From 43eadf2ec6c9629c789cde666ce42abf32cc8b2b Mon Sep 17 00:00:00 2001
From: Andrew Kingston <andrew@kingston.dev>
Date: Wed, 1 Mar 2023 08:44:02 +0000
Subject: [PATCH] Add WIP virtual dom implementation to massively increase
 performance

---
 .../src/components/sheet/NewRow.svelte        |   4 +-
 .../src/components/sheet/ResizeOverlay.svelte |   2 +-
 .../src/components/sheet/ScrollOverlay.svelte | 124 ++++++++++++++++++
 .../src/components/sheet/Sheet.svelte         |   5 +-
 .../src/components/sheet/SheetBody.svelte     |  46 ++++---
 .../src/components/sheet/SheetRow.svelte      |   7 +-
 .../src/components/sheet/stores/viewport.js   |  19 +--
 7 files changed, 168 insertions(+), 39 deletions(-)
 create mode 100644 packages/frontend-core/src/components/sheet/ScrollOverlay.svelte

diff --git a/packages/frontend-core/src/components/sheet/NewRow.svelte b/packages/frontend-core/src/components/sheet/NewRow.svelte
index 78a990ff58..11f99de5a6 100644
--- a/packages/frontend-core/src/components/sheet/NewRow.svelte
+++ b/packages/frontend-core/src/components/sheet/NewRow.svelte
@@ -14,7 +14,7 @@
   }
 </script>
 
-<div class="row new" style="--top:{($rows.length + 1) * cellHeight}px;">
+<div class="row new">
   <SheetCell label on:click={addRow} width="40" left="0">
     <Icon hoverable name="Add" size="S" />
   </SheetCell>
@@ -33,9 +33,7 @@
 <style>
   .row {
     display: flex;
-    top: var(--top);
     width: inherit;
-    position: absolute;
   }
   :global(.sheet:not(.is-resizing):not(.is-reordering) .row:hover .cell) {
     background: var(--cell-background-hover);
diff --git a/packages/frontend-core/src/components/sheet/ResizeOverlay.svelte b/packages/frontend-core/src/components/sheet/ResizeOverlay.svelte
index d6665777d8..32edc77016 100644
--- a/packages/frontend-core/src/components/sheet/ResizeOverlay.svelte
+++ b/packages/frontend-core/src/components/sheet/ResizeOverlay.svelte
@@ -12,8 +12,8 @@
   let left = 0
   let columnCount = 0
 
-  $: cutoff = $scroll.left + 40 + $columns[0]?.width || 0
   $: scrollLeft = $scroll.left
+  $: cutoff = scrollLeft + 40 + $columns[0]?.width || 0
   $: rowCount = $visibleRows.length
 
