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frontend/node_modules/culori/src/cubehelix/definition.js

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+/* 
+	Dave Green's Cubehelix
+	----------------------
+
+	Green, D. A., 2011, "A colour scheme for the display of astronomical intensity images", 
+	Bulletin of the Astronomical Society of India, 39, 289. (2011BASI...39..289G at ADS.) 
+
+	https://www.mrao.cam.ac.uk/%7Edag/CUBEHELIX/
+	https://arxiv.org/pdf/1108.5083.pdf
+
+	Although Cubehelix was defined to be a method to obtain a colour scheme,
+	it actually contains a definition of a colour space, as identified by 
+	Mike Bostock and implemented in D3.js.
+
+	Green's paper introduces the following terminology:
+
+	* 	a `lightness` dimension in the interval [0, 1] 
+		on which we interpolate to obtain the colour scheme
+	*	a `start` colour that is analogous to a Hue in HSL space
+	*	a number of `rotations` around the Hue cylinder.
+	*	a `hue` parameter which should more appropriately be called `saturation`
+	
+	As such, the original definition of the Cubehelix scheme is actually an
+	interpolation between two colors in the Cubehelix space:
+
+	H: start 				H: start + 360 * rotations
+	S: hue 			->		S: hue
+	L: 0					L: 1
+
+	We can therefore extend the interpolation to any two colors in this space,
+	with a variable Saturation and a Lightness interval other than the fixed 0 -> 1.
+*/
+
+import { fixupHueShorter } from '../fixup/hue.js';
+import { fixupAlpha } from '../fixup/alpha.js';
+import { interpolatorLinear } from '../interpolate/linear.js';
+import convertRgbToCubehelix from './convertRgbToCubehelix.js';
+import convertCubehelixToRgb from './convertCubehelixToRgb.js';
+import { differenceHueSaturation } from '../difference.js';
+import { averageAngle } from '../average.js';
+
+const definition = {
+	mode: 'cubehelix',
+	channels: ['h', 's', 'l', 'alpha'],
+	parse: ['--cubehelix'],
+	serialize: '--cubehelix',
+
+	ranges: {
+		h: [0, 360],
+		s: [0, 4.614],
+		l: [0, 1]
+	},
+
+	fromMode: {
+		rgb: convertRgbToCubehelix
+	},
+
+	toMode: {
+		rgb: convertCubehelixToRgb
+	},
+
+	interpolate: {
+		h: {
+			use: interpolatorLinear,
+			fixup: fixupHueShorter
+		},
+		s: interpolatorLinear,
+		l: interpolatorLinear,
+		alpha: {
+			use: interpolatorLinear,
+			fixup: fixupAlpha
+		}
+	},
+
+	difference: {
+		h: differenceHueSaturation
+	},
+
+	average: {
+		h: averageAngle
+	}
+};
+
+export default definition;