C++ & Qt

25 March 2026 10:20

and damn right it is faster

C++ & Qt

25 March 2026 09:57

perhaps it doesn't have to be perfect either? Skipping some lines when resizing isn't that much of a problem perhaps?

C++ & Qt

25 March 2026 09:55

also wondering what will happen if i will just be getting element in the vierwport and calling the resizeRowToContents

C++ & Qt

25 March 2026 09:53

or only on visible elements

C++ & Qt

25 March 2026 09:43

resizeToContents on first 3 columns also make gui thread go up to 100% but without visible lag. this could be made fixed size thats all

C++ & Qt

25 March 2026 09:40

so if i set all resize policies to fixed without word wrap and the 4th column to stretch(cant see full mesage) or interactive(this could work but word wrap + stretch would be beter), i get decent performance

if on to of previous i do word wrap, nothing is changing because the row height is fixed, but if i enable resizeToContents on the vertical header i get huuuge performance penalty

C++ & Qt

25 March 2026 09:26

god damn there is no valgrind on mac arm yet, constant pain in the butt, i have to use pc for this purposes

C++ & Qt

25 March 2026 09:04

so this behave same on my air m2. scroll is takin 2-3% of cpu is short bursts (idk seems ok), resize with mouse eats up entire gui thread/core to 100%

C++ & Qt

25 March 2026 00:25

Also the below calls are very expensive and should be aboided if used.

resizeColumnsToContents() / resizeRowsToContents()

C++ & Qt

24 March 2026 21:20

I have done similar things with tables in qml. Apparently qml uses single point precision for row offsets, so if the number of rows are big enough the layout gets weird (even if the performance is good)

C++ & Qt

24 March 2026 21:13

You can also do that in the parent widget by using only x rows in the listview.

C++ & Qt

24 March 2026 15:47

Uniform row heights is also good, but I suppose you want it to look as in the image above

C++ & Qt

24 March 2026 14:18

Are you using, by any chance, any call to view->setIndexWidget()? This implies a huge performance penalty. Also, if you can move to QML, it reuses delegates and has no calls to paint(), which is quite likely to be executed in CPU instead of GPU.

C++ & Qt

24 March 2026 14:05

no I did not. i guess the table resize entire table at once. if i will manage to run profiler i will get back to you

C++ & Qt

24 March 2026 14:03

l have change resizeToContents and Stretch to FIxed and yes it is fast alright

C++ & Qt

25 March 2026 10:19

so i managed to make this

log_view::log_view(log_model* lm)
    : QTableView(nullptr) {
 setModel(lm);
 setAlternatingRowColors(true);
 setSelectionMode(QAbstractItemView::SingleSelection);
 setSelectionBehavior(QAbstractItemView::SelectRows);
 setWordWrap(true);

 verticalHeader()->setSectionResizeMode(QHeaderView::Fixed);
 verticalHeader()->setDefaultSectionSize(24);

 auto header = horizontalHeader();
 // i gave up on dynamic columns, just eyeballed the default size and let the
 // user change it god damn
 header->setSectionResizeMode(0, QHeaderView::Interactive);
 header->resizeSection(0, 140);
 header->setSectionResizeMode(1, QHeaderView::Interactive);
 header->resizeSection(1, 80);
 header->setSectionResizeMode(2, QHeaderView::Interactive);
 header->resizeSection(2, 73);
 header->setSectionResizeMode(3, QHeaderView::Stretch);

 connect(
  header, &QHeaderView::sectionResized,
  this, &log_view::on_section_resized
 );

 connect(
  verticalScrollBar(), &QScrollBar::valueChanged,
  this, &log_view::schedule_visible_row_resize
 );

 connect(
  model(), &QAbstractItemModel::dataChanged, this,
  [this](const QModelIndex& topLeft, const QModelIndex& bottomRight) {
   if (topLeft.column() == 3) {
    for (int r = topLeft.row(); r <= bottomRight.row(); ++r)
    if (visualRect(model()->index(r, 0)).intersects(viewport()->rect()))
     resizeRowToContents(r);
   }
  }
 );

