path: root/doc/src/qt4-intro.qdoc

/****************************************************************************
**
** Copyright (C) 2009 Nokia Corporation and/or its subsidiary(-ies).
** Contact: Nokia Corporation (qt-info@nokia.com)
**
** This file is part of the documentation of the Qt Toolkit.
**
** $QT_BEGIN_LICENSE:LGPL$
** No Commercial Usage
** This file contains pre-release code and may not be distributed.
** You may use this file in accordance with the terms and conditions
** contained in the either Technology Preview License Agreement or the
** Beta Release License Agreement.
**
** GNU Lesser General Public License Usage
** Alternatively, this file may be used under the terms of the GNU Lesser
** General Public License version 2.1 as published by the Free Software
** Foundation and appearing in the file LICENSE.LGPL included in the
** packaging of this file.  Please review the following information to
** ensure the GNU Lesser General Public License version 2.1 requirements
** will be met: http://www.gnu.org/licenses/old-licenses/lgpl-2.1.html.
**
** In addition, as a special exception, Nokia gives you certain
** additional rights. These rights are described in the Nokia Qt LGPL
** Exception version 1.0, included in the file LGPL_EXCEPTION.txt in this
** package.
**
** GNU General Public License Usage
** Alternatively, this file may be used under the terms of the GNU
** General Public License version 3.0 as published by the Free Software
** Foundation and appearing in the file LICENSE.GPL included in the
** packaging of this file.  Please review the following information to
** ensure the GNU General Public License version 3.0 requirements will be
** met: http://www.gnu.org/copyleft/gpl.html.
**
** If you are unsure which license is appropriate for your use, please
** contact the sales department at http://www.qtsoftware.com/contact.
** $QT_END_LICENSE$
**
****************************************************************************/

/*!
    \page qt4-intro.html
    \title What's New in Qt 4

    \startpage index.html Qt Reference Documentation
    \nextpage The Tulip Container Classes

    This document covers the most important differences between Qt 3
    and Qt 4. Although it is not intended to be a comprehensive
    porting guide, it tells you about the most important portability
    issues that you may encounter. It also explains how to turn on Qt
    3 compatibility support.

    \tableofcontents

    \section1 New Technologies in Qt 4

    Qt 4 introduces the following core technologies:

    \list
    \o \l{The Tulip Container Classes}{Tulip}, a new set of template container classes.

    \o \l{The Interview Framework}{Interview}, a model/view architecture for item views.

    \o \l{The Arthur Paint System}{Arthur}, the Qt 4 painting framework.

    \o \l{The Scribe Classes}{Scribe}, the Unicode text renderer with a public API
    for performing low-level text layout.

    \o \l{The Qt 4 Main Window Classes}{Mainwindow}, a modern action-based
    mainwindow, toolbar, menu, and docking architecture.

    \o The new \l{The New Qt Designer}{\QD} user interface design tool.
    \endlist

    \section1 Recent Additions to Qt 4

    The following features have been added to Qt since the first release of Qt 4:

    In Qt 4.4:
    \list
    \o \l{QtWebkit Module}{Qt WebKit integration}, making it possible for developers
    to use a fully-featured Web browser to display documents and access online
    services.
    \o A multimedia API provided by the \l{Phonon Overview}{Phonon Multimedia Framework}.
    \o \l{QtXmlPatterns Module}{XQuery and XPath} support, providing facilities for
    XML processing beyond that supported by the QtXml module.
    \o Support for embedded widgets in \l{Graphics View} scenes.
    \o The \l{Threading and Concurrent Programming}{QtConcurrent framework} for
    concurrent programming using Qt paradigms and threading features.
    \o An \l{QtHelp Module}{improved help system} that can be used in conjunction
    with Qt Assistant or as an independent help resource manager.
    \o Printing system improvements, including the QPrinterInfo, QPrintPreviewWidget
    and QPrintPreviewDialog classes.
    \o Support for \l{Windows CE - Introduction to using Qt}{Qt for Windows CE} as
    a mainstream Qt platform.
    \o Improvements in performance of Qt for Embedded Linux and extended support for
    display hardware.
    \endlist

