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diff --git a/doc/src/examples/mandelbrot.qdoc b/doc/src/examples/mandelbrot.qdoc deleted file mode 100644 index 898741fad5..0000000000 --- a/doc/src/examples/mandelbrot.qdoc +++ /dev/null @@ -1,368 +0,0 @@ -/**************************************************************************** -** -** Copyright (C) 2012 Digia Plc and/or its subsidiary(-ies). -** Contact: http://www.qt-project.org/legal -** -** 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 Digia. For licensing terms and -** conditions see http://qt.digia.com/licensing. For further information -** use the contact form at http://qt.digia.com/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: http://www.gnu.org/copyleft/fdl.html. -** $QT_END_LICENSE$ -** -****************************************************************************/ - -/*! - \example threads/mandelbrot - \title Mandelbrot Example - - The Mandelbrot example shows how to use a worker thread to - perform heavy computations without blocking the main thread's - event loop. - - The heavy computation here is the Mandelbrot set, probably the - world's most famous fractal. These days, while sophisticated - programs such as \l{XaoS} that provide real-time zooming in the - Mandelbrot set, the standard Mandelbrot algorithm is just slow - enough for our purposes. - - \image mandelbrot-example.png Screenshot of the Mandelbrot example - - In real life, the approach described here is applicable to a - large set of problems, including synchronous network I/O and - database access, where the user interface must remain responsive - while some heavy operation is taking place. The \l - network/blockingfortuneclient example shows the same principle at - work in a TCP client. - - The Mandelbrot application supports zooming and scrolling using - the mouse or the keyboard. To avoid freezing the main thread's - event loop (and, as a consequence, the application's user - interface), we put all the fractal computation in a separate - worker thread. The thread emits a signal when it is done - rendering the fractal. - - During the time where the worker thread is recomputing the - fractal to reflect the new zoom factor position, the main thread - simply scales the previously rendered pixmap to provide immediate - feedback. The result doesn't look as good as what the worker - thread eventually ends up providing, but at least it makes the - application more responsive. The sequence of screenshots below - shows the original image, the scaled image, and the rerendered - image. - - \table - \row - \li \inlineimage mandelbrot_zoom1.png - \li \inlineimage mandelbrot_zoom2.png - \li \inlineimage mandelbrot_zoom3.png - \endtable - - Similarly, when the user scrolls, the previous pixmap is scrolled - immediately, revealing unpainted areas beyond the edge of the - pixmap, while the image is rendered by the worker thread. - - \table - \row - \li \inlineimage mandelbrot_scroll1.png - \li \inlineimage mandelbrot_scroll2.png - \li \inlineimage mandelbrot_scroll3.png - \endtable - - The application consists of two classes: - - \list - \li \c RenderThread is a QThread subclass that renders - the Mandelbrot set. - \li \c MandelbrotWidget is a QWidget subclass that shows the - Mandelbrot set on screen and lets the user zoom and scroll. - \endlist - - If you are not already familiar with Qt's thread support, we - recommend that you start by reading the \l{Thread Support in Qt} - overview. - - \section1 RenderThread Class Definition - - We'll start with the definition of the \c RenderThread class: - - \snippet examples/threads/mandelbrot/renderthread.h 0 - - The class inherits QThread so that it gains the ability to run in - a separate thread. Apart from the constructor and destructor, \c - render() is the only public function. Whenever the thread is done - rendering an image, it emits the \c renderedImage() signal. - - The protected \c run() function is reimplemented from QThread. It - is automatically called when the thread is started. - - In the \c private section, we have a QMutex, a QWaitCondition, - and a few other data members. The mutex protects the other data - member. - - \section1 RenderThread Class Implementation - - \snippet examples/threads/mandelbrot/renderthread.cpp 0 - - In the constructor, we initialize the \c restart and \c abort - variables to \c false. These variables control the flow of the \c - run() function. - - We also initialize the \c colormap array, which contains a series - of RGB colors. - - \snippet examples/threads/mandelbrot/renderthread.cpp 1 - - The destructor can be called at any point while the thread is - active. We set \c abort to \c true to tell \c run() to stop - running as soon as possible. We also call - QWaitCondition::wakeOne() to wake up the thread if it's sleeping. - (As we will see when we review \c run(), the thread is put to - sleep when it has nothing to do.) - - The important thing to notice here is that \c run() is executed - in its own thread (the worker thread), whereas the \c - RenderThread constructor and destructor (as well as the \c - render() function) are called by