Re: const version of Gdk::Pixbuf::save()

[Kjell Ahlstedt <kjell ahlstedt bredband net>]

Gdk::Pixbuf::save() and save_to_buffer() are C++ wrappers around the C 
functions gdk_pixbuf_savev() and gdk_pixbuf_save_to_buffer(), resp. 
Those C functions take a "GdkPixbuf* pixbuf" parameter (i.e. not const 
GdkPixbuf* pixbuf). I don't know why. It's unintuitive that they should 
modify the GdkPixbuf, but perhaps they do. Anyway, that's the reason why 
there are no const versions of the corresponding C++ member functions.

A solution (not very attractive, I admit) is to take a copy of the 
Pixbuf with Gdk::Pixbuf::copy() and save the copy.

If you don't get a better answer here, you can try asking on a gtk+ list 
(e.g. gtk-app-devel-list) why the gdk_pixbuf_save*() functions don't 
take const GdkPixbuf*.

Kjell

2012-06-21 09:31, Tom skrev:
> Hello,
>
> In the documentation of Pixbuf
> (http://developer.gnome.org/gtkmm/3.4/classGdk_1_1Pixbuf.html) I can not
> find const versions of save methods (save, save_to_buffer). I wonder why?
>
> In my application I show some calculated image data employing a
> Gtk::Image that is initialized with a Glib::RefPtr<Gdk::Pixbuf>.
> Within my saving method I fetch the data as follow:
>
> 1 Gtk::Image const&  img (my_canvas->getImage()); // getImage() is const
> 2 Glib::RefPtr<const Gdk::Pixbuf>  pix_buf (img.get_pixbuf());
> 3 pix_buf.save(fname, "png"); // fname is a std::string
>
> The compiler complains:
> error: passing ‘const Gdk::Pixbuf’ as ‘this’ argument of ‘void
> Gdk::Pixbuf::save(const string&, const Glib::ustring&)’ discards
> qualifiers [-fpermissive]
>
> In line 3 of the above code I need the save method to be const.
>
> In general maybe this is not the appropriate way to save the image?
>
> Thank you for your effort to read my text and hopefully answer my questions
>
> tom