GTK

GTK is a tookit for creating GUI apps, mostly targeting Linux systems and the Gnome Platform. It uses the GObject (GLib Object System) base type system.

GLib and GObject

GObject is a library that is a base for many other Gnome libraries (like GTK). It is a common base layer providing OOP paradigm to the C language. It may be seen as an alternative to C++ or ObjectiveC, since it enables developers to create classes, but in this case, directly in C (however, in a rather tedious way, since it’s still “just” C)!

GObject is a part of GLib and uses the same version numbers. GLib contains:

• GObject - type system
• GThread - threading
• GIO - I/O operations
• others…

Some features of GObject that are often used in GTK apps are:

• the GObject root base type
• signals (like events in .NET)

Bindings

The GObject libraries are written in the C language. However, there are a bunch of bindings for many other programming languages that open the toolkit to a vast group of developers. Examples of supported languages include:

• C (obviously)
• JavaScript
• Python
• Rust
• Vala
• C#
• and more…

Since there is a lot of GObject-based libraries, there is an established way of generating bindings for them - GObject Introspection. The bindings, under the hood, call the C libraries code via mechanisms similar to PInvoke.

Software Stack

Nowadays, the applications developed in GTK use the following tooling/services:

• GTK as a base for the app and widgets library
• other GObject-based libs - lots of libraries, like Soup for HTTP
• language bindings
• Libadwaita as both the widgets library and design system
• Gnome Builder as an IDE
• Flatpak for packaging the apps
• Flathub for distribution of the apps

Resources

Popularity of GTK apps development would certainly benefit from more materials being available on the topic. These are the resources that I find the most valuable:

• Gnome Developer Portal - a documentation and guides for developing for the Gnome Platform.
• GJS Guide - the Guide to GJS with a bunch of information about GObject itself.
• elementary Developer Docs - Elementary OS encourages the use of Vala and Granite widgets library, which might not be the most popular technologies out there, but the docs are a solid guide to building GTK apps, which will be useful for any developer starting out with GTK.
• Gtk Inspector - an app that allows for live inspection of GTK apps, similar to dev tools in web browsers.
• GTK API Documentation - API reference for GTK, GDK, Pango, and many other libs
• GJS API - all the APIs exposed by GJS
• Vala API - same as above, but for Vala