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fix(perf): scroll juddering when scrolling up #4725

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fix(perf): scroll juddering when scrolling up #4725

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669a86c
perf: rework _addTopRow to batch row writes
lukecotter Mar 24, 2025
0532429
perf: rework _addBottomRow to batch row writes
lukecotter Mar 24, 2025
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186 changes: 102 additions & 84 deletions src/js/core/rendering/renderers/VirtualDomVertical.js
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Original file line number Diff line number Diff line change
Expand Up @@ -287,9 +287,10 @@ export default class VirtualDomVertical extends Renderer{
rowFragment = document.createDocumentFragment();

i = 0;
index = this.vDomBottom;

while ((i < rowsToRender) && this.vDomBottom < rowsCount -1) {
index = this.vDomBottom + 1,
while ((i < rowsToRender) && this.vDomBottom < rowsCount -1) {
index++;
row = rows[index];

this.styleRow(row, index);
Expand All @@ -310,9 +311,9 @@ export default class VirtualDomVertical extends Renderer{
}

element.appendChild(rowFragment);

// NOTE: The next 3 loops are separate on purpose
// This is to batch up the dom writes and reads which drastically improves performance
// This is to batch up the dom writes and reads which drastically improves performance

renderedRows.forEach((row) => {
row.rendered();
Expand All @@ -330,7 +331,7 @@ export default class VirtualDomVertical extends Renderer{

renderedRows.forEach((row) => {
rowHeight = row.getHeight();

if(totalRowsRendered < topPad){
topPadHeight += rowHeight;
}else {
Expand Down Expand Up @@ -389,66 +390,71 @@ export default class VirtualDomVertical extends Renderer{

_addTopRow(rows, fillableSpace){
var table = this.tableElement,
addedRows = [],
paddingAdjust = 0,
index = this.vDomTop -1,
i = 0,
working = true;

while(working){
if(this.vDomTop){
let row = rows[index],
rowHeight, initialized;

if(row && i < this.vDomMaxRenderChain){
rowHeight = row.getHeight() || this.vDomRowHeight;
initialized = row.initialized;

if(fillableSpace >= rowHeight){

this.styleRow(row, index);
table.insertBefore(row.getElement(), table.firstChild);

if(!row.initialized || !row.heightInitialized){
addedRows.push(row);
}
i = 0
, working = true;

let numRowsToAdd = Math.ceil(fillableSpace / this.vDomRowHeight);
while(working && numRowsToAdd && this.vDomTop && fillableSpace > 0 && i < this.vDomMaxRenderChain){
const docFrag = document.createDocumentFragment();
const addedRows = [];
const newInitRows = [];
while( i < numRowsToAdd){
let row = rows[index], rowHeight;
if(!row){
working = false;
break;
}

row.initialize();
rowHeight = row.getHeight() || this.vDomRowHeight;
if(fillableSpace < rowHeight){
working = false;
break;
}

if(!initialized){
rowHeight = row.getElement().offsetHeight;
this.styleRow(row, index);
if(!row.initialized){
newInitRows.push(row);
}else{
addedRows.push(row);
}

if(rowHeight > this.vDomWindowBuffer){
this.vDomWindowBuffer = rowHeight * 2;
}
}
row.initialize(false, true);
docFrag.insertBefore(row.getElement(), docFrag.firstChild);

fillableSpace -= rowHeight;
paddingAdjust += rowHeight;
this.vDomTop--;
index--;
i++;
}
table.insertBefore(docFrag, table.firstChild);

this.vDomTop--;
index--;
i++;
for (let row of newInitRows){
row.clearCellHeight();
}

}else{
working = false;
}
this._quickNormalizeRowHeight(newInitRows);

}else{
working = false;
for (let row of newInitRows){
const rowHeight = row.getElement().offsetHeight;
if(rowHeight > this.vDomWindowBuffer){
this.vDomWindowBuffer = rowHeight * 2;
}
}

}else{
working = false;
let totalRowHeight = 0;
for (let row of addedRows){
const rowHeight = row.getHeight() || row.getElement().offsetHeight;
totalRowHeight += rowHeight;

fillableSpace -= rowHeight;
paddingAdjust += rowHeight;
}
}

for (let row of addedRows){
row.clearCellHeight();
const avgRowHeight = Math.max(totalRowHeight / addedRows.length, 0);
numRowsToAdd = avgRowHeight > 0 ? Math.ceil(fillableSpace / avgRowHeight) : 0;
}

this._quickNormalizeRowHeight(addedRows);

if(paddingAdjust){
this.vDomTopPad -= paddingAdjust;

Expand Down Expand Up @@ -511,59 +517,71 @@ export default class VirtualDomVertical extends Renderer{

_addBottomRow(rows, fillableSpace){
var table = this.tableElement,
addedRows = [],
paddingAdjust = 0,
index = this.vDomBottom + 1,
i = 0,
working = true;

while(working){
let row = rows[index],
rowHeight, initialized;
let numRowsToAdd = Math.ceil(fillableSpace / this.vDomRowHeight);
while(working && numRowsToAdd && this.vDomTop && fillableSpace > 0 && i < this.vDomMaxRenderChain){
const docFrag = document.createDocumentFragment();
const addedRows = [];
const newInitRows = [];
while( i < numRowsToAdd){
let row = rows[index], rowHeight;
if(!row){
working = false;
break;
}

if(row && i < this.vDomMaxRenderChain){
rowHeight = row.getHeight() || this.vDomRowHeight;
initialized = row.initialized;
if(fillableSpace < rowHeight){
working = false;
break;
}

if(fillableSpace >= rowHeight){
this.styleRow(row, index);
if(!row.initialized){
newInitRows.push(row);
}else{
addedRows.push(row);
}

this.styleRow(row, index);
table.appendChild(row.getElement());
row.initialize(false, true);
docFrag.append(row.getElement());

if(!row.initialized || !row.heightInitialized){
addedRows.push(row);
}
this.vDomTop++;
index++;
i++;
}
table.append(docFrag);

row.initialize();
for (let row of newInitRows){
row.clearCellHeight();
}

if(!initialized){
rowHeight = row.getElement().offsetHeight;
this._quickNormalizeRowHeight(newInitRows);

if(rowHeight > this.vDomWindowBuffer){
this.vDomWindowBuffer = rowHeight * 2;
}
}
for (let row of newInitRows){
const rowHeight = row.getElement().offsetHeight;
if(rowHeight > this.vDomWindowBuffer){
this.vDomWindowBuffer = rowHeight * 2;
}
}

fillableSpace -= rowHeight;
paddingAdjust += rowHeight;
let totalRowHeight = 0;
for (let row of addedRows){
const rowHeight = row.getHeight() || row.getElement().offsetHeight;
totalRowHeight += rowHeight;

this.vDomBottom++;
index++;
i++;
}else{
working = false;
}
}else{
working = false;
fillableSpace -= rowHeight;
paddingAdjust += rowHeight;
}
}

for (let row of addedRows){
row.clearCellHeight();
const avgRowHeight = Math.max(totalRowHeight / addedRows.length, 0);
numRowsToAdd = avgRowHeight > 0 ? Math.ceil(fillableSpace / avgRowHeight) : 0;
}

this._quickNormalizeRowHeight(addedRows);

if(paddingAdjust){
this.vDomBottomPad -= paddingAdjust;

Expand Down