From 0eadca9acbf68e3b47a4e7fb220baf2fb7aea9ac Mon Sep 17 00:00:00 2001
From: Andrew Kingston <andrew@kingston.dev>
Date: Sat, 25 Feb 2023 16:33:20 +0000
Subject: [PATCH] Optimise scrolling and virtual rendering performance

---
 .../app/spreadsheet/Spreadsheet.svelte        | 28 +++---
 .../app/spreadsheet/SpreadsheetBody.svelte    | 96 ++++++++++---------
 .../app/spreadsheet/SpreadsheetRow.svelte     | 13 ++-
 packages/client/src/utils/domDebounce.js      | 12 ++-
 4 files changed, 81 insertions(+), 68 deletions(-)

diff --git a/packages/client/src/components/app/spreadsheet/Spreadsheet.svelte b/packages/client/src/components/app/spreadsheet/Spreadsheet.svelte
index d57da63b19..2808b2c572 100644
--- a/packages/client/src/components/app/spreadsheet/Spreadsheet.svelte
+++ b/packages/client/src/components/app/spreadsheet/Spreadsheet.svelte
@@ -35,7 +35,8 @@
   const tableId = writable(table?.tableId)
   const changeCache = writable({})
   const newRows = writable([])
-  const visibleCells = writable({ y: [0, 0], x: [0, 0] })
+  const visibleRows = writable([0, 0])
+  const visibleColumns = writable([0, 0])
 
   // Build up spreadsheet context and additional stores
   const context = {
@@ -49,7 +50,8 @@
     changeCache,
     newRows,
     cellHeight,
-    visibleCells,
+    visibleRows,
+    visibleColumns,
   }
   const { reorder, reorderPlaceholder } = createReorderStores(context)
   const resize = createResizeStore(context)
@@ -67,7 +69,7 @@
   $: rowCount = $rows.length
   $: selectedRowCount = Object.values($selectedRows).filter(x => !!x).length
   $: updateSortedRows($fetch, $newRows)
-  $: visibleRows = $rows.slice($visibleCells.y[0], $visibleCells.y[1])
+  $: renderedRows = $rows.slice($visibleRows[0], $visibleRows[1])
 
   const createFetch = datasource => {
     return fetchData({
@@ -160,16 +162,16 @@
 
   const updateSortedRows = (unsortedRows, newRows) => {
     let foo = unsortedRows.rows
-    for (let i = 0; i < 10; i++) {
+    for (let i = 0; i < 3; i++) {
       foo = foo.concat(foo.map(x => ({ ...x, _id: x._id + "x" })))
     }
-    // let sortedRows = foo.slice()
-    // sortedRows.sort((a, b) => {
-    //   const aIndex = newRows.indexOf(a._id)
-    //   const bIndex = newRows.indexOf(b._id)
-    //   return aIndex < bIndex ? -1 : 1
-    // })
-    $rows = foo.slice()
+    let sortedRows = foo.slice()
+    sortedRows.sort((a, b) => {
+      const aIndex = newRows.indexOf(a._id)
+      const bIndex = newRows.indexOf(b._id)
+      return aIndex < bIndex ? -1 : 1
+    })
+    $rows = sortedRows
   }
 
   // API for children to consume
@@ -229,8 +231,8 @@
       </div>
 
       <!-- All real rows -->
-      {#each visibleRows as row, rowIdx (row._id)}
-        <SpreadsheetRow {row} rowIdx={rowIdx + $visibleCells.y[0]} />
+      {#each renderedRows as row, rowIdx (row._id)}
+        <SpreadsheetRow {row} rowIdx={rowIdx + $visibleRows[0]} />
       {/each}
 
