README.md

• make mac to compile on mac.
• make web to compile for web.
• make run-web to start a web server on port 8000 to visit the program in your browser.
• make run-mac to run on mac.
• make clean to wipe the slate.

ios-audio.c

#include <stdio.h>
#include <math.h>
#include <SDL.h>

#ifdef EMSCRIPTEN
#include <emscripten/emscripten.h>
#endif

#define GAME_SIZE 256
SDL_Window *window;
SDL_Renderer *renderer;
SDL_Texture *game_view;
SDL_AudioDeviceID dev;
SDL_AudioSpec want, have;
int quit = 0;

/* Generate some audio. */
#define FREQ 200
unsigned int audio_position;
int audio_len;
float audio_frequency;
float audio_volume;

void audioCallback(void* userdata, Uint8* stream, int len) {
  len /= 2;
  int i;
  Sint16* buf = (Sint16*)stream;
  for(i = 0; i < len; i++) { 
    buf[i] = audio_volume * sin(2 * M_PI * audio_position * audio_frequency);
    audio_position++;
  }
  audio_len -= len;
  return;
}

void initAudio() {
  SDL_Init(SDL_INIT_AUDIO);
  SDL_zero(want);
  want.freq = 44100;
  want.format = AUDIO_S16;
  want.channels = 1;
  want.samples = 4096;
  want.callback = audioCallback;
  dev = SDL_OpenAudioDevice(NULL, 0, &want, &have, SDL_AUDIO_ALLOW_FREQUENCY_CHANGE);
  audio_len = have.freq * 5;
  audio_position = 0;
  audio_frequency = 1.0 * FREQ / have.freq;
  audio_volume = 6000;
  SDL_PauseAudioDevice(dev, 0);
}

int eventFilter(void* userdata, SDL_Event* event) {

    switch(event->type){
      case SDL_FINGERDOWN:
      case SDL_MOUSEBUTTONDOWN:
        /*initAudio();*/
#ifdef __EMSCRIPTEN__
        EM_ASM({
          if(SDL2.audioContext && SDL2.audioContext.currentTime == 0) {
            console.log("attempting to unlock");
            var buffer = SDL2.audioContext.createBuffer(1, 1, 22050);
            var source = SDL2.audioContext.createBufferSource();
            source.buffer = buffer;
            source.connect(SDL2.audioContext.destination);
            source.noteOn(0);
          }
        });
#endif
        break;
    }
    return 1;
}

void loop_game(){
    SDL_Event event;
    while(SDL_PollEvent(&event)){
      switch(event.type){
        case SDL_QUIT:
          quit = 1;
          break;
        /*case SDL_FINGERDOWN:
        case SDL_MOUSEBUTTONDOWN:
          initAudio();
          break;*/
      }
    }

    SDL_SetRenderTarget(renderer, game_view);
    SDL_SetRenderDrawColor(renderer, 255, 0, 0, SDL_ALPHA_OPAQUE);
    SDL_RenderClear(renderer);

    SDL_SetRenderDrawColor(renderer, 0, 255, 0, SDL_ALPHA_OPAQUE/2);
    SDL_RenderDrawLine(renderer, 0, 0, GAME_SIZE, GAME_SIZE);
    SDL_SetRenderDrawColor(renderer, 0, 0, 255, SDL_ALPHA_OPAQUE/2);
    SDL_RenderDrawLine(renderer, GAME_SIZE, 0, 0, GAME_SIZE);

    SDL_SetRenderTarget(renderer, NULL);
    SDL_RenderClear(renderer);
    SDL_RenderCopy(renderer, game_view, NULL, NULL);
    SDL_RenderPresent(renderer);
}

int main(int argc, const char * argv[]) {

  SDL_Init(SDL_INIT_VIDEO);

  window = SDL_CreateWindow(
      "iOS SDL2 Audio Test",
      SDL_WINDOWPOS_UNDEFINED,
      SDL_WINDOWPOS_UNDEFINED,
      GAME_SIZE,
      GAME_SIZE,
      SDL_WINDOW_SHOWN);

  renderer = SDL_CreateRenderer(window,
      -1,
      SDL_RENDERER_ACCELERATED |
      SDL_RENDERER_TARGETTEXTURE | SDL_RENDERER_PRESENTVSYNC);

  SDL_SetRenderDrawBlendMode(renderer, SDL_BLENDMODE_BLEND);

  game_view = SDL_CreateTexture(renderer,
      SDL_PIXELFORMAT_RGBA8888,
      SDL_TEXTUREACCESS_TARGET,
      GAME_SIZE,
      GAME_SIZE);

  initAudio();
  SDL_SetEventFilter(eventFilter, NULL);

  #ifdef EMSCRIPTEN
    emscripten_set_main_loop((em_callback_func)loop_game, 0, 1);
  #else
    while(!quit){
      loop_game();
    }
  #endif

  SDL_DestroyTexture(game_view);
  SDL_DestroyRenderer(renderer);
  SDL_DestroyWindow(window);
  SDL_Quit();

  return 0;
}

Makefile

OBJS = ios-audio.c
OBJ_NAME = "ios-audio"

mac:
	mkdir -p builds/native/mac
	gcc -Wall -o $(OBJ_NAME) $(OBJS) `sdl2-config --cflags --libs`;
	mv $(OBJ_NAME) builds/native/mac

web:
	mkdir -p builds/html
	emcc $(OBJS) -O2 --memory-init-file 1 -s USE_SDL=2 -o builds/html/index.html --emrun

clean:
	rm -rf builds

run-mac:
	builds/native/mac/$(OBJ_NAME)

run-web:
	emrun --no_browser --port 8000 builds/html/index.html