From 521a05be1838ead3078dc0b43f493c8c8f615330 Mon Sep 17 00:00:00 2001
From: Dan Popescu <pdan.popescu@gmail.com>
Date: Fri, 18 Jun 2021 11:25:51 +0300
Subject: [PATCH] feat(VirtualScroll): improve scroll update #9329

---
 .../src/pages/components/virtual-scroll-2.vue |  2 +-
 .../src/pages/components/virtual-scroll-3.vue |  2 +-
 ui/src/mixins/virtual-scroll.js               | 85 +++++++++++++++----
 3 files changed, 71 insertions(+), 18 deletions(-)

diff --git a/ui/dev/src/pages/components/virtual-scroll-2.vue b/ui/dev/src/pages/components/virtual-scroll-2.vue
index a1dea4fa4e9..8bd9bb742e8 100644
--- a/ui/dev/src/pages/components/virtual-scroll-2.vue
+++ b/ui/dev/src/pages/components/virtual-scroll-2.vue
@@ -5,7 +5,7 @@
         <div class="text-h6 q-my-lg q-pa-lg bg-grey-10 text-white" style="height: 500px">
           Before list
         </div>
-        <q-virtual-scroll component="q-list" :items="heavyList" separator scroll-target="body">
+        <q-virtual-scroll component="q-list" :items="heavyList" separator scroll-target="body" :virtual-scroll-item-size="48">
           <template v-slot="{ item, index }">
             <q-item
               v-if="(index % 3) === 0"
diff --git a/ui/dev/src/pages/components/virtual-scroll-3.vue b/ui/dev/src/pages/components/virtual-scroll-3.vue
index a71bd508fd6..8799ef3f010 100644
--- a/ui/dev/src/pages/components/virtual-scroll-3.vue
+++ b/ui/dev/src/pages/components/virtual-scroll-3.vue
@@ -11,7 +11,7 @@
           component="q-list"
           :items-size="size"
           :items-fn="getItems"
-          :virtual-scroll-item-size="5"
+          :virtual-scroll-item-size="57"
           separator
           ref="list"
         >
diff --git a/ui/src/mixins/virtual-scroll.js b/ui/src/mixins/virtual-scroll.js
index f7c3ab3b678..4ac82ccfd71 100644
--- a/ui/src/mixins/virtual-scroll.js
+++ b/ui/src/mixins/virtual-scroll.js
@@ -1,6 +1,35 @@
-import debounce from '../utils/debounce.js'
 import { rtlHasScrollBug } from '../utils/scroll.js'
 
+function scrollDebounce (fn) {
+  let timeoutWait
+  let throttleCounter = 0
+
+  const fnDebounced = () => {
+    timeoutWait = void 0
+    throttleCounter = 0
+    fn()
+  }
+
+  function debounced () {
+    throttleCounter++
+    clearTimeout(timeoutWait)
+    timeoutWait = setTimeout(fnDebounced, 200)
+
+    if (throttleCounter > 50) {
+      throttleCounter = 0
+      fn(true)
+    }
+  }
+
+  debounced.cancel = () => {
+    clearTimeout(timeoutWait)
+    timeoutWait = void 0
+    throttleCounter = 0
+  }
+
+  return debounced
+}
+
 const aggBucketSize = 1000
 
 const scrollToEdges = [
@@ -300,13 +329,26 @@ export default {
       )
     },
 
-    __onVirtualScrollEvt () {
+    __onVirtualScrollEvt (throttled) {
       const scrollEl = this.__getVirtualScrollTarget()
 
       if (scrollEl === void 0 || scrollEl === null || scrollEl.nodeType === 8) {
         return
       }
 
+      if (this.$q.interaction.isKeyboard === true && this.$q.interaction.event !== null && typeof this.$q.interaction.event.key === 'string') {
+        const key = this.$q.interaction.event.key.toLowerCase()
+
+        if (key === 'home' || key === 'end') {
+          setScroll(
+            scrollEl,
+            key === 'home' ? 0 : 'end',
+            this.virtualScrollHorizontal,
+            this.$q.lang.rtl
+          )
+        }
+      }
+
       const
         scrollDetails = getScrollDetails(
           scrollEl,
@@ -382,11 +424,13 @@ export default {
         scrollEl,
         scrollDetails,
         toIndex,
-        offset
+        offset,
+        void 0,
+        throttled
       )
     },
 
