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diff --git a/examples/widgets/doc/src/concentriccircles.qdoc b/examples/widgets/doc/src/concentriccircles.qdoc deleted file mode 100644 index fdf1f88142..0000000000 --- a/examples/widgets/doc/src/concentriccircles.qdoc +++ /dev/null @@ -1,233 +0,0 @@ -/**************************************************************************** -** -** Copyright (C) 2016 The Qt Company Ltd. -** Contact: https://www.qt.io/licensing/ -** -** This file is part of the documentation of the Qt Toolkit. -** -** $QT_BEGIN_LICENSE:FDL$ -** Commercial License Usage -** Licensees holding valid commercial Qt licenses may use this file in -** accordance with the commercial license agreement provided with the -** Software or, alternatively, in accordance with the terms contained in -** a written agreement between you and The Qt Company. For licensing terms -** and conditions see https://www.qt.io/terms-conditions. For further -** information use the contact form at https://www.qt.io/contact-us. -** -** GNU Free Documentation License Usage -** 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. Please review the following information to ensure -** the GNU Free Documentation License version 1.3 requirements -** will be met: https://www.gnu.org/licenses/fdl-1.3.html. -** $QT_END_LICENSE$ -** -****************************************************************************/ - -/*! - \example painting/concentriccircles - \title Concentric Circles Example - \ingroup examples-painting - \brief Demonstrates the improved quality that antialiasing and floating point precision gives. - - \brief The Concentric Circles example shows the improved rendering - quality that can be obtained using floating point precision and - anti-aliasing when drawing custom widgets. The example also shows - how to do simple animations. - - The application's main window displays several widgets which are - drawn using the various combinations of precision and - anti-aliasing. - - \image concentriccircles-example.png - - Anti-aliasing is one of QPainter's render hints. The - QPainter::RenderHints are used to specify flags to QPainter that - may, or may not, be respected by any given - engine. QPainter::Antialiasing indicates that the engine should - anti-alias the edges of primitives if possible, i.e. put - additional pixels around the original ones to smooth the edges. - - The difference between floating point precision and integer - precision is a matter of accuracy, and is visible in the - application's main window: Even though the logic that is - calculating the circles' geometry is the same, floating points - ensure that the white spaces between each circle are of the same - size, while integers make two and two circles appear as if they - belong together. The reason is that the integer based precision - rely on rounding off non-integer calculations. - - The example consists of two classes: - - \list - \li \c CircleWidget is a custom widget which renders several animated - concentric circles. - \li \c Window is the application's main window displaying four \c - {CircleWidget}s drawn using different combinations of precision - and aliasing. - \endlist - - First we will review the CircleWidget class, then we will take a - look at the Window class. - - \section1 CircleWidget Class Definition - - The CircleWidget class inherits QWidget, and is a custom widget - which renders several animated concentric circles. - - \snippet painting/concentriccircles/circlewidget.h 0 - - We declare the \c floatBased and \c antialiased variables to hold - whether an instance of the class should be rendered with integer - or float based precision, and whether the rendering should be - anti-aliased or not. We also declare functions setting each of - these variables. - - In addition we reimplement the QWidget::paintEvent() function to - apply the various combinations of precision and anti-aliasing when - rendering, and to support the animation. We reimplement the - QWidget::minimumSizeHint() and QWidget::sizeHint() functions to - give the widget a reasonable size within our application. - - We declare the private \c nextAnimationFrame() slot, and the - associated \c frameNo variable holding the number of "animation - frames" for the widget, to facilitate the animation. - - \section1 CircleWidget Class Implementation - - In the constructor we make the widget's rendering integer based - and aliased by default: - - \snippet painting/concentriccircles/circlewidget.cpp 0 - - We initialize the widget's \c frameNo variable, and set the - widget's background color using the QWidget::setBackgroundColor() - function which takes a \l {QPalette::ColorRole}{color role} as - argument; the QPalette::Base color role is typically white. - - Then we set the widgets size policy using the - QWidget::setSizePolicy() function. QSizePolicy::Expanding means - that the widget's \l {QWidget::sizeHint()}{sizeHint()} is a - sensible size, but that the widget can be shrunk and still be - useful. The widget can also make use of extra space, so it should - get