z80/zx_speaker.cpp

#include "zx_speaker.h"
#include <SDL2/SDL.h>
#include "z80.h"
#include <vector>

namespace speaker
{
    uint16_t sampling_freq = 44100;
    uint16_t audio_buffer_size = 2048;
    SDL_AudioDeviceID sdlAudioDevice = 0;
    uint8_t *sound_buffer = nullptr;
    uint16_t sound_pos=0;
    uint16_t t_sound=0;
    std::vector<uint8_t(*)()> sources;

    float cycles_per_sample;

    void init(const uint16_t freq, const uint16_t buffer_size)
    {
        if (sound_buffer || sdlAudioDevice) quit();

        sampling_freq = freq;
        audio_buffer_size = buffer_size;

        SDL_AudioSpec audioSpec{sampling_freq, AUDIO_U8, 1, 0, (uint16_t)(audio_buffer_size>>2), 0, 0, NULL, NULL};
        sdlAudioDevice = SDL_OpenAudioDevice(NULL, 0, &audioSpec, NULL, 0);

        cycles_per_sample = z80::getClock() / sampling_freq;
        sound_buffer = (uint8_t*)malloc(audio_buffer_size);
        
        enable();
    }

    void quit()
    {
        disable();
        sources.clear();
        if (sound_buffer) {
            free(sound_buffer);
            sound_buffer = nullptr;
        }
        if (sdlAudioDevice) {
            SDL_CloseAudioDevice(sdlAudioDevice);
            sdlAudioDevice = 0;
        }
    }

    void enable()
    {
        SDL_PauseAudioDevice(sdlAudioDevice, 0);
    }

    void disable()
    {
        SDL_PauseAudioDevice(sdlAudioDevice, 1);
    }

    void register_source(uint8_t(*callback)())
    {
        sources.push_back(callback);
    }

    void update(const uint32_t dt)
    {
        t_sound += dt;
        if (t_sound>=cycles_per_sample) {
            t_sound-=cycles_per_sample;

            uint32_t sample = 0;
            for (auto callback : sources) sample += callback();
            sample /= sources.size();
            
            sound_buffer[(sound_pos++)&(audio_buffer_size-1)] = sample;
        }
        if (sound_pos>=1000) {
            SDL_QueueAudio(sdlAudioDevice, sound_buffer, sound_pos);
            sound_pos = 0;
            while (SDL_GetQueuedAudioSize(sdlAudioDevice) > (audio_buffer_size<<1) ) {}
        }
    }

}