MIDI Processors

MIDI Processors are objects which can manipulate the content of a MIDIMessage.

The abstract class MIDIProcessor defines basically an object which has a bool MIDIProcessor::Process(MIDITimedMessage* msg) method, which takes a pointer to a MIDITimedMessage as argument: it can change or inspect the message and returns an answer yes/no. Some subclasses are already built in the library:

• The MIDIProcessorTransposer transposes all note and polyphonic pressure messages by a given amount of semitones
• The MIDIProcessorRechannelizer remaps channel messages to a given channel map
• The MIDIProcessorPrinter prints the contents of the messages in a readable form
• The MIDIMultiProcessor allows to queue many MIDIProcessors giving each one the results of the previous
• The MIDISequencerTrackProcessor is a special multipurpose processor used by the AdvancedSequencer class

Many classes (see MIDIInDriver, MIDIOutDriver, MIDIThru, MIDISequencer) have a SetProcessor() method that allows the user to "plug in" a processor in their flow of incoming-outcoming messages. This is an example which could be useful for debugging purposes: plugging a MIDIProcessorPrinter to a MIDIInDriver will print all incoming messages.

#include "manager.h"                    // includes driver.h and timer.h
#include "processor.h"
 
int main() {
   MIDIInDriver* driver = MIDIManager::GetInDriver(0);
                // this is the MIDI IN port 0 in your system
   MIDIProcessorPrinter printer;        // creates a printer processor
   driver->SetProcessor(&printer);      // plugs the printer into the driver
   driver->OpenPort();                  // starts receiving messages
   MIDITimer::Wait(20000);
                // waits 20 secs: you can play with a MIDI device connected to the port
                // and the incoming messages will be printed on stdout
   driver->ClosePort();                 // closes the port
   return 0;
}

This is another example using the MIDIThru class.

 #include "manager.h"                    // includes driver.h and timer.h
 #include "thru.h"
 
 int main() {
    MIDIThru thru;                       // creates a thru object. It receives and sends
                                         // messages on MIDI IN and OUT ports 0 in your system
    MIDIProcessorTransposer tr;          // creates a transposer processor
    thru.SetProcessor(tr);               // plugs the transposer into the thru
    tr.SetAllTranspose(12);              // set transposing up an octave on all channels
    MIDIManager::AddMIDITick(&thru);     // adds the thru to the MIDIManager queue
    thru.Start();                        // starts the thru
    MIDITimer::Wait(20000);
             // waits 20 secs: you can play with a MIDI device connected to the port
             // and the notes will sound one octave up
    thru.Stop();                         // stops the thru
    return 0;
}

A similar use of the MIDIProcessorPrinter is done in the test_thru.cpp example file.