    In Qt 4.3:
    \list
    \o Support for different \l{The Qt 4 Main Window Classes}{main window paradigms and styles},
       such as those found in Visual Studio or KDevelop.
    \o The \l{QtScript} module, providing support for application scripting with ECMAScript.
    \o Improved graphics features, including an experimental Direct3D paint engine
       and improved provision for hardware accelerated rendering with OpenGL, and
       support for OpenGL ES in Qt for Embedded Linux.
    \o \l{QSvgGenerator}{Scalable Vector Graphics (SVG) export}, allowing SVG drawings to
       be created using the standard QPainter API.
    \o Support for arbitrary matrix transformations and set operations on painter paths.
    \o Native look and feel on Windows Vista; improved look and feel on Mac OS X.
    \o An improved \l{QMdiArea}{Multiple Document Interface (MDI)} implementation.
    \o Continuous improvements to \QD, including support for
       \l{Qt Designer's Widget Editing Mode#The Property Editor}{dynamic properties}.
    \o Support for Secure Socket Layer (SSL) communications via the QSslSocket class.
    \o Support for XML Localization Interchange File Format (XLIFF) files in \QL.
    \o A new font subsystem for Qt for Embedded Linux.
    \endlist

    In Qt 4.2:
    \list
    \o The \l{Graphics View} framework for producing interactive graphics.
    \o \l{Desktop Integration}{Desktop integration} facilities for applications.
    \o \l{Qt Style Sheets} enable easy, yet powerful customization of
       user interfaces.
    \o Support for the \l{intro-to-dbus.html}{D-Bus} Inter-Process Communication (IPC) and Remote Procedure Calling (RPC) mechanism.
    \o An \l{Undo Framework}{Undo framework} based on the
       \l{Books about GUI Design#Design Patterns}{Command pattern}.
    \o Support for model-based \l{QCompleter}{text completion} in standard and
       custom widgets.
    \o New widgets and GUI features, such as QCalendarWidget and
       QGLFramebufferObject.
    \o Classes to provide higher level application infrastructure, such as
       QFileSystemWatcher and QDataWidgetMapper.
    \endlist

    In Qt 4.1:
    \list
    \o Integrated support for rendering
    \l{The Arthur Paint System#SVG Rendering Support}{Scalable Vector Graphics}
    (SVG) drawings and animations.
    \o Support for
       \l{QWidget#Transparency and Double Buffering}{child widget transparency}
       on all platforms.
    \o A Portable Document Format (PDF) backend for Qt's printing system.
    \o A \l{QTestLib Manual}{unit testing framework} for Qt applications and
       libraries.
    \o Modules for \l{QtDesigner}{extending \QD} and
       \l{QtUiTools}{dynamic user interface building}.
    \o New \l{Proxy Models}{proxy models} to enable view-specific sorting and
       filtering of data displayed using item views.
    \o Support for \l{Installing Qt on Mac OS X}{universal binaries} on Mac OS X.
    \o Additional features for developers using \l{QtOpenGL}{OpenGL}, such as
    support for pixel and sample buffers.
    \o A flexible \l{QSyntaxHighlighter}{syntax highlighting class} based on the
       \l{Scribe} rich text framework.
    \o Support for \l{QNetworkProxy}{network proxy} servers using the SOCKS5
       protocol.
    \o Support for OLE verbs and MIME data handling in \l{ActiveQt}.
    \endlist

    For more information about improvements in each Qt release, see
    the \l{http://www.qtsoftware.com/developer/changes/}
    {detailed lists of changes}.

    \section1 Significant Improvements

    The following modules have been significantly improved for Qt 4:

    \list
    \o A fully cross-platform \l{accessibility}
    module, with support for the emerging SP-API Unix standard in
    addition to Microsoft and Mac Accessibility.
    \o The \l{qt4-sql.html}{SQL module}, which is now based on the
    Interview model/view framework.
    \o The \l{qt4-network.html}{network module}, with better support
    for UDP and synchronous sockets.
    \o The \l{qt4-styles.html}{style API}, which is now decoupled from
    the widgets, meaning that you can draw any user interface element on
    any device (widget, pixmap, etc.).
    \o Enhanced \l{qt4-threads.html}{thread support}, with signal-slot
    connections across threads and per-thread event loops.
    \o A new \l{resource system} for embedding images
    and other resource files into the application executable.
    \endlist

    \section1 Build System

    Unlike previous Qt releases, Qt 4 is a collection of smaller
    libraries:

