From 084306783828839b957ef5073a477122f7aed679 Mon Sep 17 00:00:00 2001 From: Christiaan Janssen Date: Tue, 18 Dec 2012 13:00:29 +0100 Subject: Qt Gui Examples: Fixed QDoc files Change-Id: I160d8d186a1078f20f2b779bfbdae90459c27641 Reviewed-by: Jerome Pasion --- examples/gui/doc/src/rasterwindow.qdoc | 161 +++++++++++++++++++++++++++++++++ 1 file changed, 161 insertions(+) create mode 100644 examples/gui/doc/src/rasterwindow.qdoc (limited to 'examples/gui/doc/src/rasterwindow.qdoc') diff --git a/examples/gui/doc/src/rasterwindow.qdoc b/examples/gui/doc/src/rasterwindow.qdoc new file mode 100644 index 0000000000..f246533c4f --- /dev/null +++ b/examples/gui/doc/src/rasterwindow.qdoc @@ -0,0 +1,161 @@ +**************************************************************************** +** +** 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 rasterwindow + \title Raster Window Example + + \brief This example shows how to create a minimal QWindow based + application using QPainter for rendering. + + + \section1 Application Entry Point + + \snippet rasterwindow/main.cpp 1 + + The entry point for a QWindow based application is the \l + QGuiApplication class. It manages the GUI application's control + flow and main settings. We pass the command line arguments which + can be used to pick up certain system wide options. + + From there, we go on to create our window instance and then call + the \l QWindow::show() function to tell the windowing system that + this window should now be made visible on screen. + + Once this is done, we enter the application's event loop so the + application can run. + + + \section1 RasterWindow Declaration + + \snippet rasterwindow/rasterwindow.h 1 + + We first start by including the the QtGui headers. This means we + can use all classes in the Qt GUI module. Classes can also be + included individually if that is preferred. + + The RasterWindow class subclasses QWindow directly and provides a + constructor which allows the window to be a sub-window of another + QWindow. Parent-less QWindows show up in the windowing system as + top-level windows. + + The class declares a QBackingStore which is what we use to manage + the window's back buffer for QPainter based graphics. + + \e {The raster window is also reused in a few other examples and adds + a few helper functions, like renderLater().} + + + \section1 RasterWindow Implementation + + \snippet rasterwindow/rasterwindow.cpp 1 + + The constructor first of all calls \l QWindow::create(). This will + create the window in the windowing system. Without calling create, + the window will not get events and will not be visible in the + windowing system. The call to create does not show the window. We + then set the geometry to be something reasonable. + + Then we create the backingstore and pass it the window instance it + is supposed to manage. + + \snippet rasterwindow/rasterwindow.cpp 2 + + Shortly after calling \l QWindow::show() on a created window, the + virtual function \l QWindow::exposeEvent() will be called to + notify us that the window's exposure in the windowing system has + changed. The event contains the exposed sub-region, but since we + will anyway draw the entire window every time, we do not make use + of that. + + The function \l QWindow::isExposed() will tell us if the window is + showing or not. We need this as the exposeEvent is called also + when the window becomes obscured in the windowing system. If the + window is showing, we call renderNow() to draw the window + immediately. We want to draw right away so we can present the + system with some visual content. + + + \snippet rasterwindow/rasterwindow.cpp 5 + + The resize event is guaranteed to be called prior to the window + being shown on screen and will also be called whenever the window + is resized while on screen. We use this to resize the back buffer + and call renderNow() if we are visible to immediately update the + visual representation of the window on screen. + + \snippet rasterwindow/rasterwindow.cpp 3 + + The renderNow function sets up what is needed for a \l QWindow to + render its content using QPainter. As obscured windows have will + not be visible, we abort if the window is not exposed in the + windowing system. This can for instance happen when another window + fully obscures this window. + + We start the drawing by calling \l QBackingStore::beginPaint() on + the region we want to draw. Then we get the \l QPaintDevice of the + back buffer and create a QPainter to render to that paint device. + + To void leaving traces from the previous rendering and start with a + clean buffer, we fill the entire buffer with the color white. Then + we call the virtual render() function which does the actual + drawing of this window. + + After drawing is complete, we call endPaint() to signal that we + are done rendering and present the contents in the back buffer + using \l QBackingStore::flush(). + + + \snippet rasterwindow/rasterwindow.cpp 4 + + The render function contains the drawing code for the window. In + this minial example, we only draw the string "QWindow" in the + center. + + + \section1 Rendering Asynchronously + + + \snippet rasterwindow/rasterwindow.cpp 6 + + We went through a few places where the window needed to repainted + immediately. There are some cases where this is not desierable, + but rather let the application return to the event loop and + later. We acheive this by posting an even to ourself which will + then be delivered when the application returns to the \l + QGuiApplication event loop. To avoid posting new requests when one + is already pending, we store this state in the \c m_update_pending + variable. + + \snippet rasterwindow/rasterwindow.cpp 7 + + We reimplement the virtual \l QObject::event() function to handle + the update event we posted to ourselves. When the event comes in + we reset the pending update flag and call renderNow() to render + the window right away. + + */ -- cgit v1.2.3