I had some time this weekend, as well as some motivation, to add a couple more things to ExifTagger.

One of the things that took longer than I expected to sort out was how to change the cursor to a watch prior to doing an expensive (time wise) operation in a call back. Loading my 7 MP digital photos takes ~ 4 secs on my laptop, which is enough time that I’d like to provide user feedback that something is happening. The naive approach to this is:

sub new_img {
    my $file = shift;
    $glade->get_widget('main_window')->window->set_cursor(
                                                          Gtk2::Gdk::Cursor->new("watch")
                                                         );
    
    $img = ExifTagger::Image->new($file);
    load_image(_target_image_size());
    _populate_fields();
    $glade->get_widget('main_window')->window->set_cursor(undef);
}

This doesn’t work, due to the way gtk works. set_cursor is effectively a signal, which triggers a built in call back just like any of the call backs you would write yourself. The net effect of this is as follows:

pop new_img_signal
start new_img
	push set_cursor_signal
	load_file
	load_image
	populate_exif_fields
	push set_cursor_signal
end
pop set_cursor_signal
start set_cursor # watch
pop set_cursor_signal
start set_cursor # normal

The following is how I solved the problem. There may be a more elegant solution, but this is working quite well for me:

sub new_img {
    my $file = shift;
    $glade->get_widget('main_window')->window->set_cursor(
                                                          Gtk2::Gdk::Cursor->new("watch")
                                                         );
       
    Glib::Idle->add(sub {
                        $img = ExifTagger::Image->new($file);
                        load_image(_target_image_size());
                        _populate_fields();
                        $glade->get_widget('main_window')->window->set_cursor(undef);
                    });
}

Which lets the set_cursor call run, has the gtk main loop go idle, then schedules the rest of the work.