Appendix A - Multiple Inheritance

Appendix B - Features of LibSigC++ (Signals)

Appendix C - QT Versus LibSigC++

AbsoluteX is an open source, free class library developed, primarily, for use with the X-Window System.

AbsoluteX, from the object-oriented design to its free software LGPL licensing, allows you to code your project with the greatest possible freedom.

With AbsoluteX, you can develop open software, free software, or even commercial non-free software, without having to spend money for licenses or royalties.

We felt that there was a need for a flexible Look & Feel for the desktop task bar and other applications. Moreover, we wanted to use libraries that have proven to be stable, documented and facilitate a fast learning curve.

After assessing the existing tool-kits and libraries, we arrived at the conclusion that the existing toolkits and libraries did not support our needs. To address this problem, we created AbsoluteX.

It is our belief that creating a class library based on multiple inheritance and templates would allow programmers to use the library more efficiently. Such a streamlined library would not contain collection classes for data structures (like a list, a map etc.), as their standards have already been set by STL.

We believe that no other alternative method of using the existing tool kit is possible, without eliminating their legacy.

AbsoluteX is an Xlib based class library. It is a C++ encapsulation for the Xlib API. In order to use AbsoluteX the following environment elements are required:

When developing applications, the trend is to ensure that it will be possible to easily and dynamically create a unique Look & Feel.

In contrast, the available tool-kits for X and Windows platforms are complex and hard to manipulate and maintain. Moreover, they do not provide adequate support for performing tasks. In the absence of an appropriate toolkit, the developer is forced to resort to endless workarounds.

Epitera’s vision is to establish a state-of-the-art C++ class library, offering the most updated programming methods that separate logic and visual aspect.

• Logic - In order to ensure the stability of the application, logics are determined at compilation time.
• Visual aspect - UI & Graphics provide a layout (XML based resource) and graphics elements, such as buttons, scroll-bars and lists, which can be set dynamically at run time.

This dynamic layout supports the possibility of gaining a perspective as to how the Look & Feel of the application will appear in different window sizes.

Important features that are integrated into AbsoluteX libraries are:

1) Increased Graphics freedom - by providing general anti-liaising support

2) Override visual functions capability - a new approach aimed at attaining special UI

AbsoluteX uses an intuitive and efficient event handling approach. Unlike other libraries, where all events are sent to a window at runtime, an AbsoluteX window receives only the events required, giving greater efficiency at runtime and a simpler interface for the developer.

The AbsoluteX approach relies on two main features:

1) Multiple inheritance design

2) LibSigc++ signal and slot library

When using the multiple inheritance approach, the window interface remains "clean", with no events. This leaves the window free to handle window properties and methods only, thus creating a simple interface for the programmer.

An event, or event group, is handled with a specific event handler that is inherited from the event handler class in conjunction with a user AbsoluteX window.

An AbsoluteX event handler holds only the methods and signals that it uses. The result is a high abstraction level and improved efficiency because this mechanism takes advantage of the X-window system ability to allocate events to windows. This feature facilitates developing by allowing the developer to select only those events that he needs.

The following steps are used to handle events in AbsoluteX when overriding the virtual method in the event handler:

1) Make your window both an xppWindowBase subclass at some points on the inheritance tree and a subclass of the event handler.

2) Override the virtual method in the event handler class, or use the signal (see 2.4).

For more information on Multiple Inheritance, see Appendix A.

The Virtual method overriding technique is not applicable for all purposes.

If, for example, there is a button in our main window that has been declared a member data, overriding the "click" event involves creating a subclass of xppButton and having this subclass declared as a member data also. This will lead to load numerous classes on each application and generate maintenance problems.

The convenient and right way will be creating, for example, a dialog box that handles all the application's logic in the dialog class while maintaining the widgets as simple widgets.

For this reason AbsoluteX uses the LibSigc++ library.

LibSigc++ (SigC for short) is an advanced and very efficient C++ implementation of the signal and slot mechanism.

SigC is an open source project that is already being used in other class libraries. SigC has shown that it has been properly designed; it is stable and very efficient.

Every AbsoluteX event handler has a corresponding signal as a public member for each virtufunction. For example, the OnKeyPress method has a corresponding signal called signal_KeyPress.

In order to connect, the developer has to declare the class receiving the signals as a subclass of SigC::Object, and to connect to the slot on the receiving class.

A developer may want to create a subclass of a button that makes a sound when clicked and have all the actions themselves applied to the signals received in some other code segment.

The Standard Template Library is a C++ library that provides a set of easily composable C++ container classes and generic algorithms (template functions).

The container classes include vectors, lists, deques, sets, multisets, maps, multimaps, stacks, queues and priority queues.

The generic algorithms include a broad range of fundamental algorithms for the most common kinds of data manipulations, such as searching, sorting, merging, copying, and transforming.

One of the goals of the Xlib project is to create a common base, written in Xlib, which will include all the functionality that is common across Linux toolkits.

In Xlib it is possible to implement internationalization without the support of the toolkit as much of the infrastructure for this purpose is already in place.

We can distinguish between several class types, each of which can be divided into the following groups:

Core & Miscellaneous - basic classes that encapsulate X structures and provide other required basic elements. These group include classes like application, point, size, dimension, reference counting etc.

X Server objects - the encapsulation of various X-server objects and functions, including drawables, such as pixmaps, windows and attributes, such as graphics context, fonts, colors etc.

Handlers - classes which handle groups of events defined in the X. These group include classes, such as key handlers, button handlers, configure, notify etc.

Layout - sets of classes that help determine position and behavior, when widgets and background elements are resized. These group include classes, such as table layouts, line layouts etc.

Widgets - reference classes for various controls, such as buttons, labels, lists.