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diff --git a/examples/widgets/doc/src/wiggly.qdoc b/examples/widgets/doc/src/wiggly.qdoc new file mode 100644 index 0000000000..e84ab00e61 --- /dev/null +++ b/examples/widgets/doc/src/wiggly.qdoc @@ -0,0 +1,167 @@ +/**************************************************************************** +** +** Copyright (C) 2012 Nokia Corporation and/or its subsidiary(-ies). +** Contact: http://www.qt-project.org/ +** +** This file is part of the documentation of the Qt Toolkit. +** +** $QT_BEGIN_LICENSE:FDL$ +** GNU Free Documentation License +** Alternatively, this file may be used under the terms of the GNU Free +** Documentation License version 1.3 as published by the Free Software +** Foundation and appearing in the file included in the packaging of +** this file. +** +** Other Usage +** Alternatively, this file may be used in accordance with the terms +** and conditions contained in a signed written agreement between you +** and Nokia. +** +** +** +** +** +** $QT_END_LICENSE$ +** +****************************************************************************/ + +/*! + \example widgets/wiggly + \title Wiggly Example + + The Wiggly example shows how to animate a widget using + QBasicTimer and \l{QObject::timerEvent()}{timerEvent()}. In + addition, the example demonstrates how to use QFontMetrics to + determine the size of text on screen. + + \image wiggly-example.png Screenshot of the Wiggly example + + QBasicTimer is a low-level class for timers. Unlike QTimer, + QBasicTimer doesn't inherit from QObject; instead of emitting a + \l{QTimer::timeout()}{timeout()} signal when a certain amount of + time has passed, it sends a QTimerEvent to a QObject of our + choice. This makes QBasicTimer a more lightweight alternative to + QTimer. Qt's built-in widgets use it internally, and it is + provided in Qt's API for highly-optimized applications (e.g., + \l{Qt for Embedded Linux} applications). + + The example consists of two classes: + + \list + \li \c WigglyWidget is the custom widget displaying the text + in a wiggly line. + + \li \c Dialog is the dialog widget allowing the user to enter a + text. It combines a \c WigglyWidget and a \c QLineEdit. + \endlist + + We will first take a quick look at the \c Dialog class, then we + will review the \c WigglyWidget class. + + \section1 Dialog Class Definition + + \snippet widgets/wiggly/dialog.h 0 + + The \c Dialog class provides a dialog widget that allows the user + to enter a text. The text is then rendered by \c WigglyWidget. + + \section1 Dialog Class Implementation + + \snippet widgets/wiggly/dialog.cpp 0 + + In the constructor we create a wiggly widget along with a + \l{QLineEdit}{line edit}, and we put the two widgets in a + vertical layout. We connect the line edit's \l + {QLineEdit::textChanged()}{textChanged()} signal to the wiggly + widget's \c setText() slot to obtain the real time interaction + with the wiggly widget. The widget's default text is "Hello + world!". + + \section1 WigglyWidget Class Definition + + \snippet widgets/wiggly/wigglywidget.h 0 + + The \c WigglyWidget class provides the wiggly line displaying the + text. We subclass QWidget and reimplement the standard \l + {QWidget::paintEvent()}{paintEvent()} and \l + {QObject::timerEvent()}{timerEvent()} functions to draw and update + the widget. In addition we implement a public \c setText() slot + that sets the widget's text. + + The \c timer variable, of type QBasicTimer, is used to update the + widget at regular intervals, making the widget move. The \c text + variable is used to store the currently displayed text, and \c + step to calculate position and color for each character on the + wiggly line. + + \section1 WigglyWidget Class Implementation + + \snippet widgets/wiggly/wigglywidget.cpp 0 + + In the constructor, we make the widget's background slightly + lighter than the usual background using the QPalette::Midlight + color role. The background role defines the brush from the + widget's palette that Qt uses to paint the background. Then we + enlarge the widget's font with 20 points. + + Finally we start the timer; the call to QBasicTimer::start() + makes sure that \e this particular wiggly widget will receive the + timer events generated when the timer times out (every 60 + milliseconds). + + \snippet widgets/wiggly/wigglywidget.cpp 1 + \snippet widgets/wiggly/wigglywidget.cpp 2 + + The \c paintEvent() function is called whenever a QPaintEvent is + sent to the widget. Paint events are sent to widgets that need to + update themselves, for instance when part of a widget is exposed + because a covering widget was moved. For the wiggly widget, a + paint event will also be generated every 60 milliseconds from + the \c timerEvent() slot. + + The \c sineTable represents y-values of the sine curve, + multiplied by 100. It is used to make the wiggly widget move + along the sine curve. + + The QFontMetrics object provides information about the widget's + font. The \c x variable is the horizontal position where we start + drawing the text. The \c y variable is the vertical position of + the text's base line. Both variables are computed so that the + text is horizontally and vertically centered. To compute the base + line, we take into account the font's ascent (the height of the + font above the base line) and font's descent (the height of the + font below the base line). If the descent equals the ascent, they + cancel out each other and the base line is at \c height() / 2. + + \snippet widgets/wiggly/wigglywidget.cpp 3 + \snippet widgets/wiggly/wigglywidget.cpp 4 + + Each time the \c paintEvent() function is called, we create a + QPainter object \c painter to draw the contents of the widget. + For each character in \c text, we determine the color and the + position on the wiggly line based on \c step. In addition, \c x + is incremented by the character's width. + + For simplicity, we assume that QFontMetrics::width(\c text) + returns the sum of the individual character widths + (QFontMetrics::width(\c text[i])). In practice, this is not + always the case because QFontMetrics::width(\c text) also takes + into account the kerning between certain letters (e.g., 'A' and + 'V'). The result is that the text isn't perfectly centered. You + can verify this by typing "AVAVAVAVAVAV" in the line edit. + + \snippet widgets/wiggly/wigglywidget.cpp 5 + \snippet widgets/wiggly/wigglywidget.cpp 6 + + The \c timerEvent() function receives all the timer events that + are generated for this widget. If a timer event is sent from the + widget's QBasicTimer, we increment \c step to make the text move, + and call QWidget::update() to refresh the display. Any other + timer event is passed on to the base class's implementation of + the \l{QWidget::timerEvent()}{timerEvent()} function. + + The QWidget::update() slot does not cause an immediate repaint; + instead the slot schedules a paint event for processing when Qt + returns to the main event loop. The paint events are then handled + by \c{WigglyWidget}'s \c paintEvent() function. +*/ |