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diff --git a/doc/src/examples/openglwindow.qdoc b/doc/src/examples/openglwindow.qdoc new file mode 100644 index 0000000000..9d93af5154 --- /dev/null +++ b/doc/src/examples/openglwindow.qdoc @@ -0,0 +1,156 @@ +/**************************************************************************** +** +** Copyright (C) 2012 Nokia Corporation and/or its subsidiary(-ies). +** Contact: http://www.qt-project.org/ +** +** This file is part of the documentation of the Qt Toolkit. +** +** $QT_BEGIN_LICENSE:FDL$ +** 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. +** +** Other Usage +** Alternatively, this file may be used in accordance with the terms +** and conditions contained in a signed written agreement between you +** and Nokia. +** +** +** +** +** +** $QT_END_LICENSE$ +** +****************************************************************************/ + +/*! + \example gui/openglwindow + \title OpenGL Window Example + + This example shows how to create a minimal QWindow based application + for the purpose of using OpenGL. + + \image openglwindow-example.png Screenshot of the OpenGLWindow example + + \section1 OpenGLWindow super class + + Our OpenGLWindow class acts as an API which is then subclassed to do the + actual rendering. It has functions to make a request for render() to be + called, either immediately with renderNow() or as soon as the event loop + has finished processing the current batch of events with renderLater(). + The OpenGLWindow subclass can either reimplement render() for OpenGL based + rendering, or render(QPainter *) for rendering with a QPainter. Use + OpenGLWindow::setAnimating(true) for render() to be called at the vertical + refresh rate, assuming vertical sync is enabled in the underlying OpenGL + drivers. + + In the class that does the OpenGL rendering you will typically want to + inherit from QOpenGLFunctions, as our OpenGLWindow does, in order to get + platform independent access to OpenGL ES 2.0 functions. By inheriting from + QOpenGLFunctions the OpenGL functions it contains will get precedence, and + you will not have to worry about resolving those functions if you want your + application to work with OpenGL as well as OpenGL ES 2.0. + + \snippet gui/openglwindow/openglwindow.h 1 + + The window's surface type must be set to QSurface::OpenGLSurface to + indicate that the window is to be used for OpenGL rendering and not for + rendering raster content with QPainter using a QBackingStore. + + \snippet gui/openglwindow/openglwindow.cpp 1 + + Any OpenGL initialization needed can be done by overriding the initialize() + function, which is called once before the first call to render(), with a + valid current QOpenGLContext. As can be seen in the following code snippet, + the default render(QPainter *) and initialize() implementations are empty, + whereas the default render() implementation initializes a + QOpenGLPaintDevice and then calls into render(QPainter *). + + \snippet gui/openglwindow/openglwindow.cpp 2 + + The renderLater() function simply puts an update request event on + the event loop, which leads to renderNow() being called once the event + gets processed. + + We also call renderNow() when we get an expose event. The exposeEvent() is + the notification to the window that its exposure, meaning visibility, on + the screen has changed. When the expose event is received you can query + QWindow::isExposed() to find out whether or not the window is currently + exposed. Do not render to or call QOpenGLContext::swapBuffers() on a window + before it has received its first expose event, as before then its final + size might be unknown, and in addition what is rendered might not even end + up on the screen. + + \snippet gui/openglwindow/openglwindow.cpp 3 + + In renderNow() we return if we are not currently exposed, in which case + rendering is delayed until we actually get an expose event. If we have not + yet done so, we create the QOpenGLContext with the same QSurfaceFormat as + was set on the OpenGLWindow, and call initialize() for the sake of the sub + class, and initializeOpenGLFunctions() in order for the QOpenGLFunctions + super class to be associated with the correct QOpenGLContext. In any case + we make the context current by calling QOpenGLContext::makeCurrent(), call + render() to do the actual rendering, and finally we schedule for the + rendered contents to be made visible by calling + QOpenGLContext::swapBuffers() with the OpenGLWindow as parameter. + + Once the rendering of a frame using an OpenGL context is initiated by + calling QOpenGLContext::makeCurrent(), giving the surface on which to + render as a parameter, OpenGL commands can be issued. The commands can be + issued either directly by including <qopengl.h>, which also includes the + system's OpenGL headers, or as by using QOpenGLFunctions, which can + either be inherited from for convenience, or accessed using + QOpenGLContext::functions(). QOpenGLFunctions gives access to all the + OpenGL ES 2.0 level OpenGL calls that are not already standard in both + OpenGL ES 2.0 and desktop OpenGL. For more information about the OpenGL and + OpenGL ES APIs, refer to the official \l{OpenGL Registry} and + \l{Khronos OpenGL ES API Registry}. + + If animation has been enabled with OpenGLWindow::setAnimating(true), we + call renderLater() to put another update request on the event loop. + + \snippet gui/openglwindow/openglwindow.cpp 4 + + Enabling animation also triggers an update request as shown in the + following code snippet. + + \snippet gui/openglwindow/openglwindow.cpp 5 + + \section1 Example OpenGL rendering sub class + + Here we sub class OpenGLWindow to show how to do OpenGL to render a + rotating triangle. By indirectly sub classing QOpenGLFunctions we gain + access to all OpenGL ES 2.0 level functionality. + + \snippet gui/openglwindow/main.cpp 1 + + In our main function we initialize QGuiApplication and instantiate our + TriangleOpenGLWindow. We give it a QSurfaceFormat specifying that we want + four samples of multisample antialiasing, as well as a default geometry. + Since we want to have animation we call the above mentioned setAnimating() + function with an argument of true. + + \snippet gui/openglwindow/main.cpp 2 + + The following code snippet shows the OpenGL shader program used in this + example. The vertex and fragment shaders are relatively simple, doing + vertex transformation and interpolated vertex coloring. + + \snippet gui/openglwindow/main.cpp 3 + + Here is the code that loads the shaders and initializes the shader program + By using QOpenGLShaderProgram instead of raw OpenGL we get the convenience + that strips out the highp, mediump, and lowp qualifiers on desktop OpenGL, + where they are not part of the standard. We store the attribute and uniform + locations in member variables to avoid having to do the location lookup + each frame. + + \snippet gui/openglwindow/main.cpp 4 + + Finally, here is our render() function, where we use OpenGL to set up the + viewport, clear the background, and render a rotating triangle. + + \snippet gui/openglwindow/main.cpp 5 +*/ diff --git a/doc/src/images/openglwindow-example.png b/doc/src/images/openglwindow-example.png Binary files differnew file mode 100644 index 0000000000..63ba4ed2f4 --- /dev/null +++ b/doc/src/images/openglwindow-example.png |
