lemur/audio.c

#include <audio.h>
#include <stdio.h>

void audioCallback(void *userdata, uint8_t *stream, int len) {
    AudioContext *aud;
    SDL_assert(len == 834 * 4);

    aud = userdata;
    if (!aud->filled) {
        /* too little data, play silence */
        SDL_memset4(stream, 0, 834);
        return;
    }
    SDL_memcpy4(stream, aud->buffers[aud->current], 834);
    ++aud->current;
    aud->current %= 2;
    aud->filled -= 1;
} 

int audioInit(AudioContext *aud) {
    SDL_AudioSpec spec;
    spec.freq = 41700;
    spec.format = AUDIO_S16;
    spec.channels = 2;
    spec.samples = 834;
    spec.callback = &audioCallback;
    spec.userdata = aud;

    aud->id = SDL_OpenAudioDevice(NULL, 0, &spec, NULL, 0);
    aud->paused = true;
    if (!aud->id) {
        fprintf(stderr, "could not open audio device: %s\n", SDL_GetError());
        return -1;
    }
    aud->current = 0;
    aud->filled = 0;
    return 0;
}

int audioUpdate(AudioContext *aud, void *data, uint32_t bytes) {
    int filled;
    if (!aud->id) return -1;
    SDL_assert(bytes == 834 * 4);

    SDL_LockAudioDevice(aud->id);
    if (aud->filled < 2) {
        int next = (aud->current + aud->filled) % 2;
        SDL_memcpy4(aud->buffers[next], data, bytes / 4);
        aud->filled += 1;
    }
    filled = aud->filled;
    SDL_UnlockAudioDevice(aud->id);

    if (aud->paused) {
        SDL_PauseAudioDevice(aud->id, false);
        aud->paused = false;
    }

    while (filled > 1) {
        SDL_Delay(0);
        filled = aud->filled;
    }

    return 0;
}