Improve emoji picker performance

A simple virtual scroller is now used for the emoji grid. This avoids
loading all emoji images at once, saving network bandwidth and
reducing load on the server, while also putting less work on the
browser's DOM and layout engine.

src/components/emoji_grid/emoji_grid.js

@@ -0,0 +1,125 @@
+const EMOJI_SIZE = 32 + 8;
+const GROUP_TITLE_HEIGHT = 24;
+const BUFFER_SIZE = 3*EMOJI_SIZE;
+
+const EmojiGrid = {
+  props: {
+    groups: {
+      required: true,
+      type: Array
+    }
+  },
+  data() {
+    return {
+      containerWidth: 0,
+      containerHeight: 0,
+      scrollPos: 0,
+      resizeObserver: null,
+    }
+  },
+  mounted() {
+    const rect = this.$refs.container.getBoundingClientRect();
+    this.containerWidth = rect.width;
+    this.containerHeight = rect.height;
+    this.resizeObserver = new ResizeObserver((entries) => {
+      for (const entry of entries) {
+        this.containerWidth = entry.contentRect.width;
+        this.containerHeight = entry.contentRect.height;
+      }
+    })
+    this.resizeObserver.observe(this.$refs.container);
+  },
+  beforeUnmount() {
+    this.resizeObserver.disconnect();
+    this.resizeObserver = null;
+  },
+  watch: {
+    groups() {
+      // Scroll to top when grid content changes
+      if (this.$refs.container) {
+        this.$refs.container.scrollTo(0, 0);
+      }
+    },
+    activeGroup(group) {
+      this.$emit('activeGroup', group);
+    }
+  },
+  methods: {
+    onScroll() {
+      this.scrollPos = this.$refs.container.scrollTop
+    },
+    onEmoji(emoji) {
+      this.$emit('emoji', emoji)
+    },
+    scrollToItem(itemId) {
+      const container = this.$refs.container;
+      if (!container) return;
+
+      for (const item of this.itemList) {
+        if (item.id === itemId) {
+          container.scrollTo(0, item.position.y);
+          return;
+        }
+      }
+    }
+  },
+  computed: {
+    // Total height of scroller content
+    gridHeight() {
+      if (this.itemList.length == 0) return 0;
+      const lastItem = this.itemList[this.itemList.length - 1];
+      return lastItem.position.y + ('title' in lastItem ? GROUP_TITLE_HEIGHT : EMOJI_SIZE)
+    },
+    activeGroup() {
+      const items = this.itemList;
+      for (let i = items.length - 1; i >= 0; i--) {
+        const item = items[i];
+        if ('title' in item && item.position.y <= this.scrollPos) {
+          return item.id;
+        }
+      }
+      return null;
+    },
+    itemList() {
+      const items = [];
+      let x = 0, y = 0;
+      for (const group of this.groups) {
+        items.push({ position: {x, y}, id: group.id, title: group.text });
+        if (group.text.length) {
+          y += GROUP_TITLE_HEIGHT;
+        }
+        for (const emoji of group.emojis) {
+          items.push({ position: {x, y}, id: `${group.id}-${emoji.displayText}`, emoji })
+          x += EMOJI_SIZE;
+          if (x + EMOJI_SIZE > this.containerWidth) {
+            y += EMOJI_SIZE;
+            x = 0;
+          }
+        }
+        if (x > 0) {
+          y += EMOJI_SIZE;
+          x = 0;
+        }
+      }
+      return items;
+    },
+    visibleItems() {
+      const startPos = this.scrollPos - BUFFER_SIZE;
+      const endPos = this.scrollPos + this.containerHeight + BUFFER_SIZE;
+      return this.itemList.filter(i => {
+        return i.position.y >= startPos && i.position.y < endPos;
+      });
+    },
+    scrolledClass() {
+      if (this.scrollPos <= 5) {
+        return 'scrolled-top'
+      } else if (this.scrollPos >= this.gridHeight - this.containerHeight - 5) {
+        return 'scrolled-bottom'
+      } else {
+        return 'scrolled-middle'
+      }
+    }
+  }
+}
+
+export default EmojiGrid

