_color-a11y.scss

////
/// @group theme
////

@use 'sass:math';

@import './color-palette';

/// This is the default contrast ratio to use for color accessibility between
/// background and foreground colors. This number should be at least:
/// - 3 for large text (18pt normal or 14pt bold)
/// - 4.5 for normal text
/// - 7.1 for Level AAA requirements.
///
/// @link https://www.w3.org/TR/WCAG20/#visual-audio-contrast-contrast
/// @type Number
$rmd-theme-default-contrast-ratio: 3 !default;

/// Boolean if the newer contrast ration defaults should be used. This basically
/// will try to choose colors with a higher aspect ratio for all the default
/// color variables in react md.
///
/// @example scss - Better Contrast Enabled
///   @use "@react-md/theme/dist/color-palette" as colors;
///   @use "react-md" as * with (
///     $rmd-theme-better-contrast-colors: true,
///     $rmd-theme-primary: colors.$rmd-teal-500,
///     $rmd-theme-secondary: colors.$rmd-pink-a-200,
///   );
///   // OVERRIDE_USE
///
///   // these are the rmd-defaults
///   // $rmd-theme-on-primary: rmd-theme-best-contrast-color($rmd-theme-primary) !default;
///   // $rmd-theme-on-secondary: rmd-theme-best-contrast-color($rmd-theme-secondary) !default;
///
///   .output {
///     --p: #{$rmd-theme-primary};
///     --s: #{$rmd-theme-secondary};
///
///     // since black has a ~5.3 color ratio as compared to white with ~3.6
///     --op: #{$rmd-theme-on-primary};
///     --os: #{$rmd-theme-on-secondary};
///   }
///
/// @example scss - Better Contrast Disabled
///   @use "@react-md/theme/dist/color-palette" as colors;
///   @use "react-md" as * with (
///     $rmd-theme-better-contrast-colors: false,
///     $rmd-theme-primary: colors.$rmd-teal-500,
///     $rmd-theme-secondary: colors.$rmd-pink-a-200,
///   );
///   // OVERRIDE_USE
///
///   // these are the rmd-defaults
///   // $rmd-theme-on-primary: rmd-theme-best-contrast-color($rmd-theme-primary) !default;
///   // $rmd-theme-on-secondary: rmd-theme-best-contrast-color($rmd-theme-secondary) !default;
///
///   .output {
///     --p: #{$rmd-theme-primary};
///     --s: #{$rmd-theme-secondary};
///
///     // white has a ~3.6 color ratio so it _is_ contrast compliant with the
///     // minimal contrast ratios even though black would be ~5.6
///     --op: #{$rmd-theme-on-primary};
///     --os: #{$rmd-theme-on-secondary};
///   }
///
/// @since 2.4.0
/// @type Boolean
$rmd-theme-better-contrast-colors: true !default;