as much space as possible. - - \snippet painting/concentriccircles/circlewidget.cpp 1 - \codeline - \snippet painting/concentriccircles/circlewidget.cpp 2 - - The public \c setFloatBased() and \c setAntialiased() functions - update the widget's rendering preferences, i.e. whether the widget - should be rendered with integer or float based precision, and - whether the rendering should be anti-aliased or not. - - The functions also generate a paint event by calling the - QWidget::update() function, forcing a repaint of the widget with - the new rendering preferences. - - \snippet painting/concentriccircles/circlewidget.cpp 3 - \codeline - \snippet painting/concentriccircles/circlewidget.cpp 4 - - The default implementations of the QWidget::minimumSizeHint() and - QWidget::sizeHint() functions return invalid sizes if there is no - layout for the widget, otherwise they return the layout's minimum and - preferred size, respectively. - - We reimplement the functions to give the widget minimum and - preferred sizes which are reasonable within our application. - - \snippet painting/concentriccircles/circlewidget.cpp 5 - - The nextAnimationFrame() slot simply increments the \c frameNo - variable's value, and calls the QWidget::update() function which - schedules a paint event for processing when Qt returns to the main - event loop. - - \snippet painting/concentriccircles/circlewidget.cpp 6 - - A paint event is a request to repaint all or part of the - widget. The \c paintEvent() function is an event handler that can - be reimplemented to receive the widget's paint events. We - reimplement the event handler to apply the various combinations of - precision and anti-aliasing when rendering the widget, and to - support the animation. - - First, we create a QPainter for the widget, and set its - antialiased flag to the widget's preferred aliasing. We also - translate the painters coordinate system, preparing to draw the - widget's cocentric circles. The translation ensures that the - center of the circles will be equivalent to the widget's center. - - \snippet painting/concentriccircles/circlewidget.cpp 7 - - When painting a circle, we use the number of "animation frames" to - determine the alpha channel of the circle's color. The alpha - channel specifies the color's transparency effect, 0 represents a - fully transparent color, while 255 represents a fully opaque - color. - - \snippet painting/concentriccircles/circlewidget.cpp 8 - - If the calculated alpha channel is fully transparent, we don't - draw anything since that would be equivalent to drawing a white - circle on a white background. Instead we skip to the next circle - still creating a white space. If the calculated alpha channel is - fully opaque, we set the pen (the QColor passed to the QPen - constructor is converted into the required QBrush by default) and - draw the circle. If the widget's preferred precision is float - based, we specify the circle's bounding rectangle using QRectF and - double values, otherwise we use QRect and integers. - - The animation is controlled by the public \c nextAnimationFrame() - slot: Whenever the \c nextAnimationFrame() slot is called the - number of frames is incremented and a paint event is - scheduled. Then, when the widget is repainted, the alpha-blending - of the circles' colors change and the circles appear as animated. - - \section1 Window Class Definition - - The Window class inherits QWidget, and is the application's main - window rendering four \c {CircleWidget}s using different - combinations of precision and aliasing. - - \snippet painting/concentriccircles/window.h 0 - - We declare the various components of the main window, i.e., the text - labels and a double array that will hold reference to the four \c - {CircleWidget}s. In addition we declare the private \c - createLabel() function to simplify the constructor. - - \section1 Window Class Implementation - - \snippet painting/concentriccircles/window.cpp 0 - - In the constructor, we first create the various labels and put - them in a QGridLayout. - - \snippet painting/concentriccircles/window.cpp 1 - - Then we create a QTimer. The QTimer class is a high-level - programming interface for timers, and provides repetitive and - single-shot timers. - - We create a timer to facilitate the animation of our concentric - circles; when we create the four CircleWidget instances (and add - them to the layout), we connect the QTimer::timeout() signal to - each of the widgets' \c nextAnimationFrame() slots. - - \snippet painting/concentriccircles/window.cpp 2 - - Before we set the layout and window title for our main window, we - make the timer start with a timeout interval of 100 milliseconds, - using the QTimer::start() function. That means that the - QTimer::timeout() signal will be emitted, forcing a repaint of the - four \c {CircleWidget}s, every 100 millisecond which is the reason - the circles appear as animated. - - \snippet painting/concentriccircles/window.cpp 3 - - The private \c createLabel() function is implemented to simlify - the constructor. -*/ |