@antv/g2
Version:
the Grammar of Graphics in Javascript
48 lines • 1.62 kB
JavaScript
import { maxIndex } from 'd3-array';
import { parseToRGB } from '../utils/color';
function getsRGB(s) {
let c = s / 255;
c = c <= 0.03928 ? c / 12.92 : Math.pow((c + 0.055) / 1.055, 2.4);
return c;
}
function getL(r, g, b) {
return 0.2126 * getsRGB(r) + 0.7152 * getsRGB(g) + 0.0722 * getsRGB(b);
}
/**
* Calculate the contrast. see https://webaim.org/resources/contrastchecker/
* @param foreground
* @param background
*/
function contrast(foreground, background) {
const { r, g, b } = foreground;
const { r: rb, g: gb, b: bb } = background;
const L1 = getL(r, g, b);
const L2 = getL(rb, gb, bb);
return (Math.max(L1, L2) + 0.05) / (Math.min(L1, L2) + 0.05);
}
/**
* Reverse color for max contrast.
*/
function mostContrast(color, palette) {
const i = maxIndex(palette, (c) => contrast(color, parseToRGB(c)));
return palette[i];
}
/**
* Reverse the label color when the contrast is lower then `threshold`.
* The default value of `threshold` is 4.5.
* More about contract, see https://webaim.org/resources/contrastchecker/
*/
export const ContrastReverse = (options) => {
const { threshold = 4.5, palette = ['#000', '#fff'] } = options;
return (labels) => {
labels.forEach((l) => {
const background = l.attr('dependentElement').parsedStyle.fill;
const foreground = l.parsedStyle.fill;
const c = contrast(foreground, background);
if (c < threshold)
l.attr('fill', mostContrast(background, palette));
});
return labels;
};
};
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