/**

* HWB — Hue, Whiteness, Blackness, devised by Alvy Ray Smith in 1996 as an even more

* intuitive alternative to HSV for humans mixing colors by hand. Instead of

* saturation and value, it describes a color as a pure hue diluted with some amount

* of white and some amount of black, mirroring how painters think about tinting and

* shading a pigment. It is standardized in CSS Color 4 as the `hwb()` notation.

*

* @see {@link https://www.w3.org/TR/css-color-4/#the-hwb-notation}

* @wiki {@link https://en.wikipedia.org/wiki/HWB_color_model}

* @year 1996

* @by Alvy Ray Smith

* @use Intuitive tint/shade color picking; current, standardized as CSS Color 4's hwb().

* @channel {H} 0 360 Hue angle in degrees

* @channel {W} 0 100 Whiteness percentage

* @channel {B} 0 100 Blackness percentage

* @method cylindrical

* @encoding gamma

* @referred display

* @dynamic sdr

*/

import rgb from './rgb.js';

import hsv from './hsv.js';

import hsl from './hsl.js';

var hwb = {

name: 'hwb',

range: [[0, 360], [0, 100], [0, 100]],

rgb: function (h, wh, bl) {

// Convert from H: 0-360, W/B: 0-100 to normalized

h = h / 360;

wh = wh / 100;

bl = bl / 100;

var ratio = wh + bl,

i, v, f, n;

var r, g, b;

// white + black >= 1 is achromatic: an EXACT gray = white / (white + black),

// per CSS Color 4. Computing it through the sector machinery below instead

// (v = 1 - bl vs wh) leaves ~1e-14 residue between the channels, which any

// downstream hue read (rgb -> hsv / hsl) amplifies into a random hue — so the

// neighbouring hue sliders jump as whiteness is dragged past this point.

// @see https://www.w3.org/TR/css-color-4/#hwb-to-rgb

if (ratio >= 1) {

var gray = wh / ratio * 255;

return [gray, gray, gray];

}

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;

}

// Scale to 0-255

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

},

// http://alvyray.com/Papers/CG/HWB_JGTv208.pdf

hsv: function (h, w, b) {

// Convert from H: 0-360, W/B: 0-100

w = w / 100;

b = b / 100;

var s, v;

//if w+b > 100% - take proportion (how many times )

if (w + b >= 1) {

s = 0;

v = w / (w + b);

}

//by default - take wiki formula

else {

s = 1 - (w / (1 - b));

v = 1 - b;

}

// Output: H: 0-360, S/V: 0-100

return [h, s * 100, v * 100];

},

hsl: function (h, w, b) {

return hsv.hsl(...hwb.hsv(h, w, b));

}

};

export default (hwb);

// extend rgb

rgb.hwb = function (r, g, b) {

// Normalize from 0-255 to 0-1

r = r / 255;

g = g / 255;

b = b / 255;

var h = rgb.hsl(r * 255, g * 255, b * 255)[0],

w = Math.min(r, Math.min(g, b));

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

// Output: H: 0-360, W/B: 0-100

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

};

// keep proper hue on 0 values (conversion to rgb loses hue on zero-lightness)

hsv.hwb = function (h, s, v) {

// Input/Output: H: 0-360, S/V/W/B: 0-100

s = s / 100;

v = v / 100;

return [h, (v === 0 ? 0 : (v * (1 - s))) * 100, (1 - v) * 100];

};

//extend hsl with proper conversions

hsl.hwb = function (h, s, l) {

return hsv.hwb(...hsl.hsv(h, s, l));

};