the thread that created the - worker thread. Therefore, we need a mutex to protect accesses to - the \c abort and \c condition variables, which might be accessed - at any time by \c run(). - - At the end of the destructor, we call QThread::wait() to wait - until \c run() has exited before the base class destructor is - invoked. - - \snippet examples/threads/mandelbrot/renderthread.cpp 2 - - The \c render() function is called by the \c MandelbrotWidget - whenever it needs to generate a new image of the Mandelbrot set. - The \c centerX, \c centerY, and \c scaleFactor parameters specify - the portion of the fractal to render; \c resultSize specifies the - size of the resulting QImage. - - The function stores the parameters in member variables. If the - thread isn't already running, it starts it; otherwise, it sets \c - restart to \c true (telling \c run() to stop any unfinished - computation and start again with the new parameters) and wakes up - the thread, which might be sleeping. - - \snippet examples/threads/mandelbrot/renderthread.cpp 3 - - \c run() is quite a big function, so we'll break it down into - parts. - - The function body is an infinite loop which starts by storing the - rendering parameters in local variables. As usual, we protect - accesses to the member variables using the class's mutex. Storing - the member variables in local variables allows us to minimize the - amout of code that needs to be protected by a mutex. This ensures - that the main thread will never have to block for too long when - it needs to access \c{RenderThread}'s member variables (e.g., in - \c render()). - - The \c forever keyword is, like \c foreach, a Qt pseudo-keyword. - - \snippet examples/threads/mandelbrot/renderthread.cpp 4 - \snippet examples/threads/mandelbrot/renderthread.cpp 5 - \snippet examples/threads/mandelbrot/renderthread.cpp 6 - \snippet examples/threads/mandelbrot/renderthread.cpp 7 - - Then comes the core of the algorithm. Instead of trying to create - a perfect Mandelbrot set image, we do multiple passes and - generate more and more precise (and computationally expensive) - approximations of the fractal. - - If we discover inside the loop that \c restart has been set to \c - true (by \c render()), we break out of the loop immediately, so - that the control quickly returns to the very top of the outer - loop (the \c forever loop) and we fetch the new rendering - parameters. Similarly, if we discover that \c abort has been set - to \c true (by the \c RenderThread destructor), we return from - the function immediately, terminating the thread. - - The core algorithm is beyond the scope of this tutorial. - - \snippet examples/threads/mandelbrot/renderthread.cpp 8 - \snippet examples/threads/mandelbrot/renderthread.cpp 9 - - Once we're done with all the iterations, we call - QWaitCondition::wait() to put the thread to sleep by calling, - unless \c restart is \c true. There's no use in keeping a worker - thread looping indefinitely while there's nothing to do. - - \snippet examples/threads/mandelbrot/renderthread.cpp 10 - - The \c rgbFromWaveLength() function is a helper function that - converts a wave length to a RGB value compatible with 32-bit - \l{QImage}s. It is called from the constructor to initialize the - \c colormap array with pleasing colors. - - \section1 MandelbrotWidget Class Definition - - The \c MandelbrotWidget class uses \c RenderThread to draw the - Mandelbrot set on screen. Here's the class definition: - - \snippet examples/threads/mandelbrot/mandelbrotwidget.h 0 - - The widget reimplements many event handlers from QWidget. In - addition, it has an \c updatePixmap() slot that we'll connect to - the worker thread's \c renderedImage() signal to update the - display whenever we receive new data from the thread. - - Among the private variables, we have \c thread of type \c - RenderThread and \c pixmap, which contains the last rendered - image. - - \section1 MandelbrotWidget Class Implementation - - \snippet examples/threads/mandelbrot/mandelbrotwidget.cpp 0 - - The implementation starts with a few contants that we'll need - later on. - - \snippet examples/threads/mandelbrot/mandelbrotwidget.cpp 1 - - The interesting part of the constructor is the - qRegisterMetaType() and QObject::connect() calls. Let's start - with the \l{QObject::connect()}{connect()} call. - - Although it looks like a standard signal-slot connection between - two \l{QObject}s, because the signal is emitted in a different - thread than the receiver lives in, the connection is effectively a - \l{Qt::QueuedConnection}{queued connection}. These connections are - asynchronous (i.e., non-blocking), meaning that the slot will be - called at some point after the \c emit statement. What's more, the - slot will be invoked in the thread in which the receiver lives. - Here, the signal is emitted in the worker thread, and the slot is - executed in the GUI thread when control returns to the event loop. - - With queued connections, Qt must store a copy of the arguments - that were passed to the signal so that it can pass them to the - slot later on. Qt knows how to take of copy of many C++ and Qt - types, but QImage isn't one of them. We must therefore call the - template function qRegisterMetaType() before we can use QImage - as parameter in queued connections. - - \snippet examples/threads/mandelbrot/mandelbrotwidget.cpp 2 - \snippet examples/threads/mandelbrot/mandelbrotwidget.cpp 3 - \snippet examples/threads/mandelbrot/mandelbrotwidget.cpp 4 - - In \l{QWidget::paintEvent()}{paintEvent()}, we start by filling - the background with black. If we have nothing yet to paint (\c - pixmap is null), we print a message on the widget asking the user - to be patient and return from the function immediately. - - \snippet examples/threads/mandelbrot/mandelbrotwidget.cpp 5 - \snippet examples/threads/mandelbrot/mandelbrotwidget.cpp 6 - \snippet examples/threads/mandelbrot/mandelbrotwidget.cpp 7 - \snippet examples/threads/mandelbrot/mandelbrotwidget.cpp 8 - - If the pixmap has the right scale factor, we draw the pixmap directly onto - the widget. Otherwise, we scale and translate the \l{Coordinate - System}{coordinate system} before we draw the pixmap. By reverse mapping - the widget's rectangle using the scaled painter matrix, we also make sure - that only the exposed areas of the pixmap are drawn. The calls to - QPainter::save() and QPainter::restore() make sure that any painting - performed afterwards uses the standard coordinate system. - - \snippet examples/threads/mandelbrot/mandelbrotwidget.cpp 9 - - At the end of the paint event handler, we draw a text string and - a semi-transparent rectangle on top of the fractal. - - \snippet examples/threads/mandelbrot/mandelbrotwidget.cpp 10 - - Whenever the user resizes the widget, we call \c render() to - start generating a new image, with the same \c centerX, \c - centerY, and \c curScale parameters but with the new widget size. - - Notice that we rely on \c resizeEvent() being automatically - called by Qt when the widget is shown the first time to generate - the image the very first time. - - \snippet examples/threads/mandelbrot/mandelbrotwidget.cpp 11 - - The key press event handler provides a few keyboard bindings for - the benefit of users who don't have a mouse. The \c zoom() and \c - scroll() functions will be covered later. - - \snippet examples/threads/mandelbrot/mandelbrotwidget.cpp 12 - - The wheel event handler is reimplemented to make the mouse wheel - control the zoom level. QWheelEvent::delta() returns the angle of - the wheel mouse movement, in eights of a degree. For most mice, - one wheel step corresponds to 15 degrees. We find out how many - mouse steps we have and determine the zoom factor in consequence. - For example, if we have two wheel steps in the positive direction - (i.e., +30 degrees), the zoom factor becomes \c ZoomInFactor - to the second power, i.e. 0.8 * 0.8 = 0.64. - - \snippet examples/threads/mandelbrot/mandelbrotwidget.cpp 13 - - When the user presses the left mouse button, we store the mouse - pointer position in \c lastDragPos. - - \snippet examples/threads/mandelbrot/mandelbrotwidget.cpp 14 - - When the user moves the mouse pointer while the left mouse button - is pressed, we adjust \c pixmapOffset to paint the pixmap at a - shifted position and call QWidget::update() to force a repaint. - - \snippet examples/threads/mandelbrot/mandelbrotwidget.cpp 15 - - When the left mouse button is released, we update \c pixmapOffset - just like we did on a mouse move and we reset \c lastDragPos to a - default value. Then, we call \c scroll() to render a new image - for the new position. (Adjusting \c pixmapOffset isn't sufficient - because areas revealed when dragging the pixmap are drawn in - black.) - - \snippet examples/threads/mandelbrot/mandelbrotwidget.cpp 16 - - The \c updatePixmap() slot is invoked when the worker thread has - finished rendering an image. We start by checking whether a drag - is in effect and do nothing in that case. In the normal case, we - store the image in \c pixmap and reinitialize some of the other - members. At the end, we call QWidget::update() to refresh the - display. - - At this point, you might wonder why we use a QImage for the - parameter and a QPixmap for the data member. Why not stick to one - type? The reason is that QImage is the only class that supports - direct pixel manipulation, which we need in the worker thread. On - the other hand, before an image can be drawn on screen, it must - be converted into a pixmap. It's better to do the conversion once - and for all here, rather than in \c paintEvent(). - - \snippet examples/threads/mandelbrot/mandelbrotwidget.cpp 17 - - In \c zoom(), we recompute \c curScale. Then we call - QWidget::update() to draw a scaled pixmap, and we ask the worker - thread to render a new image corresponding to the new \c curScale - value. - - \snippet examples/threads/mandelbrot/mandelbrotwidget.cpp 18 - - \c scroll() is similar to \c zoom(), except that the affected - parameters are \c centerX and \c centerY. - - \section1 The main() Function - - The application's multithreaded nature has no impact on its \c - main() function, which is as simple as usual: - - \snippet examples/threads/mandelbrot/main.cpp 0 -*/ |