src/components/emoji_grid/emoji_grid.scss

@@ -0,0 +1,60 @@
+.emoji {
+  &-grid {
+    flex: 1 1 1px;
+    position: relative;
+    overflow: auto;
+    user-select: none;
+    mask: linear-gradient(to top, white 0, transparent 100%) bottom no-repeat,
+          linear-gradient(to bottom, white 0, transparent 100%) top no-repeat,
+          linear-gradient(to top, white, white);
+    transition: mask-size 150ms;
+    mask-size: 100% 20px, 100% 20px, auto;
+    // Autoprefixed seem to ignore this one, and also syntax is different
+    -webkit-mask-composite: xor;
+    mask-composite: exclude;
+    &.scrolled {
+      &-top {
+        mask-size: 100% 20px, 100% 0, auto;
+      }
+      &-bottom {
+        mask-size: 100% 0, 100% 20px, auto;
+      }
+    }
+    margin-left: 5px;
+    min-height: 200px;
+  }
+
+  &-group-title {
+    position: absolute;
+    font-size: 0.85em;
+    width: 100%;
+    margin: 0;
+    height: 24px;
+    display: flex;
+    align-items: end;
+
+    &.disabled {
+        display: none;
+    }
+  }
+
+  &-item {
+    position: absolute;
+    width: 32px;
+    height: 32px;
+    box-sizing: border-box;
+    display: flex;
+    font-size: 32px;
+    align-items: center;
+    justify-content: center;
+    margin: 4px;
+
+    cursor: pointer;
+
+    img {
+      object-fit: contain;
+      max-width: 100%;
+      max-height: 100%;
+    }
+  }
+}

src/components/emoji_grid/emoji_grid.vue

@@ -0,0 +1,48 @@
+<template>
+  <div
+    ref="container"
+    class="emoji-grid"
+    :class="scrolledClass"
+    @scroll.passive="onScroll"
+  >
+    <div
+      :style="{
+        height: `${gridHeight}px`,
+      }"
+    >
+      <template v-for="item in visibleItems">
+        <h6
+          v-if="'title' in item && item.title.length"
+          :key="'title-' + item.id"
+          class="emoji-group-title"
+          :style="{
+            top: item.position.y + 'px',
+            left: item.position.x + 'px'
+          }"
+        >
+          {{ item.title }}
+        </h6>
+        <span
+          v-else-if="'emoji' in item"
+          :key="'emoji-' + item.id"
+          class="emoji-item"
+          :title="item.emoji.displayText"
+          :style="{
+            top: item.position.y + 'px',
+            left: item.position.x + 'px'
+          }"
+          @click.stop.prevent="onEmoji(item.emoji)"
+        >
+          <span v-if="!item.emoji.imageUrl">{{ item.emoji.replacement }}</span>
+          <img
+            v-else
+            :src="item.emoji.imageUrl"
+          >
+        </span>
+      </template>
+    </div>
+  </div>
+</template>
+
+<script src="./emoji_grid.js"></script>
+<style lang="scss" src="./emoji_grid.scss"></style>

src/components/emoji_input/emoji_input.js

@@ -202,7 +202,6 @@ const EmojiInput = {
     },
     triggerShowPicker () {
       this.showPicker = true
-      this.$refs.picker.startEmojiLoad()
       this.$nextTick(() => {
         this.scrollIntoView()
         this.focusPickerInput()
@@ -220,7 +219,6 @@ const EmojiInput = {
       this.showPicker = !this.showPicker
       if (this.showPicker) {
         this.scrollIntoView()
-        this.$refs.picker.startEmojiLoad()
         this.$nextTick(this.focusPickerInput)
       }
     },

src/components/emoji_picker/emoji_picker.js

@@ -1,5 +1,6 @@
 import { defineAsyncComponent } from 'vue'
 import Checkbox from '../checkbox/checkbox.vue'
+import EmojiGrid from '../emoji_grid/emoji_grid.vue'
 import { library } from '@fortawesome/fontawesome-svg-core'
 import {
   faBoxOpen,
@@ -14,13 +15,6 @@ library.add(
   faSmileBeam
 )
 
