How to keep aspect ratio of QLabel after QPixmap?

[jrod2much]

Hello,
I have a Qlabel that I load an image to and I have read a lot of forum posts but can't seem to keep the aspect ratio. and one time I was successful but it ruined the resolution of the image. How can i do this.

void MainWindow::chromaticity() {
  int h = m_ui->label_3->height();
  int w = m_ui->label_3->width();
  QPixmap pix(w, h);
  m_ui->label_3->setPixmap(pix.scaled(w,h,Qt::KeepAspectRatio));
  pix.load(":/icons/icons/chromeL.png");


  QPainter paint(&pix);



  paint.setPen(QColor(0, 0, 0, 255));
  int y = 0;
  int x = 0;
  int bw = 10; // bar width
  for (int barcount = 0; barcount < 50; ++barcount) {
    paint.setBrush(QColor(255, 0, 255, 255));
    paint.drawRect(78+x, 825,  4, 4 );
    x += bw + 3;
  }
  paint.end();
  m_ui->label_3->setPixmap(pix);
}

[J.Hilk]

hi @jrod2much

without regards on perfomance:

.....
 m_ui->label_3->setPixmap(pix.scaled(  m_ui->label_3->size(), Qt::KeepAspectRatio, Qt::SmoothTransformation) );

[jrod2much]

@J-Hilk
It isn't working, where do I put it in my code? Maybe Im placing it in the wrong place.

[J.Hilk]

@jrod2much
did you move pix.scaled outside the setPixmap call ? because scaled returns a new Scaled pixmap.

[jrod2much]

@J-Hilk I know exactly what you are saying but my friend is pretty dumb, maybe you could explain it for them. Thanks

void MainWindow::chromaticity() {
    int h = m_ui->label_3->height();
    int w = m_ui->label_3->width();
    QPixmap pix(":/icons/icons/chromeL.png");
    m_ui->label_3->setPixmap(pix.scaled(  m_ui->label_3->size(), Qt::KeepAspectRatio, Qt::SmoothTransformation) );

    if(chromeX != 0 && chromeX != 0)
    {
        QPainter paint(&pix);
        paint.setPen(QColor(0, 0, 0, 255));
        paint.setBrush(QColor(255, 255, 255, 255));
        paint.drawRect(chromeX - 4, chromeY- 4,  8, 8);
        paint.end();
    }
    m_ui->label_3->setPixmap(pix.scaled(  m_ui->label_3->size(), Qt::KeepAspectRatio, Qt::SmoothTransformation) );

}

[J.Hilk]

alright, imagine the following, I'm using qDebug() to print some numbers.

   qDebug() << "Size of the Label" << m_ui->label_3->size();

    QPixmap pix(":/icons/icons/chromeL.png");

    qDebug() << "Size of the original Image" << pix.size();

    QPixmap pixScaled = pix.scaled(  m_ui->label_3->size(), Qt::KeepAspectRatio, Qt::SmoothTransformation);
    //Either pixScaled.width() == label_3->width() or pixScaled.height() == label_3->height() with the companion parameter beeing smaller to guaranty aspec-ratio

    qDebug() << "Size of the scaled Pixmap" << pixScaled.size();
    m_ui->label_3->setPixmap(pixScaled);