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27
28/*!
29    \example gestures/imagegestures
30    \title Image Gestures Example
31
32    \brief The Image Gestures example shows how to enable gestures for a widget and use gesture input
33    to perform actions.
34
35    We use two classes to create the user interface for the application: \c MainWidget
36    and \c ImageWidget. The \c MainWidget class is simply used as a container for the
37    \c ImageWidget class, which we will configure to accept gesture input. Since we
38    are interested in the way gestures are used, we will concentrate on the
39    implementation of the \c ImageWidget class.
40
41    \section1 ImageWidget Class Definition
42
43    The \c ImageWidget class is a simple QWidget subclass that reimplements the general
44    QWidget::event() handler function in addition to several more specific event handlers:
45
46    \snippet examples/gestures/imagegestures/imagewidget.h class definition begin
47    \dots
48    \snippet examples/gestures/imagegestures/imagewidget.h class definition end
49
50    We also implement a private helper function, \c gestureEvent(), to help manage
51    gesture events delivered to the widget, and three functions to perform actions
52    based on gestures: \c panTriggered(), \c pinchTriggered() and \c swipeTriggered().
53
54    \section1 ImageWidget Class Implementation
55
56    In the widget's constructor, we begin by setting up various parameters that will
57    be used to control the way images are displayed.
58
59    \snippet examples/gestures/imagegestures/imagewidget.cpp constructor
60
61    We enable three of the standard gestures for the widget by calling QWidget::grabGesture()
62    with the types of gesture we need. These will be recognized by the application's
63    default gesture recognizer, and events will be delivered to our widget.
64
65    Since QWidget does not define a specific event handler for gestures, the widget
66    needs to reimplement the general QWidget::event() to receive gesture events.
67
68    \snippet examples/gestures/imagegestures/imagewidget.cpp event handler
69
70    We implement the event handler to delegate gesture events to a private function
71    specifically written for the task, and pass all other events to QWidget's
72    implementation.
73
74    The \c gestureHandler() function examines the gestures supplied by the
75    newly-delivered QGestureEvent. Since only one gesture of a given type can be
76    used on a widget at any particular time, we can check for each gesture type
77    using the QGestureEvent::gesture() function:
78
79    \snippet examples/gestures/imagegestures/imagewidget.cpp gesture event handler
80
81    If a QGesture object is supplied for a certain type of gesture, we call a special
82    purpose function to deal with it, casting the gesture object to the appropriate
83    QGesture subclass.
84
85    To illustrate how a standard gesture can be interpreted by an application, we
86    show the implementation of the \c swipeTriggered() function, which handles the
87    gesture associated with a brushing or swiping motion on the user's display or
88    input device:
89
90    \snippet examples/gestures/imagegestures/imagewidget.cpp swipe function
91
92    The QSwipeGesture class provides specialized functions and defines a enum
93    to make it more convenient for developers to discover which direction, if
94    any, the user swiped the display. Here, we simply navigate to the previous
95    image in the collection if the user swiped upwards or to the left; otherwise
96    we navigate to the next image in the collection.
97
98    The other gestures are also handled by special purpose functions, but use
99    the values of properties held by the QGesture object passed to them.
100*/
101