Maintaining aspect ratio of qlabel

[J.Hilk]

you can override paintEvent and do it yourself:

for example (assuming its a square image)

void myLabel::paintEvent( QPaintEvent* event )
{
     int min = qMin(height(), width());
     int xOff = (width() - min) / 2;
     int yOff = (height() - min) / 2;

    QPainter p(this);
    p.drawImage(QRect(xOff,yOff,min,min), m_myImage);
}

[Kira]

@J-Hilk : Thanks for the reply:
Current I am using the following:

void LabelAnnotation::resizeEvent(QResizeEvent *pQEvent)
{
    QLabel::resizeEvent(pQEvent);
    setPixmap(_qPixmap, pQEvent->size());
}

void LabelAnnotation::setPixmap(const QPixmap &qPixmap, const QSize &size)
{
    QPixmap _qPixmapScaled;
    _qPixmap = qPixmap;
    _qPixmapScaled = _qPixmap.scaled(size, Qt::KeepAspectRatioByExpanding, Qt::SmoothTransformation);
    QLabel::setPixmap(_qPixmapScaled);
}

Will I have to remove the above function if i override paintEvent as mentioned ?

[J.Hilk]

@Kira I don't think so,

you can access your modified/scaled pixmap by calling pixmap() and QPainter has a drawPixmap method as well.

---

just noticed, that what I wrote, does not actually match what you want.

Do I understand it correctly, that you want a way to rescale your QLabel, so that it fits the Pixmap ?

[Kira]

@J-Hilk : yes
I tried running your code its shrinks my pixmap a bit :p

[Kira]

@jsulm : Just a strange thing the program crashes after some time without throwing any specific error

[J.Hilk]

@Kira well, is your label part of a layout or do you resize it manually?

because you will have to resize it manually, having it in a layout will make things tricky

[Kira]

@J-Hilk : My label is part of the Grid layout.
I have seen various articles related to the issue, but none of them provide an exact solution. Is there a specific way to handle such a scenario.

[J.Hilk]

@Kira
Ok, I suggest the following, I used it before with moderate success rate.

set the SizePolcy of either width or height to fixed.

inside the overloaded resizeEvent, set the min width/height of your fixed side to the appropriate length (according to the pixmap ratio)

It should work, but be beware of potential recursive resizeEvents, as this is a clunky workaround.

[Kira]

@J-Hilk :
OK, thanks, understood.
What does moderate success mean?
How can I determine the aspect ratio ?
I will figure the code but would be grateful if you have any working sample.

[J.Hilk]

@Kira

What does moderate success mean

when actively resizing the window, you may get "flickering" as the new min size may tricker a new recalculating of the other widgets inside the layout

How can I determine the aspect ratio
I will figure the code but would be grateful if you have any working sample

untested:

//Assuming horizontal size policy is fixed
void LabelAnnotation::resizeEvent(QResizeEvent *pQEvent)
{
    double minw = (static_cast<double>(_qPixmap.width()) * height()) / _qPixmap.height();
   setMinimumWidth(static_cast<int>(minw));
}

[Kira]

@J-Hilk :Thanks a lot will implement it and let you know.

[Kira]

@J-Hilk : Here are we resizing the window or the QLabel.
I implemented the following, but still, there is space left when I make the window to full screen.

[J.Hilk]

@Kira said in Maintaining aspect ratio of qlabel:

I implemented the following

I don't see it. May be lost in the depth of the forum ?

[Kira]

@J-Hilk said in Maintaining aspect ratio of qlabel:

void LabelAnnotation::resizeEvent(QResizeEvent *pQEvent)
{
double minw = (static_cast<double>(_qPixmap.width()) * height()) / _qPixmap.height();
setMinimumWidth(static_cast<int>(minw));
}

This one :)

[J.Hilk]

can you show us a screenshot of the image inside the layout, it's still difficult for me to visualize what the issue is exactly ;)

[Kira]

@J-Hilk : Sure