source: trunk/src/gui/kernel/qdesktopwidget.qdoc@ 667

/****************************************************************************
**
** Copyright (C) 2010 Nokia Corporation and/or its subsidiary(-ies).
** All rights reserved.
** Contact: Nokia Corporation (qt-info@nokia.com)
**
** This file is part of the documentation of the Qt Toolkit.
**
** $QT_BEGIN_LICENSE:LGPL$
** Commercial Usage
** Licensees holding valid Qt Commercial licenses may use this file in
** accordance with the Qt Commercial License Agreement provided with the
** Software or, alternatively, in accordance with the terms contained in
** a written agreement between you and Nokia.
**
** 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 1.1, 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 have questions regarding the use of this file, please contact
** Nokia at qt-info@nokia.com.
** $QT_END_LICENSE$
**
****************************************************************************/

/*!
    \class QDesktopWidget
    \brief The QDesktopWidget class provides access to screen information on multi-head systems.

    \ingroup advanced
    \ingroup desktop

    Systems with more than one graphics card and monitor can manage the
    physical screen space available either as multiple desktops, or as a
    large virtual desktop.

    This class provides information about the user's desktop, such as its
    total size, number of screens, the geometry of each screen, and whether
    they are configured as separate desktops or a single virtual desktop.

    Widgets provided by Qt use this class to place tooltips, menus and
    dialog boxes on the correct screen for their parent or application
    widgets. Applications can use this class to obtain information that
    can be used to save window positions, or to place child widgets and
    dialogs on one particular screen.

    \section1 Obtaining a Desktop Widget

    The QApplication::desktop() function is used to get an instance of
    QDesktopWidget.

    The widget's screenGeometry() function provides information about the
    geometry of the available screens with. The number of screens
    available is returned by screenCount, and the screenCountChanged()
    signal is emitted when screens are added or removed.
    The screen number that a particular point or widget is located in
    is returned by screenNumber().

    \section1 Screen Geometry

    To obtain the dimensions of a particular screen, call the screenGeometry()
    function. On some desktop environments, not all of the screen is
    available for applications to use; for example, an application dock or
    menu bar may take up some space. Use the availableGeometry() function
    to obtain the available area for applications.

    QDesktopWidget also inherits the QWidget properties, width() and
    height(), which specify the size of the desktop. However, for
    desktops with multiple screens, the size of the desktop is the union
    of all the screen sizes, so width() and height() should \e not be
    used for computing the size of a widget to be placed on one of the
    screens.

    On systems that are configured to use the available screens as a
    single, large virtual desktop, the virtualDesktop property will be
    set to true. In this case, the widget's size is usually the size of
    the bounding rectangle of all the screens.

    \section1 Use of the Primary Screen

    For an application, the screen where the main widget resides is the
    primary screen. This is stored in the primaryScreen property.
    All windows opened in the context of the application should be
    constrained to the boundaries of the primary screen; for example,
    it would be inconvenient if a dialog box popped up on a different
    screen, or split over two screens.

    \image qdesktopwidget.png Managing Multiple Screens

    In the illustration above, Application One's primary screen is
    screen 0, and App Two's primary screen is screen 1.

    \sa QApplication, QApplication::desktop(), QX11Info::appRootWindow()
*/

/*!
    \fn QDesktopWidget::QDesktopWidget()

    \internal

    Creates the desktop widget.

    If the system supports a virtual desktop, this widget will have
    the size of the virtual desktop; otherwise this widget will have
    the size of the primary screen.

    Instead of using QDesktopWidget directly, use QApplication::desktop().
*/

/*!
    \fn QDesktopWidget::~QDesktopWidget()

    \internal

    Destroys the desktop widget and frees any allocated resources.
*/

/*!
    \fn int QDesktopWidget::numScreens() const
    
    Returns the number of available screens.
    
    \obsolete

    This function is deprecated. Use screenCount instead.

    \sa primaryScreen
*/

/*!
    \fn QWidget *QDesktopWidget::screen(int screen)

    Returns a widget that represents the screen with index \a screen
    (a value of -1 means the default screen).

    If the system uses a virtual desktop, the returned widget will
    have the geometry of the entire virtual desktop; i.e., bounding
    every \a screen.

    \sa primaryScreen, screenCount, virtualDesktop
*/

/*!
    \fn const QRect QDesktopWidget::availableGeometry(int screen) const

     Returns the available geometry of the screen with index \a screen. What
     is available will be subrect of screenGeometry() based on what the
     platform decides is available (for example excludes the dock and menu bar
     on Mac OS X, or the task bar on Windows). The default screen is used if
     \a screen is -1.

     \sa screenNumber(), screenGeometry()
*/

/*!
    \fn const QRect QDesktopWidget::availableGeometry(const QWidget *widget) const
    \overload

    Returns the available geometry of the screen which contains \a widget.

    \sa screenGeometry()
*/

/*!
    \fn const QRect QDesktopWidget::availableGeometry(const QPoint &p) const
    \overload

    Returns the available geometry of the screen which contains \a p.

    \sa screenGeometry()
*/


/*!
    \fn const QRect QDesktopWidget::screenGeometry(int screen) const

    Returns the geometry of the screen with index \a screen. The default
    screen is used if \a screen is -1.

    \sa screenNumber()
*/

/*!
    \fn const QRect QDesktopWidget::screenGeometry(const QWidget *widget) const
    \overload

    Returns the geometry of the screen which contains \a widget.
*/

/*!
    \fn const QRect QDesktopWidget::screenGeometry(const QPoint &p) const
    \overload

    Returns the geometry of the screen which contains \a p.
*/


/*!
    \fn int QDesktopWidget::screenNumber(const QWidget *widget) const

    Returns the index of the screen that contains the largest
    part of \a widget, or -1 if the widget not on a screen.

    \sa primaryScreen
*/

/*!
    \fn int QDesktopWidget::screenNumber(const QPoint &point) const

    \overload
    Returns the index of the screen that contains the \a point, or the
    screen which is the shortest distance from the \a point.

    \sa primaryScreen
*/

/*!
    \fn void QDesktopWidget::resizeEvent(QResizeEvent *event)
    \reimp
*/

/*!
    \fn void QDesktopWidget::resized(int screen)

    This signal is emitted when the size of \a screen changes.
*/

/*!
    \fn void QDesktopWidget::workAreaResized(int screen)

    This signal is emitted when the work area available on \a screen changes.
*/

/*!
    \property QDesktopWidget::screenCount
    \brief the number of screens currently available on the system.

    \since 4.6
    
    \sa screenCountChanged()
*/

/*!
    \property QDesktopWidget::primaryScreen
    \brief the index of the screen that is configured to be the primary screen
    on the system.
*/

/*!
    \property QDesktopWidget::virtualDesktop

    \brief if the system manages the available screens in a virtual desktop.

    For virtual desktops, screen() will always return the same widget.
    The size of the virtual desktop is the size of this desktop
    widget.
*/

/*!
    \fn void QDesktopWidget::screenCountChanged(int newCount)

    \since 4.6

    This signal is emitted when the number of screens changes to \a newCount.
    
    \sa screenCount
*/