@Pl45m4 Here is a short video of the application showing the issue:
https://github.com/letsfindaway/OpenBoard/issues/203#issuecomment-2595705681

The rubber is a pixmap cursor using QCursor. The circle is repositioned at each mouseMoveEvent. You see that it is lagging behind the cursor. The preview image to the left is the second view attached to the same scene.

So you see, nothing complicated. And as I already said in the beginning: when I run the same program using Qt5, then the lag is much smaller, because the repetition rate of the mouseMoveEvents is higher.

I have setMouseTracking(true), so that I get the events even when the mouse button is not pressed.

And no, there are no further actions connected to the movement as long as the mouse button is not pressed.

Seems you need to enable mouse tracking for widget1, see:

void setMouseTracking(bool enable)
If mouse tracking is switched off, mouse move events only occur if a mouse button is pressed while the mouse is being moved. If mouse tracking is switched on, mouse move events occur even if no mouse button is pressed.

I solved my problem via event filter of scene.

ui->graphicsView->scene()->installEventFilter(this); bool MainWindow::eventFilter(QObject* obj, QEvent* event){ if(event->type() == QEvent::GraphicsSceneMousePress){ if(ui->addServerBtn->isChecked()){ QGraphicsSceneMouseEvent* mouseSceneEvent; mouseSceneEvent = static_cast<QGraphicsSceneMouseEvent *>(event); Server *serv = new Server(mouseSceneEvent->scenePos().toPoint()); scene->addItem((QGraphicsPixmapItem*)serv); } } return false; }