hue-module/lib/colors.js

A client library for interacting with the Philips Hue lighting products

/**
 * Color utility functions.
 * No external dependencies.
 * Rewritten for use as a node.js module.
 * Special thanks for the RGB to CIE conversion code goes out to the Q42 team
 * for their Q42.HueApi work. Dank u!
 * More info: https://github.com/Q42/Q42.HueApi.
 *
 * https://github.com/bjohnso5/hue-hacking
 * Copyright (c) 2013 Bryan Johnson; Licensed MIT */

var XYPoint = function(x, y) {
		this.x = x;
		this.y = y;
	},
	Red = new XYPoint(0.675, 0.322),
	Lime = new XYPoint(0.4091, 0.518),
	Blue = new XYPoint(0.167, 0.04);

exports.rgbToCIE1931 = function(red, green, blue) {
	var point = _getXYPointFromRGB(red, green, blue);
	return [point.x, point.y];
};


function _randomFromInterval(from /* Number */ , to /* Number */ ) {
	return Math.floor(Math.random() * (to - from + 1) + from);
}

function _randomRGBValue() {
	return _randomFromInterval(0, 255);
}

function _crossProduct(p1, p2) {
	return (p1.x * p2.y - p1.y * p2.x);
}

function _checkPointInLampsReach(p) {
	var v1 = new XYPoint(Lime.x - Red.x, Lime.y - Red.y),
		v2 = new XYPoint(Blue.x - Red.x, Blue.y - Red.y),
		q = new XYPoint(p.x - Red.x, p.y - Red.y),
		s = _crossProduct(q, v2) / _crossProduct(v1, v2),
		t = _crossProduct(v1, q) / _crossProduct(v1, v2);
	return (s >= 0.0) && (t >= 0.0) && (s + t <= 1.0);
}

function _getClosestPointToPoint(A, B, P) {
	var AP = new XYPoint(P.x - A.x, P.y - A.y),
		AB = new XYPoint(B.x - A.x, B.y - A.y),
		ab2 = AB.x * AB.x + AB.y * AB.y,
		ap_ab = AP.x * AB.x + AP.y * AB.y,
		t = ap_ab / ab2;
	if (t < 0.0) t = 0.0;
	else if (t > 1.0) t = 1.0;
	return new XYPoint(A.x + AB.x * t, A.y + AB.y * t);
}

function _getDistanceBetweenTwoPoints(one, two) {
	var dx = one.x - two.x,
		// horizontal difference
		dy = one.y - two.y; // vertical difference
	return Math.sqrt(dx * dx + dy * dy);
}

function _getXYPointFromRGB(red, green, blue) {
	var r = (red > 0.04045) ? Math.pow((red + 0.055) / (1.0 + 0.055), 2.4) : (red / 12.92),
		g = (green > 0.04045) ? Math.pow((green + 0.055) / (1.0 + 0.055), 2.4) : (green / 12.92),
		b = (blue > 0.04045) ? Math.pow((blue + 0.055) / (1.0 + 0.055), 2.4) : (blue / 12.92),
		X = r * 0.4360747 + g * 0.3850649 + b * 0.0930804,
		Y = r * 0.2225045 + g * 0.7168786 + b * 0.0406169,
		Z = r * 0.0139322 + g * 0.0971045 + b * 0.7141733,
		cx = X / (X + Y + Z),
		cy = Y / (X + Y + Z);
	cx = isNaN(cx) ? 0.0 : cx;
	cy = isNaN(cy) ? 0.0 : cy;
	//Check if the given XY value is within the colourreach of our lamps.
	var xyPoint = new XYPoint(cx, cy),
		inReachOfLamps = _checkPointInLampsReach(xyPoint);
	if (!inReachOfLamps) {
		//Color is unreproducible, find the closest point on each line in the CIE 1931 'triangle'.
		var pAB = _getClosestPointToPoint(Red, Lime, xyPoint),
			pAC = _getClosestPointToPoint(Blue, Red, xyPoint),
			pBC = _getClosestPointToPoint(Lime, Blue, xyPoint),
			// Get the distances per point and see which point is closer to our Point.
			dAB = _getDistanceBetweenTwoPoints(xyPoint, pAB),
			dAC = _getDistanceBetweenTwoPoints(xyPoint, pAC),
			dBC = _getDistanceBetweenTwoPoints(xyPoint, pBC),
			lowest = dAB,
			closestPoint = pAB;
		if (dAC < lowest) {
			lowest = dAC;
			closestPoint = pAC;
		}
		if (dBC < lowest) {
			lowest = dBC;
			closestPoint = pBC;
		}
		// Change the xy value to a value which is within the reach of the lamp.
		cx = closestPoint.x;
		cy = closestPoint.y;
	}

	return new XYPoint(cx, cy);
}