-    __setVirtualScrollSliceRange (scrollEl, scrollDetails, toIndex, offset, align) {
+    __setVirtualScrollSliceRange (scrollEl, scrollDetails, toIndex, offset, align, throttled) {
       const alignForce = typeof align === 'string' && align.indexOf('-force') > -1
       const alignEnd = alignForce === true ? align.replace('-force', '') : align
       const alignRange = alignEnd !== void 0 ? alignEnd : 'start'
@@ -416,13 +460,18 @@ export default {
         rangeChanged === true &&
         contentEl !== void 0 &&
         contentEl !== activeElement &&
-        contentEl.contains(activeElement) === true
+        contentEl.contains(activeElement) === true &&
+        contentEl.qVsFocusout !== true
       ) {
+        contentEl.qVsFocusout = true
         contentEl.addEventListener('focusout', this.__onBlurRefocusFn)
 
         setTimeout(() => {
-          contentEl !== void 0 && contentEl.removeEventListener('focusout', this.__onBlurRefocusFn)
-        })
+          if (contentEl !== void 0) {
+            contentEl.removeEventListener('focusout', this.__onBlurRefocusFn)
+            contentEl.qVsFocusout = false
+          }
+        }, 500)
       }
 
       setOverflowAnchor(contentEl, toIndex - from)
@@ -441,7 +490,8 @@ export default {
         this.virtualScrollPaddingBefore = sumSize(this.virtualScrollSizesAgg, this.virtualScrollSizes, 0, from)
         this.virtualScrollPaddingAfter = sumSize(this.virtualScrollSizesAgg, this.virtualScrollSizes, this.virtualScrollSliceRange.to, this.virtualScrollLength)
 
-        requestAnimationFrame(() => {
+        cancelAnimationFrame(this.vsRangeToAnimationFrame)
+        this.vsRangeToAnimationFrame = requestAnimationFrame(() => {
           if (this.virtualScrollSliceRange.to !== to && this.prevScrollStart === scrollDetails.scrollStart) {
             this.virtualScrollSliceRange = { from: this.virtualScrollSliceRange.from, to }
             this.virtualScrollPaddingAfter = sumSize(this.virtualScrollSizesAgg, this.virtualScrollSizes, to, this.virtualScrollLength)
@@ -449,7 +499,8 @@ export default {
         })
       }
 
-      requestAnimationFrame(() => {
+      cancelAnimationFrame(this.vsScrollAnimationFrame)
+      this.vsScrollAnimationFrame = requestAnimationFrame(() => {
         // if the scroll was changed give up
         // (another call to __setVirtualScrollSliceRange before animation frame)
         if (this.prevScrollStart !== scrollDetails.scrollStart) {
@@ -482,12 +533,14 @@ export default {
 
         this.prevScrollStart = scrollPosition
 
-        setScroll(
-          scrollEl,
-          scrollPosition,
-          this.virtualScrollHorizontal,
-          this.$q.lang.rtl
-        )
+        if (throttled !== true || (scrollEl === window && this.$q.platform.is.ios !== true)) {
+          setScroll(
+            scrollEl,
+            scrollPosition,
+            this.virtualScrollHorizontal,
+            this.$q.lang.rtl
+          )
+        }
 
         this.__emitScroll(toIndex)
       })
@@ -716,7 +769,7 @@ export default {
   },
 
   beforeMount () {
-    this.__onVirtualScrollEvt = debounce(this.__onVirtualScrollEvt, this.$q.platform.is.ios === true ? 120 : 35)
+    this.__onVirtualScrollEvt = scrollDebounce(this.__onVirtualScrollEvt)
     this.__setVirtualScrollSize()
   },