Rotate an QLabel

[CptN3m0]

Hello,
Im trying to rotate my QLabel in a timer with this code

QPainter p(ui->label_19);
p.rotate(90);
p.end();

all what I got are this errors:

QWidget::paintEngine: Should no longer be called
QPainter::begin: Paint device returned engine == 0, type: 1
QPainter::rotate: Painter not active
QPainter::end: Painter not active, aborted

how can I fix them and let my qlabel rotate.

[jsulm]

@CptN3m0
You can only use QPainter in a paintEvent()
http://doc.qt.io/qt-5/qpainter.html

void SimpleExampleWidget::paintEvent(QPaintEvent *)
{
    QPainter painter(this);
    painter.setPen(Qt::blue);
    painter.setFont(QFont("Arial", 30));
    painter.drawText(rect(), Qt::AlignCenter, "Qt");
}

[CptN3m0]

@jsulm is there any other way to rotate QLabel? Or just an image inside QLabel.

[mrjj]

@CptN3m0
Hi
Yes, you can paint to a pixmap and set that to QLabel.

QPixmap pix(500,500);
QPainter paint (&pix);
.. rotate and draw text..
label->addPixmap(pix);

[SGaist]

Hi,

Or you can use QImage::transformed passing it a rotation matrix.

[CptN3m0]

Okey I found a solution for me

QPixmap pixmap(*ui->label->pixmap());
QMatrix rm;
rm.rotate(50);
pixmap = pixmap.transformed(rm);
ui->label->setPixmap(pixmap);

but the problem ist now, Im trying to draw the pixmap every time at the different rotate which was saved at mine vector. what is happening, it´s just rotate further

[mrjj]

@CptN3m0
Well the normal solution is to keep the original unrotated bitmap and
assign a copy to the label. Then when new rotate is need , the original image is used
and not the already rotated version.

You can also rotate it back, and rotate to a new angle but that often
distorts the image slowly.

[CptN3m0]

@mrjj can u write an example?

[SGaist]

Hi,

Where does your QPixmap come from in the first place ?

[mrjj]

@CptN3m0
Wait i just realized. you are just doing it to rotate text right ?
Not the actual image ?
So only the text matters. so u can just clear it and redraw text.

QPixmap pixmap(*ui->label->pixmap());
pixmap.fill( Qr::red ); // just clear old
QMatrix rm;
rm.rotate(50);
pixmap = pixmap.transformed(rm);
...drawtext..
ui->label->setPixmap(pixmap);

[CptN3m0]

@mrjj seems like it is a text, instead .png file

[mrjj]

@CptN3m0
So you have 2.png in a resource file ?
alo, the goal is to rotate text, so the image has nothing u want to show. Just used to draw the text on ?

[CptN3m0]

@mrjj I need to rotate this 2.png inside my QLabel. There is no thext inside

[mrjj]

@CptN3m0
Ok, so the the goal is to rotate 2.png ? and not text.
Anyhow, just add a QPixmap to .h and save the
2.png to it.
Then when you rotate always use the copy and not the already rotated one.