We've always been using Glade to design our UI, and GtkBuilder to load the design at runtime. We will use Glade in the rest of our book, but now let's try to do GTK+ programming at a lower level to grasp the essentials of GTK+, which is not obvious when using Glade. This knowledge becomes more important when our project becomes larger and larger, and at some point will stumble upon performance problems, layout problems, and so on.