Make egui work on WebGPU out of the box.

[Wumpf]

BREAKING: Makes WebGL for wgpu opt-in. By default wasm builds for egui will now use WebGPU. To use WebGL, you need to add wgpu = { version = "0.16.0", features = ["webgl"] } now to your Cargo.toml.

Works around a surface creation issue which made any subsequent call to any method on the surface fail (in a rather arcane manner) - see gfx-rs/wgpu#3710

Regarding the breaking change: Wgpu doesn't allow both WebGPU and a "direct" backend, like WebGL, to live side by side (i.e. wgpu is either in a "wrap WebGPU" or "implement WebGPU" mode). Therefore, egui now inherits the webgl-opt-in behavior. Since Web is memory constraint and availability of WebGPU can be queried easily, two separate builds for WebGPU and WebGL seem to be desirable regardless, so I don't think this is a big issue.

Fixes #2137

[Wumpf]

./scripts/build_demo_web.sh --release with feature glow changed to wgpu

egui_demo_app_bg.wasm filesize:

before: 6.62mb
after: 4.96mb

not too bad (:

[emilk]

So WebGPU must be configured at compile-time to user either WebGL or WebGPU, but you cannot ever configure it so that you pick at runtime?

So in effect we'll need to have a app_gl.wasm and app_wgpu.wasm and pick the correct one using JavaScript?

[Wumpf]

yes, that's my understanding of the state of things!

[Wumpf]

confirmed that now: gfx-rs/wgpu#3119 (comment)
Concluded that more from the code I debugged, but didn't go into the details. Personally I only ever looked at the backends that go through direct.rs (all backends except WebGPU, including webgl) and never looked at the mechanism that dispatches to web.rs instead.

[emilk]

Very cool!

It would be nice with a --webgpu flag to scripts/build_demo_web.sh so this can be easily tested

[Wumpf]

confirmed non-workaround path working with pending fix on wgpu