chord_speller.js

var ChordSpeller = {
    chord: {}, // this represents the cord the user is holding down. map[string] -> int
    chordView: null, // cached chord view
    self: this,
    init: function() {
        console.log("requesting MIDI access");
        if (navigator.requestMIDIAccess) {
            navigator.requestMIDIAccess({
                sysex: false
            }).then(ChordSpeller.onMIDISuccess, ChordSpeller.onMIDIFailure);
        } else {
            alert("No MIDI support in your browser.");
        }

        return;
    },

    onMIDIMessage: function(event) {
        console.log(event.data)
        switch (event.data[0] & 0xf0) {
        case 0x90:
            if (event.data[2]!=0) {  // if velocity != 0, this is a note-on message
                ChordSpeller.noteOn(event.data[1]);
                return;
            }
            // if velocity == 0, fall thru: it's a note-off.  MIDI's weird, y'all.
        case 0x80:
            ChordSpeller.noteOff(event.data[1]);
            return;
        }
    },

    onMIDIFailure: function(error) {
        // when we get a failed response, run this code
        console.log("No access to MIDI devices or your browser doesn't support WebMIDI API. Please use WebMIDIAPIShim " + error);
    },

    // midi functions
    onMIDISuccess: function(midiAccess) {
        midi = midiAccess;

        var inputs = midi.inputs.values();
        // loop over all available inputs and listen for any MIDI input
        for (var input = inputs.next(); input && !input.done; input = inputs.next()) {
            // each time there is a midi message call the onMIDIMessage function
            console.log("detected input: " + input.value.manufacturer + " " + input.value.name);
            input.value.onmidimessage = ChordSpeller.onMIDIMessage;
        }
    },

    noteNumberToLetter: function(noteNumber, bias) {
        if (bias === null){
            bias = "#";
        }

        switch (noteNumber % 12) {
        case 0:
            return "C"+bias;
            break;
        case 1:
            return "C#"+bias;
            break;
        case 2:
            return "D"+bias;
            break;
        case 3:
            return "D#"+bias;
            break;
        case 4:
            return "E"+bias;
            break;
        case 5:
            return "F"+bias;
            break;
        case 6:
            return "F#"+bias;
            break;
        case 7:
            return "G"+bias;
            break;
        case 8:
            return "G#"+bias;
            break;
        case 9:
            return "A"+bias;
            break;
        case 10:
            return "A#"+bias;
            break;
        case 11:
            return "B"+bias;
            break;
        default:
            console.log("math is broken");
            break;
        }
    },

    MIDIMessageEventHandler: function (event) {
        // Mask off the lower nibble (MIDI channel, which we don't care about)
        switch (event.data[0] & 0xf0) {
        case 0x90:
            if (event.data[2]!=0) {  // if velocity != 0, this is a note-on message
                noteOn(event.data[1]);
                return;
            }
            // if velocity == 0, fall thru: it's a note-off.  MIDI's weird, y'all.;
        case 0x80:
            noteOff(event.data[1]);
            return;
        }
    },

    renderChord: function() {
        console.log(ChordSpeller.chord)
        if (this.chordView === null) {
            this.chordView = document.getElementById('chord');
        }
        this.chordView.innerHTML = Object.keys(this.chord).join(" ");
    },

    addToChord: function(noteNumber) {
        name = ChordSpeller.noteNumberToLetter(noteNumber);
        ChordSpeller.chord[name] = true; // TODO store velocity instead
        ChordSpeller.renderChord();
    },

    removeFromChord: function(noteNumber) {
        name = ChordSpeller.noteNumberToLetter(noteNumber);
        delete ChordSpeller.chord[name];
        ChordSpeller.renderChord();
    },

    noteOn: function(noteNumber) {
        return this.addToChord(noteNumber);
    },
    noteOff: function(noteNumber) {
        return this.removeFromChord(noteNumber);
    },

}