audio_pcm.c

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#include <banjo/api.h>
#include <banjo/app.h>
#include <banjo/main.h>
#include <banjo/audio.h>
#include <banjo/log.h>
#include <banjo/system.h>
#include <banjo/time.h>
 
// Data passed to the audio callback. The callback reads this to know what
// frequency to generate. We modify it in real-time to change the pitch.
bj_audio_play_note_data data = {0};
bj_audio_device* p_device    = 0;
 
static void* setup(struct bj_app* app, void* init_data) {
    (void)init_data;
 
    // Initialize the audio subsystem.
    if (!bj_begin(BJ_AUDIO_SYSTEM, 0)) {
        bj_quit_app(app, 1);
        return 0;
    }
 
    // Choose which waveform to generate. BJ_AUDIO_PLAY_SINE creates smooth
    // sine wave tones. Other options include square, triangle, and sawtooth.
    data.function = BJ_AUDIO_PLAY_SINE;
 
    // Open an audio device with specific properties:
    //   - format: BJ_AUDIO_FORMAT_F32 uses 32-bit float samples (-1.0 to 1.0)
    //   - sample_rate: 44100 Hz (CD quality)
    //   - channels: 2 (stereo output)
    // The callback bj_play_audio_note will be called repeatedly to fill buffers.
    // We pass &data so the callback knows what frequency to generate.
    p_device = bj_open_audio_device(&(bj_audio_properties){
        .format      = BJ_AUDIO_FORMAT_F32,  /* float buffer */
        .amplitude   = 16000,                /* used only for INT16 path */
        .sample_rate = 44100,
        .channels    = 2,
    }, bj_play_audio_note, &data, 0);
 
    if (!p_device) {
        bj_quit_app(app, 1);
        return 0;
    }
 
    // Start audio playback. The callback will now run in a separate thread,
    // continuously filling audio buffers.
    bj_play_audio_device(p_device);
    return 0;
}
 
static void step(struct bj_app* app, struct bj_tick_info tick, void* user_data) {
    (void)tick;
    (void)user_data;
 
    // Simple melody: C-D-E-F-G-F-E-D-C (frequencies in Hz).
    // Middle C (C4) = 261.63 Hz, D4 = 293.66 Hz, etc.
    static const double melody[] = {
        261.63, 293.66, 329.63,
        349.23, 392.00, 349.23,
        329.63, 293.66, 261.63
    };
    enum { MELODY_LEN = 9 };
 
    // Use runtime as note index - changes once per second.
    int note = (int)bj_run_time();
 
    if (note >= MELODY_LEN) {
        bj_quit_app(app, 0);
        return;
    }
 
    // Update the frequency. The audio callback runs in a separate thread and
    // will immediately pick up this change, smoothly transitioning to the new note.
    data.frequency = melody[note];
}
 
static void teardown(struct bj_app* app, void* user_data) {
    (void)user_data;
    // Stop audio playback and close the device.
    if (p_device) bj_close_audio_device(p_device);
    bj_end();
}
 
int main(int argc, char* argv[]) {
    (void)argc; (void)argv;
    return bj_run_app(setup, step, 0, teardown, 0);
}