Cover QLabel with QPixmap in C++ - c++

Question

My goal
This is an example of how I want the QPixmap to be contained inside the QLabel. The image keeps its aspect ratio and fills the given dimension. It will be clipped to fit.
Here is the CSS equivalent:
object-fit: cover;
Current code
This almost does what I want, but it stretches the image to cover the QLabel, so the aspect ratio isn't reserved.
QPixmap *img = new QPixmap("image.png");
ui->label->setPixmap(*img);
ui->label->setScaledContents(true);
delete img;

Answer 1

Can be implemented as QWidget subclass using QTransform.
class Label : public QWidget
{
Q_OBJECT
public:
explicit Label(QWidget *parent = nullptr);
void setPixmap(const QPixmap& image);
protected:
void paintEvent(QPaintEvent *event);
QPixmap mPixmap;
};
Label::Label(QWidget *parent) : QWidget(parent) {
}
void Label::setPixmap(const QPixmap &pixmap)
{
mPixmap = pixmap;
update();
}
void Label::paintEvent(QPaintEvent *event)
{
if (mPixmap.isNull()) {
return;
}
double width = this->width();
double height = this->height();
double pixmapWidth = mPixmap.width();
double pixmapHeight = mPixmap.height();
double scale = qMax(width / pixmapWidth, height / pixmapHeight);
QTransform transform;
transform.translate(width / 2, height / 2);
transform.scale(scale, scale);
transform.translate(-pixmapWidth / 2, -pixmapHeight / 2);
QPainter painter(this);
painter.setTransform(transform);
painter.drawPixmap(QPoint(0,0), mPixmap);
}