QImage Rotation

rtavakko

Hey guys,

I'm trying to create a customized qdial by making my own paintevent to display and rotate a QImage:

void Knob::paintEvent(QPaintEvent *)
{
QPainter painter(this);

QImage knobPix("C:\\Users\\Roham\\Documents\\Buzz\\knob.png");

QMatrix rot;

qDebug() << ((double)(this->value())/(double)(this->maximum()))*270;

rot.rotate((double)((double)(this->value())/(double)(this->maximum())*270));

QImage out = knobPix.transformed(rot);

qDebug() << QString::number(this->width()) << "," << QString::number(this->height());

painter.drawImage(QPoint(0,0),out);

}

This code doesnt rotate my QImage properly, it distorts and moves it around (it doesnt rotate the image around its center). It seems to be working fine for angles that are multiples of 90 degrees. I've tried translating the image to its width/2, height/2 and back afterwards with the same results.

Any tips or advice you guys would have will be much appreciated!!

Thanks a bunch!

jsulm

@rtavakko Wouldn't it be easier and probably faster to use a set of pictures each one rotated relative to previous one? Then simply paint one after another (similar to animated GIF).

Konstantin Tokarev

@rtavakko Don't use QImage::transformed, instead set transform to your QPainter

mrjj

Hi
as @Konstantin-Tokarev suggests , just use painter
http://www.bogotobogo.com/Qt/Qt5_QPainter_Transformation.php