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/****************************************************************************
**
** Copyright (C) 2009 Nokia Corporation and/or its subsidiary(-ies).
** All rights reserved.
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** this package.
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** ensure the GNU Lesser General Public License version 2.1 requirements
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**
** 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.
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** Nokia at qt-info@nokia.com.
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****************************************************************************/
/*!
\example widgets/shapedclock
\title Shaped Clock Example
The Shaped Clock example shows how to apply a widget mask to a top-level
widget to produce a shaped window.
\image shapedclock-example.png
Widget masks are used to customize the shapes of top-level widgets by restricting
the available area for painting. On some window systems, setting certain window flags
will cause the window decoration (title bar, window frame, buttons) to be disabled,
allowing specially-shaped windows to be created. In this example, we use this feature
to create a circular window containing an analog clock.
Since this example's window does not provide a \gui File menu or a close
button, we provide a context menu with an \gui Exit entry so that the example
can be closed. Click the right mouse button over the window to open this menu.
\section1 ShapedClock Class Definition
The \c ShapedClock class is based on the \c AnalogClock class defined in the
\l{Analog Clock Example}{Analog Clock} example. The whole class definition is
presented below:
\snippet examples/widgets/shapedclock/shapedclock.h 0
The \l{QWidget::paintEvent()}{paintEvent()} implementation is the same as that found
in the \c AnalogClock class. We implement \l{QWidget::sizeHint()}{sizeHint()}
so that we don't have to resize the widget explicitly. We also provide an event
handler for resize events. This allows us to update the mask if the clock is resized.
Since the window containing the clock widget will have no title bar, we provide
implementations for \l{QWidget::mouseMoveEvent()}{mouseMoveEvent()} and
\l{QWidget::mousePressEvent()}{mousePressEvent()} to allow the clock to be dragged
around the screen. The \c dragPosition variable lets us keep track of where the user
last clicked on the widget.
\section1 ShapedClock Class Implementation
The \c ShapedClock constructor performs many of the same tasks as the \c AnalogClock
constructor. We set up a timer and connect it to the widget's update() slot:
\snippet examples/widgets/shapedclock/shapedclock.cpp 0
We inform the window manager that the widget is not to be decorated with a window
frame by setting the Qt::FramelessWindowHint flag on the widget. As a result, we need
to provide a way for the user to move the clock around the screen.
Mouse button events are delivered to the \c mousePressEvent() handler:
\snippet examples/widgets/shapedclock/shapedclock.cpp 1
If the left mouse button is pressed over the widget, we record the displacement in
global (screen) coordinates between the top-left position of the widget's frame (even
when hidden) and the point where the mouse click occurred. This displacement will be
used if the user moves the mouse while holding down the left button. Since we acted
on the event, we accept it by calling its \l{QEvent::accept()}{accept()} function.
\image shapedclock-dragging.png
The \c mouseMoveEvent() handler is called if the mouse is moved over the widget.
\snippet examples/widgets/shapedclock/shapedclock.cpp 2
If the left button is held down while the mouse is moved, the top-left corner of the
widget is moved to the point given by subtracting the \c dragPosition from the current
cursor position in global coordinates. If we drag the widget, we also accept the event.
The \c paintEvent() function is given for completeness. See the
\l{Analog Clock Example}{Analog Clock} example for a description of the process used
to render the clock.
\snippet examples/widgets/shapedclock/shapedclock.cpp 3
In the \c resizeEvent() handler, we re-use some of the code from the \c paintEvent()
to determine the region of the widget that is visible to the user:
\snippet examples/widgets/shapedclock/shapedclock.cpp 4
Since the clock face is a circle drawn in the center of the widget, this is the region
we use as the mask.
Although the lack of a window frame may make it difficult for the user to resize the
widget on some platforms, it will not necessarily be impossible. The \c resizeEvent()
function ensures that the widget mask will always be updated if the widget's dimensions
change, and additionally ensures that it will be set up correctly when the widget is
first displayed.
Finally, we implement the \c sizeHint() for the widget so that it is given a reasonable
default size when it is first shown:
\snippet examples/widgets/shapedclock/shapedclock.cpp 5
\section1 Notes on Widget Masks
Since QRegion allows arbitrarily complex regions to be created, widget masks can be
made to suit the most unconventionally-shaped windows, and even allow widgets to be
displayed with holes in them.
Widget masks can also be constructed by using the contents of pixmap to define the
opaque part of the widget. For a pixmap with an alpha channel, a suitable mask can be
obtained with QPixmap::mask().
*/
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