chroma-js/src/interpolator/_hsx.js

JavaScript library for color conversions

const Color = require('../Color');

module.exports = (col1, col2, f, m) => {
    let xyz0, xyz1;
    if (m === 'hsl') {
        xyz0 = col1.hsl();
        xyz1 = col2.hsl();
    } else if (m === 'hsv') {
        xyz0 = col1.hsv();
        xyz1 = col2.hsv();
    } else if (m === 'hcg') {
        xyz0 = col1.hcg();
        xyz1 = col2.hcg();
    } else if (m === 'hsi') {
        xyz0 = col1.hsi();
        xyz1 = col2.hsi();
    } else if (m === 'lch' || m === 'hcl') {
        m = 'hcl';
        xyz0 = col1.hcl();
        xyz1 = col2.hcl();
    }

    let hue0, hue1, sat0, sat1, lbv0, lbv1;
    if (m.substr(0, 1) === 'h') {
        [hue0, sat0, lbv0] = xyz0;
        [hue1, sat1, lbv1] = xyz1;
    }

    let sat, hue, lbv, dh;

    if (!isNaN(hue0) && !isNaN(hue1)) {
        // both colors have hue
        if (hue1 > hue0 && hue1 - hue0 > 180) {
            dh = hue1-(hue0+360);
        } else if (hue1 < hue0 && hue0 - hue1 > 180) {
            dh = hue1+360-hue0;
        } else{
            dh = hue1 - hue0;
        }
        hue = hue0 + f * dh;
    } else if (!isNaN(hue0)) {
        hue = hue0;
        if ((lbv1 == 1 || lbv1 == 0) && m != 'hsv') sat = sat0;
    } else if (!isNaN(hue1)) {
        hue = hue1;
        if ((lbv0 == 1 || lbv0 == 0) && m != 'hsv') sat = sat1;
    } else {
        hue = Number.NaN;
    }

    if (sat === undefined) sat = sat0 + f * (sat1 - sat0);
    lbv = lbv0 + f * (lbv1-lbv0)
    return new Color([hue, sat, lbv], m);
}