winit + wgpu, rendering in a Web Worker

Minimal demo: winit runs on the main thread, wgpu renders in a worker.

main thread                      worker
─────────────                    ──────────────────────
winit EventLoop                  wgpu Surface
  ↓ transferControlToOffscreen    on OffscreenCanvas
  ↓ postMessage("init", canvas)  ─→  surface / device / queue
  ↓ postMessage("render")  ─────→  render frame
  ↓ postMessage("resize")  ─────→  reconfigure surface

winit's web event loop must live on the main thread (DOM + rAF). So the canvas is transferred to a worker via transferControlToOffscreen(), and all GPU work happens there.

Layout

File	Role
src/bin/app.rs	Main thread: canvas + winit event loop + worker spawn + render ticks
src/bin/worker.rs	Worker: wgpu surface/device/queue + frame rendering
src/lib.rs	Shared postMessage helpers

Two separate wasm modules, built via Trunk's data-type="main" / data-type="worker".

Run

rustup target add wasm32-unknown-unknown
cargo install --locked trunk
trunk serve --open

Opens at http://127.0.0.1:8080. Resize the window; the surface reconfigures.

Requires a browser with WebGPU.