Getting music to play on key presses

[mobyvb]

Ok here's what I'm thinking

We need some sort of mapping from keyboard keys to notes. This will look something like:

var noteMap = {
  65: 'C5', // a
  83: 'D5', // s
  68: 'E5', // d
  70: 'F5' // f
}

We can add more later but this should be good for now.

We also need some sort of data structure for storing the current notes played by users:

var userNotes = {
  '0hFf738zgw5yzQsEAAAD': {
    65: someAudiobuffer // this means "a" is currently pressed for this user, and contains the note being played
  }
}

Now comes the more complicated task of

1. Receiving the updated keys from the server
2. Checking to see if any new keys are pressed, and starting the corresponding notes
3. Checking to see if any keys are no longer pressed, and stopping the corresponding notes

We can get a note right now by typing var note = getAudioBuffer(someNote, someInstrument);
To start playing that note, we call note.start(); and to stop playing we call note.stop();.

In our keysUpdated listener we might have something like this:

socket.on('keysUpdated', function(keyData) {
  var id = keyData.id;
  if (!userNotes[id]) {
    userNotes[id] = {};
  }
  var currentKeysPressed = userNotes[id];
  var currentKeysPressedArr = Object.keys(currentKeysPressed);
  var newKeysPressed = keyData.keysPressed;
  var newKeysPressedArr = Object.keys(newKeysPressed);

  for (var key in currentKeysPressedArr) {
    if (!newKeysPressed[key]) {
      currentKeysPressed[key].stop(); // stop note, key was released
      delete currentKeysPressed[key];
    }
  }

  for (var key in newKeysPressedArr) {
    if (!currentKeysPressed[key] && noteMap[key]) {
      var newNote = getAudioBuffer(noteMap[key], grandPianoBuffers);
      currentKeysPressed[key] = newNote;
      newNote.start(); // start note, key was pressed
    }
  }
});