    \table
    \header \o Library          \o Description
    \row    \o \l{QtCore}       \o Core non-GUI functionality
    \row    \o \l{QtGui}        \o Core GUI functionality
    \row    \o \l{QtNetwork}    \o Network module
    \row    \o \l{QtOpenGL}     \o OpenGL module
    \row    \o \l{QtSql}        \o SQL module
    \row    \o \l{QtSvg}        \o SVG rendering classes
    \row    \o \l{QtXml}        \o XML module
    \row    \o \l{Qt3Support}   \o Qt 3 support classes
    \row    \o \l{QAxContainer} \o ActiveQt client extension
    \row    \o \l{QAxServer}    \o ActiveQt server extension
    \row    \o \l{QtAssistant}  \o Classes for launching Qt Assistant
    \row    \o \l{QtDesigner}   \o Classes for extending and embedding Qt Designer
    \row    \o \l{QtUiTools}       \o Classes for dynamic GUI generation
    \row    \o \l{QtTest}       \o Tool classes for unit testing
    \endtable

    QtCore contains tool classes like QString, QList, and QFile, as
    well as kernel classes like QObject and QTimer. The QApplication
    class has been refactored so that it can be used in non-GUI
    applications. It is split into QCoreApplication (in \l QtCore)
    and QApplication (in \l QtGui).

    This split makes it possible to develop server applications using Qt
    without linking in any unnecessary GUI-related code and without
    requiring GUI-related system libraries to be present on the target
    machine (e.g. Xlib on X11, Carbon on Mac OS X).

    If you use qmake to generate your makefiles, qmake will by default
    link your application against QtCore and QtGui. To remove the
    dependency upon QtGui, add the line

    \snippet doc/src/snippets/code/doc_src_qt4-intro.qdoc 0

    to your .pro file. To enable the other libraries, add the line

    \snippet doc/src/snippets/code/doc_src_qt4-intro.qdoc 1

    Another change to the build system is that moc now understands
    preprocessor directives. qmake automatically passes the defines set
    for your project (using "DEFINES +=") on to moc, which has its own
    built-in C++ preprocessor.

    To compile code that uses UI files, you will also need this line in
    the .pro file:

    \snippet doc/src/snippets/code/doc_src_qt4-intro.qdoc 2

    \section1 Include Syntax

    The syntax for including Qt class definitions has become

    \snippet doc/src/snippets/code/doc_src_qt4-intro.qdoc 3

    For example:

    \snippet doc/src/snippets/code/doc_src_qt4-intro.qdoc 4

    This is guaranteed to work for any public Qt class. The old syntax,

    \snippet doc/src/snippets/code/doc_src_qt4-intro.qdoc 5

    still works, but we encourage you to switch to the new syntax.

    If you attempt to include a header file from a library that isn't
    linked against the application, this will result in a
    compile-time warning (e.g., "QSqlQuery: No such file or
    directory"). You can remedy to this problem either by removing
    the offending include or by specifying the missing library in the
    QT entry of your \c .pro file (see \l{Build System} above).

    To include the definitions for all the classes in a library, simply
    specify the name of that library. For example:

    \snippet doc/src/snippets/code/doc_src_qt4-intro.qdoc 6

    \section1 Namespaces

    Qt 2 introduced a class called Qt for global-like constants
    (e.g., \c{Qt::yellow}). The C++ namespace construct was not used
    because not all compilers understood it when it was released.

    With Qt 4, the Qt class has become the Qt namespace. If you want
    to access a constant that is part of the Qt namespace, prefix it
    with \c Qt:: (e.g., \c{Qt::yellow}), or add the directive

    \snippet doc/src/snippets/code/doc_src_qt4-intro.qdoc 7

    at the top of your source files, after your \c #include
    directives. If you use the \c{using namespace} syntax you don't
    need the prefix (e.g., \c yellow is sufficient).

    When porting Qt 3 applications, you may run into some source
    compatibility problems with some of these symbols. For example,
    in Qt 3, it was legal to write \c QWidget::yellow instead of \c
    Qt::yellow, because QWidget inherited from Qt. This won't work in
    Qt 4; you must write \c Qt::yellow or add the "using namespace"
    directive and drop the \c Qt:: prefix.

    The \l{qt3to4 - The Qt 3 to 4 Porting Tool}{qt3to4} porting tool
    automates this conversion.

