Error while opening png image with Gdk::Pixbuf::create_from_resource - c++

Question

I'm trying to read the png image with Gdk::Pixbuf::create_from_resource:
#include <iostream>
#include <gtkmm.h>
int main(int argc, char *argv[])
{
auto app = Gtk::Application::create(argc, argv, "org.gtkmm.examples.base");
Gtk::Window window;
window.set_default_size(100, 100);
try {
Glib::RefPtr<Gdk::Pixbuf> image
= Gdk::Pixbuf::create_from_resource("image.png");
} catch (const Glib::Error &error) {
std::cerr << "Failed to load an image: " << error.what() << std::endl;
}
return app->run(window);
}
But an error occurs:
$ ./a.out
Failed to load an image: The resource at “image.png” does not exist
$ ls -l
total 128
-rwxrwxr-x. 1 user user 36528 Jul 18 15:01 a.out
-rw-r--r--. 1 user user 88792 Jul 18 15:00 image.png
-rw-r--r--. 1 user user 449 Jul 18 15:00 main.cpp
gtkmm version 3.24.6

Answer 1

If you want to load an image file directly into your program, instead of:
Glib::RefPtr<Gdk::Pixbuf> image
= Gdk::Pixbuf::create_from_resource("image.png");
you would use the following statement:
Glib::RefPtr<Gdk::Pixbuf> image
= Gdk::Pixbuf::create_from_file("image.png");
If you do want to use the image file as a resource, you would need to first generate a resource file with the "glib-compile-resources" function using a resource definition XML file. For example.
glib-compile-resources --target=image.c --generate-source resource.xml
In your XML file, you probably would have some type of definition such as the following.
<gresources>
<gresource prefix="Image">
<file preprocess="xml-stripblanks">image.png</file>
</gresource>
</gresources>
Then in your program, your creation statement would be similar to the following.
Glib::RefPtr<Gdk::Pixbuf> image = Gdk::Pixbuf::create_from_resource("Image/image.png");
Finally, you would revise your compile command to include the generated resource file with your "main.cpp" file to create your program.
g++ -Wno-format -o a.out main.cpp image.c `pkg-config --cflags --libs gtkmm-3.0` `pkg-config --cflags --libs gdkmm-3.0`
Hope that clarifies things.
Regards.