Background

GTK+ (acronym for the GIMP Toolkit) is a library for creating graphical user interfaces. It works on many UNIX-like platforms, Windows, and OS X.

Vala is a new programming language that aims to bring modern programming language features to GNOME developers without imposing any additional runtime requirements and without using a different ABI compared to applications and libraries written in C.

Added on 30th July 2013

About GTK

GTK+ (acronym for the GIMP Toolkit) is a library for creating graphical user interfaces. It works on many UNIX-like platforms, Windows, and OS X.

It's called the GIMP toolkit because it was originally written for developing the GNU Image Manipulation Program (GIMP), but GTK+ has now been used in a large number of software projects, including the GNOME project.

GTK+ is released under the GNU Library General Public License (GNU LGPL), which allows for flexible licensing of client applications. You can develop open software, free software, or even commercial non-free software using GTK+ without having to spend anything for licenses or royalties. GTK+ has a C-based object-oriented architecture that allows for maximum flexibility.

Bindings for many other languages have been written, including C++, Objective-C, Guile/Scheme, Perl, Python, TOM, Ada95, Free Pascal, Eiffel and Vala. This tutorial describes the Vala interface to GTK.

GTK+ depends on the following libraries:

  • GLib

    GLib is a general-purpose utility library, not specific to graphical user interfaces. GLib provides many useful data types, macros, type conversions, string utilities, file utilities, a main loop abstraction, and so on.

  • GObject

    GObject is library that provides a type system, a collection of fundamental types including an object type, a signal system.GObject, and its lower-level type system, GType, are used by GTK+ and most GNOME libraries to provide Object-oriented C-based APIs and automatic transparent API bindings to other compiled or interpreted languages.

  • GIO

    GIO is a modern, easy-to-use Virtual File System API including abstractions for files, drives, volumes, stream IO, as well as network programming and DBus communication.

    A virtual file system (VFS) or virtual filesystem switch is an abstraction layer on top of a more concrete file system. The purpose of a VFS is to allow client applications to access different types of concrete file systems (Ext3, FAT, NTFS, etc) in a uniform way.

  • Cairo

    Cairo is a 2D graphics library with support for multiple output devices.

  • Pango

    Pango is a library for internationalized text handling. It centers around the PangoLayout object, representing a paragraph of text. Pango provides the engine for Gtk.TextView, Gtk.Label, Gtk.Entry, and other widgets that display text.

  • ATK

    ATK is the Accessibility Toolkit. It provides a set of generic interfaces allowing accessibility technologies (technologies that allow people with physical disabilities, e.g. blindness to use computers) to interact with a graphical user interface. For example, a screen reader uses ATK to discover the text in an interface and read it to blind users. GTK+ widgets have built-in support for accessibility using the ATK framework.

  • GdkPixbuf

    GdkPixbuf is a small library which allows you to create GdkPixbuf ("pixel buffer") objects from image data or image files. Use a GdkPixbuf in combination with Gtk.Image to display images.

  • GDK

    GDK is the abstraction layer that allows GTK+ to support multiple windowing systems. GDK provides window system facilities on X11, Windows, and OS X.

GTK+ is essentially an object oriented application programming interface (API). Although written completely in C, it is implemented using the idea of classes and callback functions.

About Vala

Vala is a new programming language that aims to bring modern programming language features to GNOME developers without imposing any additional runtime requirements and without using a different ABI compared to applications and libraries written in C.

According to the Vala tutorial:

Vala is a new programming language that allows modern programming techniques to be used to write applications that run on the GNOME runtime libraries, particularly GLib and GObject. This platform has long provided a very complete programming environment, with such features as a dynamic type system and assisted memory management. Before Vala, the only ways to program for the platform were with the machine native C API, which exposes a lot of often unwanted detail, with a high level language that has an attendant virtual machine, such as Python or the Mono C# language, or alternatively, with C++ through a wrapper library.

Vala is different from all these other techniques, as it outputs C code which can be compiled to run with no extra library support beyond the GNOME platform. This has several consequences, but most importantly:

  • Programs written in Vala should have broadly similar performance to those written directly in C, whilst being easier and faster to write and maintain.
  • A Vala application can do nothing that a C equivalent cannot. Whilst Vala introduces a lot of language features that are not available in C, these are all mapped to C constructs, although they are often ones that are difficult or too time consuming to write directly.

As such, whilst Vala is a modern language with all of the features you would expect, it gains its power from an existing platform, and must in some ways comply with the rules set down by it.

References