    \section1 QObject/QWidget Constructors

    In Qt 4 we have tried to simplify the constructors of QObject/QWidget
    subclasses. This makes subclassing easier, at the same time as it
    helps make the Qt library more efficient.

    Constructors no longer take a "const char *name" parameter. If
    you want to specify a name for a QObject, you must call
    QObject::setObjectName() after construction. The object name is
    now a QString. The reasons for this change are:

    \list
    \o  Code that used it looked confusing, for example:

        \snippet doc/src/snippets/code/doc_src_qt4-intro.qdoc 8

        \c label1 is a QLabel that displays the text "Hello"; \c
        label2 is a QLabel with no text, with the object name
        "Hello".

    \o  From surveys we did, most users didn't use the name, although
        they blindly followed Qt's convention and provided a "const
        char *name" in their subclasses's constructors. For example:

        \snippet doc/src/snippets/code/doc_src_qt4-intro.qdoc 9

    \o  The name parameter was in Qt since version 1, and it always
        was documented as: "It is not very useful in the current
        version of Qt, but it will become increasingly important in
        the future." Ten years later, it still hasn't fulfilled its
        promise.
    \endlist

    QWidget's \c WFlags data type has been split in two:
    Qt::WindowFlags specifies low-level window flags (the type of
    window and the frame style), whereas Qt::WidgetAttribute
    specifies various higher-level attributes about the widget (e.g.,
    WA_StaticContents). Widget attributes can be set at any time
    using QWidget::setAttribute(); low-level window flags can be
    passed to the QWidget constructor or set later using
    QWidget::setParent(). As a consequence, the constructors of most
    QWidget subclasses don't need to provide a \c WFlags parameter.

    The \e parent parameter of all QObject classes in Qt defaults to
    a 0 pointer, as it used to do in Qt 1. This enables a style of
    programming where widgets are created without parents and then
    inserted in a layout, at which point the layout automatically
    reparents them.

    \section1 Dynamic Casts

    Qt 4 provides a qobject_cast<>() function that performs a dynamic cast
    based on the meta-information generated by moc for QObject
    subclasses. Unlike the standard C++ dynamic_cast<>() construct,
    qobject_cast<>() works even when RTTI is disabled, and it works correctly
    across DLL boundaries.

    Here's the Qt 3 idiom to cast a type to a subtype:

    \snippet doc/src/snippets/code/doc_src_qt4-intro.qdoc 10

    The Qt 4 idiom is both cleaner and safer, because typos will always
    result in compiler errors:

    \snippet doc/src/snippets/code/doc_src_qt4-intro.qdoc 11

    \section1 QPointer<T>

    The QPointer<T> class provides a pointer to type T (where T inherits
    from QObject) that is automatically set to 0 when the referenced
    object is destroyed. Guarded pointers are useful whenever you want to
    store a pointer to an object you do not own.

    Example:

    \snippet doc/src/snippets/code/doc_src_qt4-intro.qdoc 12

    QPointer<T> is more or less the same as the old QGuardedPtr<T> class,
    except that it is now implemented in a much more lightweight manner
    than before. The cost of one QPointer<T> object is now approximately
    the same as that of a signal--slot connection.

    \section1 Paint Events

    Qt 4 supports double buffering transparently on all platforms. This
    feature can be turned off on a per-widget basis by calling
    QWidget::setAttribute(Qt::WA_PaintOnScreen).

    A consequence of this is that all painting must now be done from the
    paintEvent() function. This is also required by the HIView API on Mac
    OS X. In practice, this is seldom a problem, since you can call
    update() from anywhere in your code to create a paint event, with the
    region to update as the argument.

    To help porting, QWidget supports a Qt::WA_PaintOutsidePaintEvent
    attribute that can be set to make it possible to paint outside
    \l{QWidget::paintEvent()}{paintEvent()} on Windows and X11.

    \section1 Qt 3 Support Layer

    Qt 4 provides an extension library that applications based on Qt 3,
    called Qt3Support, that Qt applications can link against. This allows
    for more compatibility than ever before, without bloating Qt.

    \list
    \o  Classes that have been replaced by a different class with the
        same name, such as QListView, and classes that no longer exist in Qt 4
        are available with a \c 3 in their name (e.g., Q3ListView, Q3Accel).

