Using QPropertyAnimation with QGraphicsPixmapItem

[Luc4]

Hi! Is it possible to use QPropertyAnimation with a QGraphicsPixmapItem? I read it is possible by creating a subclass and making it inherit from QObject as well. So, I created it and defined the property like:

class MyPixmap : public QObject, public QGraphicsPixmapItem {
   Q_OBJECT
   Q_PROPERTY (qreal rotation READ rotation WRITE setRotation)
...

class MyPixmap : public QObject, public QGraphicsPixmapItem {
   Q_OBJECT
   Q_PROPERTY (qreal rotation READ rotation WRITE setRotation)
...

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but when running the animation I get a crash. I made the same for a QGraphicsItem and it worked, but this isn't. Any idea why?
Thanks!

[Lykurg]

that is strange. Run a debugger and see where exactly your app crashes.

[Luc4]

I already tried that: it crashes when it executes the instruction:

QPropertyAnimation* anim = new QPropertyAnimation(item, "rotation");

QPropertyAnimation* anim = new QPropertyAnimation(item, "rotation");

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I checked item and it seems it's my class correctly, not a NULL pointer. Everything seems OK to me... any idea? Thanks!

[Lykurg]

what does the backtrace say?

[Lykurg]

Well, it must be in your definition of the class. Following works fine on my system:

class MyPixmap : public QObject, public QGraphicsPixmapItem
{
  Q_OBJECT
  Q_PROPERTY (qreal rotation READ rotation WRITE setRotation)
};
 
int main(int argc, char **argv)
{
  QApplication app(argc, argv);
  MyPixmap *it = new MyPixmap();
  QPropertyAnimation* anim = new QPropertyAnimation(it, "rotation");
  qWarning() << anim->propertyName();
  delete anim;
  delete it;
  return 0;
}

class MyPixmap : public QObject, public QGraphicsPixmapItem
{
  Q_OBJECT
  Q_PROPERTY (qreal rotation READ rotation WRITE setRotation)
};

int main(int argc, char **argv)
{
  QApplication app(argc, argv);
  MyPixmap *it = new MyPixmap();
  QPropertyAnimation* anim = new QPropertyAnimation(it, "rotation");
  qWarning() << anim->propertyName();
  delete anim;
  delete it;
  return 0;
}

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[Luc4]

I get: undefined reference to `vtable for MyPixmap'...

[Lykurg]

Well here is the full code. You have to rerun qmake:

#include <QtGui>
 
class MyPixmap : public QObject, public QGraphicsPixmapItem
{
  Q_OBJECT
  Q_PROPERTY (qreal rotation READ rotation WRITE setRotation)
};
 
int main(int argc, char **argv)
{
  QApplication app(argc, argv);
  MyPixmap *it = new MyPixmap();
  QPropertyAnimation* anim = new QPropertyAnimation(it, "rotation");
  qWarning() << anim->propertyName();
  delete anim;
  delete it;
  return 0;
}
 
#include "main.moc"

#include <QtGui>

class MyPixmap : public QObject, public QGraphicsPixmapItem
{
  Q_OBJECT
  Q_PROPERTY (qreal rotation READ rotation WRITE setRotation)
};

int main(int argc, char **argv)
{
  QApplication app(argc, argv);
  MyPixmap *it = new MyPixmap();
  QPropertyAnimation* anim = new QPropertyAnimation(it, "rotation");
  qWarning() << anim->propertyName();
  delete anim;
  delete it;
  return 0;
}

#include "main.moc"

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[Luc4]

Yes, now its working... There must be an error in my implementation. I will try to find it. Anyway, another solution was to use a QGraphicsProxyWidget. From the point of view of the performance (of animations for instance), is there any difference between using QGraphicsPixmapItems or other types of items like QGraphicsProxyWidgets? Sometimes I wonder if it would be better to use widgets or items in QGraphicsView to play animations.
Thanks for the information!

[Lykurg]

I would go for a normal item since it is not so big and heavy like a QGraphicsWidget. But if you only use a small number it does not make a big difference.