 QMetaObject::invokeMethod(this, &log_view::schedule_visible_row_resize, Qt::QueuedConnection);
}

void log_view::on_section_resized(int logicalIndex, int oldSize, int newSize) {
 if (logicalIndex == 3)
  schedule_visible_row_resize();
}

void log_view::schedule_visible_row_resize() {
 QMetaObject::invokeMethod(
  this, &log_view::update_visible_row_heights,
  Qt::QueuedConnection
 );
}

void log_view::update_visible_row_heights() {
 if (!model() || model()->rowCount() == 0)
  return;

 setUpdatesEnabled(false);

 const int first = rowAt(0);
 if (first < 0) {
  setUpdatesEnabled(true);
  return;
 }

 int last = rowAt(viewport()->height() - 1);
 if (last < 0)
  last = model()->rowCount() - 1;

 for (int row = first; row <= last; ++row)
  resizeRowToContents(row);

 setUpdatesEnabled(true);
}

void log_view::resizeEvent(QResizeEvent* ev) {
 setUpdatesEnabled(false); // importand to not let the table view do nothin by itlself
 QTableView::resizeEvent(ev);
 setUpdatesEnabled(true);
 schedule_visible_row_resize();
}

Qt’s standard “do it once, later” pattern

When the current event loop finishes processing all the resize/scroll/paint events that are already queued, then run this once

C++ & Qt

25 March 2026 09:55

but the scrollbar wont cbe in correct scale

C++ & Qt

25 March 2026 09:54

it has to look at all elements above at least (and perhaps the rest of them to get the scrollbar size right)

C++ & Qt

25 March 2026 09:52

With dynamic row height it has to do that i suppose, but perhaps it could happen less often

C++ & Qt

25 March 2026 09:41

i wonder as if the widget tries to recalculate all the heights, maybe this could be optimized to only update visible elements somehow

C++ & Qt

25 March 2026 09:27

not as bad as this though

C++ & Qt

25 March 2026 09:13

this defenitetly helps with performance with 200 elements. but with 10k it is not enough

C++ & Qt

25 March 2026 07:09

@Dolfost i tried this and it doesn't feel that slow on my machine:

QStandardItemModel* lm = new QStandardItemModel();
lm->setColumnCount(4);

for(int i = 0; i < 2000; ++i)
{
QList<QStandardItem*> row;

row << new QStandardItem(QString::number(i)) << new QStandardItem("A") << new QStandardItem("B");
if(i % 20 == 0)
row << new QStandardItem("CCCCCCCCCC CCCCCCCCCC CCCCCCCCCC CCCCCCCCCC CCCCCCCCCC CCCCCCCCCC CCCCCCCCCC CCCCCCCCCC CCCCCCCCCC CCCCCCCCCC CCCCCCCCCC CCCCCCCCCC CCCCCCCCCC CCCCCCCCCC CCCCCCCCCC CCCCCCCCCC ");
else
row << new QStandardItem("C");

lm->appendRow(row);
}

ui->log_view->setModel(lm);
ui->log_view->setAlternatingRowColors(true);
ui->log_view->setSelectionMode(QAbstractItemView::SelectionMode::SingleSelection);
ui->log_view->setSelectionBehavior(QAbstractItemView::SelectionBehavior::SelectRows);
ui->log_view->verticalHeader()->setSectionResizeMode(QHeaderView::ResizeMode::ResizeToContents);

auto header = ui->log_view->horizontalHeader();

header->setSectionResizeMode(0, QHeaderView::ResizeMode::ResizeToContents);
header->setSectionResizeMode(1, QHeaderView::ResizeMode::ResizeToContents);
header->setSectionResizeMode(2, QHeaderView::ResizeMode::ResizeToContents);

header->setSectionResizeMode(3, QHeaderView::ResizeMode::Stretch);
ui->log_view->setWordWrap(true);
connect(header, &QHeaderView::sectionResized, this,
[this](int logicalIndex, int /*oldSize*/, int /*newSize*/) {
if (logicalIndex == 3)
ui->log_view->resizeRowsToContents();
}
);

C++ & Qt

25 March 2026 00:18

It's been quite a long since I used widgets. I can suggest the below solution.

Try disable updates while resizing.

Qt repaints continuously during a resize event. You can suppress this.

Override resizeEvent.

void MyWidget::resizeEvent(QResizeEvent *event)
{
tableWidget->setUpdatesEnabled(false);
QWidget::resizeEvent(event);
tableWidget->setUpdatesEnabled(true);
}

C++ & Qt

24 March 2026 21:15

In one of my projects, I have a thumbnail view that with about 100k pictures. Performance was really bad - in the end, I just implemented the paintEvent() myself. It's really nice now.

C++ & Qt

24 March 2026 21:13

I'd probably subclass the list widget and only render the visible portion of the list.

C++ & Qt

24 March 2026 15:08

200 rows should work even without models I think

C++ & Qt

24 March 2026 14:05

I think there may be ways to make the size estimation faster

C++ & Qt

24 March 2026 14:04

Did you try running callgrind (or any other profiler) to reveal where the bootleneck is in?

C++ & Qt

24 March 2026 13:59

Is it faster if all columns have fixed with?