hwb.js

/**
 * @module color-space/hwb
 */
import rgb from './rgb.js';
import hsv from './hsv.js';
import hsl from './hsl.js';


var hwb = {
	name: 'hwb',
	min: [0,0,0],
	max: [360,100,100],
	channel: ['hue', 'whiteness', 'blackness'],
	alias: ['HWB'],

	// http://dev.w3.org/csswg/css-color/#hwb-to-rgb
	rgb: function(hwb) {
		var h = hwb[0] / 360,
			wh = hwb[1] / 100,
			bl = hwb[2] / 100,
			ratio = wh + bl,
			i, v, f, n;

		var r, g, b;

		// wh + bl cant be > 1
		if (ratio > 1) {
			wh /= ratio;
			bl /= ratio;
		}

		i = Math.floor(6 * h);
		v = 1 - bl;
		f = 6 * h - i;

		//if it is even
		if ((i & 0x01) !== 0) {
			f = 1 - f;
		}

		n = wh + f * (v - wh);  // linear interpolation

		switch (i) {
			default:
			case 6:
			case 0: r = v; g = n; b = wh; break;
			case 1: r = n; g = v; b = wh; break;
			case 2: r = wh; g = v; b = n; break;
			case 3: r = wh; g = n; b = v; break;
			case 4: r = n; g = wh; b = v; break;
			case 5: r = v; g = wh; b = n; break;
		}

		return [r * 255, g * 255, b * 255];
	},


	// http://alvyray.com/Papers/CG/HWB_JGTv208.pdf
	hsv: function(arg){
		var h = arg[0], w = arg[1], b = arg[2], s, v;

		//if w+b > 100% - take proportion (how many times )
		if (w + b >= 100){
			s = 0;
			v = 100 * w/(w+b);
		}

		//by default - take wiki formula
		else {
			s = 100-(w/(1-b/100));
			v = 100-b;
		}


		return [h, s, v];
	},

	hsl: function(arg){
		return hsv.hsl(hwb.hsv(arg));
	}
};

export default hwb;


//extend rgb
rgb.hwb = function(val) {
	var r = val[0],
			g = val[1],
			b = val[2],
			h = rgb.hsl(val)[0],
			w = 1/255 * Math.min(r, Math.min(g, b));

			b = 1 - 1/255 * Math.max(r, Math.max(g, b));

	return [h, w * 100, b * 100];
};



//keep proper hue on 0 values (conversion to rgb loses hue on zero-lightness)
hsv.hwb = function(arg){
	var h = arg[0], s = arg[1], v = arg[2];
	return [h, v === 0 ? 0 : (v * (1-s/100)), 100 - v];
};


//extend hsl with proper conversions
hsl.hwb = function(arg){
	return hsv.hwb(hsl.hsv(arg));
};