Automatic image resizing too slow

[ecanela]

According to Qt Documentationo of QWidget::resizeEvent
The widget will be erased and receive a paint event immediately after processing the resize event. No drawing need be (or should be) done inside this handler.

you don't mencioned in what function scale the pixmap, if the pixmap is called in the funtion resize event, MAYBE that is the problem. indirectly you enforce a redraw of the widget, but i need see the your source code.

try to use Qt::FastTransformation instead of Qt::SmoothTransformation.

imageContainer->setPixmap(pix.scaled(sizex, Qt::KeepAspectRatio, Qt::FastTransformation));

imageContainer->setPixmap(pix.scaled(sizex, Qt::KeepAspectRatio, Qt::FastTransformation));

To copy to clipboard, switch view to plain text mode 

Another detail. resizeEvent is a event not a Qt signal. Signals are useful when using a widget, whereas events are useful when implementing a widget.

sorry my poor english. my natural lenguege is spanish