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Code Issues Releases Wiki Activity

Use WCAG contrast algo (#30168)

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This commit is contained in:
Gaël Poupard
2020-03-23 18:03:56 +01:00
committed by GitHub
parent 2e150e722a
commit 03908ea37a
7 changed files with 155 additions and 116 deletions
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41
scss/_functions.scss
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@@ -88,14 +88,43 @@
}
// Color contrast
@function color-yiq($color, $dark: $yiq-text-dark, $light: $yiq-text-light) {
$r: red($color);
$g: green($color);
$b: blue($color);
// See https://github.com/twbs/bootstrap/pull/30168
$yiq: (($r * 299) + ($g * 587) + ($b * 114)) / 1000;
// A list of pre-calculated numbers of pow(($value / 255 + .055) / 1.055, 2.4). (from 0 to 255)
// stylelint-disable-next-line scss/dollar-variable-default, scss/dollar-variable-pattern
$_luminance-list: .0008 .001 .0011 .0013 .0015 .0017 .002 .0022 .0025 .0027 .003 .0033 .0037 .004 .0044 .0048 .0052 .0056 .006 .0065 .007 .0075 .008 .0086 .0091 .0097 .0103 .011 .0116 .0123 .013 .0137 .0144 .0152 .016 .0168 .0176 .0185 .0194 .0203 .0212 .0222 .0232 .0242 .0252 .0262 .0273 .0284 .0296 .0307 .0319 .0331 .0343 .0356 .0369 .0382 .0395 .0409 .0423 .0437 .0452 .0467 .0482 .0497 .0513 .0529 .0545 .0561 .0578 .0595 .0612 .063 .0648 .0666 .0685 .0704 .0723 .0742 .0762 .0782 .0802 .0823 .0844 .0865 .0887 .0908 .0931 .0953 .0976 .0999 .1022 .1046 .107 .1095 .1119 .1144 .117 .1195 .1221 .1248 .1274 .1301 .1329 .1356 .1384 .1413 .1441 .147 .15 .1529 .1559 .159 .162 .1651 .1683 .1714 .1746 .1779 .1812 .1845 .1878 .1912 .1946 .1981 .2016 .2051 .2086 .2122 .2159 .2195 .2232 .227 .2307 .2346 .2384 .2423 .2462 .2502 .2542 .2582 .2623 .2664 .2705 .2747 .2789 .2831 .2874 .2918 .2961 .3005 .305 .3095 .314 .3185 .3231 .3278 .3325 .3372 .3419 .3467 .3515 .3564 .3613 .3663 .3712 .3763 .3813 .3864 .3916 .3968 .402 .4072 .4125 .4179 .4233 .4287 .4342 .4397 .4452 .4508 .4564 .4621 .4678 .4735 .4793 .4851 .491 .4969 .5029 .5089 .5149 .521 .5271 .5333 .5395 .5457 .552 .5583 .5647 .5711 .5776 .5841 .5906 .5972 .6038 .6105 .6172 .624 .6308 .6376 .6445 .6514 .6584 .6654 .6724 .6795 .6867 .6939 .7011 .7084 .7157 .7231 .7305 .7379 .7454 .7529 .7605 .7682 .7758 .7835 .7913 .7991 .807 .8148 .8228 .8308 .8388 .8469 .855 .8632 .8714 .8796 .8879 .8963 .9047 .9131 .9216 .9301 .9387 .9473 .956 .9647 .9734 .9823 .9911 1;
@return if($yiq >= $yiq-contrasted-threshold, $dark, $light);
@function color-contrast($background, $color-contrast-dark: $color-contrast-dark, $color-contrast-light: $color-contrast-light) {
$l1: luminance($background);
$l2: luminance(opaque($background, $color-contrast-light));
$contrast: if($l1 > $l2, ($l1 + .05) / ($l2 + .05), ($l2 + .05) / ($l1 + .05));
@return if($contrast < $min-contrast-ratio, $color-contrast-dark, $color-contrast-light);
}
// Return WCAG2.0 relative luminance
// See https://www.w3.org/WAI/GL/wiki/Relative_luminance
// See https://www.w3.org/TR/WCAG20-TECHS/G17.html#G17-tests
@function luminance($color) {
$rgb: (
"r": red($color),
"g": green($color),
"b": blue($color)
);
@each $name, $value in $rgb {
$value: if($value / 255 < .03928, $value / 255 / 12.92, nth($_luminance-list, $value + 1));
$rgb: map-merge($rgb, ($name: $value));
}
@return (map-get($rgb, "r") * .2126) + (map-get($rgb, "g") * .7152) + (map-get($rgb, "b") * .0722);
}
// Return opaque color
// opaque(#fff, rgba(0, 0, 0, .5)) => #808080
@function opaque($background, $foreground) {
@return mix(rgba($foreground, 1), $background, opacity($foreground) * 100);
}
// Request a color level