-// At widest, approximately 20 emoji are visible in a row,
-// loading 3 rows, could be overkill for narrow picker
-const LOAD_EMOJI_BY = 60
-
-// When to start loading new batch emoji, in pixels
-const LOAD_EMOJI_MARGIN = 64
-
 const EmojiPicker = {
   props: {
     enableStickerPicker: {
@@ -34,16 +28,13 @@ const EmojiPicker = {
       keyword: '',
       activeGroup: 'standard',
       showingStickers: false,
-      groupsScrolledClass: 'scrolled-top',
-      keepOpen: false,
-      customEmojiBufferSlice: LOAD_EMOJI_BY,
-      customEmojiTimeout: null,
-      customEmojiLoadAllConfirmed: false
+      keepOpen: false
     }
   },
   components: {
     StickerPicker: defineAsyncComponent(() => import('../sticker_picker/sticker_picker.vue')),
-    Checkbox
+    Checkbox,
+    EmojiGrid
   },
   methods: {
     onStickerUploaded (e) {
@@ -56,12 +47,6 @@ const EmojiPicker = {
       const value = emoji.imageUrl ? `:${emoji.displayText}:` : emoji.replacement
       this.$emit('emoji', { insertion: value, keepOpen: this.keepOpen })
     },
-    onScroll (e) {
-      const target = (e && e.target) || this.$refs['emoji-groups']
-      this.updateScrolledClass(target)
-      this.scrolledGroup(target)
-      this.triggerLoadMore(target)
-    },
     onWheel (e) {
       e.preventDefault()
       this.$refs['emoji-tabs'].scrollBy(e.deltaY, 0)
@@ -69,68 +54,12 @@ const EmojiPicker = {
     highlight (key) {
       this.setShowStickers(false)
       this.activeGroup = key
-    },
-    updateScrolledClass (target) {
-      if (target.scrollTop <= 5) {
-        this.groupsScrolledClass = 'scrolled-top'
-      } else if (target.scrollTop >= target.scrollTopMax - 5) {
-        this.groupsScrolledClass = 'scrolled-bottom'
-      } else {
-        this.groupsScrolledClass = 'scrolled-middle'
+      if (this.keyword.length) {
+        this.$refs.emojiGrid.scrollToItem(key)
       }
     },
-    triggerLoadMore (target) {
-      const ref = this.$refs['group-end-custom']
-      if (!ref) return
-      const bottom = ref.offsetTop + ref.offsetHeight
-
-      const scrollerBottom = target.scrollTop + target.clientHeight
-      const scrollerTop = target.scrollTop
-      const scrollerMax = target.scrollHeight
-
-      // Loads more emoji when they come into view
-      const approachingBottom = bottom - scrollerBottom < LOAD_EMOJI_MARGIN
-      // Always load when at the very top in case there's no scroll space yet
-      const atTop = scrollerTop < 5
-      // Don't load when looking at unicode category or at the very bottom
-      const bottomAboveViewport = bottom < scrollerTop || scrollerBottom === scrollerMax
-      if (!bottomAboveViewport && (approachingBottom || atTop)) {
-        this.loadEmoji()
-      }
-    },
-    scrolledGroup (target) {
-      const top = target.scrollTop + 5
-      this.$nextTick(() => {
-        this.emojisView.forEach(group => {
-          const ref = this.$refs['group-' + group.id]
-          if (ref.offsetTop <= top) {
-            this.activeGroup = group.id
-          }
-        })
-      })
-    },
-    loadEmoji () {
-      const allLoaded = this.customEmojiBuffer.length === this.filteredEmoji.length
-
-      if (allLoaded) {
-        return
-      }
-
-      this.customEmojiBufferSlice += LOAD_EMOJI_BY
-    },
-    startEmojiLoad (forceUpdate = false) {
-      if (!forceUpdate) {
-        this.keyword = ''
-      }
-      this.$nextTick(() => {
-        this.$refs['emoji-groups'].scrollTop = 0
-      })
-      const bufferSize = this.customEmojiBuffer.length
-      const bufferPrefilledAll = bufferSize === this.filteredEmoji.length
-      if (bufferPrefilledAll && !forceUpdate) {
-        return
-      }
-      this.customEmojiBufferSlice = LOAD_EMOJI_BY
+    onActiveGroup (group) {
+      this.activeGroup = group
     },
     toggleStickers () {
       this.showingStickers = !this.showingStickers
@@ -146,13 +75,6 @@ const EmojiPicker = {
       })
     }
   },
-  watch: {
-    keyword () {
-      this.customEmojiLoadAllConfirmed = false
-      this.onScroll()
-      this.startEmojiLoad(true)
-    }
-  },
   computed: {
     activeGroupView () {
       return this.showingStickers ? '' : this.activeGroup
@@ -168,9 +90,6 @@ const EmojiPicker = {
         this.$store.state.instance.customEmoji || []
       )
     },
-    customEmojiBuffer () {
-      return this.filteredEmoji.slice(0, this.customEmojiBufferSlice)
-    },
     emojis () {
       const standardEmojis = this.$store.state.instance.emoji || []
       const customEmojis = this.sortedEmoji

