source: trunk/doc/src/examples/shapedclock.qdoc@ 534

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41
42/*!
43 \example widgets/shapedclock
44 \title Shaped Clock Example
45
46 The Shaped Clock example shows how to apply a widget mask to a top-level
47 widget to produce a shaped window.
48
49 \image shapedclock-example.png
50
51 Widget masks are used to customize the shapes of top-level widgets by restricting
52 the available area for painting. On some window systems, setting certain window flags
53 will cause the window decoration (title bar, window frame, buttons) to be disabled,
54 allowing specially-shaped windows to be created. In this example, we use this feature
55 to create a circular window containing an analog clock.
56
57 Since this example's window does not provide a \gui File menu or a close
58 button, we provide a context menu with an \gui Exit entry so that the example
59 can be closed. Click the right mouse button over the window to open this menu.
60
61 \section1 ShapedClock Class Definition
62
63 The \c ShapedClock class is based on the \c AnalogClock class defined in the
64 \l{Analog Clock Example}{Analog Clock} example. The whole class definition is
65 presented below:
66
67 \snippet examples/widgets/shapedclock/shapedclock.h 0
68
69 The \l{QWidget::paintEvent()}{paintEvent()} implementation is the same as that found
70 in the \c AnalogClock class. We implement \l{QWidget::sizeHint()}{sizeHint()}
71 so that we don't have to resize the widget explicitly. We also provide an event
72 handler for resize events. This allows us to update the mask if the clock is resized.
73
74 Since the window containing the clock widget will have no title bar, we provide
75 implementations for \l{QWidget::mouseMoveEvent()}{mouseMoveEvent()} and
76 \l{QWidget::mousePressEvent()}{mousePressEvent()} to allow the clock to be dragged
77 around the screen. The \c dragPosition variable lets us keep track of where the user
78 last clicked on the widget.
79
80 \section1 ShapedClock Class Implementation
81
82 The \c ShapedClock constructor performs many of the same tasks as the \c AnalogClock
83 constructor. We set up a timer and connect it to the widget's update() slot:
84
85 \snippet examples/widgets/shapedclock/shapedclock.cpp 0
86
87 We inform the window manager that the widget is not to be decorated with a window
88 frame by setting the Qt::FramelessWindowHint flag on the widget. As a result, we need
89 to provide a way for the user to move the clock around the screen.
90
91 Mouse button events are delivered to the \c mousePressEvent() handler:
92
93 \snippet examples/widgets/shapedclock/shapedclock.cpp 1
94
95 If the left mouse button is pressed over the widget, we record the displacement in
96 global (screen) coordinates between the top-left position of the widget's frame (even
97 when hidden) and the point where the mouse click occurred. This displacement will be
98 used if the user moves the mouse while holding down the left button. Since we acted
99 on the event, we accept it by calling its \l{QEvent::accept()}{accept()} function.
100
101 \image shapedclock-dragging.png
102
103 The \c mouseMoveEvent() handler is called if the mouse is moved over the widget.
104
105 \snippet examples/widgets/shapedclock/shapedclock.cpp 2
106
107 If the left button is held down while the mouse is moved, the top-left corner of the
108 widget is moved to the point given by subtracting the \c dragPosition from the current
109 cursor position in global coordinates. If we drag the widget, we also accept the event.
110
111 The \c paintEvent() function is given for completeness. See the
112 \l{Analog Clock Example}{Analog Clock} example for a description of the process used
113 to render the clock.
114
115 \snippet examples/widgets/shapedclock/shapedclock.cpp 3
116
117 In the \c resizeEvent() handler, we re-use some of the code from the \c paintEvent()
118 to determine the region of the widget that is visible to the user:
119
120 \snippet examples/widgets/shapedclock/shapedclock.cpp 4
121
122 Since the clock face is a circle drawn in the center of the widget, this is the region
123 we use as the mask.
124
125 Although the lack of a window frame may make it difficult for the user to resize the
126 widget on some platforms, it will not necessarily be impossible. The \c resizeEvent()
127 function ensures that the widget mask will always be updated if the widget's dimensions
128 change, and additionally ensures that it will be set up correctly when the widget is
129 first displayed.
130
131 Finally, we implement the \c sizeHint() for the widget so that it is given a reasonable
132 default size when it is first shown:
133
134 \snippet examples/widgets/shapedclock/shapedclock.cpp 5
135
136 \section1 Notes on Widget Masks
137
138 Since QRegion allows arbitrarily complex regions to be created, widget masks can be
139 made to suit the most unconventionally-shaped windows, and even allow widgets to be
140 displayed with holes in them.
141
142 Widget masks can also be constructed by using the contents of pixmap to define the
143 opaque part of the widget. For a pixmap with an alpha channel, a suitable mask can be
144 obtained with QPixmap::mask().
145*/
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