PiClient.js

var ws281x = require('rpi-ws281x-native');

var NUM_LEDS = parseInt(process.argv[2], 10) || 8,
    pixelData = new Uint32Array(NUM_LEDS);

var brightness = 128;

ws281x.init(NUM_LEDS);


var lightsOff = function () {
    for (var i = 0; i < NUM_LEDS; i++) {
        pixelData[i] = color(0, 0, 0);
    }
    ws281x.render(pixelData);
    ws281x.reset();
}

var signals = {
    'SIGINT': 2,
    'SIGTERM': 15
};

function shutdown(signal, value) {
    console.log('Stopped by ' + signal);
    lightsOff();
    process.nextTick(function () { process.exit(0); });
}

Object.keys(signals).forEach(function (signal) {
    process.on(signal, function () {
        shutdown(signal, signals[signal]);
    });
});

// ---- animation-loop
var offset = 0;
setInterval(function () {
    for (var i = 0; i < NUM_LEDS; i++) {
        pixelData[i] = wheel(((i * 256 / NUM_LEDS) + offset) % 256);
    }

    offset = (offset + 1) % 256;
    ws281x.render(pixelData);
}, 1000 / 30);

console.log('Rainbow started. Press <ctrl>+C to exit.');

// generate rainbow colors accross 0-255 positions.
function wheel(pos) {
    pos = 255 - pos;
    if (pos < 85) { return color(255 - pos * 3, 0, pos * 3); }
    else if (pos < 170) { pos -= 85; return color(0, pos * 3, 255 - pos * 3); }
    else { pos -= 170; return color(pos * 3, 255 - pos * 3, 0); }
}

// generate integer from RGB value
function color(r, g, b) {
    r = r * brightness / 255;
    g = g * brightness / 255;
    b = b * brightness / 255;
    return ((r & 0xff) << 16) + ((g & 0xff) << 8) + (b & 0xff);
}