/// Precomputed linear color channel values, for use in contrast calculations.
/// See https://www.w3.org/TR/WCAG20-TECHS/G17.html#G17-tests
///
/// Algorithm:
///
/// ```
///   for c in 0 to 255:
///   f(c) {
///     c = c / 255;
///     return c < 0.03928 ? c / 12.92 : Math.pow((c + 0.055) / 1.055, 2.4);
///   }
/// ```
///
/// This lookup table is needed since there is no `pow` in SCSS/Sass. You _can_
/// make your own, but it is recommended to pass the computed values from a
/// 'more complete' layer (like node) as a lookup table to speed up compilation
/// time.
///
/// @access private
/// @type List
$rmd-theme-linear-channel-values: (
  0 0.0003035269835488375 0.000607053967097675 0.0009105809506465125
    0.00121410793419535 0.0015176349177441874 0.001821161901293025
    0.0021246888848418626 0.0024282158683907 0.0027317428519395373
    0.003035269835488375 0.003346535763899161 0.003676507324047436
    0.004024717018496307 0.004391442037410293 0.004776953480693729
    0.005181516702338386 0.005605391624202723 0.006048833022857054
    0.006512090792594475 0.006995410187265387 0.007499032043226175
    0.008023192985384994 0.008568125618069307 0.009134058702220787
    0.00972121732023785 0.010329823029626936 0.010960094006488246
    0.011612245179743885 0.012286488356915872 0.012983032342173012
    0.013702083047289686 0.014443843596092545 0.01520851442291271
    0.01599629336550963 0.016807375752887384 0.017641954488384078
    0.018500220128379697 0.019382360956935723 0.0202885630566524
    0.021219010376003555 0.022173884793387385 0.02315336617811041
    0.024157632448504756 0.02518685962736163 0.026241221894849898
    0.027320891639074894 0.028426039504420793 0.0295568344378088
    0.030713443732993635 0.03189603307301153 0.033104766570885055
    0.03433980680868217 0.03560131487502034 0.03688945040110004
    0.0382043715953465 0.03954623527673284 0.04091519690685319
    0.042311410620809675 0.043735029256973465 0.04518620438567554
    0.046665086336880095 0.04817182422688942 0.04970656598412723
    0.05126945837404324 0.052860647023180246 0.05448027644244237
    0.05612849004960009 0.05780543019106723 0.0595112381629812
    0.06124605423161761 0.06301001765316767 0.06480326669290577
    0.06662593864377289 0.06847816984440017 0.07036009569659588
    0.07227185068231748 0.07421356838014963 0.07618538148130785
    0.07818742180518633 0.08021982031446832 0.0822827071298148
    0.08437621154414882 0.08650046203654976 0.08865558628577294
    0.09084171118340768 0.09305896284668745 0.0953074666309647
    0.09758734714186246 0.09989872824711389 0.10224173308810132
    0.10461648409110419 0.10702310297826761 0.10946171077829933
    0.1119324278369056 0.11443537382697373 0.11697066775851084
    0.11953842798834562 0.12213877222960187 0.12477181756095049
    0.12743768043564743 0.1301364766903643 0.13286832155381798
    0.13563332965520566 0.13843161503245183 0.14126329114027164
    0.14412847085805777 0.14702726649759498 0.14995978981060856
    0.15292615199615017 0.1559264637078274 0.1589608350608804 0.162029375639111
    0.1651321945016676 0.16826940018969075 0.1714411007328226
    0.17464740365558504 0.17788841598362912 0.18116424424986022
    0.184474994500441 0.18782077230067787 0.19120168274079138 0.1946178304415758
    0.19806931955994886 0.20155625379439707 0.20507873639031693
    0.20863687014525575 0.21223075741405523 0.21586050011389926
    0.2195261997292692 0.2232279573168085 0.22696587351009836
    0.23074004852434915 0.23455058216100522 0.238397573812271
    0.24228112246555486 0.24620132670783548 0.25015828472995344
    0.25415209433082675 0.2581828529215958 0.26225065752969623
    0.26635560480286247 0.2704977910130658 0.27467731206038465
    0.2788942634768104 0.2831487404299921 0.2874408377269175 0.29177064981753587
    0.2961382707983211 0.3005437944157765 0.3049873140698863 0.30946892281750854
    0.31398871337571754 0.31854677812509186 0.32314320911295075
    0.3277780980565422 0.33245153634617935 0.33716361504833037
    0.3419144249086609 0.3467040563550296 0.35153259950043936 0.3564001441459435
    0.3613067797835095 0.3662525955988395 0.3712376804741491 0.3762621229909065
    0.38132601143253014 0.386429433787049 0.39157247774972326
    0.39675523072562685 0.4019777798321958 0.4072402119017367
    0.41254261348390375 0.4178850708481375 0.4232676699860717 0.4286904966139066
    0.43415363617474895 0.4396571738409188 0.44520119451622786
    0.45078578283822346 0.45641102318040466 0.4620769996544071 0.467783796112159
    0.47353149614800955 0.4793201831008268 0.4851499400560704 0.4910208498478356
    0.4969329950608704 0.5028864580325687 0.5088813208549338 0.5149176653765214
    0.5209955732043543 0.5271151257058131 0.5332764040105052 0.5394794890121072
    0.5457244613701866 0.5520114015120001 0.5583403896342679 0.5647115057049292
    0.5711248294648731 0.5775804404296506 0.5840784178911641 0.5906188409193369
    0.5972017883637634 0.6038273388553378 0.6104955708078648 0.6172065624196511
    0.6239603916750761 0.6307571363461468 0.6375968739940326 0.6444796819705821
    0.6514056374198242 0.6583748172794485 0.665387298282272 0.6724431569576875
    0.6795424696330938 0.6866853124353135 0.6938717612919899 0.7011018919329731
    0.7083757798916868 0.7156935005064807 0.7230551289219693 0.7304607400903537
    0.7379104087727308 0.7454042095403874 0.7529422167760779 0.7605245046752924
    0.768151147247507 0.7758222183174236 0.7835377915261935 0.7912979403326302
    0.799102738014409 0.8069522576692516 0.8148465722161012 0.8227857543962835
    0.8307698767746546 0.83879901174074 0.846873231509858 0.8549926081242338
    0.8631572134541023 0.8713671191987972 0.8796223968878317 0.8879231178819663
    0.8962693533742664 0.9046611743911496 0.9130986517934192 0.9215818562772946
    0.9301108583754237 0.938685728457888 0.9473065367331999 0.9559733532492861
    0.9646862478944651 0.9734452903984125 0.9822505503331171 0.9911020971138298
    1
);

