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# Objective NOTE: This depends on #7267 and should not be merged until #7267 is merged. If you are reviewing this before that is merged, I highly recommend viewing the Base Sets commit instead of trying to find my changes amongst those from #7267. "Default sets" as described by the [Stageless RFC](https://github.com/bevyengine/rfcs/pull/45) have some [unfortunate consequences](https://github.com/bevyengine/bevy/discussions/7365). ## Solution This adds "base sets" as a variant of `SystemSet`: A set is a "base set" if `SystemSet::is_base` returns `true`. Typically this will be opted-in to using the `SystemSet` derive: ```rust #[derive(SystemSet, Clone, Hash, Debug, PartialEq, Eq)] #[system_set(base)] enum MyBaseSet { A, B, } ``` **Base sets are exclusive**: a system can belong to at most one "base set". Adding a system to more than one will result in an error. When possible we fail immediately during system-config-time with a nice file + line number. For the more nested graph-ey cases, this will fail at the final schedule build. **Base sets cannot belong to other sets**: this is where the word "base" comes from Systems and Sets can only be added to base sets using `in_base_set`. Calling `in_set` with a base set will fail. As will calling `in_base_set` with a normal set. ```rust app.add_system(foo.in_base_set(MyBaseSet::A)) // X must be a normal set ... base sets cannot be added to base sets .configure_set(X.in_base_set(MyBaseSet::A)) ``` Base sets can still be configured like normal sets: ```rust app.add_system(MyBaseSet::B.after(MyBaseSet::Ap)) ``` The primary use case for base sets is enabling a "default base set": ```rust schedule.set_default_base_set(CoreSet::Update) // this will belong to CoreSet::Update by default .add_system(foo) // this will override the default base set with PostUpdate .add_system(bar.in_base_set(CoreSet::PostUpdate)) ``` This allows us to build apis that work by default in the standard Bevy style. This is a rough analog to the "default stage" model, but it use the new "stageless sets" model instead, with all of the ordering flexibility (including exclusive systems) that it provides. --- ## Changelog - Added "base sets" and ported CoreSet to use them. ## Migration Guide TODO |
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|---|---|---|
| .. | ||
| 2d | ||
| 3d | ||
| android | ||
| animation | ||
| app | ||
| asset | ||
| async_tasks | ||
| audio | ||
| diagnostics | ||
| ecs | ||
| games | ||
| input | ||
| ios | ||
| reflection | ||
| scene | ||
| shader | ||
| stress_tests | ||
| tools | ||
| transforms | ||
| ui | ||
| wasm | ||
| window | ||
| hello_world.rs | ||
| README.md | ||
| README.md.tpl | ||
Examples
These examples demonstrate the main features of Bevy and how to use them.
To run an example, use the command cargo run --example <Example>, and add the option --features x11 or --features wayland to force the example to run on a specific window compositor, e.g.
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 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
- Specific version, such as
0.4: 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:
# `latest` always points to the newest release
git checkout latest
# or use a specific version
git checkout v0.4.0
Table of Contents
The Bare Minimum
Hello, World!
| Example | Description |
|---|---|
hello_world.rs |
Runs a minimal example that outputs "hello world" |
Cross-Platform Examples
2D Rendering
| Example | Description |
|---|---|
| 2D Rotation | Demonstrates rotating entities in 2D with quaternions |
| 2D Shapes | Renders a rectangle, circle, and hexagon |
| Manual Mesh 2D | Renders a custom mesh "manually" with "mid-level" renderer apis |
| Mesh 2D | Renders a 2d mesh |
| Mesh 2D With Vertex Colors | Renders a 2d mesh with vertex color attributes |
| Move Sprite | Changes the transform of a sprite |
| Pixel Perfect | Demonstrates pixel perfect in 2d |
| Sprite | Renders a sprite |
| Sprite Flipping | Renders a sprite flipped along an axis |
| Sprite Sheet | Renders an animated sprite |
| Text 2D | Generates text in 2D |
| Texture Atlas | Generates a texture atlas (sprite sheet) from individual sprites |
| Transparency in 2D | Demonstrates transparency in 2d |
3D Rendering
| Example | Description |
|---|---|
| 3D Scene | Simple 3D scene with basic shapes and lighting |
| 3D Shapes | A scene showcasing the built-in 3D shapes |
| Atmospheric Fog | A scene showcasing the atmospheric fog effect |
| Blend Modes | Showcases different blend modes |
| Bloom | Illustrates bloom configuration using HDR and emissive materials |
