townengine/src/audio.c

#include "private/audio.h"
#include "audio.h"
#include "context.h"
#include "util.h"

#include <SDL2/SDL.h>
#include <stb_ds.h>
#include <physfs.h>

#define STB_VORBIS_HEADER_ONLY
#include <stb_vorbis.c>

#include <stdint.h>
#include <string.h>

/* TODO: default to float sampling format? */

static const char *audio_exts[audio_file_type_count] = {
    ".ogg", /* audio_file_type_ogg */
    ".xm",  /* audio_file_type_xm */
};


/* TODO: count frames without use, free the memory when threshold is met */
/* stores path to data hash, useful for sound effects */
static struct audio_file_cache {
    char *key;
    struct audio_file_cache_value {
        unsigned char *data;
        size_t len;
    } value;
} *audio_file_cache;


static int64_t get_audio_data(const char *path, unsigned char **data) {
    const struct audio_file_cache *cache = shgetp_null(audio_file_cache, path);
    if (!cache) {
        unsigned char *file;
        int64_t len = file_to_bytes(path, &file);
        if (len == -1) {
            CRY("Audio error", "Error reading file");
            return -1;
        }

        const struct audio_file_cache_value value = { file, (size_t)len };
        shput(audio_file_cache, path, value);

        *data = file;
        return len;
    }

    *data = cache->value.data;
    return (int64_t)cache->value.len;
}


void play_audio(const char *path, const char *channel) {
    const struct audio_channel_pair *pair = shgetp_null(ctx.audio_channels, channel);
    if (!pair)
        play_audio_ex(path, channel, get_default_audio_args());
    else
        play_audio_ex(path, channel, pair->value.args);
}


static t_audio_file_type infer_audio_file_type(const char *path) {
    size_t path_len = strlen(path);

    for (int i = 0; i < audio_file_type_count; ++i) {
        size_t ext_length = strlen(audio_exts[i]);
        if (path_len <= ext_length)
            continue;

        if (strcmp(&path[path_len - ext_length], audio_exts[i]) == 0)
            return (t_audio_file_type)i;
    }

    return audio_file_type_unknown;
}


/* TODO: error propagation and clearing of resources on partial success? */
/*       or should we expect things to simply fail? */
static union audio_context init_audio_context(const char *path, t_audio_file_type type) {
    switch (type) {
    case audio_file_type_ogg: {
        unsigned char *data;
        int64_t len = get_audio_data(path, &data);
        if (len == -1) {
            CRY("Audio error", "Error reading file");
            break;
        }

        int error = 0;
        stb_vorbis* handle = stb_vorbis_open_memory(data, (int)len, &error, NULL);
        if (error != 0) {
            CRY("Audio error", "Error reading .ogg file");
            break;
        }

        stb_vorbis_info info = stb_vorbis_get_info(handle);

        return (union audio_context){
            .vorbis = {
                .data = data,
                .handle = handle,
                .frequency = info.sample_rate,
                .channel_count = (uint8_t)info.channels,
            }
        };
    }

    default:
        CRY("Audio error", "Unhandled audio format (in init)");
        return (union audio_context){0};
    }

    return (union audio_context){0};
}


static void repeat_audio(struct audio_channel *channel) {
    (void)channel;

    /* TODO */
}


void play_audio_ex(const char *path, const char *channel, t_play_audio_args args) {
    struct audio_channel_pair *pair = shgetp_null(ctx.audio_channels, channel);

    /* create a channel if it doesn't exist */
    if (!pair) {
        t_audio_file_type file_type = infer_audio_file_type(path);
        struct audio_channel new_channel = {
            .args = args,
            .file_type = file_type,
            .context = init_audio_context(path, file_type),
            .path = path,
        };
        shput(ctx.audio_channels, channel, new_channel);
        pair = shgetp_null(ctx.audio_channels, channel);
    }

    /* TODO: destroy and create new context when channel is reused for different file */

    /* works for both restarts and new audio */
    if (strcmp(pair->value.path, path) == 0)
        repeat_audio(&pair->value);
}


t_play_audio_args get_default_audio_args(void) {
    return (t_play_audio_args){
        .repeat = false,
        .crossfade = false,
        .volume = 1.0f,
        .panning = 0.0f,
    };
}


static void audio_sample_and_mixin_channel(struct audio_channel *channel,
                                           uint8_t *stream,
                                           int len) {
    int16_t *const sstream = (int16_t *)stream;
    static uint8_t buffer[16384];
    const int buffer_frames = sizeof (buffer) / sizeof (int16_t);

    switch (channel->file_type) {
    case audio_file_type_ogg: {
        /* feed stream for needed conversions */
        for (int i = 0; i < (len / 2);) {
            const int n_frames = ((len / 2) - i) > buffer_frames ? buffer_frames : (len / 2) - i;

            /* TODO: handle end of file */
            const int samples_per_channel = stb_vorbis_get_samples_short_interleaved(
                channel->context.vorbis.handle,
                channel->context.vorbis.channel_count,
                (int16_t *)buffer,
                n_frames);

            /* handle end of file */
            if (samples_per_channel == 0) {
                if (channel->args.repeat)
                    /* seek to start and try sampling some more */
                    stb_vorbis_seek_start(channel->context.vorbis.handle);
                else
                    /* leave silence */
                    break;
            }

            /* panning and mixing */

#if AUDIO_N_CHANNELS == 2

            for (int s = 0; s < samples_per_channel * ctx.audio_stream_channel_count; s += 2) {
                /* left channel */
                {
                    const float panning = fminf(fabsf(channel->args.panning - 1.0f), 1.0f);
                    const float volume = channel->args.volume * panning;
                    sstream[i + s] += (int16_t)(((int16_t *)buffer)[s] * volume);
                }

                /* right channel */
                {
                    const float panning = fminf(fabsf(channel->args.panning + 1.0f), 1.0f);
                    const float volume = channel->args.volume * panning;
                    sstream[i + s + 1] += (int16_t)(((int16_t *)buffer)[s + 1] * volume);
                }
            }
#else
#error "Unimplemented channel count"
#endif

            i += samples_per_channel * ctx.audio_stream_channel_count;
        }

        break;
    }

    default:
        CRY("Audio error", "Unhandled audio format (in sampling)");
        break;
    }
}


void audio_callback(void *userdata, uint8_t *stream, int len) {
    (void)userdata;

    /* prepare for mixing */
    SDL_memset(stream, sizeof (uint16_t), len * ctx.audio_stream_channel_count);

    for (int i = 0; i < shlen(ctx.audio_channels); ++i) {
        audio_sample_and_mixin_channel(&ctx.audio_channels[i].value, stream, len);
    }
}