"audio plugin host" MIDI Output

General JUCE discussion
7

As promised, here are the instructions originally posted by oxxyyd on how to modify the plugin host to handle midi out, updated to JUCE version 5.4.4:

1 First you need to add some code to actually create the midi out connection so to say
In InternalPlugins.h you change

PluginDescription audioInDesc, audioOutDesc, midiInDesc;

to

PluginDescription audioInDesc, audioOutDesc, midiInDesc, midiOutDesc;

in InternalPlugins.cpp you add in the relevant places:

{
    AudioProcessorGraph::AudioGraphIOProcessor p (AudioProcessorGraph::AudioGraphIOProcessor::midiOutputNode);
    p.fillInPluginDescription (midiOutDesc);
}

and

if (name == midiOutDesc.name)  return std::make_unique<AudioProcessorGraph::AudioGraphIOProcessor> (AudioProcessorGraph::AudioGraphIOProcessor::midiOutputNode);

and

midiOutDesc,

to the line that says

results.add (audioInDesc, audioOutDesc, midiInDesc,

(hint: search for midiInDesc and add the corresponding code for midiOutDesc).

In PluginGraph.cpp you add

addPlugin (internalFormat.midiOutDesc,  { 0.25, 0.9 });

NOTE: at this point your code should be in a state that will compile and the MIDI Output node should appear in the plugin graph (but it doesn’t work yet).

2 Some more updates
Add to the collection of privates of GraphDocumentComponent in GraphEditorPanel.h

MidiOutput *midiOut;

Make GraphDocumentComponent a ChangeListener i.e in GraphEditorPanel.h it should look like

class GraphDocumentComponent  : public Component,
                                public DragAndDropTarget,
                                public DragAndDropContainer,
                                public ChangeListener

and add the following line to the public part of the class declaration:

void changeListenerCallback(ChangeBroadcaster* source) override;

3 Add to GraphEditorPanel.cpp

void GraphDocumentComponent::changeListenerCallback(ChangeBroadcaster* source) {
  if (source == &deviceManager) {
    midiOut = deviceManager.getDefaultMidiOutput();
    
    if (midiOut) {
        midiOut->startBackgroundThread();
    }
    
    graphPlayer.setMidiOutput(midiOut);
  }
}

4 Now add the line

changeListenerCallback(&deviceManager);

somewhere in the constructor of GraphDocumentComponent (GraphEditorPanel.cpp).

and put following at the to beginning of ~GraphDocumentComponent

if (midiOut)
    midiOut->stopBackgroundThread();

and add to the method init(), after the line that begins with “keyState.addListener”, the line

deviceManager.addChangeListener(this);

5 Now we’ve come to the part where midi output is actually taken from the AudioProcessorGraph.
Modify the code below by adding the 7 lines after

// modification for MIDI output:

In juce_AudioProcessorPlayer.cpp:

        if (! processor->isSuspended())
        {
            if (processor->isUsingDoublePrecision())
            {
                conversionBuffer.makeCopyOf (buffer, true);
                processor->processBlock (conversionBuffer, incomingMidi);
                buffer.makeCopyOf (conversionBuffer, true);
            }
            else
            {
                processor->processBlock (buffer, incomingMidi);
            }

            // modification for MIDI output:
            AudioProcessorGraph* processorgraph=dynamic_cast<AudioProcessorGraph*>(processor);
            if (processorgraph) {
                MidiBuffer* midiBuffer (processorgraph->getCurrentMidiOutputBuffer());
                if (midiBuffer && !midiBuffer->isEmpty() && midiOutput) {
                    midiOutput->sendBlockOfMessages(*midiBuffer, Time::getMillisecondCounter(), getCurrentProcessor()->getSampleRate());
                }
            }

            return;
        }

6 And last add following method declaration to the publics of juce_AudioProcessorGraph.h

// modification for MIDI output:
MidiBuffer* getCurrentMidiOutputBuffer();

and the corresponding implementation in juce_AudioProcessorGraph.cpp:

// modification for MIDI output:
MidiBuffer* AudioProcessorGraph::getCurrentMidiOutputBuffer() {
  if (isUsingDoublePrecision()) {
    if (renderSequenceDouble != nullptr) {
        return &renderSequenceDouble->currentMidiOutputBuffer;
    } else {
        return nullptr;
    }
} else {
    if (renderSequenceFloat != nullptr) {
        return &renderSequenceFloat->currentMidiOutputBuffer;
    } else {
        return nullptr;
    }
  }
}

After building and starting the plugin host you should now have a MIDI output. Draw a connection between midi input and midi output. If you have selected a midiout device in the audiosettings (e.g Microsft GS Wavetable Synth in windows) you should now here a piano when playing on the midikeyboard (or see the MIDI Out LED blink if you selected a physical MIDI interface).

Note from original instructions (which I would not necessarily recommend, especially if it involves copying and pasting a lot of JUCE library code, which then has to be maintained to keep track with the changes that are being made to JUCE), added here for the sake of completeness:

If you’re more into copy & paste programming you could instead of modifying the two [now three] juce files create a “midiout processor” by subclassing juce_AudioProcessor. But I leave that as an excersise for the reader…

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