/// Calculate the luminance for a color.
///
/// @access private
/// @link https://www.w3.org/TR/WCAG20-TECHS/G17.html#G17-tests
/// @param {Color} color - The color to check
/// @returns {Number} A number representing the luminance for the color.
@function rmd-theme-luminance($color) {
  $red: nth($rmd-theme-linear-channel-values, red($color) + 1);
  $red-multiplier: 0.2126;
  $green: nth($rmd-theme-linear-channel-values, green($color) + 1);
  $green-multiplier: 0.7152;
  $blue: nth($rmd-theme-linear-channel-values, blue($color) + 1);
  $blue-multiplier: 0.0722;

  @return ($red * $red-multiplier) + ($green * $green-multiplier) +
    ($blue * $blue-multiplier);
}

/// Gets the contrast between two colors.
///
/// @access private
/// @param {Color} back - The background color
/// @param {Color} front - The foreground color that should be compared to
/// the background color for contrast ratio.
/// @returns {Number} The contrast ratio between the background and foreground colors
@function rmd-theme-contrast($back, $front) {
  $back-luminance: rmd-theme-luminance($back) + 0.05;
  $front-luminance: rmd-theme-luminance($front) + 0.05;

  @return math.div(
    max($back-luminance, $front-luminance),
    min($back-luminance, $front-luminance)
  );
}

/// Determines if a provided color is considered light or dark.
///
/// @param {Color} color - The color to test.
/// @param {Number} min-contrast [$rmd-theme-default-contrast-ratio] - The
/// minimum contrast that should be applied. The min contrast for normal text
/// should be 4.5 while large or 14px bold text should be 3.1. See the link for
/// contrasts for more information.
/// @returns {String} - The string 'light' if the color is considered light, otherwise 'dark'.
/// @link https://www.w3.org/TR/WCAG20/#visual-audio-contrast-contrast
@function rmd-theme-tone(
  $color,
  $min-contrast: $rmd-theme-default-contrast-ratio
) {
  @if $color == 'dark' or $color == 'light' {
    @return $color;
  }

  $light-contrast: rmd-theme-contrast($color, $rmd-white-base);
  $dark-contrast: rmd-theme-contrast($color, rgba($rmd-black-base, 0.87));

  @if ($light-contrast < $min-contrast) and ($dark-contrast > $light-contrast) {
    @return 'light';
  } @else {
    @return 'dark';
  }
}

