WebMIDI vars & functions (WIP)

webMidiWrap.js

//  
// useful WebMIDI variables and functions
// 

//
// Chrome only; no iOS; does *not* incorporate shims
//


// Initialize WebMidi; create dropdown selector for output port

//
// HTML component:
// <select id="outputSelector" onchange="updatePort()">
//    <option value="null" selected>[none]</option>
// </select>
//

// access output selector
var outputSelector = document.querySelector('#outputSelector');

// empty var to hold "midiAccess" 
var midi; 

// empty var to hold selected MIDI output port ID
var mOutPort;

// initialize WebMIDI 
function onMIDISuccess( midiAccess ) {
  midi = midiAccess;  
  midi.outputs.forEach( 
  	function(port, key) {
    var portName = port.name;
    var portID = port.id;
    var option = document.createElement("option");
    option.setAttribute("value", portID);
    var textNode = document.createTextNode(portName);
    option.appendChild(textNode);
    outputSelector.appendChild(option);    
	});
}

navigator.requestMIDIAccess().then(onMIDISuccess);

// define output port upon selection
function updatePort() {
    var i = outputSelector.selectedIndex;
    mOutPort = outputSelector.options[i].value;
}

//
// create Web Audio context for access to more convenient timing functions
//

window.AudioContext = window.AudioContext || window.webkitAudioContext;
var audioContext = new AudioContext();

// set latency hint; conditional feature detection to prevent errors
if ("latencyHint" in audioContext) {
audioContext.latencyHint = "playback";
};

// define current time
var now = audioContext.currentTime;

// additional basic web audio variables
// var baseFreq = 440;
// var audioOut = audioContext.destination;


//
// useful midi variables
//

// set output channel
var midiChannel = 1; // 1-16

// define commands
// var noteOn = 0x90 + (midiChannel - 1);


// define tempo

var midiTempo = 120;

// define (note) pitches

// see note name to MIDI number conversion here:
// https://github.com/sole/MIDIUtils/blob/master/src/MIDIUtils.js
//
// additional note/frequency conversion algorithms:
// https://github.com/sole/MIDIUtils


// define velocities

var maxVel = 127;
var midVel = 64;
var muteVel = 0;

// define durations 
// n4 = quarter note; t4 = quarter-note triplet; m4 = four measures 
// timing in ms (60000 = 60s)

var n4 = (60000 / midiTempo);  
var n1 = n4 * 4;
var n2 = n4 * 2;
var n8 = n4 / 2;
var n16 = n4 / 4;
var n32 = n4 / 8;  
var t4 = (40000 / midiTempo);
var t2 = t4 * 2;
var t8 = t4 / 2;
var t16 = t4 / 4;  
var t32 = t4 / 8;  
var m1 = n4 * 4;  
var m2 = m1 * 2;  
var m4 = m1 * 4;  
var m8 = m1 * 8;  

// add dotted durations?
//

// define midi messages; [command, data1, data2]
// var midiNoteBegin = [noteOn, midiNote, midiVel];
// var midiNoteEnd = [noteOn, midiNote, midiVel];


// midi -- single note function

function sendMidiNote( note, vel, dur ) {
 var noteOn = 0x90 + (midiChannel - 1);
 var noteOff = 0x80 + (midiChannel - 1);	
 var midiNoteBegin = [noteOn, note, vel];
 var midiNoteEnd = [noteOff, note, muteVel];  
 var midiNoteEndAlt = [noteOn, note, muteVel];  

	
 var output = midi.outputs.get(mOutPort);

  output.send(midiNoteBegin);  
  output.send(midiNoteEnd, now + dur); 

//
// optionally include a safety margin/buffer;
// var safety = 150; // 150ms
//
// output.send(midiNoteBegin, now + safety);
// output.send(midiNoteEnd, now + safety + dur);
//	
}

// use above function with MIDI note number, velocity (0-127), and duration;
// example -- A4 (440Hz), quarter note, at a velocity of 127,
// sendMidiNote(69, maxVel, n4);

//
// TODO fundamentals: 
// add more MIDI commands;
// add clock input/output; 
// add queue/scheduler (via Tale of Two Clocks); 
// add chord player function; 
// add scale creator w/ MIDI pitches/notes; 
// add roman numeral chord progression vars; 
// add (global) chord progression player; 
// add melody generator/arpeggiator; 
// add chord comp generator; 
// add bassline generator; 
// add polyrhythm creator; 
// add composition-structure manager; 
// add chaining methods; 
// add percussion player; 
// add percussion generator/controller; 
// add LFO(s); 
// add more durations; 
// add MIDI tuning adjuster; 
// add MIDI-to-freq func; 
// add method to create html dropdown component in js;
//
// TODO abstractions:
// reich pulse (w/ volume swells)
// drone gen 
// "black midi"
// interlocking gens 
// CC controllers/gens 
// game of life 
// stats-based gens 
// buffer manipulation via midi 
// midi jitter-er (input/output)
// hyper-fast, super-quiet, pseudo-pads
// responsive methods -- ie chord gens that dynamically react to external impetus
//


// random value generator
// The returned value is no lower than (and may possibly equal) min, 
// and is less than (but not equal to) max.

function randRange(min, max) {
  return Math.random() * (max - min) + min;
}

// optional functions to convert frequencies to MIDI notes

// log function for MIDI converstion
	function getBaseLog(value, base) {
		return Math.log(value) / Math.log(base);
	}

// Frequency to Midi Note Number
	function freqNote(f) {
		return Math.round(12.0 * getBaseLog(f / baseFreq, 2) + 69);
	}