Qt3-QPainter rotate exception

[Raccoon29]

Hi everyone,

I know this is a nooby problem, and however I'm a Qt noob...
My application has a window that loads an image and stores it in a QPixmapLabel.
Then there is a button that pressed should rotate the loaded image of 27 degrees.
The problem is that the first time it works perfectly, the second push (doing nothing else
in the meanwhile) shows an exception, and crushes the program.
Here I report the routine that fails:

QPicture pic;
    QPainter paint;
    QPixmap *pix=pxldest->pixmap();
 
    if(paint.begin(&pic))
    {
        paint.rotate(27);
        paint.drawPixmap(0,0,*pix);
        paint.end();
        pxldest->setPicture(pic);
        QMessageBox::information(this,"Rotated","Image rotated");
    }

QPicture pic;
    QPainter paint;
    QPixmap *pix=pxldest->pixmap();

    if(paint.begin(&pic))
    {
        paint.rotate(27);
        paint.drawPixmap(0,0,*pix);
        paint.end();
        pxldest->setPicture(pic);
        QMessageBox::information(this,"Rotated","Image rotated");
    }

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"pxldest" is the QPixmapLabel's name. Note that the exception is thrown by the line 8 during the second rotation.

I would appreciate any sort of tip or warn about this code
and thank you in advance to all will help!

[marcel]

Because the second time the label's pixmap is null since you set a QPicture instead.
You shouldn't use setPicture, but setPixmap and instead of a QPicture use a QPixmap.

So:

QPainter paint;
          QPixmap *pix=pxldest->pixmap();
 
          if(pix)
          {
              QPixmap rotated(pix->size().width(), pix->size().height());
              paint.rotate(27);
              paint.drawPixmap(0,0,*pix);
              paint.end();
              pxldest->setPixmap(rotated);
              QMessageBox::information(this,"Rotated","Image rotated");
          }

QPainter paint;
          QPixmap *pix=pxldest->pixmap();
       
          if(pix)
          {
              QPixmap rotated(pix->size().width(), pix->size().height());
              paint.rotate(27);
              paint.drawPixmap(0,0,*pix);
              paint.end();
              pxldest->setPixmap(rotated);
              QMessageBox::information(this,"Rotated","Image rotated");
          }

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Regards

[Raccoon29]

...ohhhh but sure!!!
Well, I'm right a noob...
Thank you very very much marcel !

[Raccoon29]

Thank you marcel, but just a little modification to make it work for who watch this thread:

QPainter paint;
    QPixmap *pix=pxldest->pixmap();
    if(pix)
    {
        QPixmap rotated(pix->size().width(), pix->size().height());
        paint.begin(&rotated);
        paint.rotate(27);
        paint.drawPixmap(0,0,*pix);
        paint.end();
        pxldest->setPixmap(rotated);
        QMessageBox::information(this,"Rotated","Image rotated");
    }

QPainter paint;
    QPixmap *pix=pxldest->pixmap();
    if(pix)
    {
        QPixmap rotated(pix->size().width(), pix->size().height());
        paint.begin(&rotated);
        paint.rotate(27);
        paint.drawPixmap(0,0,*pix);
        paint.end();
        pxldest->setPixmap(rotated);
        QMessageBox::information(this,"Rotated","Image rotated");
    }

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you just forgot the "begin" to make it be handled, did you?

Greetings

[marcel]

Yes, I removed from the condition and forgot to add it back.
Well, that's what happens when you write code inline, without testing it .

Regards