Re: how to handle an array of Pixbuf?

[jody <jody xha gmail com>]

You are right - this was a stupid mistake of mine:
the constructor does not copy the array, so the pointer ended up dangling.
(i probably assumed some magic from the Refptr ... ;) )

When i rewrote the constructor to copy the data from the array,
everything workled as expected.

Thank YOu again
  Jody


On Sat, Mar 2, 2013 at 10:31 AM, Kjell Ahlstedt
<kjell ahlstedt bredband net> wrote:
> In the code snippet that you've shown, image2 is allocated on the stack.
> Then of course it's deleted when the creating method is terminated. The
> reference count of Gdk::Pixbuf is decreased, when Glib::RefPtr<Gdk::Pixbuf>
> is deleted. If the reference count reaches 0, Gdk::Pixbuf is also deleted.
> The next question is: How do you copy image2 in XMLSeq's constructor? If you
> use memcpy() or a similar function, neither RefPtr's copy constructor nor
> its assignment operator will be called. The reference count of Gdk::Pixbuf
> is not increased as it should be when Glib::RefPtr<Gdk::Pixbuf> is copied.
> And if you only copy a pointer to the array, you will have a dangling
> pointer after the array has been deleted in the creating method.
>
> If it works with std::vector, and you are satisfied with that, we need not
> try to find out exactly what happened to your array, unless you're
> interested.
>
> 2013-03-01 21:03, jody skrev:
>
> > I just passed the array to a constructor of an object who later draws
> > itself
> >      XLMSeq *pXLM3 = new XLMSeq(77, 1.0, 1, EAST, 3, image2);
> >
> > in the constructor i copy the array 'image2' to the object's member
> > variable 'image2',
> > which is later used for drawing.
> >
> > If i understand it correctly, by passing the pointer, the images were
> > deleted after the method which created them terminated?
> >
> > But now I tried it  with a std::vector and that worked - thank you!
> >   jody
> >
> > On Fri, Mar 1, 2013 at 8:30 PM, Kjell Ahlstedt
> > <kjell ahlstedt bredband net> wrote:
> > > How do you transfer the array from the creating method to the painting
> > > method? With arrays it's easy to (by mistake) copy a pointer to the array
> > > when you should have copied the whole array. A std::vector is often
> > > safer,
> > >
> > > std::vector< Glib::RefPtr<Gdk::Pixbuf> > image2(3);
> > >
> > > Kjell
> > >
> > > 2013-03-01 19:17, jody skrev:
> > > > Follow up:
> > > > when i fill the PixBuf array in the same method where i paint its
> > > > element this works...
> > > > Jody
> > > >
> > > > On Fri, Mar 1, 2013 at 7:10 PM, jody <jody xha gmail com> wrote:
> > > > > Hi
> > > > >
> > > > > When i do
> > > > >      Glib::RefPtr<Gdk::Pixbuf> image1 =
> > > > > Gdk::Pixbuf::create_from_file("base1.png");
> > > > >
> > > > > i can later (in a different method) paint this into a cairo context
> > > > > like
> > > > > this:
> > > > >      Gdk::Cairo::set_source_pixbuf(cr, image1, 0, 0);
> > > > >
> > > > >
> > > > > Now i wanted to do the same with an array of PixBufs:
> > > > >       Glib::RefPtr<Gdk::Pixbuf> image2[3];
> > > > >       image2[0] =  Gdk::Pixbuf::create_from_file("hexT1.png");
> > > > >       image2[1] =  Gdk::Pixbuf::create_from_file("hexT2.png");
> > > > >       image2[2] =  Gdk::Pixbuf::create_from_file("hexT3.png");
> > > > > this compiles and seems to work, but painting (in a different method) :
> > > > >       Gdk::Cairo::set_source_pixbuf(cr, image2[0], 0, 0);
> > > > > fails with a segmentation fault.
> > > > >
> > > > > I suspect that for some reason the RefPtr died, but i actually have no
> > > > > idea.
> > > > >
> > > > > Can anybody help me?
> > > > >
> > > > > Thank You
> > > > >     Jody
> > > >
> > > > _______________________________________________