   const startResizing = (idx, e) => {
diff --git a/packages/frontend-core/src/components/sheet/ScrollOverlay.svelte b/packages/frontend-core/src/components/sheet/ScrollOverlay.svelte
new file mode 100644
index 0000000000..5750d7e0c2
--- /dev/null
+++ b/packages/frontend-core/src/components/sheet/ScrollOverlay.svelte
@@ -0,0 +1,124 @@
+<script>
+  import { getContext } from "svelte"
+  import { domDebounce, debounce, throttle } from "../../utils/utils"
+
+  const { scroll, bounds, rows, cellHeight, columns } =
+    getContext("spreadsheet")
+
+  // Bar config
+  const barOffset = 4
+
+  // State for dragging bars
+  let initialMouse
+  let initialScroll
+
+  // Memoize store primitives to reduce reactive statement invalidations
+  $: scrollTop = $scroll.top
+  $: scrollLeft = $scroll.left
+  $: height = $bounds.height
+  $: width = $bounds.width
+
+  // Calculate V scrollbar size and offset
+  $: contentHeight = ($rows.length + 1) * cellHeight
+  $: barHeight = Math.max(50, (height / contentHeight) * height)
+  $: availHeight = height - barHeight - 2 * barOffset
+  $: maxScrollTop = contentHeight - height
+  $: barTop = barOffset + availHeight * (scrollTop / maxScrollTop)
+
+  // Calculate H scrollbar size and offset
+  $: lastCol = $columns[$columns.length - 1]
+  $: contentWidth = lastCol ? lastCol?.left + lastCol?.width : 0
+  $: barWidth = Math.max(50, (width / contentWidth) * width)
+  $: availWidth = width - barWidth - 8
+  $: maxScrollLeft = contentWidth - width
+  $: barLeft = 4 + availWidth * (scrollLeft / maxScrollLeft)
+
+  // Calculate whether to show scrollbars or not
+  $: showVScrollbar = contentHeight > height
+  $: showHScrollbar = contentWidth > width
+
+  // V scrollbar drag handlers
+  const startVDragging = e => {
+    e.preventDefault()
+    initialMouse = e.clientY
+    initialScroll = scrollTop
+    document.addEventListener("mousemove", moveVDragging)
+    document.addEventListener("mouseup", stopVDragging)
+  }
+  const moveVDragging = domDebounce(e => {
+    const delta = e.clientY - initialMouse
+    const weight = delta / availHeight
+    const newScrollTop = initialScroll + weight * maxScrollTop
+    scroll.update(state => ({
+      ...state,
+      top: Math.max(0, Math.min(newScrollTop, maxScrollTop)),
+    }))
+  })
+  const stopVDragging = () => {
+    document.removeEventListener("mousemove", moveVDragging)
+    document.removeEventListener("mouseup", stopVDragging)
+  }
+
+  // H scrollbar drag handlers
+  const startHDragging = e => {
+    e.preventDefault()
+    initialMouse = e.clientX
+    initialScroll = scrollLeft
+    document.addEventListener("mousemove", moveHDragging)
+    document.addEventListener("mouseup", stopHDragging)
+  }
+  const moveHDragging = domDebounce(e => {
+    const delta = e.clientX - initialMouse
+    const weight = delta / availWidth
+    const newScrollLeft = initialScroll + weight * maxScrollLeft
+    scroll.update(state => ({
+      ...state,
+      left: Math.max(0, Math.min(newScrollLeft, maxScrollLeft)),
+    }))
+  })
+  const stopHDragging = () => {
+    document.removeEventListener("mousemove", moveHDragging)
+    document.removeEventListener("mouseup", stopHDragging)
+  }
+</script>
+
+{#if showVScrollbar}
+  <div
+    class="v-scrollbar"
+    style="--top:{barTop}px; height:{barHeight}px;"
+    on:mousedown={startVDragging}
+  />
+{/if}
+{#if showHScrollbar}
+  <div
+    class="h-scrollbar"
+    style="--left:{barLeft}px; width:{barWidth}px;"
+    on:mousedown={startHDragging}
+  />
+{/if}
+
+<style>
+  div {
+    position: absolute;
+    background: var(--spectrum-global-color-gray-600);
+    opacity: 0.6;
+    border-radius: 4px;
+    z-index: 20;
+    transition: opacity 130ms ease-out;
+  }
+  div:hover {
+    opacity: 0.9;
+  }
+  .v-scrollbar {
+    top: var(--top);
+    height: var(--height);
+    right: 4px;
+    width: 8px;
+  }
+  .h-scrollbar {
+    bottom: 4px;
+    height: 8px;
+    width: var(--width);
+    left: var(--left);
+  }
+</style>
diff --git a/packages/frontend-core/src/components/sheet/Sheet.svelte b/packages/frontend-core/src/components/sheet/Sheet.svelte
index 72d648c32c..920964e758 100644
--- a/packages/frontend-core/src/components/sheet/Sheet.svelte
+++ b/packages/frontend-core/src/components/sheet/Sheet.svelte
@@ -100,9 +100,10 @@
 
 <div class="sheet" style="--cell-height:{cellHeight}px;" id="sheet-{rand}">
   <SheetHeader />
+  <HeaderRow />
+
   <SheetBody>
-    <HeaderRow />
-    {#each $visibleRows as row (row._id)}
+    {#each $visibleRows as row}
       <SheetRow {row} />
     {/each}
     <NewRow />
diff --git a/packages/frontend-core/src/components/sheet/SheetBody.svelte b/packages/frontend-core/src/components/sheet/SheetBody.svelte
index f7cf7c63ab..6a5bfe68d5 100644
--- a/packages/frontend-core/src/components/sheet/SheetBody.svelte
+++ b/packages/frontend-core/src/components/sheet/SheetBody.svelte
@@ -1,6 +1,7 @@
 <script>
   import { getContext, onMount } from "svelte"
   import { Utils } from "../../utils"
+  import ScrollOverlay from "./ScrollOverlay.svelte"
 
   const { columns, selectedCellId, cellHeight, rows, bounds, scroll } =
     getContext("spreadsheet")
@@ -12,6 +13,7 @@
   $: contentHeight = ($rows.length + 2) * cellHeight
   $: contentWidth = computeContentWidth($columns)
   $: scrollLeft = $scroll.left
+  $: scrollTop = $scroll.top
 
   const computeContentWidth = columns => {
     if (!columns.length) {
@@ -29,6 +31,26 @@
     updateScrollStore(e.target.scrollLeft, e.target.scrollTop)
   }
 
