [`mobile/src/lib.rs`](./mobile/src/lib.rs) | A 3d Scene with a button and playing sound ## WASM ### Setup ```sh rustup target add wasm32-unknown-unknown cargo install wasm-bindgen-cli ``` ### Build & Run Following is an example for `lighting`. For other examples, change the `lighting` in the following commands. ```sh cargo build --release --example lighting --target wasm32-unknown-unknown wasm-bindgen --out-name wasm_example \ --out-dir examples/wasm/target \ --target web target/wasm32-unknown-unknown/release/examples/lighting.wasm ``` The first command will build the example for the wasm target, creating a binary. Then, [wasm-bindgen-cli](https://rustwasm.github.io/wasm-bindgen/reference/cli.html) is used to create javascript bindings to this wasm file in the output file `examples/wasm/target/wasm_example.js`, which can be loaded using this [example HTML file](./wasm/index.html). Then serve `examples/wasm` directory to browser. i.e. ```sh # cargo install basic-http-server basic-http-server examples/wasm # with python python3 -m http.server --directory examples/wasm # with ruby ruby -run -ehttpd examples/wasm ``` #### WebGL2 and WebGPU Bevy support for WebGPU is being worked on, but is currently experimental. To build for WebGPU, you'll need to enable the `webgpu` feature. This will override the `webgl2` feature, and builds with the `webgpu` feature enabled won't be able to run on browsers that don't support WebGPU. WebGPU depends on unstable APIs so you will also need to pass the `web_sys_unstable_apis` flag to your builds. For example: ```sh RUSTFLAGS=--cfg=web_sys_unstable_apis cargo build ... ``` Check `wasm-bindgen` [docs on Unstable APIs](https://rustwasm.github.io/wasm-bindgen/web-sys/unstable-apis.html) for more details. Bevy has an helper to build its examples: - Build for WebGL2: `cargo run -p build-wasm-example -- --api webgl2 load_gltf` - Build for WebGPU: `cargo run -p build-wasm-example -- --api webgpu load_gltf` This helper will log the command used to build the examples. ### Audio in the browsers For the moment, everything is single threaded, this can lead to stuttering when playing audio in browsers. Not all browsers react the same way for all games, you will have to experiment for your game. In browsers, audio is not authorized to start without being triggered by an user interaction. This is to avoid multiple tabs all starting to auto play some sounds. You can find more context and explanation for this on [Google Chrome blog](https://developer.chrome.com/blog/web-audio-autoplay/). This page also describes a JS workaround to resume audio as soon as the user interact with your game. ### Optimizing On the web, it's useful to reduce the size of the files that are distributed. With rust, there are many ways to improve your executable sizes. Here are some. #### 1. Tweak your `Cargo.toml` Add a new [profile](https://doc.rust-lang.org/cargo/reference/profiles.html) to your `Cargo.toml`: ```toml [profile.wasm-release] # Use release profile as default values inherits = "release" # Optimize with size in mind, also try "s", sometimes it is better. # This doesn't increase compilation times compared to -O3, great improvements opt-level = "z" # Do a second optimization pass removing duplicate or unused code from dependencies. # Slows compile times, marginal improvements lto = "fat" # When building crates, optimize larger chunks at a time # Slows compile times, marginal improvements codegen-units = 1 ``` Now, when building the final executable, use the `wasm-release` profile by replacing `--release` by `--profile wasm-release` in the cargo command. ```sh cargo build --profile wasm-release --example lighting --target wasm32-unknown-unknown ``` Make sure your final executable size is smaller, some of those optimizations may not be worth keeping, due to compilation time increases. #### 2. Use `wasm-opt` from the binaryen package Binaryen is a set of tools for working with wasm. It has a `wasm-opt` CLI tool. First download the `binaryen` package, then locate the `.wasm` file generated by `wasm-bindgen`. It should be in the `--out-dir` you specified in the command line, the file name should end in `_bg.wasm`. Then run `wasm-opt` with the `-Oz` flag. Note that `wasm-opt` is _very slow_. Note that `wasm-opt` optimizations might not be as effective if you didn't apply the optimizations from the previous section. ```sh wasm-opt -Oz --output optimized.wasm examples/wasm/target/lighting_bg.wasm mv optimized.wasm examples/wasm/target/lighting_bg.wasm ``` For a small project with a basic 3d model and two lights, the generated file sizes are, as of July 2022, as follows: |profile | wasm-opt | no wasm-opt | |----------------------------------|----------|-------------| |Default | 8.5M | 13.0M | |opt-level = "z" | 6.1M | 12.7M | |"z" + lto = "thin" | 5.9M | 12M | |"z" + lto = "fat" | 5.1M | 9.4M | |"z" + "thin" + codegen-units = 1 | 5.3M | 11M | |"z" + "fat" + codegen-units = 1 | 4.8M | 8.5M | There are more advanced optimization options available, check the following pages for more info: - - - ### Loading Assets To load assets, they need to be available in the folder examples/wasm/assets. Cloning this repository will set it up as a symlink on Linux and macOS, but you will need to manually move the assets on Windows.