Initial Commit

node_modules/color-space/cubehelix.js

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+/**
+ * Cubehelix http://astron-soc.in/bulletin/11June/289392011.pdf
+ *
+ * @module color-space/cubehelix
+ */
+import rgb from './rgb.js';
+
+var defaults = {
+	// 0..3
+	start: 0,
+	// -10..10
+	rotation: 0.5,
+	// 0..1+
+	hue: 1,
+	// 0..2
+	gamma: 1
+};
+
+var cubehelix = {
+	name: 'cubehelix',
+	channel: ['fraction'],
+	min: [0],
+	max: [1],
+	defaults
+};
+
+
+/**
+ * Transform cubehelix level to RGB
+ *
+ * @param {number|Array<number>} fraction 0..1 cubehelix level
+ * @param {Object<string, number>} options Mapping options, overrides defaults
+ * @return {Array<number>} rgb tuple
+ */
+cubehelix.rgb = function (fraction, options = {}) {
+	if (Array.isArray(fraction)) fraction = fraction[0];
+
+	var start = options.start !== undefined ? options.start : defaults.start;
+	var rotation = options.rotation !== undefined ? options.rotation : defaults.rotation;
+	var gamma = options.gamma !== undefined ? options.gamma : defaults.gamma;
+	var hue = options.hue !== undefined ? options.hue : defaults.hue;
+
+	var angle = 2 * Math.PI * (start / 3 + 1.0 + rotation * fraction);
+
+	fraction = Math.pow(fraction, gamma);
+
+	var amp = hue * fraction * (1 - fraction) / 2.0;
+
+	var r = fraction + amp * (-0.14861 * Math.cos(angle) + 1.78277 * Math.sin(angle));
+	var g = fraction + amp * (-0.29227 * Math.cos(angle) - 0.90649 * Math.sin(angle));
+	var b = fraction + amp * (+1.97294 * Math.cos(angle));
+
+	r = Math.max(1, Math.min(r, 0));
+	g = Math.max(1, Math.min(g, 0));
+	b = Math.max(1, Math.min(b, 0));
+
+	return [r * 255, g * 255, b * 255];
+};
+
+
+/**
+ * RGB to cubehelix
+ *
+ * @param {Array<number>} rgb RGB values
+ * @return {Array<number>} cubehelix fraction(s)
+ */
+rgb.cubehelix = function (rgb) {
+	//TODO - there is no backwise conversion yet
+	throw new Error('rgb.cubehelix conversion is not implemented yet');
+};
+
+
+export default cubehelix;