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diff --git a/doc/src/platforms/emb-opengl.qdocinc b/doc/src/platforms/emb-opengl.qdocinc new file mode 100644 index 0000000..dac5379 --- /dev/null +++ b/doc/src/platforms/emb-opengl.qdocinc @@ -0,0 +1,85 @@ +\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 designed for use with embedded systems, it has a smaller, more +constrained API. + +\l {http://www.khronos.org/opengles/1_X}{OpenGL ES version 1.x} is designed for +fixed function hardware, while its successor \l +{http://www.khronos.org/opengles/2_X}{OpenGL ES version 2.x} is designed for +programmable hardware. It is worth noting that there is a significant +difference between the two, and that they are not compatible with each +other. OpenGL ES 1.x limits processing to a pre-defined set of fixed +options for drawing and lighting objects. OpenGL 2.x has a significantly +shorter graphics pipeline than 1.x. Instead of using function +transformation and a fragment pipeline, 2.x uses the \l +{http://www.khronos.org/registry/gles/specs/2.0/GLSL_ES_Specification_1.0.17.pdf}{OpenGL +ES Shading Language (GLSL ES)}. Instead of using the pre-defined functions, +the programmer writes small shader programs telling the hardware in detail +how to render each object. + +The \l {QtOpenGL module} offers classes that make it easy to draw 3D +graphics in GUI applications using OpenGL ES. Qt provides a plugin that +integrates both OpenGL ES versions \l +{http://www.khronos.org/opengles/1_X}{1.x} and \l +{http://www.khronos.org/opengles/2_X}{2.x} with Qt for Embedded. However, +Qt for Embedded can be adapted to a wide range of OpenGL versions. + +To translate QPainter operations into OpenGL ES calls (there are actually +two subclasses, one for OpenGL/ES 1.1 and another for OpenGL/ES 2.0), Qt +uses a subclass of QPaintEngine. 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. + +\tableofcontents + +\section1 Using OpenGL ES with Qt +To use OpenGL-enabled widgets in a Qt for Embedded application, all that is +required is to subclass QGLWidget and draw into instances of the subclass +with standard OpenGL functions. The current implementation only +supports OpenGL ES and 2D painting within a QGLWidget. Using OpenGL ES to +accelerate regular widgets as well as compositing top-level windows with +OpenGL ES are not currently supported. These issues will be addressed in +future versions of Qt. + +\note 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.setHorizontalScrollBarPolicy(Qt::ScrollBarAlwaysOff); + view.setVerticalScrollBarPolicy(Qt::ScrollBarAlwaysOff); + view.setViewportUpdateMode(QGraphicsView::FullViewportUpdate); + view.setFrameStyle(0); + 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. + +\note OpenGL ES 2.X does not support PBuffers, so QGLPixelBuffer will not +work. In this case, QGLFramebufferObject should be used instead. However, +OpenGL ES 1.X does not support Framebuffer objects, with the exception of +some OpenGL ES 1.X extensions. In this case, please use QGLPixelBuffer. + +\note 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. + |