bevy-wasm-webgpu

Bevy 0.19 — browser WASM

When to use this skill

Build a Bevy client for wasm32-unknown-unknown.
Choose the broadly compatible WebGL2 path or WebGPU path.
Generate JS bindings, serve assets, and reduce artifact size.
Diagnose missing canvas, insecure-context, codec, or asset-path failures.

Canonical manifest

[package]
name = "myclient"
version = "0.1.0"
edition = "2024"

[dependencies] bevy = { version = "0.19", default-features = false, features = [ "3d", "ui", "touch", ] }

[profile.wasm-release] inherits = "release" opt-level = "z" lto = "fat" codegen-units = 1 strip = "debuginfo"


The `3d` profile supplies Bevy's renderer, Winit, and the default WebGL2 path.
Add `audio` only if needed; browser audio must begin after user interaction.

## Build and serve

```bash
rustup target add wasm32-unknown-unknown
cargo install wasm-bindgen-cli

cargo build --profile wasm-release --target wasm32-unknown-unknown
wasm-bindgen --target web --out-name myclient --out-dir public \
  target/wasm32-unknown-unknown/wasm-release/myclient.wasm

# Optional: install Binaryen first, then verify this actually reduces size.
wasm-opt -Oz public/myclient_bg.wasm -o public/myclient_bg.opt.wasm
mv public/myclient_bg.opt.wasm public/myclient_bg.wasm

python3 -m http.server --directory public 8080

Copy or link the project assets/ directory to public/assets/; Bevy fetches assets over HTTP relative to the served page/asset root.

Minimal HTML

<!doctype html>
<html lang="en">
  <head>
    <meta charset="utf-8">
    <meta name="viewport" content="width=device-width,initial-scale=1">
    <title>My Bevy game</title>
    <style>html,body,#bevy{width:100%;height:100%;margin:0;background:#000}</style>
  </head>
  <body>
    <canvas id="bevy"></canvas>
    <script type="module">
      import init from "./myclient.js";
      await init();
    </script>
  </body>
</html>

Bind the primary window to that existing canvas. Otherwise Window::default() has canvas: None, so Bevy/Winit creates and appends a second canvas:

use bevy::{prelude::*, window::WindowPlugin};

fn main() {
    App::new()
        .add_plugins(DefaultPlugins.set(WindowPlugin {
            primary_window: Some(Window {
                canvas: Some("#bevy".into()),
                fit_canvas_to_parent: true,
                ..default()
            }),
            ..default()
        }))
        .run();
}

Serve over HTTP; opening the file directly does not provide the fetch and module semantics the generated glue expects.

WebGL2 versus WebGPU

Choice	Cargo features	Choose when
WebGL2	profile defaults / `webgl2`	Browser reach matters; no compute dependency
WebGPU	add `webgpu`	A tested target browser supports it and effects need compute

In Bevy 0.19, webgpu overrides webgl2. One binary cannot dynamically fall back between them. Produce two artifacts or choose one based on the supported browser matrix. Check current browser support during release testing rather than hard-coding browser-version claims in application logic.

Gotchas

3d_api only supplies types; it does not render. Use 3d or compose 3d_bevy_render with the app/platform collections.
default-features = false matters. Cargo features are additive; adding 3d without disabling defaults keeps the full default set.
WebGL2 has no compute shaders. Hanabi and other compute-heavy plugins require the WebGPU artifact and their own current Bevy-compatible release.
Browser filesystems and child processes are not native capabilities. Capture, save, and export flows need explicit web APIs/JS interop.
Audio playback is normally blocked until a user gesture resumes the browser audio context.
Asset 404s are deployment-layout errors: inspect the requested URL in browser devtools and make the served assets/ tree match it.
A configured Window.canvas selector must resolve before startup and cannot be changed later. If you omit it, remove any placeholder canvas and let Bevy append its own.
Test on actual target browsers and GPUs. cargo check cannot validate adapter limits, shader translation, texture formats, or browser security policy.

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