Fwd: Re: OffscreenWindow returns empty pixbuf

[Ian Martin <martin_id vodafone co nz>]

Hi,
2 reasons.  The first is you didn't add any image data to it, at least 
in the code here.

Second, because (as per the gtkmm docs) "OffscreenWindow is strictly 
intended to be used for obtaining snapshots of widgets that are not part 
of a normal widget hierarchy."

so writing to the pixbuf returned by it is likely to fail.  More usual 
would be to create a Gtk::Image and add that to the window, either 
writing to the image's pixbuf or if appropriate - and easier- passing an 
image file in the constructor.

Ian.

On 02/09/14 11:23, Phil Wolff wrote:
> Can anybody tell me why this code returns a properly sized Pixbuf with 
> no image data?
>
> #include <gtkmm.h>
> #include <iostream>
>
> class Test : public Gtk::Window
> {
> public:
>     Test ();
> };
>
> Test::Test ()
> {
>     set_size_request ( 160, 90 );
>     set_position ( Gtk::WIN_POS_CENTER );
>     try {
>         // Put something offscreen
>         Gtk::OffscreenWindow* pw = new Gtk::OffscreenWindow ();
>         Gtk::Label* pl = new Gtk::Label ( "Test OffscreenWindow" );
>         pw->add ( *pl );
>         pw->show_all ();
>         // Retrieve it
>         Glib::RefPtr<Gdk::Pixbuf > refPixbuf = pw->get_pixbuf ();
>         // Show pixbuf dimensions
>         set_title ( Glib::ustring::format ( refPixbuf->get_width (), " 
> x ",
>                 refPixbuf->get_height () ) );
>         // Show pixbuf contents onscreen
>         Gtk::Image* pi = new Gtk::Image ( refPixbuf );
>         add ( *pi );
>         //refPixbuf->save ( "pixbuf.png", "png" );
>         //system ( "eog pixbuf.png" );
>         show_all_children ();
>     }
>     catch ( const Glib::FileError& ex ) {
>         std::cerr << "File error: " << ex.what () << std::endl;
>     }
>     catch ( const Gdk::PixbufError& ex ) {
>         std::cerr << "Pixbuf error: " << ex.what () << std::endl;
>     }
> }
>
> int main ( int argc, char *argv[] )
> {
>     Glib::RefPtr<Gtk::Application> refApp = Gtk::Application::create ( 
> argc,
>             argv, "org.gtkmm.example" );
>     Test window;
>     return refApp->run ( window );
> }
>
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