We'll start with the definition of the \c RenderThread class:
- \snippet examples/threads/mandelbrot/renderthread.h 0
+ \snippet 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
\section1 RenderThread Class Implementation
- \snippet examples/threads/mandelbrot/renderthread.cpp 0
+ \snippet 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
We also initialize the \c colormap array, which contains a series
of RGB colors.
- \snippet examples/threads/mandelbrot/renderthread.cpp 1
+ \snippet 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
until \c run() has exited before the base class destructor is
invoked.
- \snippet examples/threads/mandelbrot/renderthread.cpp 2
+ \snippet 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.
computation and start again with the new parameters) and wakes up
the thread, which might be sleeping.
- \snippet examples/threads/mandelbrot/renderthread.cpp 3
+ \snippet mandelbrot/renderthread.cpp 3
\c run() is quite a big function, so we'll break it down into
parts.
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
+ \snippet mandelbrot/renderthread.cpp 4
+ \snippet mandelbrot/renderthread.cpp 5
+ \snippet mandelbrot/renderthread.cpp 6
+ \snippet 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
The core algorithm is beyond the scope of this tutorial.
- \snippet examples/threads/mandelbrot/renderthread.cpp 8
- \snippet examples/threads/mandelbrot/renderthread.cpp 9
+ \snippet mandelbrot/renderthread.cpp 8
+ \snippet 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
+ \snippet 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
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
+ \snippet 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
\section1 MandelbrotWidget Class Implementation
- \snippet examples/threads/mandelbrot/mandelbrotwidget.cpp 0
+ \snippet mandelbrot/mandelbrotwidget.cpp 0
The implementation starts with a few contants that we'll need
later on.
- \snippet examples/threads/mandelbrot/mandelbrotwidget.cpp 1
+ \snippet mandelbrot/mandelbrotwidget.cpp 1
The interesting part of the constructor is the
qRegisterMetaType() and QObject::connect() calls. Let's start
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
+ \snippet mandelbrot/mandelbrotwidget.cpp 2
+ \snippet mandelbrot/mandelbrotwidget.cpp 3
+ \snippet 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
+ \snippet mandelbrot/mandelbrotwidget.cpp 5
+ \snippet mandelbrot/mandelbrotwidget.cpp 6
+ \snippet mandelbrot/mandelbrotwidget.cpp 7
+ \snippet 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
QPainter::save() and QPainter::restore() make sure that any painting
performed afterwards uses the standard coordinate system.
- \snippet examples/threads/mandelbrot/mandelbrotwidget.cpp 9
+ \snippet 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
+ \snippet 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
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
+ \snippet 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
+ \snippet 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
(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
+ \snippet 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
+ \snippet 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
+ \snippet 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
because areas revealed when dragging the pixmap are drawn in
black.)
- \snippet examples/threads/mandelbrot/mandelbrotwidget.cpp 16
+ \snippet 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
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
+ \snippet 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
+ \snippet mandelbrot/mandelbrotwidget.cpp 18
\c scroll() is similar to \c zoom(), except that the affected
parameters are \c centerX and \c centerY.
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
+ \snippet mandelbrot/main.cpp 0
*/
constructor and destructor in the public section of the class that the
meta-object system requires. It describes a colored rectangle.
- \snippet examples/threads/queuedcustomtype/block.h custom type definition and meta-type declaration
+ \snippet queuedcustomtype/block.h custom type definition and meta-type declaration
We will still need to register it with the meta-object system at
run-time by calling the qRegisterMetaType() template function before
\c Block object. The rest of the class is concerned with managing the
user interface and handling images.
- \snippet examples/threads/queuedcustomtype/window.h Window class definition
+ \snippet queuedcustomtype/window.h Window class definition
The \c Window class also contains a worker thread, provided by a
\c RenderThread object. This will emit signals to send \c Block objects
interface containing a label and two push buttons that are connected to
slots in the same class.
- \snippet examples/threads/queuedcustomtype/window.cpp Window constructor start
- \snippet examples/threads/queuedcustomtype/window.cpp set up widgets and connections
- \snippet examples/threads/queuedcustomtype/window.cpp connecting signal with custom type
+ \snippet queuedcustomtype/window.cpp Window constructor start
+ \snippet queuedcustomtype/window.cpp set up widgets and connections
+ \snippet queuedcustomtype/window.cpp connecting signal with custom type
In the last of these connections, we connect a signal in the
\c RenderThread object to the \c addBlock(Block) slot in the window.
\dots
- \snippet examples/threads/queuedcustomtype/window.cpp Window constructor finish
+ \snippet queuedcustomtype/window.cpp Window constructor finish
The rest of the constructor simply sets up the layout of the window.
The \c addBlock(Block) slot receives blocks from the rendering thread via
the signal-slot connection set up in the constructor:
- \snippet examples/threads/queuedcustomtype/window.cpp Adding blocks to the display
+ \snippet queuedcustomtype/window.cpp Adding blocks to the display
We simply paint these onto the label as they arrive.
and using the \c sendBlock(Block) signal to send them to other components
in the example.
- \snippet examples/threads/queuedcustomtype/renderthread.h RenderThread class definition
+ \snippet queuedcustomtype/renderthread.h RenderThread class definition
The constructor and destructor are not quoted here. These take care of
setting up the thread's internal state and cleaning up when it is destroyed.
Processing is started with the \c processImage() function, which calls the
\c RenderThread class's reimplementation of the QThread::run() function:
- \snippet examples/threads/queuedcustomtype/renderthread.cpp processing the image (start)
+ \snippet queuedcustomtype/renderthread.cpp processing the image (start)
Ignoring the details of the way the image is processed, we see that the
signal containing a block is emitted in the usual way:
\dots
- \snippet examples/threads/queuedcustomtype/renderthread.cpp processing the image (finish)
+ \snippet queuedcustomtype/renderthread.cpp processing the image (finish)
Each signal that is emitted will be queued and delivered later to the
window's \c addBlock(Block) slot.
\c Block class as a custom type with the meta-object system by calling the
qRegisterMetaType() template function:
- \snippet examples/threads/queuedcustomtype/main.cpp main function
+ \snippet queuedcustomtype/main.cpp main function
This call is placed here to ensure that the type is registered before any
signal-slot connections are made that use it.
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