    \o  Other classes provide compatibility functions. Most of these are
        implemented inline, so that they don't bloat the Qt libraries.
    \endlist

    To enable the Qt 3 support classes and functions, add the line

    \snippet doc/src/snippets/code/doc_src_qt4-intro.qdoc 13

    to your \c .pro file.

    On Visual C++ 7 and GCC 3.2+, using compatibility functions often results
    in a compiler warning (e.g., "'find' is deprecated"). If you want to turn
    off that warning, add the line

    \snippet doc/src/snippets/code/doc_src_qt4-intro.qdoc 14

    to your \c .pro file.

    If you want to use compatibility functions but don't want to link
    against the Qt3Support library, add the line

    \snippet doc/src/snippets/code/doc_src_qt4-intro.qdoc 15

    or

    \snippet doc/src/snippets/code/doc_src_qt4-intro.qdoc 16

    to your \c .pro file, depending on whether you want compatibility
    function calls to generate compiler warnings or not.
*/

/*!
    \page qt4-5-intro.html
    \title What's New in Qt 4.5

    Qt 4.5 provides many improvements and enhancements over the previous releases
    in the Qt 4 series. This document covers the most important features in this
    release, separated by category.

    A comprehensive list of changes between Qt 4.4 and Qt 4.5 is included
    in the \c changes-4.5.0 file
    \l{http://www.qtsoftware.com/developer/changes/changes-4.5.0}{available online}.
    A \l{Known Issues in %VERSION%}{list of known issues} for this release is also
    available.

    Changes between this release and the previous release are provided
    in the \c{changes-%VERSION%} file (also
    \l{http://www.qtsoftware.com/developer/changes/changes-%VERSION%}{available online}).

    A list of other Qt 4 features can be found on the
    \bold{\l{What's New in Qt 4}} page.

    \bold{Highlights}

    \tableofcontents

    \section1 Qt WebKit Integration

    \image webkit-netscape-plugin.png

    The WebKit browser engine included with Qt has been upgraded to the latest
    upstream (trunk) version of WebKit, bringing the latest features and
    improvements to Qt applications. These include:

    \list
    \o Support for full page zooming, with appropriate rescaling of images and fonts.
    \o The CSS-based transformation and animation features provided by a WebKit
    extension.
    \o Performance improvements due to faster JavaScript engine and optimized
    page loading.
    \endlist

    Standards compatibility improvements include provision for the Netscape plugin
    API, allowing most Netscape plugins to be used in-process, support for HTML 5
    audio and video elements using Qt's Phonon integration, and
    \l{Web Application Support}{facilities for client-side storage of Web content}.

    \section1 Performance Improvements

    The introduction of the QtBenchLib performance benchmarking library enables
    performance benchmarking and regression testing. Core parts of Qt itself have
    undergone focused re-engineering for improved graphics performance, including
    paint engine and text rendering improvements, Graphics View and style sheet
    performance improvements.

    The X11 paint engine now uses XSHM (the X shared memory extension), resulting
    in reduced overhead for painting operations.

    A new OpenGL ES 2.0-based paint engine complements the existing OpenGL paint
    engine, but with a focus on embedded devices.

    Qt now features a pluggable graphics system, making it possible for users
    and developers to select raster, OpenGL or native graphics systems to take
    into account the specific needs of their applications and get the best
    performance out of them.

    \section1 Mac OS X Cocoa Support

    \image mac-cocoa.png

    Qt for Mac OS X has been substantially rewritten to use Apple's Cocoa API,
    enabling Qt applications to be deployed on 64-bit Macintosh hardware.
    In addition, the new QMacCocoaViewContainer and QMacNativeWidget classes
    provide integration with Cocoa's own features and controls.

    For many applications, a simple recompilation is all that is required
    to produce an executable for 64-bit systems. Applications that use
    specific features may require a few changes first.

    \section1 Windows CE Feature Parity

    Qt for Windows CE has been updated to bring features of Qt 4.4 and Qt 4.5
    to the Windows CE platform, including:

    \list
    \o Phonon Multimedia Framework, using a Direct-Show based backend for audio
    and video playback and a Simple WaveOut backend for devices without DirectShow.
    \o The inclusion of Qt WebKit integration features previously unavailable for
    Qt 4.4 on Windows CE.
    \endlist

    Support on all Windows CE platforms; recommended for WinCE 6 and higher.

