"screen is not defined" when used with PROXY_TO_PTHREAD

[lwb4]

When compiled with -s PROXY_TO_PTHREAD=1, calls to SDL_Init() fail with the error "screen is not defined".

This is important to me because proxying all socket commands through a local websocket server as described here is the only way I can get any networking to work in my project.

Here's my source file, poc.c:

#include "SDL.h"

int main() {
  SDL_Init(SDL_INIT_VIDEO);
  SDL_Quit();
}

And here's my commands to compile and run:

emcc poc.c -s USE_SDL=2 -s USE_PTHREADS=1 -s PROXY_POSIX_SOCKETS=1 -s PROXY_TO_PTHREAD=1 -o poc.html
python -m SimpleHTTPServer 5000

Open localhost:5000/poc.html in a browser, open the developer console, and you see this error:

poc.worker.js:175 Uncaught ReferenceError: screen is not defined
    at 37846 (http://localhost:2222/poc.js:1908:21)
    at _emscripten_asm_const_iii (http://localhost:2222/poc.js:1927:27)
    at wasm-function[968]:0x6a84c
    at wasm-function[852]:0x603e7
    at wasm-function[260]:0x3472
    at wasm-function[261]:0x35b0
    at wasm-function[258]:0x339a
    at wasm-function[259]:0x33a9
    at Module._main (http://localhost:2222/poc.js:9838:32)
    at ___call_main (http://localhost:2222/poc.js:2312:24)

From jakogut's comments on this site, it appears that the problem is simply that the screen object is not proxied to the new main thread. Relevant lines from video/emscripten/SDL_emscriptenvideo.c:

mode.w = EM_ASM_INT_V({
    return screen.width;
}); 

mode.h = EM_ASM_INT_V({
    return screen.height;
}); 

Indeed, the documentation on PROXY_TO_PTHREAD only says that the canvas object is proxied to the new main thread. How can we get screen proxied as well? I'm happy to contribute code, just need to be pointed in the right direction!

[Daft-Freak]

Hmm, there was some discussion on this here #77 and some work on new APIs here emscripten-core/emscripten#9336.

The quickest solution is probably to switch to MAIN_THREAD_EM_ASM_INT. (Though a get_screen_size API would still be nice...)

[lwb4]

Oh nice, glad to see it's being worked on. I'll just use a workaround for now!

[danielknobe]

This commits solves the problem but hidden error become visible.
The GL Context (GLctx) is undefined, when I try to run this short example:

	SDL_Init(SDL_INIT_VIDEO);

	auto mWindow = SDL_CreateWindow("Title",
	SDL_WINDOWPOS_UNDEFINED,
	SDL_WINDOWPOS_UNDEFINED,
	800, 600,
	0);

	auto mRenderer = SDL_CreateRenderer(mWindow, -1, SDL_RENDERER_ACCELERATED);

Stacktrace:

TypeError: Cannot read property 'getParameter' of undefined
    at emscriptenWebGLGet (http://localhost:6931/test.js:8035:28)
    at _emscripten_glGetIntegerv (http://localhost:6931/test.js:8136:7)
    at GLES2_CreateRenderer (wasm-function[5809]:0x131cc8)
    at SDL_CreateRenderer (wasm-function[5777]:0x12e043)
    at main (wasm-function[3132]:0x6f43a)
    at Module._main (http://localhost:6931/test.js:11010:32)
    at ___call_main (http://localhost:6931/test.js:2646:24)
    at __emscripten_thread_main (wasm-function[8646]:0x1cd812)
    at dynCall_ii (wasm-function[8678]:0x1cf7f4)
    at Object.Module.dynCall_ii (http://localhost:6931/test.js:11332:38)

[Daft-Freak]

Yeah, there are still other issues, that one can be fixed with -s OFFSCREEN_FRAMEBUFFER=1, but then you hit emscripten-core/emscripten#7684.

EDIT: The workaround from that issue needs a small tweak (emscripten_webgl_create_context("#canvas", &attr))

[danielknobe]

Yes this fixes that problem. Ty.