Fix usage of SDL_Init for emscripten

[connorjclark]

This patch fixes audio for emscripten.

I printed errors as SDL_GetError was called, and saw this:

Debugging told me the audio system was being initialized, but then shut down. Turns out that if any subsytem requested by SDL_Init cannot start, SDL will shutdown everything. So the haptic subsystem failing was problematic.

It fails because SDL configured the haptic subsytem to not build for emscripten (guess it's not supported).

This behavior in SDL_Init is a recent change. About 6 months ago SDL changed the init function to shutdown things when any requested subsystem failed to start: libsdl-org/SDL@0e294e9 . Previously, it would just return -1, but allegro ignores the return code, so it didn't matter (not fully understanding why everything still worked even though every subsystem after the haptic would have not been initialized...shrug)

I confirmed that the audio demos now play sound in the browser when built locally, using the instructions found in the SDL readme.

Fixes #1321

[connorjclark]

Aside: I was only able to start debugging when I added logging to SDL_SetError in my local emscripten ports build cache. I noticed that allegro doesn't provide a logging interface in its System driver, and only in one place does it ever call SDL_GetError (when making a window). Would it make sense to extend the system driver interface to include logging, and somehow wire SDL's logging infrastructure into allegro? Or is there already a way to get SDL logging from allegro that I'm overlooking?

[SiegeLord]

That looks very odd... I'd rather see this as sdl_flags &= ~SDL_INIT_HAPTIC;

[pedro-w]

Is it possible to do this by trying to init with SDL_INIT_EVERYTHING and falling back to SDL_INIT_EVERYTHING & ~SDL_INIT_HAPTIC if it fails? The reason being that, if SDL ever does implement a haptic driver for Emscripten, it will work without having to change this code back.

[connorjclark]

@pedro-w Good idea. There is a Web api for vibration, so it's certainly possible that one day the haptic system will work. I'll try your backing-off strategy this evening.

[connorjclark]

There seemed to be some sound issues when I did the backoff approach. I'm not confident that SDL truly cleans up everything when it shutsdown its systems.

[SiegeLord]

Thanks for investigating this.

What do you mean by a logging interface? You want an Allegro function that one can call to add to a log? If SDL has something like https://liballeg.org/a5docs/trunk/system.html#al_register_trace_handler, then we could pass it a function that appends to logs (via ALLEGRO_INFO etc macros).

[SiegeLord]

Something like:

void log_to_allegro(void *userdata, int category, SDL_LogPriority priority, const char *message) {
  (void)userdata;
  const char* category_string;
  switch (category_string) {
    case SDL_LOG_CATEGORY_APPLICATION:
      category_string: "SDL_LOG_CATEGORY_APPLICATION",
      break;
    ...
  }
  switch (priority) {
    case SDL_LOG_PRIORITY_INFO:
      ALLEGRO_INFO("%s: %s\n", category_string, message);
      break;
    ...
  }
}

SDL_LogSetOutputFunction(log_to_allegro, NULL)

[connorjclark]

What do you mean by a logging interface?

I don't have any particular ideas re: implementation, mainly just voicing an annoyance that whatever logging SDL is doing is not accessible to allegro / configurable. Sorry, I'm not being very constructive here :)

There does seem to be a way to set a callback function for logging in SDL: https://github.com/EddieRingle/SDL/blob/master/src/SDL_log.c#L361

EDIT: ah, based on your example code you've found the same.