WIP - wasm_bindgen backend for eventloop-2.0

[spennydl]

wasm_bindgen support

This PR adds a wasm backend using wasm_bindgen and web-sys. This backend will be used when target_arch=wasm32 and the websys feature is enabled.

Implemenation status and todo

• selectable backend
• basic event loop and window creation
• wrap a canvas
• control flow
  • ControllFlow::Poll
  • ControlFlow::Wait
  • ControlFlow::WaitUntil
  • ControlFlow::Exit
• install handlers for mouse and keyboard events - In Progress
• install handlers for resize events - In Progress
• milestone 1 event loop feature-complete
• pointer capture/manipulation - rethinking this. i'm not sure it makes sense to support?
• canvas placement/resize through window's getters and setters
• be responsive - play nice with media queries etc that resize the canvas
• Tested on all platforms changed - I'm testing using the wasm-pack-template and wasm-app project templates
• Added an entry to CHANGELOG.md if knowledge of this change could be valuable to users
• Updated documentation to reflect any user-facing changes, including notes of platform-specific behavior
• Created an example program if it would help users understand this functionality
• Updated feature matrix, if new features were added or implemented
• and more i'm sure! i'll be updating this list closer to milestone 1 being completed

Closes #395

[goddessfreya]

Nit: A lot of your files are missing a new line at the end.

[goddessfreya]

Question: Do you intend to update the emscripten backend in an other PR, or are you not interested?

[goddessfreya]

Question: Will emscripten conflict with websys with some targets?

[spennydl]

i don't believe so, the target triple used for websys is wasm32-unknown-unknown. i would assume that if someone is building for wasm32-unknown-emscripten they wouldn't also have the websys feature set. i could add something like target_os = "unknown" to the cfg condition below (line21) to be safe

[goddessfreya]

Just a question.

[iceiix]

Is this PR missing some files or expected to not compile yet? Getting this error when trying to build, the CI systems are also failing with the same error:

error[E0463]: can't find crate for `wasm_bindgen`
 --> src/platform/websys.rs:1:1
  |
1 | extern crate wasm_bindgen;
  | ^^^^^^^^^^^^^^^^^^^^^^^^^^ can't find crate

[spennydl]

Is this PR missing some files or expected to not compile yet? Getting this error when trying to build, the CI systems are also failing with the same error:

error[E0463]: can't find crate for `wasm_bindgen`
 --> src/platform/websys.rs:1:1
  |
1 | extern crate wasm_bindgen;
  | ^^^^^^^^^^^^^^^^^^^^^^^^^^ can't find crate

This backend needs to be built for the wasm32-unkown-unkown target, and it looks like none of the jobs are currently building for that. The build command we need is cargo build --target wasm32-unkown-unknown --features="websys".

I'll be pushing some changes tomorrow sometime, i can update the circleci config to include it.

[blm768]

So, I had no idea this PR existed, and I started hacking on the stdweb support PR (#797) to add web-sys support. So far, it seems like there will end up being a fair bit of duplication between the two implementations because they need to interface with the same Web APIs, so it might be worthwhile to consider whether all the WebAssembly efforts thus far could be merged into something more coherent.

[spennydl]

So, I had no idea this PR existed, and I started hacking on the stdweb support PR (#797) to add web-sys support. So far, it seems like there will end up being a fair bit of duplication between the two implementations because they need to interface with the same Web APIs, so it might be worthwhile to consider whether all the WebAssembly efforts thus far could be merged into something more coherent.

I agree! In part I feel like that reflects the state of webassembly right now 😝 I'd be interested to hear @ryanisaacg's opinion given he's so far into the stdweb work, as well as from the project owners. Maybe open an issue?

[ryanisaacg]

I think the stdweb version will be pretty much feature-complete within the month. At this point it can already run a full application, given you're not using one of the things I haven't implemented yet.

I think it probably makes the most sense to finish the stdweb version and then add web-sys alongside, possibly inline with cfg declarations to switch between them. This means that changes can be easily applied to both web backends at once. However, I don't know much about idioms in web-sys, and it may be difficult to exactly mirror the structure of the stdweb code.

[goddessfreya]

Hey, we got a new web branch for all this web stuff! Closing. If there is any features in this PR not present in the new branch, file us a new PR. Thanks!