       <!-- New row placeholder -->
diff --git a/packages/client/src/components/app/spreadsheet/SpreadsheetBody.svelte b/packages/client/src/components/app/spreadsheet/SpreadsheetBody.svelte
index 185dc518f5..a8a5985f4c 100644
--- a/packages/client/src/components/app/spreadsheet/SpreadsheetBody.svelte
+++ b/packages/client/src/components/app/spreadsheet/SpreadsheetBody.svelte
@@ -1,8 +1,16 @@
 <script>
   import { getContext, onMount } from "svelte"
+  import { domDebounce } from "../../../utils/domDebounce"
 
-  const { columns, selectedCellId, rand, visibleCells, cellHeight, rows } =
-    getContext("spreadsheet")
+  const {
+    columns,
+    selectedCellId,
+    rand,
+    visibleRows,
+    visibleColumns,
+    cellHeight,
+    rows,
+  } = getContext("spreadsheet")
 
   const padding = 180
 
@@ -12,7 +20,8 @@
   let scrollLeft = 0
   let scrollTop = 0
 
-  $: computeVisibleCells($columns, scrollLeft, scrollTop, width, height)
+  $: updateVisibleRows($columns, scrollTop, height)
+  $: updateVisibleColumns($columns, scrollLeft, width)
   $: contentHeight = ($rows.length + 2) * cellHeight + padding
   $: contentWidth = computeContentWidth($columns)
   $: horizontallyScrolled = scrollLeft > 0
@@ -26,35 +35,52 @@
   }
 
   // Store the current scroll position
-  const handleScroll = e => {
-    // Only update scroll offsets when a sizable change happens
-    if (Math.abs(scrollTop - e.target.scrollTop) > 10) {
-      scrollTop = e.target.scrollTop
-    }
-    if (Math.abs(scrollLeft - e.target.scrollLeft) > 10) {
-      scrollLeft = e.target.scrollLeft
-    }
-    if (e.target.scrollLeft === 0) {
-      scrollLeft = 0
-    }
-  }
+  // let lastTop
+  // let lastLeft
+  // let ticking = false
+  // const handleScroll = e => {
+  //   lastTop = e.target.scrollTop
+  //   lastLeft = e.target.scrollLeft
+  //   if (!ticking) {
+  //     ticking = true
+  //     requestAnimationFrame(() => {
+  //       if (Math.abs(lastTop - scrollTop) > 100) {
+  //         scrollTop = lastTop
+  //       }
+  //       if (lastLeft === 0 || Math.abs(lastLeft - scrollLeft) > 100) {
+  //         scrollLeft = lastLeft
+  //       }
+  //       ticking = false
+  //     })
+  //   }
+  // }
 
-  const computeVisibleCells = (
-    columns,
-    scrollLeft,
-    scrollTop,
-    width,
-    height
-  ) => {
+  const handleScroll = domDebounce(
+    ({ left, top }) => {
+      if (Math.abs(top - scrollTop) > 100) {
+        scrollTop = top
+      }
+      if (left === 0 || Math.abs(left - scrollLeft) > 100) {
+        scrollLeft = left
+      }
+    },
+    e => ({ left: e.target.scrollLeft, top: e.target.scrollTop })
+  )
+
+  const updateVisibleRows = (columns, scrollTop, height) => {
     if (!columns.length) {
       return
     }
-
     // Compute row visibility
     const rows = Math.ceil(height / cellHeight) + 8
     const firstRow = Math.max(0, Math.floor(scrollTop / cellHeight) - 4)
-    const visibleRows = [firstRow, firstRow + rows]
+    visibleRows.set([firstRow, firstRow + rows])
+  }
 
+  const updateVisibleColumns = (columns, scrollLeft, width) => {
+    if (!columns.length) {
+      return
+    }
     // Compute column visibility
     let startColIdx = 1
     let rightEdge = columns[1].width
@@ -68,12 +94,7 @@
       leftEdge += columns[endColIdx]?.width
       endColIdx++
     }
-    const visibleColumns = [Math.max(1, startColIdx - 2), endColIdx + 2]
-
-    visibleCells.set({
-      x: visibleColumns,
-      y: visibleRows,
-    })
+    visibleColumns.set([Math.max(1, startColIdx - 2), endColIdx + 2])
   }
 
   onMount(() => {
@@ -87,26 +108,15 @@
       observer.disconnect()
     }
   })
-
-  let sheetStyles = ""
-  let left = 0
-  for (let i = 0; i < 20; i++) {
-    if (i === 1) {
-      left += 40
-    }
-    sheetStyles += `--col-${i}-width:${160}px; --col-${i}-left:${left}px;`
-    left += 160
-  }
 </script>
 
