How load image and create Gdk.Pixbuf from it used Gegl?

GTK 4.6.3
I’m trying to load a picture into Gdk.Pixbuf and display it using Gegl.

I’ve tried different variations, but I couldn’t get it to work.
Below is the workpiece with which I experimented.

int main(string[] args) {
  Gegl.init(ref args);

  var path = "/path/to/file/test.png";


  Gdk.Pixbuf *pixbuf_ptr = null;


  var root = new Gegl.Node();
  var load = root.new_child("operation", "gegl:load", "path", path);
  var to_pixbuf = root.new_child("operation", "gegl:save-pixbuf", "pixbuf", pixbuf_ptr);

  load.link(to_pixbuf);

  to_pixbuf.process();

  var app = new Gtk.Application(null, GLib.ApplicationFlags.FLAGS_NONE); 

  app.activate.connect(() => {
    var win = new Gtk.ApplicationWindow(app);

    var pic = new Gtk.Picture.for_pixbuf(pixbuf_ptr);


    win.child = pic;
    win.present();
  });

  return app.run(args);
}
$ valac --debug --pkg gtk4 --pkg glib-2.0 --pkg gegl-0.4 ./main.vala
$ ./main