This causes a stack overflow because calling the paintEvent is virtual,
meaning that calling it on your 'this' pointer will call
derived->paintEvent, even if you cast your this pointer to a Base type.
So you're calling the function recursively forever, overflowing the stack.
A better solution would be to add a function to the base class called
'draw' which takes a QPainter*. In the base class paintEvent, just make
a QPainter in the standard way, and call the draw function. In the
derived class, open a QPainter on an appropriately sized QImage, and
then pass that along to the draw function.
Ender EREL wrote:
> Hi Folks,
> I have a Base class and a Derived class. Both have to do some painting
> in their paint events.
> In the derived class, i want my drawings to be xor'ed with the drawings
> of the base class.
> Since the documentation clearly says "Warning: You can only set the
> composition mode for QPainter objects that operates on a QImage.", I
> tried a workaround.
> I tried grabbing the drawings of my base widget using
> QPixmap::grabWidget((Base*)this), then convert the result to a QImage,
> then construct a QPainter with the image and
> setCompositionMode(CompositionMode_Xor), and then do my drawings onto
> that image and finally draw this image to the widget. Since just
> explaining that method took this long, i don't think it is an elegant
> solution. Also it doesn't work because QPixmap::grabWidget((Base*)this)
> causes a stack overflow.
> Anyone have any ideas on how to achieve this? Or any leads on where to
> Thanks in advance.
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