Rotating a QWidget

sunil.nair

Hi,

I am trying to rotate a QWidget. I am already able to rotate a QPixmap using QPainter. I know you can't rotate a QLabel but how can I rotate a Qwidget or some container.

 QPixmap pixmap(":/logo_new.png");
    QPixmap rotate(pixmap.size());
QPainter p(&rotate);
    p.setRenderHint(QPainter::Antialiasing);
    p.setRenderHint(QPainter::SmoothPixmapTransform);
    p.setRenderHint(QPainter::HighQualityAntialiasing);
    p.translate(rotate.size().width()/2,rotate.size().height()/2);
    p.rotate(counter);
    p.translate(-rotate.size().width()/2,-rotate.size().height()/2);
    p.drawPixmap(0,0,pixmap);
    p.end();

VRonin

it's not perfect (in fact I wouldn't say it works) but it's a start:
this will rotate 90 degrees anti-clockwise the widget you set in setBaseWidget

#include <QWidget>
#include <QPixmap>
#include <QPainter>
class RotateWidget : public QWidget
{
    Q_OBJECT
public:
    RotateWidget(QWidget *parent = nullptr): QWidget(parent){}
    virtual QSize sizeHint() const override{
        const QSize origHint=m_baseWidget->sizeHint();
        return QSize(origHint.height(),origHint.width());
    }
    QWidget *baseWidget() const
    {
        return m_baseWidget;
    }
    void setBaseWidget(QWidget *baseWidget)
    {
        m_baseWidget = baseWidget;
    }
protected:
    virtual void paintEvent(QPaintEvent * event) override{
        if(!m_baseWidget)
            return QWidget::paintEvent(event);
        QPixmap basePixmap(m_baseWidget->size());
        m_baseWidget->render(&basePixmap);
        QPainter p(this);
        p.setRenderHint(QPainter::Antialiasing);
        p.setRenderHint(QPainter::SmoothPixmapTransform);
        p.setRenderHint(QPainter::HighQualityAntialiasing);
        p.translate(m_baseWidget->width()/2,m_baseWidget->height()/2);
        p.rotate(-90);
        p.translate(-m_baseWidget->width()/2,-m_baseWidget->height()/2);
        p.drawPixmap(0,0,basePixmap);
        p.end();
    }
private:
    QWidget* m_baseWidget;
};

for example:

#include <QApplication>
#include <QLabel>
#include "rotatewidget.h"

 int main ( int argc , char *argv[] )
{
    QApplication app(argc,argv);
    QLabel* tempLabel=new QLabel("Testing");


    RotateWidget mainWid;

    mainWid.setBaseWidget(tempLabel);
    mainWid.show();
    return app.exec();

}

sunil.nair

Hi, Thanks for the reply. What I understand from your code is that you are doing a 90 degree rotation using width and height. But, a 90 degree rotation is anyway possible directly with a QLabel.

QMatrix rm;
rm.rotate(90);
pixmap = pixmap.transformed(rm);
ui->Image->setPixmap(pixmap);

The problem is that I cannot rotate a qlabel by any other value between 0 and 90.

VRonin

I did 90 degrees because it is a straight inversion between width and height. to rotate any other angle you have to apply a bit of trigonometry to calculate the dimension of the rectangles around the rotated widget