+  const handleWheel = e => {
+    const step = cellHeight * 3
+    const deltaY = e.deltaY < 0 ? -1 : 1
+    const offset = deltaY * step
+    let newScrollTop = scrollTop
+    newScrollTop += offset
+    newScrollTop = Math.max(0, newScrollTop)
+    newScrollTop = Math.min(
+      newScrollTop,
+      $rows.length * cellHeight - $bounds.height
+    )
+    scroll.update(state => ({
+      ...state,
+      top: newScrollTop,
+    }))
+  }
+
+  $: fakeOffsetY = -1 * (scrollTop % cellHeight)
+  $: fakeOffsetX = -1 * scrollLeft
+
   onMount(() => {
     // Observe and record the height of the body
     const observer = new ResizeObserver(() => {
@@ -46,20 +68,15 @@
   class="sheet-body"
   class:horizontally-scrolled={scrollLeft > 0}
   on:click|self={() => ($selectedCellId = null)}
-  on:scroll={handleScroll}
+  on:wheel|passive={handleWheel}
 >
   <div
     class="content"
-    style="height:{contentHeight + padding}px; width:{contentWidth +
-      padding}px;"
+    style="width:{contentWidth}px; --offset-y:{fakeOffsetY}px; --offset-x:{fakeOffsetX}px;"
   >
-    <div
-      class="data-content"
-      style="height:{contentHeight}px; width:{contentWidth}px;"
-    >
-      <slot />
-    </div>
+    <slot />
   </div>
+  <ScrollOverlay />
 </div>
 
 <style>
@@ -67,24 +84,19 @@
     display: block;
     position: relative;
     cursor: default;
-    overflow: auto;
+    overflow: hidden;
     flex: 1 1 auto;
     height: 0;
   }
   .sheet-body::-webkit-scrollbar-track {
     background: transparent;
   }
-  .content,
-  .data-content {
-    position: absolute;
-  }
   .content {
     min-width: 100%;
     min-height: 100%;
     background: var(--background-alt);
-  }
-  .data-content {
-    background: var(--cell-background);
+    transform: translate3d(var(--offset-x), var(--offset-y), 0);
+    overflow: hidden;
   }
 
   /* Add shadow to sticky cells when horizontally scrolled */
diff --git a/packages/frontend-core/src/components/sheet/SheetRow.svelte b/packages/frontend-core/src/components/sheet/SheetRow.svelte
index 67a479963a..5129ec0b98 100644
--- a/packages/frontend-core/src/components/sheet/SheetRow.svelte
+++ b/packages/frontend-core/src/components/sheet/SheetRow.svelte
@@ -29,6 +29,8 @@
     link: RelationshipCell,
   }
 
+  console.log("mount")
+
   $: rowSelected = !!$selectedRows[row._id]
 
   const selectRow = id => {
@@ -39,7 +41,7 @@
   }
 </script>
 
-<div class="row" style="--top:{(row.__idx + 1) * cellHeight}px;">
+<div class="row">
   <SpreadsheetCell label {rowSelected} on:click={() => selectRow(row._id)}>
     <div class="checkbox" class:visible={rowSelected}>
       <Checkbox value={rowSelected} />
@@ -76,8 +78,7 @@
 <style>
   .row {
     display: flex;
-    position: absolute;
-    top: var(--top);
+    position: relative;
     width: inherit;
   }
   :global(.sheet:not(.is-resizing):not(.is-reordering) .row:hover .cell) {
diff --git a/packages/frontend-core/src/components/sheet/stores/viewport.js b/packages/frontend-core/src/components/sheet/stores/viewport.js
index 9379c1670b..82df7739e7 100644
--- a/packages/frontend-core/src/components/sheet/stores/viewport.js
+++ b/packages/frontend-core/src/components/sheet/stores/viewport.js
@@ -16,25 +16,18 @@ export const createViewportStores = context => {
 
   // Debounce scroll updates so we can slow down visible row computation
   scroll.subscribe(({ left, top }) => {
-    window.requestAnimationFrame(() => {
-      // Only update local state when big changes occur
-      if (Math.abs(top - scrollTop) > cellHeight * 4) {
-        scrollTop = top
-        scrollTopStore.set(top)
-      }
-      if (Math.abs(left - scrollLeft) > 100) {
-        scrollLeft = left
-        scrollLeftStore.set(left)
-      }
-    })
+    scrollTop = top
+    scrollTopStore.set(top)
+    scrollLeft = left
+    scrollLeftStore.set(left)
   })
 
   // Derive visible rows
   const visibleRows = derived(
     [rows, scrollTopStore, height],
     ([$rows, $scrollTop, $height]) => {
-      const maxRows = Math.ceil($height / cellHeight) + 16
-      const firstRow = Math.max(0, Math.floor($scrollTop / cellHeight) - 8)
+      const maxRows = Math.ceil($height / cellHeight) + 1
+      const firstRow = Math.max(0, Math.floor($scrollTop / cellHeight))
       return $rows.slice(firstRow, firstRow + maxRows)
     }
   )