/// Determines if the provided color should have a light or dark contrast using
/// the luminance algorithm to maintain a required contrast ratio for
/// accessibility.
///
/// @param {Color} color - The color to test.
/// @param {Number} min-contrast [$rmd-theme-default-contrast-ratio] - The
/// minimum contrast that should be applied. The min contrast for normal text
/// should be 4.5 while large or 14px bold text should be 3.1. See the link for
/// contrasts for more information.
/// @returns {String} - The string 'dark' if the color is considered light, or
/// 'light' if the color is considered dark.
/// @link https://www.w3.org/TR/WCAG20/#visual-audio-contrast-contrast
@function rmd-theme-contrast-tone(
  $color,
  $min-contrast: $rmd-theme-default-contrast-ratio
) {
  @return if(rmd-theme-tone($color) == 'dark', 'light', 'dark');
}

/// Compares a color to a provided light and dark color. If the
/// `$rmd-theme-better-contrast-colors` variable is `true`, the color with the
/// bigger contrast ratio will be chosen. If the variable is `false`, the light
/// color will be returned when it meets the minimum contrast ratio and fallback
/// to the dark color.
///
/// @example scss - Better Contrast Enabled
///   @use "@react-md/theme/dist/color-palette" as colors;
///   @use "react-md" as * with (
///     $rmd-theme-better-contrast-colors: true,
///     $rmd-theme-primary: colors.$rmd-teal-500,
///     $rmd-theme-secondary: colors.$rmd-pink-a-200,
///   );
///   // OVERRIDE_USE
///
///   // these are the rmd-defaults
///   // $rmd-theme-on-primary: rmd-theme-best-contrast-color($rmd-theme-primary) !default;
///   // $rmd-theme-on-secondary: rmd-theme-best-contrast-color($rmd-theme-secondary) !default;
///
///   .output {
///     --p: #{$rmd-theme-primary};
///     --s: #{$rmd-theme-secondary};
///
///     // since black has a ~5.3 color ratio as compared to white with ~3.6
///     --op: #{$rmd-theme-on-primary};
///     --os: #{$rmd-theme-on-secondary};
///   }
///
/// @example scss - Better Contrast Disabled
///   @use "@react-md/theme/dist/color-palette" as colors;
///   @use "react-md" as * with (
///     $rmd-theme-better-contrast-colors: false,
///     $rmd-theme-primary: colors.$rmd-teal-500,
///     $rmd-theme-secondary: colors.$rmd-pink-a-200,
///   );
///   // OVERRIDE_USE
///
///   // these are the rmd-defaults
///   // $rmd-theme-on-primary: rmd-theme-best-contrast-color($rmd-theme-primary) !default;
///   // $rmd-theme-on-secondary: rmd-theme-best-contrast-color($rmd-theme-secondary) !default;
///
///   .output {
///     --p: #{$rmd-theme-primary};
///     --s: #{$rmd-theme-secondary};
///
///     // white has a ~3.6 color ratio so it _is_ contrast compliant with the
///     // minimal contrast ratios even though black would be ~5.6
///     --op: #{$rmd-theme-on-primary};
///     --os: #{$rmd-theme-on-secondary};
///   }
///
/// @param {Color} color - The color to check against
/// @param {Color} light-color [$rmd-white-base] - A light color to try to use
/// @param {Color} dark-color [$rmd-white-base] - A dark color to try to use
/// @param {Boolean} enabled [$rmd-theme-better-contrast-colors] - Boolean if
/// the new/better contrast ratios should be used. When this is false, it will
/// return the lighter color as long as it meets the minimum contrast ratio even
/// if the darker color would have a greater contrast ratio.
/// @since 2.4.0
/// @returns {Color} Either the `$light-color` or `$dark-color` depending on
/// contrast ratios.
@function rmd-theme-best-contrast-color(
  $color,
  $light-color: $rmd-white-base,
  $dark-color: $rmd-black-base,
  $enabled: $rmd-theme-better-contrast-colors
) {
  @if not $enabled {
    @return if(
      rmd-theme-tone($color) == light,
      $rmd-black-base,
      $rmd-white-base
    );
  }

  $light-contrast: rmd-theme-contrast($color, $light-color);
  $dark-contrast: rmd-theme-contrast($color, $dark-color);

  @return if($light-contrast > $dark-contrast, $light-color, $dark-color);
}