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authorMorten Engvoldsen <morten.engvoldsen@nokia.com>2009-11-05 13:29:48 (GMT)
committerMorten Engvoldsen <morten.engvoldsen@nokia.com>2009-11-05 13:29:48 (GMT)
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Documentation: Updating Embedded HW acc. docs
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-/****************************************************************************
-**
-** Copyright (C) 2009 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.
-**
-** $QT_BEGIN_LICENSE:LGPL$
-** 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 Lesser General Public License Usage
-** Alternatively, this file may be used under the terms of the GNU Lesser
-** General Public License version 2.1 as published by the Free Software
-** Foundation and appearing in the file LICENSE.LGPL included in the
-** packaging of this file. Please review the following information to
-** ensure the GNU Lesser General Public License version 2.1 requirements
-** will be met: http://www.gnu.org/licenses/old-licenses/lgpl-2.1.html.
-**
-** In addition, as a special exception, Nokia gives you certain additional
-** rights. These rights are described in the Nokia Qt LGPL Exception
-** version 1.1, included in the file LGPL_EXCEPTION.txt in this package.
-**
-** If you have questions regarding the use of this file, please contact
-** Nokia at qt-info@nokia.com.
-**
-**
-**
-**
-**
-**
-**
-**
-** $QT_END_LICENSE$
-**
-****************************************************************************/
-
-/*!
-\page qt-embedded-opengl.html
-
-\title Qt for Embedded Linux and OpenGL
-\ingroup qt-embedded-linux
-
-\section1 Introduction
-
-\l {http://www.opengl.org}{OpenGL} is an industry standard API for
-2D/3D graphics. It provides a powerful, low-level interface between
-software and acceleration hardware, and it is operating system and
-window system independent.
-
-\l {http://www.khronos.org/opengles}{OpenGL ES} is a subset
-of the \l {http://www.opengl.org}{OpenGL} standard.
-Because it is meant for use in embedded systems, it has a smaller,
-more constrained API.
-
-For reference, Nokia provides support for integrating \l
-{http://www.khronos.org/opengles}{OpenGL ES} with Qt for Embedded Linux
-for drawing into a QGLWidget.
-
-The current implementation supports OpenGL and 2D painting within a
-QGLWidget. Using OpenGL to accelerate regular widgets and compositing
-top-level windows with OpenGL are not currently supported. These issues
-will be addressed in future versions of Qt.
-
-It is recommended that Qt for Embedded Linux is configured with the
-\c{-DQT_QWS_CLIENTBLIT} and \c{-DQT_NO_QWS_CURSOR} options for optimum
-performance. OpenGL is rendered direct to the screen and these options
-prevent Qt for Embedded Linux from trying to do its own non-OpenGL
-compositing on the QGLWidget contents.
-
-\section2 Using OpenGL 3D Graphics in Applications
-
-The \l {QtOpenGL module} offers classes that make it easy to draw 3D
-graphics in GUI applications. The module API is cross-platform, so it
-is also available on Windows, X11, and Mac OS X.
-
-To use OpenGL-enabled widgets in a Qt for Embedded Linux application,
-all that is required is to subclass the QGLWidget and draw into instances of
-the subclass with standard OpenGL functions.
-
-Note that on most embedded hardware, the OpenGL implementation is
-actually \l{http://www.khronos.org/opengles/1_X/}{OpenGL/ES 1.1} or
-\l{http://www.khronos.org/opengles/2_X/}{OpenGL/ES 2.0}. When painting
-within a QGLWidget::paintGL() override, it is necessary to limit the
-application to only the features that are present in the OpenGL/ES
-implementation.
-
-\section2 Using OpenGL to Accelerate Normal 2D Painting
-
-Qt provides a subclass of QPaintEngine that translates QPainter operations
-into OpenGL calls (there are actually two subclasses, one for OpenGL/ES 1.1
-and another for OpenGL/ES 2.0). This specialized paint engine can be used
-to improve 2D rendering performance on appropriate hardware. It can also
-overlay controls and decorations onto 3D scenes drawn using OpenGL.
-
-As mentioned above, the OpenGL paint engine is not currently supported
-in regular widgets. However, any application that uses QGraphicsView
-can set a QGLWidget as the viewport and obtain access to the
-OpenGL paint engine that way:
-
-\code
-QGraphicsView view(&scene);
-view.setViewport(new QGLWidget);
-view.setViewportUpdateMode(QGraphicsView::FullViewportUpdate);
-view.showFullScreen();
-\endcode
-
-It is recommended that the QGraphicsView::FullViewportUpdate flag
-be set because the default double-buffered behavior of QGLWidget
-does not support partial updates. It is also recommended that the
-window be shown full-screen because that usually has the best
-performance on current OpenGL/ES implementations.
-
-Once a QGraphicsView has been initialized as above, regular widgets
-can be added to the canvas using QGraphicsProxyWidget if the
-application requires them.
