diff options
Diffstat (limited to 'doc/src/frameworks-technologies/gestures.qdoc')
| -rw-r--r-- | doc/src/frameworks-technologies/gestures.qdoc | 170 |
1 files changed, 170 insertions, 0 deletions
diff --git a/doc/src/frameworks-technologies/gestures.qdoc b/doc/src/frameworks-technologies/gestures.qdoc new file mode 100644 index 0000000..316d74d --- /dev/null +++ b/doc/src/frameworks-technologies/gestures.qdoc @@ -0,0 +1,170 @@ +/**************************************************************************** +** +** 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.example.com/contact. +** $QT_END_LICENSE$ +** +****************************************************************************/ + +/*! + \page gestures-overview.html + \startpage index.html Qt Reference Documentation + + \title Gestures Programming + \ingroup howto + \brief An overview of the Qt support for Gesture programming. + + The QGesture class provides the ability to form gestures from a series + of events independent of the input method. A gesture could be a particular + movement of a mouse, a touch screen action, or a series of events from + some other source. The nature of the input, the interpretation + of the gesture and the action taken are the choice of the implementing + developer. + + \tableofcontents + + + \section1 Creating Your Own Gesture Recognizer + + QGesture is a base class for a user defined gesture recognizer class. In + order to implement the recognizer you will need to subclass the + QGesture class and implement the pure virtual function \l{QGesture::filterEvent()}{filterEvent()}. Once + you have implemented the \l{QGesture::filterEvent()}{filterEvent()} function to + make your own recognizer you can process events. A sequence of events may, + according to your own rules, represent a gesture. The events can be singly + passed to the recognizer via the \l{QGesture::filterEvent()}{filterEvent()} function or as a stream of + events by specifying a parent source of events. The events can be from any + source and could result in any action as defined by the user. The source + and action need not be graphical though that would be the most likely + scenario. To find how to connect a source of events to automatically feed into the recognizer see QGesture. + + Recognizers based on QGesture can emit any of the following signals: + + \snippet doc/src/snippets/gestures/qgesture.h qgesture-signals + + These signals are emitted when the state changes with the call to + \l{QGesture::updateState()}{updateState()}, more than one signal may + be emitted when a change of state occurs. There are four GestureStates + + \table + \header \o New State \o Description \o QGesture Actions on Entering this State + \row \o Qt::NoGesture \o Initial value \o emit \l {QGesture::cancelled()}{cancelled()} + \row \o Qt::GestureStarted \o A continuous gesture has started \o emit \l{QGesture::started()}{started()} and emit \l{QGesture::triggered()}{triggered()} + \row \o Qt::GestureUpdated \o A gesture continues \o emit \l{QGesture::triggered()}{triggered()} + \row \o Qt::GestureFinished \o A gesture has finished. \o emit \l{QGesture::finished()}{finished()} + \endtable + + \note \l{QGesture::started()}{started()} can be emitted if entering any + state greater than NoGesture if NoGesture was the previous state. This + means that your state machine does not need to explicitly use the + Qt::GestureStarted state, you can simply proceed from NoGesture to + Qt::GestureUpdated to emit a \l{QGesture::started()}{started()} signal + and a \l{QGesture::triggered()}{triggered()} signal. + + You may use some or all of these states when implementing the pure + virtual function \l{QGesture::filterEvent()}{filterEvent()}. + \l{QGesture::filterEvent()}{filterEvent()} will usually implement a + state machine using the GestureState enums, but the details of which + states are used is up to the developer. + + You may also need to reimplement the virtual function \l{QGesture::reset()}{reset()} + if internal data or objects need to be re-initialized. The function must + conclude with a call to \l{QGesture::updateState()}{updateState()} to + change the current state to Qt::NoGesture. + + \section1 An Example, ImageViewer + + To illustrate how to use QGesture we will look at the ImageViewer + example. This example uses QPanGesture, standard gesture, and an + implementation of TapAndHoldGesture. Note that TapAndHoldGesture is + platform dependent. + + \snippet doc/src/snippets/gestures/imageviewer/tapandholdgesture.cpp tapandhold-reset + + In ImageViewer we see that the ImageWidget class uses two gestures: + \l QPanGesture and TapAndHoldGesture. The + QPanGesture is a standard gesture which is part of Qt. + TapAndHoldGesture is defined and implemented as part of the example. + The ImageWidget listens for signals from the gestures, but is not + interested in the \l{QGesture::started()}{started()} signal. + + \snippet doc/src/snippets/gestures/imageviewer/imagewidget.h imagewidget-slots + + TapAndHoldGesture uses QTouchEvent events and mouse events to detect + start, update and end events that can be mapped onto the GestureState + changes. The implementation in this case uses a timer as well. If the + timeout event occurs a given number of times after the start of the gesture + then the gesture is considered to have finished whether or not the + appropriate touch or mouse event has occurred. Also if a large jump in + the position of the event occurs, as calculated by the \l {QPoint::manhattanLength()}{manhattanLength()} + call, then the gesture is cancelled by calling \l{QGesture::reset()}{reset()} + which tidies up and uses \l{QGesture::updateState()}{updateState()} to + change state to NoGesture which will result in the \l{QGesture::cancelled()}{cancelled()} + signal being emitted by the recognizer. + + ImageWidget handles the signals by connecting the slots to the signals, + although \c cancelled() is not connected here. + + \snippet doc/src/snippets/gestures/imageviewer/imagewidget.cpp imagewidget-connect + + These functions in turn will have to be aware of which gesture + object was the source of the signal since we have more than one source + per slot. This is easily done by using the QObject::sender() function + as shown here + + \snippet doc/src/snippets/gestures/imageviewer/imagewidget.cpp imagewidget-triggered-1 + + As \l{QGesture::triggered()}{triggered()} signals are handled by + gestureTriggered() there may be position updates invoking calls to, + for example, goNextImage(), this will cause a change in the image + handling logic of ImageWidget and a call to updateImage() to display + the changed state. + + Following the logic of how the QEvent is processed we can summmarize + it as follows: + \list + \o filterEvent() becomes the event filter of the parent ImageWidget object for a QPanGesture object and a + TapAndHoldGesture object. + \o filterEvent() then calls updateState() to change states + \o updateState() emits the appropriate signal(s) for the state change. + \o The signals are caught by the defined slots in ImageWidget + \o The widget logic changes and an update() results in a paint event. + \endlist + + + +*/ + |