Engine decoupling proposal

[M374LX]

I have a proposal for a large step to reduce the coupling between components managed by Engine.

Certain components currently managed by Mixer could be managed by Engine directly: the audio and MIDI devices, MixerProfiler, fifo, and FifoWriter. Engine would also check for metronome samples and manage the song playing position (PlayPos), as the metronome also needs it.

The core method for buffer rendering (Mixer::renderNextBuffer()) would also be moved to Engine, while the parts of the rendering process handled by Mixer would be split into two methods (startNextBuffer() and finishBuffer()). Here is a pseudocode illustrating the new method:

void Engine::renderNextBuffer()
{
    mixerProfiler.startPeriod();

    mixer->startNextBuffer();
    song->processNextBuffer(m_playPos[m_playMode]); //The argument is a reference
    checkForMetronome(); //Decide if a metronome sample needs to be played
    mixer->finishBuffer();

    EnvelopeAndLfoParameters::instances()->trigger();
    Controller::triggerFrameCounter();
    AutomatableModel::incrementPeriodCounter();

    BufferManager::refresh();

    mixerProfiler.finishPeriod();
}

Similarly, Engine would look like:

class Engine
{
public:
    getNextBuffer(); //Decide between reading from the FIFO or calling renderNextBuffer(). Used by the audio device

    /// [...]

private:
    renderNextBuffer();

    m_playPos;
    m_playMode;

    m_song;
    m_bbTrackContainer;
    m_dummyTrackContainer;

    m_fxMixer;
    m_mixer;

    m_fifo;
    m_fifoWriter;

    m_ladspaManager;

    m_audioDevice;
    m_oldAudioDevice;

    m_midiDevice;

    m_instanceOfMe;
}

There are still other coupling problems, but these can be solved later. These include:

• The dependency of many objects on Mixer methods providing information, like framesPerPeriod(), baseSampleRate(), and processingSampleRate(), which are accessible globally.
• Similarly, we have the methods addPlayHandle() and removePlayHandle(). A possibility is to create a PlayHandleManager and free Mixer from the task of managing play handles.

In case no one has objections, I can start writing the new code and create a pull request.

[Rossmaxx]

@sakertooth might wanna look at this.