| FXAA | Compares MSAA (Multi-Sample Anti-Aliasing) and FXAA (Fast Approximate Anti-Aliasing) |
| Fog | A scene showcasing the distance fog effect |
| Lighting | Illustrates various lighting options in a simple scene |
| Lines | Create a custom material to draw 3d lines |
| Load glTF | Loads and renders a glTF file as a scene |
| MSAA | Configures MSAA (Multi-Sample Anti-Aliasing) for smoother edges |
| Orthographic View | Shows how to create a 3D orthographic view (for isometric-look in games or CAD applications) |
| Parenting | Demonstrates parent->child relationships and relative transformations |
| Physically Based Rendering | Demonstrates use of Physically Based Rendering (PBR) properties |
| Render to Texture | Shows how to render to a texture, useful for mirrors, UI, or exporting images |
| Shadow Biases | Demonstrates how shadow biases affect shadows in a 3d scene |
| Shadow Caster and Receiver | Demonstrates how to prevent meshes from casting/receiving shadows in a 3d scene |
| Skybox | Load a cubemap texture onto a cube like a skybox and cycle through different compressed texture formats. |
| Spherical Area Lights | Demonstrates how point light radius values affect light behavior |
| Split Screen | Demonstrates how to render two cameras to the same window to accomplish "split screen" |
| Spotlight | Illustrates spot lights |
| Texture | Shows configuration of texture materials |
| Transparency in 3D | Demonstrates transparency in 3d |
| Two Passes | Renders two 3d passes to the same window from different perspectives |
| Update glTF Scene | Update a scene from a glTF file, either by spawning the scene as a child of another entity, or by accessing the entities of the scene |
| Vertex Colors | Shows the use of vertex colors |
| Wireframe | Showcases wireframe rendering |
Animation
| Example | Description |
|---|---|
| Animated Fox | Plays an animation from a skinned glTF |
| Animated Transform | Create and play an animation defined by code that operates on the Transform component |
| Custom Skinned Mesh | Skinned mesh example with mesh and joints data defined in code |
| glTF Skinned Mesh | Skinned mesh example with mesh and joints data loaded from a glTF file |
Application
| Example | Description |
|---|---|
| Custom Loop | Demonstrates how to create a custom runner (to update an app manually) |
| Drag and Drop | An example that shows how to handle drag and drop in an app |
| Empty | An empty application (does nothing) |
| Empty with Defaults | An empty application with default plugins |
| Headless | An application that runs without default plugins |
| Logs | Illustrate how to use generate log output |
| No Renderer | An application that runs with default plugins and displays an empty window, but without an actual renderer |
| Plugin | Demonstrates the creation and registration of a custom plugin |
| Plugin Group | Demonstrates the creation and registration of a custom plugin group |
| Return after Run | Show how to return to main after the Bevy app has exited |
| Thread Pool Resources | Creates and customizes the internal thread pool |
| Without Winit | Create an application without winit (runs single time, no event loop) |
Assets
| Example | Description |
|---|---|
| Asset Loading | Demonstrates various methods to load assets |
| Custom Asset | Implements a custom asset loader |
| Custom Asset IO | Implements a custom asset io loader |
| Hot Reloading of Assets | Demonstrates automatic reloading of assets when modified on disk |
Async Tasks
| Example | Description |
|---|---|
| Async Compute | How to use AsyncComputeTaskPool to complete longer running tasks |
| External Source of Data on an External Thread | How to use an external thread to run an infinite task and communicate with a channel |
Audio
| Example | Description |
|---|---|
| Audio | Shows how to load and play an audio file |
| Audio Control | Shows how to load and play an audio file, and control how it's played |
| Decodable | Shows how to create and register a custom audio source by implementing the Decodable type. |
Diagnostics
| Example | Description |
|---|---|
| Custom Diagnostic | Shows how to create a custom diagnostic |
| Log Diagnostics | Add a plugin that logs diagnostics, like frames per second (FPS), to the console |
ECS (Entity Component System)
| Example | Description |
|---|---|
| Component Change Detection | Change detection on components |
| Custom Query Parameters | Groups commonly used compound queries and query filters into a single type |
| ECS Guide | Full guide to Bevy's ECS |
| Event | Illustrates event creation, activation, and reception |