    The inclusion of these features enables developers to easily integrate Web and
    multimedia content into Qt applications on Windows CE Standard Edition while
    retaining full cross-platform compatibility with other Qt platforms.

    \section1 XML Transformations with XSLT

    The QtXmlPatterns module has been extended to cover XSLT, a transformation language
    for XML documents. A common application of this is the transformation of XML data
    into human-readable formats for reporting purposes.

    XSLT makes it simple to reformat XML content without changing data structures,
    removes the need for an intermediate DOM layer for presentation, and enables
    rapid solutions to be created; for example, creating reports as HTML or PDF.

    \section1 Qt Script Debugger

    \image qtscript-debugger-small.png

    Developers using Qt Script in their applications can take advantage of
    the new \l{Qt Script Debugger Manual}{Qt Script Debugger} to provide
    error reporting for scripts, and to let users track down bugs in their
    own scripts.

    Many standard features of GUI debugging tools are present, allowing the
    developer to step through running script code, inspect variables,
    automatically catch exceptions, and set conditional breakpoints.

    \section1 OpenDocument File Format Support

    Qt 4.5 includes support for writing rich text documents as OpenDocument files via
    the newly-introduced QTextDocumentWriter class. This provides an generic mechanism
    for file export that can be used to introduce support for additional formats in
    future releases.

    \section1 Improved Network Proxy Support

    Qt's networking classes have been updated with
    \l{QtNetwork Module#Support for Network Proxies}{improved proxy support}.
    This includes improved integration with system proxy settings and the added
    ability to handle non-trivial proxy cases.

    \section1 Qt Designer Improvements

    \image designer-screenshot-small.png

    Qt Designer 4.5 boasts some improvements on usability, for example:

    \list
    \o  \bold{Icon Mode} for the widget box which substantially reduces
        scrolling.
    \o  \bold{Morphing Widgets} which lets you morph similar widget types,
        e.g., a QWidget to a QFrame, types via the context menu's
        \e{Morph into} entry.
    \o  \bold{Filters} for the \gui{Property Editor} that lets you find
        properties or widgets quickly.
    \o  \bold{Find option} for the \gui{Object Inspector} that performs an
        incremental search on the form's widgets. Also, the objects' layout
        state is displayed here with using an icon on the left. Broken
        layouts are represented with the same icon used for the
        \e{Break Layout} action.
    \endlist

    In addition, Qt Designer now features an \gui{Embedded Design} tab that can
    be found in the \gui Preferences dialog. Within this tab, you can define
    embedded device profiles. These profiles contains screen settings, e.g.,
    display resolution, default font and default style. Qt Designer will use
    these settings when you edit forms.

    More information about these improvements can be found in the
    \l{What's New in Qt Designer 4.5} overview.

    \section1 Qt Linguist Improvements

    Qt Linguist can now load and edit multiple translation files simultaneously.

    Support for XML Localization Interchange File Format (XLIFF) files, previously added
    to the \c lupdate tool in Qt 4.3, has been improved and extended to the rest of the
    Qt Linguist toolchain. This enables files stored in Qt's TS translation format to
    be exported for use with other tools.

    The GNU Gettext PO format, which is commonly used in Open Source projects,
    is now supported by Qt Linguist.

    Support for a new way to annotate messages, using comments in the source code,
    has been added to the toolchain. See the QObject::tr() documentation for a detailed
    description and examples.

    The new \c lconvert filter tool facilitates conversion between file formats and
    can be used to perform other transformations on collections of translatable strings.

    \section1 Graphics Enhancements

    In addition to the performance improvements in this release, a number of graphics
    enhancements extend support for existing features to more platforms and expand Qt's
    core set of features with successful add-ons.

    Widget style sheets can now be used on Mac OS X, making this approach to theming
    and styling viable for truly cross-platform applications.

    Support for ARGB top-level widgets, previously available as a separate solution,
    is now provided as an integral part of Qt. This makes it possible to create windows
    with translucent regions on systems with the appropriate support from the user's
    window system. See the \l{QWidget#Creating Translucent Windows}{Creating Translucent
    Windows} section of the QWidget documentation for details of this feature.


    \image gtk-style-screenshot.png

    Improved GTK+ integration provided by the QGtkStyle class improves the look and feel
    of Qt applications in GNOME and other GTK-based environments. The screenshot above
    illustrates this clearly.
*/