src/components/emoji_picker/emoji_picker.scss

@@ -69,10 +69,6 @@
     flex-grow: 1;
   }
 
-  .emoji-groups {
-    min-height: 200px;
-  }
-
   .additional-tabs {
     border-left: 1px solid;
     border-left-color: $fallback--icon;
@@ -151,76 +147,12 @@
     }
   }
 
-  .emoji {
-    &-search {
-      padding: 5px;
-      flex: 0 0 auto;
+  .emoji-search {
+    padding: 5px;
+    flex: 0 0 auto;
 
-      input {
-        width: 100%;
-      }
+    input {
+      width: 100%;
     }
-
-    &-groups {
-      flex: 1 1 1px;
-      position: relative;
-      overflow: auto;
-      user-select: none;
-      mask: linear-gradient(to top, white 0, transparent 100%) bottom no-repeat,
-            linear-gradient(to bottom, white 0, transparent 100%) top no-repeat,
-            linear-gradient(to top, white, white);
-      transition: mask-size 150ms;
-      mask-size: 100% 20px, 100% 20px, auto;
-      // Autoprefixed seem to ignore this one, and also syntax is different
-      -webkit-mask-composite: xor;
-      mask-composite: exclude;
-      &.scrolled {
-        &-top {
-          mask-size: 100% 20px, 100% 0, auto;
-        }
-        &-bottom {
-          mask-size: 100% 0, 100% 20px, auto;
-        }
-      }
-    }
-
-    &-group {
-      display: flex;
-      align-items: center;
-      flex-wrap: wrap;
-      padding-left: 5px;
-      justify-content: left;
-
-      &-title {
-        font-size: 0.85em;
-        width: 100%;
-        margin: 0;
-
-        &.disabled {
-          display: none;
-        }
-      }
-    }
-
-    &-item {
-      width: 32px;
-      height: 32px;
-      box-sizing: border-box;
-      display: flex;
-      font-size: 32px;
-      align-items: center;
-      justify-content: center;
-      margin: 4px;
-
-      cursor: pointer;
-
-      img {
-        object-fit: contain;
-        max-width: 100%;
-        max-height: 100%;
-      }
-    }
-
   }
-
 }

src/components/emoji_picker/emoji_picker.vue

@@ -2,9 +2,9 @@
   <div class="emoji-picker panel panel-default panel-body">
     <div class="heading">
       <span
+        ref="emoji-tabs"
         class="emoji-tabs"
         @wheel="onWheel"
-        ref="emoji-tabs"
       >
         <span
           v-for="group in emojis"
@@ -51,40 +51,16 @@
             @input="$event.target.composing = false"
           >
         </div>
+        <EmojiGrid
+          ref="emojiGrid"
+          :groups="emojisView"
+          @emoji="onEmoji"
+          @active-group="onActiveGroup"
+        />
         <div
-          ref="emoji-groups"
-          class="emoji-groups"
-          :class="groupsScrolledClass"
-          @scroll="onScroll"
+          v-if="showKeepOpen"
+          class="keep-open"
         >
-          <div
-            v-for="group in emojisView"
-            :key="group.id"
-            class="emoji-group"
-          >
-            <h6
-              :ref="'group-' + group.id"
-              class="emoji-group-title"
-            >
-              {{ group.text }}
-            </h6>
-            <span
-              v-for="emoji in group.emojis"
-              :key="group.id + emoji.displayText"
-              :title="emoji.displayText"
-              class="emoji-item"
-              @click.stop.prevent="onEmoji(emoji)"
-            >
-              <span v-if="!emoji.imageUrl">{{ emoji.replacement }}</span>
-              <img
-                v-else
-                :src="emoji.imageUrl"
-              >
-            </span>
-            <span :ref="'group-end-' + group.id" />
-          </div>
-        </div>
-        <div class="keep-open">
           <Checkbox v-model="keepOpen">
             {{ $t('emoji.keep_open') }}
           </Checkbox>