| Fixed Timestep | Shows how to create systems that run every fixed timestep, rather than every tick |
| Generic System | Shows how to create systems that can be reused with different types |
| Hierarchy | Creates a hierarchy of parents and children entities |
| Iter Combinations | Shows how to iterate over combinations of query results |
| Nondeterministic System Order | Systems run in paralell, but their order isn't always deteriministic. Here's how to detect and fix this. |
| Parallel Query | Illustrates parallel queries with ParallelIterator |
| Removal Detection | Query for entities that had a specific component removed earlier in the current frame |
| Startup System | Demonstrates a startup system (one that runs once when the app starts up) |
| State | Illustrates how to use States to control transitioning from a Menu state to an InGame state |
| System Closure | Show how to use closures as systems, and how to configure Local variables by capturing external state |
| System Parameter | Illustrates creating custom system parameters with SystemParam |
| System Piping | Pipe the output of one system into a second, allowing you to handle any errors gracefully |
| Timers | Illustrates ticking Timer resources inside systems and handling their state |
Games
| Example | Description |
|---|---|
| Alien Cake Addict | Eat the cakes. Eat them all. An example 3D game |
| Breakout | An implementation of the classic game "Breakout" |
| Contributors | Displays each contributor as a bouncy bevy-ball! |
| Game Menu | A simple game menu |
Input
| Example | Description |
|---|---|
| Char Input Events | Prints out all chars as they are inputted |
| Gamepad Input | Shows handling of gamepad input, connections, and disconnections |
| Gamepad Input Events | Iterates and prints gamepad input and connection events |
| Keyboard Input | Demonstrates handling a key press/release |
| Keyboard Input Events | Prints out all keyboard events |
| Keyboard Modifiers | Demonstrates using key modifiers (ctrl, shift) |
| Mouse Grab | Demonstrates how to grab the mouse, locking the cursor to the app's screen |
| Mouse Input | Demonstrates handling a mouse button press/release |
| Mouse Input Events | Prints out all mouse events (buttons, movement, etc.) |
| Text Input | Simple text input with IME support |
| Touch Input | Displays touch presses, releases, and cancels |
| Touch Input Events | Prints out all touch inputs |
Reflection
| Example | Description |
|---|---|
| Generic Reflection | Registers concrete instances of generic types that may be used with reflection |
| Reflection | Demonstrates how reflection in Bevy provides a way to dynamically interact with Rust types |
| Reflection Types | Illustrates the various reflection types available |
| Trait Reflection | Allows reflection with trait objects |
Scene
| Example | Description |
|---|---|
| Scene | Demonstrates loading from and saving scenes to files |
Shaders
These examples demonstrate how to implement different shaders in user code.
A shader in its most common usage is a small program that is run by the GPU per-vertex in a mesh (a vertex shader) or per-affected-screen-fragment (a fragment shader.) The GPU executes these programs in a highly parallel way.
There are also compute shaders which are used for more general processing leveraging the GPU's parallelism.
| Example | Description |
|---|---|
| Animated | A shader that uses dynamic data like the time since startup |
| Array Texture | A shader that shows how to reuse the core bevy PBR shading functionality in a custom material that obtains the base color from an array texture. |
| Compute - Game of Life | A compute shader that simulates Conway's Game of Life |
| Custom Vertex Attribute | A shader that reads a mesh's custom vertex attribute |
| Instancing | A shader that renders a mesh multiple times in one draw call |
| Material | A shader and a material that uses it |
| Material - GLSL | A shader that uses the GLSL shading language |
| Material - Screenspace Texture | A shader that samples a texture with view-independent UV coordinates |
| Material Prepass | A shader that uses the depth texture generated in a prepass |
| Post Processing | A custom post processing effect, using two cameras, with one reusing the render texture of the first one |
| Shader Defs | A shader that uses "shaders defs" (a bevy tool to selectively toggle parts of a shader) |
| Texture Binding Array (Bindless Textures) | A shader that shows how to bind and sample multiple textures as a binding array (a.k.a. bindless textures). |
Stress Tests
These examples are used to test the performance and stability of various parts of the engine in an isolated way.
