Hi! I mentioned I started working on wasm support here: https://github.com/aclysma/basis-universal-rs/issues/10. I've been using this on a branch of this crate for a while but I thought I'd just now have a go at merging my changes. This PR isn't super ready yet but some aspect could be merged. I've rewritten some calls like basis_transcoder_format_is_uncompressed and validate_output_buffer_size in rust so there are less bindings to the basis-universal wasm binary that I have to implement.

I have similar code for at least transcode_slice() for the low-level ETC1S transcoder but I didn't yet figure out how to get BasisLZ/ETC1S data from KTX2 and feed it into that function. This, however, for UASTC is working.

CC @superdump

I've been working on writing bindings for the transcoder wasm that basis_universal provides so that I can parse and transcode basis files in wasm. I've got a repo for this here: https://github.com/expenses/basis-universal-rs-wasm

It'd be fantastic if we could get support for this into this crate, so that wasm support just works. A couple of notes:

• I had to set EXPORT_ES6=1 in the emscripten link flags:

  https://github.com/BinomialLLC/basis_universal/blob/b38c3e4a9bf85d2fe13e2a9d5495be90eb927381/webgl/transcoder/CMakeLists.txt#L51

  I don't know if I strictly needed to do this, but it made binding with wasm-bindgen via #[wasm_bindgen(js_name = default)] a lot easier.

• The emscripten code loads the module asyncronously, which means you can't directly import the exports in wasm-bindgen because they're only created after initialisation. To work around this I had to use reflection to create the javascript classes: https://github.com/expenses/basis-universal-rs-wasm/blob/8274f56092c930bb0dfbb35b0386235a3c5a9813/src/lib.rs#L36-L38

• By default the emscripten code attempts to load the wasm binary from a relative url. Because wasm-bindgen copies the referenced javascript module to a snippet such as pkg/snippets/basis-universal-wasm-8dd816e8505190b7/basis_universal/webgl/transcoder/build/basis_transcoder.js but does not copy anything else. this load fails.

  Luckily the code allows settings a wasmBinary key in the object that's passed in, so you can provide your own wasm file: https://github.com/expenses/basis-universal-rs-wasm/blob/master/src/lib.rs#L26-L31. I just include_bytes! the file for ease of use.

• Because the wrapper API is quite different from the normal API, we're probably going to have to write our own wrapper to bring the APIs to parity.

This will all take a while, but I'll try to create good bindings for the .basisu transcoder and work from there.

Could consider implementing:

• Send, Sync
• Debug, Clone, Copy, PartialEq, Eq, Hash
• Serialize/Deserialize (probably gated by feature flag)
• Anything else?

It's possible to get a CompressorImageRef from CompressorParams, drop CompressorParams, and cause undefined behavior by using CompressorImageRef. Some API improvements would enable rust borrow checking to catch this at compile time.