Introduction to PHPGTK | Advanced PHP for Web Professionals

PHPGTK is an extension to PHP that allows you to create graphical user interface (GUI) applications. Instead of running in a browser, your PHP application runs in its own application window. These applications are client-side only. They do not reside on the Web server. The files instead reside on the user's hard drive. For users to use the PHPGTK application, they must have the proper version of PHP (with the GTK+ extension) installed on their system.

GTK+ was originally designed for the open-source image editing program called the GIMP (GNU Image Manipulation Program). GTK stands for the GIMP Tool Kit. Later, the Gnome team decided to use GTK+ to create their desktop environment for Linux. GTK+ has been ported to Windows, Linux, and BeOS, and thus makes for a good cross-platform GUI library.

PHPGTK uses GTK+ to draw the "widgets" required in any GUI application. Widgets are things like scroll bars, text input fields, and buttons, among other things. When you start almost any Windows application, such as a Web browser, you are looking at a collection of widgets.

Widgets need to be contained in some type of framework to be useful and logical. You can't just have a bunch of buttons and text fields scattered randomly about the screen. To solve this problem, we use a special kind of widget called a container. A container is another structure that organizes the widgets however you think it best for your application. For example, the menu bar at the top of most applications is a container.

Widgets have many different properties that control how they look and act. Each type of widget has its own unique set of properties, in addition to properties that are common to other widgets.

Widgets send signals to your program when they are activated. An example of widget activation is when a user clicks on a button. Once a widget sends a signal, you generally respond to that signal with a callback. A callback is basically just a function. Some signals end up in callbacks that are automatically handled by GTK (default handlers). Other signals end up executing one of your functions (user-defined handlers). The user-defined functions are written in PHP.

As of the writing of this document, the current version of PHPGTK was 0.5.1, released on April 26, 2002. While still in its early stages, PHPGTK 0.5.1 is a vast improvement over the original 0.1 release.

PHPGTK is very complex. It takes basically two complete languages and puts them together. This lone chapter cannot hope to explain in detail the many methods and classes that are available, but I wish to provide a general overview of PHPGTK insofar as this space allows. Check the PHPGTK Web site at http://gtk.php.net for a wealth of information!

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