 <div
   bind:this={ref}
   class="spreadsheet"
   class:horizontally-scrolled={horizontallyScrolled}
-  on:scroll={handleScroll}
   on:click|self={() => ($selectedCellId = null)}
   id={`sheet-${rand}-body`}
-  style={sheetStyles}
+  on:scroll={handleScroll}
 >
   <div
     class="content"
@@ -119,10 +129,10 @@
 <style>
   .spreadsheet {
     display: block;
-    overflow: auto;
     height: 800px;
     position: relative;
     cursor: default;
+    overflow: auto;
   }
   .content {
     min-width: 100%;
diff --git a/packages/client/src/components/app/spreadsheet/SpreadsheetRow.svelte b/packages/client/src/components/app/spreadsheet/SpreadsheetRow.svelte
index fcba9caf88..595f2d1742 100644
--- a/packages/client/src/components/app/spreadsheet/SpreadsheetRow.svelte
+++ b/packages/client/src/components/app/spreadsheet/SpreadsheetRow.svelte
@@ -1,7 +1,6 @@
 <script>
   import { getContext } from "svelte"
   import SpreadsheetCell from "./SpreadsheetCell.svelte"
-  import SpacerCell from "./SpacerCell.svelte"
   import OptionsCell from "./cells/OptionsCell.svelte"
   import DateCell from "./cells/DateCell.svelte"
   import MultiSelectCell from "./cells/MultiSelectCell.svelte"
@@ -20,16 +19,16 @@
     selectedRows,
     changeCache,
     spreadsheetAPI,
-    visibleCells,
+    visibleColumns,
     cellHeight,
   } = getContext("spreadsheet")
 
   $: rowSelected = !!$selectedRows[row._id]
   $: rowHovered = $hoveredRowId === row._id
   $: data = { ...row, ...$changeCache[row._id] }
-  $: visibleColumns = [
+  $: renderedColumns = [
     $columns[0],
-    ...$columns.slice($visibleCells.x[0], $visibleCells.x[1]),
+    ...$columns.slice($visibleColumns[0], $visibleColumns[1]),
   ]
   $: containsSelectedCell = $selectedCellId?.split("-")[0] === row._id
 
@@ -77,7 +76,7 @@
       </span>
     {/if}
   </SpreadsheetCell>
-  {#each visibleColumns as column (column.name)}
+  {#each renderedColumns as column (column.name)}
     {@const cellIdx = `${row._id}-${column.name}`}
     <SpreadsheetCell
       {rowSelected}
@@ -116,7 +115,7 @@
     z-index: 1;
   }
 
-  .row :global(>:last-child) {
-      border-right-width: 1px;
+  .row :global(> :last-child) {
+    border-right-width: 1px;
   }
 </style>
diff --git a/packages/client/src/utils/domDebounce.js b/packages/client/src/utils/domDebounce.js
index b7fc017247..b15d2698b4 100644
--- a/packages/client/src/utils/domDebounce.js
+++ b/packages/client/src/utils/domDebounce.js
@@ -1,12 +1,14 @@
-export const domDebounce = callback => {
+export const domDebounce = (callback, extractParams = x => x) => {
   let active = false
-  return e => {
+  let lastParams
+  return (...params) => {
+    lastParams = extractParams(...params)
     if (!active) {
-      window.requestAnimationFrame(() => {
-        callback(e)
+      active = true
+      requestAnimationFrame(() => {
+        callback(lastParams)
         active = false
       })
-      active = true
     }
   }
 }