Emscripten support.

[agausmann]

wasm32-unknown-emscripten is a great target for compiling and running games using WebAssembly, particularly because it can produce web pages that run on most browser platforms instead of having to maintain and ship binaries for Windows, Linux, etc. separately.

There is a port of SDL2 officially maintained by the emscripten project. I have been using it off and on for about a year, bundling and statically linking it with this crate behind pistoncore-sdl_window

You can see the progress I've made on my rust-sdl2 fork, though it is hacked together and breaks other targets in its current state, that can theoretically be fixed. I'd love to eventually get it cleaned up and merged upstream.

[tanis2000]

@agausmann if you're still interested I've got rust-sdl2 partially working with Emscripten. My prototype at https://github.com/tanis2000/minigame-rust/tree/webgl is actually compiling to wasm through Emscripten but I've still got an issue with the SDL_Renderer that seems to be invalid in the browser for some unknown reason.

The error I get is the following:

thread 'main' panicked at 'Invalid renderer', /Users/tanis/Documents/tanis2000-rust-sdl2/src/sdl2/render.rs:912:13

Maybe you already stumbled upon it and know why it's happening?

[hikari-no-yume]

As I unfortunately discovered here, that this crate wants to link against SDL2 (i.e. links = "SDL2" which results in -lSDL2) means it doesn't “just work” for newer Emscripten SDKs, at least for me. If it weren't for that it would at least partially work out-of-the-box.

[Cobrand]

@hikari-no-yume This is extremely simple to fix, remove links = "SDL2" https://github.com/Rust-SDL2/rust-sdl2/blob/master/sdl2-sys/Cargo.toml (which has been an issue of dual -lSDL2 output for quite some time), and fix the function link_sdl2 whenever a target has -lSDL2 missing in sdl2-sys's build.rs

However, this line https://github.com/Rust-SDL2/rust-sdl2/blob/master/sdl2-sys/build.rs#L304 hints that someone was actually able to run this as emscripten, but I could be wrong?

[hikari-no-yume]

@Cobrand Indeed it's a trivial fix, I might contribute a pull request with that at some point (once I can, unfortunately can't for reasons). I think that either a previous Emscripten toolchain or a previous version of this crate worked, just not any more.

[tanis2000]

@Cobrand that line in build.rs comes from me and yeah it used to work with Emscripten back then when I made that change. I haven't been using Emscripten lately so I don't know if one of the latest releases changed anything in their toolchain.

[bsurmanski]

Emscripten targeting should be fixed by #937

But on Windows specifically, there is still an issue when building the emscripten ports for SDL_mixer. I think it's using a 32bit binary when it expected a 64bit or vice versa. It gives an error of the form "%1 is not an application" or something like that. Workaround for now: build on OSX/Linux ¯_(ツ)_/¯

[hikari-no-yume]

@bsurmanski unfortunately, that does not fix it for me:

          error: undefined symbol: SDL_CreateWindow
          warning: To disable errors for undefined symbols use `-s ERROR_ON_UNDEFINED_SYMBOLS=0`
          error: undefined symbol: SDL_GL_CreateContext
          Error: Aborting compilation due to previous errors
          shared:ERROR: '/Users/ajf/Apps/emsdk/node/12.9.1_64bit/bin/node /Users/ajf/Apps/emsdk/fastcomp/emscripten/src/compiler.js /var/folders/2n/tv3h_lg12f97hnc070p3dxqh0000gn/T/tmpQN5vpn.txt /Users/ajf/Apps/emsdk/fastcomp/emscripten/src/library_pthread_stub.js' failed (1)

I think this library needs to tell emscripten USE_SDL=2 itself.

[hikari-no-yume]

Ah, but while it doesn't tell emscripten to use its SDL2 port, it does appear fix the -l SDL2 problem, so it's progress. Thank you!

[bsurmanski]

How are you targeting emscripten? It works for me if I use Cargo Web. Creating a Web.toml will allow you to pass in the USE_SDL=2 flags. See: https://github.com/koute/cargo-web

[hikari-no-yume]

I'm not using Cargo web, just plain cargo. But I'll check that out, it sounds useful.

[agausmann]

Even without cargo-web, it is possible:

.cargo/config

[target.wasm32-unknown-emscripten]
rustflags = [
    "-C", "link-arg=-s", "-C", "link-arg=USE_SDL=2",
]

[hikari-no-yume]

I'm doing exactly that right now, but it feels like a hack. I don't know enough to think of what a better way would be though.