-
-\section2 Using OpenGL to Implement Window Compositing and Effects
-
-Compositing effects can be simulated by adjusting the opacity and
-other parameters of the items within a QGraphicsView canvas on a
-QGLWidget viewport.
-
-While Qt for Embedded Linux does include a complete windowing system,
-using OpenGL to composite regular window surfaces can be quite difficult.
-Most of Qt for Embedded Linux assumes that the window surface is a plain
-raster memory buffer, with QGLWidget being the sole exception.
-The need to constantly re-upload the raster memory buffers into OpenGL
-textures for compositing can have a significant impact on performance,
-which is why we do not recommend implementing that form of compositing.
-We intend to address this problem in future versions of Qt.
-
-\section1 Integrating OpenGL/ES into Qt for Embedded Linux
-
-\section2 Reference Integration
-
-The reference integration for OpenGL into Qt for Embedded Linux
-is for the PowerVR chipset from \l{http://www.imgtec.com/}{Imagination
-Technologies}. It consists of two components: \c{pvreglscreen} which
-provides the Qt for Embedded Linux screen driver, and \c{QWSWSEGL}
-which implements a plug-in to the PowerVR EGL implementation to
-implement low-level OpenGL drawing surfaces.
-
-\section2 Integrating Other Chipsets
-
-In this section we discuss the essential features of the reference
-integration that need to be provided for any other chipset integration.
-
-The QtOpenGL module assumes that a QGLWidget can be represented
-by a \c EGLNativeWindowType value in some underlying window system
-implementation, and that \c{eglSwapBuffers()} is sufficient to copy
-the contents of the native window to the screen when requested.
-
-However, many EGL implementations do not have a pre-existing window system.
-Usually only a single full-screen window is provided, and everything else
-must be simulated some other way. This can be a problem because
-of QtOpenGL's assumptions. We intend to address these assumptions in a
-future version of Qt, but for now it is the responsibility of the integrator
-to provide a rudimentary window system within the EGL implementation.
-This is the purpose of \c{QWSWSEGL} in the reference integration.
-
-If it isn't possible for the EGL implementation to provide a rudimentary
-window system, then full-screen windows using QGLWidget can be supported,
-but very little else.
-
-The screen driver needs to inherit from QGLScreen and perform the
-following operations in its constructor:
-
-\snippet src/plugins/gfxdrivers/powervr/pvreglscreen/pvreglscreen.cpp 0
-
-The \c{setSurfaceFunctions()} call supplies an object that takes care
-of converting Qt paint devices such as widgets and pixmaps into
-\c EGLNativeWindowType and \c EGLNativePixmapType values. Here we
-only support native windows. Because OpenGL rendering is direct to
-the screen, we also indicate that client blit is supported.
-
-Next, we override the \c{createSurface()} functions in QGLScreen:
-
-\snippet src/plugins/gfxdrivers/powervr/pvreglscreen/pvreglscreen.cpp 1
-
-Even if Qt for Embedded Linux is used in single-process mode, it is
-necessary to create both client-side and server-side versions of the
-window surface. In our case, the server-side is just a stub because
-the client side directly renders to the screen.
-
-Note that we only create a \c{PvrEglWindowSurface} if the widget is a
-QGLWidget. All other widgets use the normal raster processing.
-It can be tempting to make \c{createSurface()} create an OpenGL
-window surface for other widget types as well. This has not been
-extensively tested and we do not recommend its use at this time.
-
-The other main piece is the creation of the \c EGLNativeWindowType
-value for the widget. This is done in the \c{createNativeWindow()}
-override:
-
-\snippet src/plugins/gfxdrivers/powervr/pvreglscreen/pvreglscreen.cpp 2
-
-The details of what needs to be placed in this function will vary
-from chipset to chipset. The simplest is to return the native window
-handle corresponding to the "root" full-screen window:
-
-\code
-*native = rootWindowHandle;
-return true;
-\endcode
-
-The most common value for \c rootWindowHandle is zero, but this may
-not always be the case. Consult the chipset documentation for the
-actual value to use. The important thing is that whatever value is
-returned must be suitable for passing to the \c{eglCreateWindowSurface()}
-function of the chipset's EGL implementation.
-
-In the case of PowerVR, the rudimentary window system in \c{QWSWSEGL}
-provides a \c PvrQwsDrawable object to represent the \c EGLNativeWindowType
-value for the widget.
-
-\section1 OpenVG Support
-
-\l {http://www.khronos.org/openvg} {OpenVG} is a dedicated API for 2D
-graphics on mobile devices. It is therefore more likely to be a better
-alternative for 2D acceleration than OpenGL/ES. Acceleration of
-regular widgets is supported with OpenVG, unlike with OpenGL/ES.
-See \l{OpenVG Rendering in Qt} for more information on the
-OpenVG support in Qt.
-
-*/