41 lines
944 B
JavaScript
41 lines
944 B
JavaScript
/*
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Convert a RGB color to the Cubehelix HSL color space.
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This computation is not present in Green's paper:
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https://arxiv.org/pdf/1108.5083.pdf
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...but can be derived from the inverse, HSL to RGB conversion.
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It matches the math in Mike Bostock's D3 implementation:
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https://github.com/d3/d3-color/blob/master/src/cubehelix.js
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*/
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import { radToDeg, M } from './constants.js';
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let DE = M[3] * M[4];
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let BE = M[1] * M[4];
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let BCAD = M[1] * M[2] - M[0] * M[3];
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const convertRgbToCubehelix = ({ r, g, b, alpha }) => {
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let l = (BCAD * b + r * DE - g * BE) / (BCAD + DE - BE);
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let x = b - l;
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let y = (M[4] * (g - l) - M[2] * x) / M[3];
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let res = {
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mode: 'cubehelix',
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l: l,
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s:
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l === 0 || l === 1
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? undefined
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: Math.sqrt(x * x + y * y) / (M[4] * l * (1 - l))
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};
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if (res.s) res.h = Math.atan2(y, x) * radToDeg - 120;
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if (alpha !== undefined) res.alpha = alpha;
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return res;
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};
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export default convertRgbToCubehelix;
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