satimer.cpp

class SampleAccurateTimer
{
  public:
    SampleAccurateTimer() {}
    void setIntervalSamples(int samples)
    {
        m_counter = 0;
        m_period = samples;
    }
    std::function<void(int)> Callback;
    void advance(int numsamples)
    {
        jassert(m_period > 0);
        jassert(Callback); // callback must be set
        // this could be done more elegantly/efficiently, perhaps...
        // but this brute force approach is simple to understand
        for (int i = 0; i < numsamples; ++i)
        {
            if (m_counter == 0)
            {
                Callback(i);
            }
            ++m_counter;
            if (m_counter == m_period)
                m_counter = 0;
        }
    }
    void reset() { m_counter = 0; }

  private:
    int m_period = 0;
    int m_counter = 0;
};

// just a mock processor, we don't want to inherit juce AudioProcessor here
// and needlessly fill in all the needed virtual methods...
class MyProcessor
{
  public:
    MyProcessor() { m_satimer.setIntervalSamples(11337); }
    void processBlock(juce::AudioBuffer<float> &buffer, juce::MidiBuffer &midiBuffer)
    {
        m_satimer.Callback = [&midiBuffer](int samplepos) {
            midiBuffer.addEvent(juce::MidiMessage::noteOn(1, 60, 1.0f), samplepos);
            // std::cout << "added midi event at buffer position " << samplepos << "\n";
        };
        m_satimer.advance(buffer.getNumSamples());
    }

  private:
    SampleAccurateTimer m_satimer;
};

void test_sa_timer()
{
    MyProcessor proc;
    // simulate what the host is conceptually doing
    int blocksize = 441;
    int outcounter = 0;
    int outlen = 2.5 * 44100; // run simulation for 2.5 seconds
    juce::AudioBuffer<float> buf(1, blocksize);
    juce::MidiBuffer midibuffer;
    while (outcounter < outlen)
    {
        proc.processBlock(buf, midibuffer);
        midibuffer.clear();
        outcounter += blocksize;
    }
}