09.midi.md

# MIDI I/O

In PureData there are objects to handle interfacing with a machines MIDI device.

heavy doesn't provide cross-platform implementation for MIDI I/O as the requirements tend to change depending on the platform or framework being used.

Instead, it provides wrappers around these objects that route the data to specific hard-coded receivers/parameters in the patch context. For example a [notein] object will be replaced by a [r __hv_notein] receiver with input data split into its constituent parts and routed to the appropriate outlet.

[notein] wrapper implementation:

Inputs

The following Pd objects are mapped to their corresponding heavy parameter.

Pd object	heavy param
[notein]	__hv_notein
[ctlin]	__hv_ctlin
[pgmin]	__hv_pgmin
[bendin]	__hv_bendin
[touchin]	__hv_touchin

Outputs

The same principle applies for sending MIDI data out of the heavy context. If you add a [noteout] object there'll be a corresponding sendhook callback with a message containing the MIDI data sent by the patch.

Pd object	heavy sendhook
[noteout]	__hv_noteout
[ctlout]	__hv_ctlout
[pgmout]	__hv_pgmout
[bendout]	__hv_bendout
[touchout]	__hv_touchout

Note!

It is generally the users responsibility to convert to and from the MIDI byte data to the float values used by heavy.

Some framework targets like vst2 already have implementations available. However, if you're integrating the C/C++ code on a custom platform then you'll need to provide your own conversion process.

Here's the vst2 implementation as an example:

VstInt32 HeavyVst2_sine::processEvents(VstEvents* events) {
  for (int i = 0; i < events->numEvents; ++i) {
    VstEvent *vste = events->events[i];
    switch (vste->type) {
      case kVstMidiType: {
        VstMidiEvent *vstme = (VstMidiEvent *) vste;

        const unsigned char command = vstme->midiData[0] & 0xF0;
        const unsigned char channel = vstme->midiData[0] & 0x0F;
        const unsigned char data0   = vstme->midiData[1] & 0x7F;
        const unsigned char data1   = vstme->midiData[2] & 0x7F;

        hv_uint32_t receiverHash = 0;
        switch (command) {
          case 0x80:   // note off
          case 0x90: { // note on
            receiverHash = 0x67E37CA3; // __hv_notein
            break;
          }
          case 0xB0: { // control change
            receiverHash = 0x41BE0F9C; // __hv_ctlin
            break;
          }
          default: continue;
        }

        _context->sendMessageToReceiverV(receiverHash, 1000.0*vste->deltaFrames/sampleRate, "fffff",
            (float) data1,
            (float) data0,
            (float) channel,
            (float) command,
            0.0f // port
        );
        break;
      }
      case kVstSysExType: {
        // not handling this case at the moment, VstMidiSysexEvent *vstmse;
        break;
      }
      default: break;
    }
  }
  return 1;
}