Improve rendering of emoji which do not contrast with background (#13772)

* Refactor list of emoji requiring added outlines so that it can be theme-specific

* Split inaccessible emoji to emoji requiring an outline and ones that can be inverted

* Drop the “silouhettes” from black emoji as they seem to have changed color

* Add inaccessible emojis list for the light theme

* Use bordered emoji variant instead of unreliable CSS

app/javascript/mastodon/features/emoji/__tests__/emoji-test.js

@@ -76,7 +76,7 @@ describe('emoji', () => {
 
     it('skips the textual presentation VS15 character', () => {
       expect(emojify('✴︎')) // This is U+2734 EIGHT POINTED BLACK STAR then U+FE0E VARIATION SELECTOR-15
-        .toEqual('<img draggable="false" class="emojione" alt="✴" title=":eight_pointed_black_star:" src="/emoji/2734.svg" />');
+        .toEqual('<img draggable="false" class="emojione" alt="✴" title=":eight_pointed_black_star:" src="/emoji/2734_border.svg" />');
     });
   });
 });

app/javascript/mastodon/features/emoji/emoji.js

@@ -6,6 +6,15 @@ const trie = new Trie(Object.keys(unicodeMapping));
 
 const assetHost = process.env.CDN_HOST || '';
 
+// Emoji requiring extra borders depending on theme
+const darkEmoji = '🎱🐜⚫🖤⬛◼️◾◼️✒️▪️💣🎳📷📸♣️🕶️✴️🔌💂‍♀️📽️🍳🦍💂🔪🕳️🕹️🕋🖊️🖋️💂‍♂️🎤🎓🎥🎼♠️🎩🦃📼📹🎮🐃🏴';
+const lightEmoji = '👽⚾🐔☁️💨🕊️👀🍥👻🐐❕❔⛸️🌩️🔊🔇📃🌧️🐏🍚🍙🐓🐑💀☠️🌨️🔉🔈💬💭🏐🏳️⚪⬜◽◻️▫️';
+
+const emojiFilename = (filename, match) => {
+  const borderedEmoji = document.body.classList.contains('theme-mastodon-light') ? lightEmoji : darkEmoji;
+  return borderedEmoji.includes(match) ? (filename + '_border') : filename;
+};
+
 const emojify = (str, customEmojis = {}) => {
   const tagCharsWithoutEmojis = '<&';
   const tagCharsWithEmojis = Object.keys(customEmojis).length ? '<&:' : '<&';
@@ -60,7 +69,7 @@ const emojify = (str, customEmojis = {}) => {
     } else { // matched to unicode emoji
       const { filename, shortCode } = unicodeMapping[match];
       const title = shortCode ? `:${shortCode}:` : '';
-      replacement = `<img draggable="false" class="emojione" alt="${match}" title="${title}" src="${assetHost}/emoji/${filename}.svg" />`;
+      replacement = `<img draggable="false" class="emojione" alt="${match}" title="${title}" src="${assetHost}/emoji/${emojiFilename(filename, match)}.svg" />`;
       rend = i + match.length;
       // If the matched character was followed by VS15 (for selecting text presentation), skip it.
       if (str.codePointAt(rend) === 65038) {

app/javascript/styles/mastodon-light/variables.scss

@@ -39,3 +39,5 @@ $account-background-color: $white !default;
 @function lighten($color, $amount) {
   @return hsl(hue($color), saturation($color), lightness($color) - $amount);
 }
+
+$emojis-requiring-inversion: 'chains';

app/javascript/styles/mastodon/accessibility.scss

-$black-emojis: '8ball' 'ant' 'back' 'black_circle' 'black_heart' 'black_large_square' 'black_medium_small_square' 'black_medium_square' 'black_nib' 'black_small_square' 'bomb' 'bowling' 'bust_in_silhouette' 'busts_in_silhouette' 'camera' 'camera_with_flash' 'clubs' 'copyright' 'curly_loop' 'currency_exchange' 'dark_sunglasses' 'eight_pointed_black_star' 'electric_plug' 'end' 'female-guard' 'film_projector' 'fried_egg' 'gorilla' 'guardsman' 'heavy_check_mark' 'heavy_division_sign' 'heavy_dollar_sign' 'heavy_minus_sign' 'heavy_multiplication_x' 'heavy_plus_sign' 'hocho' 'hole' 'joystick' 'kaaba' 'lower_left_ballpoint_pen' 'lower_left_fountain_pen' 'male-guard' 'microphone' 'mortar_board' 'movie_camera' 'musical_score' 'on' 'registered' 'soon' 'spades' 'speaking_head_in_silhouette' 'spider' 'telephone_receiver' 'tm' 'top' 'tophat' 'turkey' 'vhs' 'video_camera' 'video_game' 'water_buffalo' 'waving_black_flag' 'wavy_dash';
+$emojis-requiring-inversion: 'back' 'copyright' 'curly_loop' 'currency_exchange' 'end' 'heavy_check_mark' 'heavy_division_sign' 'heavy_dollar_sign' 'heavy_minus_sign' 'heavy_multiplication_x' 'heavy_plus_sign' 'on' 'registered' 'soon' 'spider' 'telephone_receiver' 'tm' 'top' 'wavy_dash' !default;
 
-%white-emoji-outline {
-  filter: drop-shadow(1px 1px 0 $white) drop-shadow(-1px 1px 0 $white) drop-shadow(1px -1px 0 $white) drop-shadow(-1px -1px 0 $white);
-  transform: scale(.71);
+%emoji-color-inversion {
+  filter: invert(1);
 }
 
 .emojione {
-  @each $emoji in $black-emojis {
+  @each $emoji in $emojis-requiring-inversion {
     &[title=':#{$emoji}:'] {
-      @extend %white-emoji-outline;
+      @extend %emoji-color-inversion;
     }
   }
 }