Due to the focus on performance it's recommended to run the stress tests in release mode:
cargo run --release --example <example name>
| Example | Description |
|---|---|
| Bevymark | A heavy sprite rendering workload to benchmark your system with Bevy |
| Many Animated Sprites | Displays many animated sprites in a grid arrangement with slight offsets to their animation timers. Used for performance testing. |
| Many Buttons | Test rendering of many UI elements |
| Many Cubes | Simple benchmark to test per-entity draw overhead. Run with the sphere argument to test frustum culling |
| Many Foxes | Loads an animated fox model and spawns lots of them. Good for testing skinned mesh performance. Takes an unsigned integer argument for the number of foxes to spawn. Defaults to 1000 |
| Many Lights | Simple benchmark to test rendering many point lights. Run with WGPU_SETTINGS_PRIO=webgl2 to restrict to uniform buffers and max 256 lights |
| Many Sprites | Displays many sprites in a grid arrangement! Used for performance testing. Use --colored to enable color tinted sprites. |
| Transform Hierarchy | Various test cases for hierarchy and transform propagation performance |
Tools
| Example | Description |
|---|---|
| Gamepad Viewer | Shows a visualization of gamepad buttons, sticks, and triggers |
| Scene Viewer | A simple way to view glTF models with Bevy. Just run cargo run --release --example scene_viewer /path/to/model.gltf#Scene0, replacing the path as appropriate. With no arguments it will load the FieldHelmet glTF model from the repository assets subdirectory |
Transforms
| Example | Description |
|---|---|
| 3D Rotation | Illustrates how to (constantly) rotate an object around an axis |
| Scale | Illustrates how to scale an object in each direction |
| Transform | Shows multiple transformations of objects |
| Translation | Illustrates how to move an object along an axis |
UI (User Interface)
| Example | Description |
|---|---|
| Button | Illustrates creating and updating a button |
| Font Atlas Debug | Illustrates how FontAtlases are populated (used to optimize text rendering internally) |
| Relative Cursor Position | Showcases the RelativeCursorPosition component |
| Text | Illustrates creating and updating text |
| Text Debug | An example for debugging text layout |
| Text Layout | Demonstrates how the AlignItems and JustifyContent properties can be composed to layout text |
| Transparency UI | Demonstrates transparency for UI |
| UI | Illustrates various features of Bevy UI |
| UI Scaling | Illustrates how to scale the UI |
| UI Z-Index | Demonstrates how to control the relative depth (z-position) of UI elements |
| Window Fallthrough | Illustrates how to access winit::window::Window's hittest functionality. |
Window
| Example | Description |
|---|---|
| Clear Color | Creates a solid color window |
| Low Power | Demonstrates settings to reduce power use for bevy applications |
| Multiple Windows | Demonstrates creating multiple windows, and rendering to them |
| Scale Factor Override | Illustrates how to customize the default window settings |
| Transparent Window | Illustrates making the window transparent and hiding the window decoration |
| Window Resizing | Demonstrates resizing and responding to resizing a window |
| Window Settings | Demonstrates customizing default window settings |
Tests
| Example | Description |
|---|---|
| How to Test Systems | How to test systems with commands, queries or resources |
Platform-Specific Examples
Android
Setup
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:
cargo apk run --example android_example
When using Bevy as a library, the following fields must be added to Cargo.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 for other Android Manifest fields.
Debugging
You can view the logs with the following command:
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:
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. 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:
[package.metadata.android.sdk]
target_sdk_version = >>API<<
min_sdk_version = >>API or less<<
| Example | File | Description |
|---|---|---|
android |
android/android.rs |
The 3d/3d_scene.rs example for Android |
iOS
Setup
You need to install the correct rust targets:
aarch64-apple-ios: iOS devicesx86_64-apple-ios: iOS simulator on x86 processorsaarch64-apple-ios-sim: iOS simulator on Apple processors
rustup target add aarch64-apple-ios x86_64-apple-ios aarch64-apple-ios-sim
Build & Run
Using bash:
cd examples/ios
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:
DEVICE_ID=${YOUR_DEVICE_ID} make run
If you'd like to see xcode do stuff, you can run
open bevy_ios_example.xcodeproj/
which will open xcode. You then must push the zoom zoom play button and wait for the magic.
| Example | File | Description |
|---|---|---|
ios |
ios/src/lib.rs |
The 3d/3d_scene.rs example for iOS |
WASM
Setup
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.
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 is used to create javascript bindings to this wasm file, which can be loaded using this example HTML file.
Then serve examples/wasm directory to browser. i.e.
# 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
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
to your Cargo.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.
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.
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 Jully 2022 as following:
| 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:
- 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
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.