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diff --git a/doc/src/examples/2dpainting.qdoc b/doc/src/examples/2dpainting.qdoc new file mode 100644 index 0000000000..e90788e38c --- /dev/null +++ b/doc/src/examples/2dpainting.qdoc @@ -0,0 +1,210 @@ +/**************************************************************************** +** +** Copyright (C) 2011 Nokia Corporation and/or its subsidiary(-ies). +** All rights reserved. +** Contact: Nokia Corporation (qt-info@nokia.com) +** +** This file is part of the documentation of the Qt Toolkit. +** +** $QT_BEGIN_LICENSE:FDL$ +** 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 Technology Preview License Agreement accompanying +** this package. +** +** 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. +** +** If you have questions regarding the use of this file, please contact +** Nokia at qt-info@nokia.com. +** $QT_END_LICENSE$ +** +****************************************************************************/ + +/*! + \example opengl/2dpainting + \title 2D Painting Example + + The 2D Painting example shows how QPainter and QGLWidget can be used + together to display accelerated 2D graphics on supported hardware. + + \image 2dpainting-example.png + + The QPainter class is used to draw 2D graphics primitives onto + paint devices provided by QPaintDevice subclasses, such as QWidget + and QImage. + + Since QGLWidget is a subclass of QWidget, it is possible + to reimplement its \l{QWidget::paintEvent()}{paintEvent()} and use + QPainter to draw on the device, just as you would with a QWidget. + The only difference is that the painting operations will be accelerated + in hardware if it is supported by your system's OpenGL drivers. + + In this example, we perform the same painting operations on a + QWidget and a QGLWidget. The QWidget is shown with anti-aliasing + enabled, and the QGLWidget will also use anti-aliasing if the + required extensions are supported by your system's OpenGL driver. + + \section1 Overview + + To be able to compare the results of painting onto a QGLWidget subclass + with native drawing in a QWidget subclass, we want to show both kinds + of widget side by side. To do this, we derive subclasses of QWidget and + QGLWidget, using a separate \c Helper class to perform the same painting + operations for each, and lay them out in a top-level widget, itself + provided a the \c Window class. + + \section1 Helper Class Definition + + In this example, the painting operations are performed by a helper class. + We do this because we want the same painting operations to be performed + for both our QWidget subclass and the QGLWidget subclass. + + The \c Helper class is minimal: + + \snippet examples/opengl/2dpainting/helper.h 0 + + Apart from the constructor, it only provides a \c paint() function to paint + using a painter supplied by one of our widget subclasses. + + \section1 Helper Class Implementation + + The constructor of the class sets up the resources it needs to paint + content onto a widget: + + \snippet examples/opengl/2dpainting/helper.cpp 0 + + The actual painting is performed in the \c paint() function. This takes + a QPainter that has already been set up to paint onto a paint device + (either a QWidget or a QGLWidget), a QPaintEvent that provides information + about the region to be painted, and a measure of the elapsed time (in + milliseconds) since the paint device was last updated. + + \snippet examples/opengl/2dpainting/helper.cpp 1 + + We begin painting by filling in the region contained in the paint event + before translating the origin of the coordinate system so that the rest + of the painting operations will be displaced towards the center of the + paint device. + + We draw a spiral pattern of circles, using the elapsed time specified to + animate them so that they appear to move outward and around the coordinate + system's origin: + + \snippet examples/opengl/2dpainting/helper.cpp 2 + + Since the coordinate system is rotated many times during + this process, we \l{QPainter::save()}{save()} the QPainter's state + beforehand and \l{QPainter::restore()}{restore()} it afterwards. + + \snippet examples/opengl/2dpainting/helper.cpp 3 + + We draw some text at the origin to complete the effect. + + \section1 Widget Class Definition + + The \c Widget class provides a basic custom widget that we use to + display the simple animation painted by the \c Helper class. + + \snippet examples/opengl/2dpainting/widget.h 0 + + Apart from the constructor, it only contains a + \l{QWidget::paintEvent()}{paintEvent()} function, that lets us draw + customized content, and a slot that is used to animate its contents. + One member variable keeps track of the \c Helper that the widget uses + to paint its contents, and the other records the elapsed time since + it was last updated. + + \section1 Widget Class Implementation + + The constructor only initializes the member variables, storing the + \c Helper object supplied and calling the base class's constructor, + and enforces a fixed size for the widget: + + \snippet examples/opengl/2dpainting/widget.cpp 0 + + The \c animate() slot is called whenever a timer, which we define later, times + out: + + \snippet examples/opengl/2dpainting/widget.cpp 1 + + Here, we determine the interval that has elapsed since the timer last + timed out, and we add it to any existing value before repainting the + widget. Since the animation used in the \c Helper class loops every second, + we can use the modulo operator to ensure that the \c elapsed variable is + always less than 1000. + + Since the \c Helper class does all of the actual painting, we only have + to implement a paint event that sets up a QPainter for the widget and calls + the helper's \c paint() function: + + \snippet examples/opengl/2dpainting/widget.cpp 2 + + \section1 GLWidget Class Definition + + The \c GLWidget class definition is basically the same as the \c Widget + class except that it is derived from QGLWidget. + + \snippet examples/opengl/2dpainting/glwidget.h 0 + + Again, the member variables record the \c Helper used to paint the + widget and the elapsed time since the previous update. + + \section1 GLWidget Class Implementation + + The constructor differs a little from the \c Widget class's constructor: + + \snippet examples/opengl/2dpainting/glwidget.cpp 0 + + As well as initializing the \c elapsed member variable and storing the + \c Helper object used to paint the widget, the base class's constructor + is called with the format that specifies the \l QGL::SampleBuffers flag. + This enables anti-aliasing if it is supported by your system's OpenGL + driver. + + The \c animate() slot is exactly the same as that provided by the \c Widget + class: + + \snippet examples/opengl/2dpainting/glwidget.cpp 1 + + The \c paintEvent() is almost the same as that found in the \c Widget class: + + \snippet examples/opengl/2dpainting/glwidget.cpp 2 + + Since anti-aliasing will be enabled if available, we only need to set up + a QPainter on the widget and call the helper's \c paint() function to display + the widget's contents. + + \section1 Window Class Definition + + The \c Window class has a basic, minimal definition: + + \snippet examples/opengl/2dpainting/window.h 0 + + It contains a single \c Helper object that will be shared between all + widgets. + + \section1 Window Class Implementation + + The constructor does all the work, creating a widget of each type and + inserting them with labels into a layout: + + \snippet examples/opengl/2dpainting/window.cpp 0 + + A timer with a 50 millisecond time out is constructed for animation purposes, + and connected to the \c animate() slots of the \c Widget and \c GLWidget objects. + Once started, the widgets should be updated at around 20 frames per second. + + \section1 Running the Example + + The example shows the same painting operations performed at the same time + in a \c Widget and a \c GLWidget. The quality and speed of rendering in the + \c GLWidget depends on the level of support for multisampling and hardware + acceleration that your system's OpenGL driver provides. If support for either + of these is lacking, the driver may fall back on a software renderer that + may trade quality for speed. +*/ |