Lines thickness changes spontaneously when scaling QGraphicsView

I am drawing lines in Qt using Graphics View framework. Since i want my picture to take the same portion of space when the window is resized, I override MainWindow::resizeEvent, so that graphics view is rescaled according to the resize event:

void MainWindow::resizeEvent(QResizeEvent *event) {
    int w = event->size().width(), h = event->size().height();
    int prev_w = event->oldSize().width(), prev_h = event->oldSize().height();
    if (prev_w != -1) {
        int s1 = std::min(prev_w, prev_h), s2 = std::min(w, h);
        qreal k = (qreal)s2 / s1;
        std::cerr << k << std::endl;
        ui->graphicsView->scale(k, k);
    }
}

However, doing so, my lines (that should have thickness of 1 pixel) sometimes have different thickness after resize. As I understand, it happens because coordinates of the objects after transforming to the GraphicsView are real, so are sometimes drawn with different number of pixels. That is unacceptable! I want lines to have same 1-pixel thickness all the time.

So, my question is: what is the usual solution for this problem? For now (based on my assumption above) I can only think of deleting all objects and creating new with integer coordinates, but rescaled (manually).

You need to set your line drawing to "cosmetic" in the QPen. This makes the lines non-scalable. Otherwise, Qt scales the line widths along with the scaling of the view. Look up QPen::setCosmetic. By default, drawing lines is not cosmetic.