| 1 | \section1 Introduction
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| 2 |
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| 3 | \l {http://www.opengl.org}{OpenGL} is an industry standard API for
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| 4 | 2D/3D graphics. It provides a powerful, low-level interface between
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| 5 | software and acceleration hardware, and it is operating system and
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| 6 | window system independent. \l {http://www.khronos.org/opengles}{OpenGL ES}
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| 7 | is a subset of the \l {http://www.opengl.org}{OpenGL} standard. Because it
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| 8 | is designed for use with embedded systems, it has a smaller, more
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| 9 | constrained API.
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| 10 |
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| 11 | \l {http://www.khronos.org/opengles/1_X}{OpenGL ES version 1.x} is designed for
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| 12 | fixed function hardware, while its successor \l
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| 13 | {http://www.khronos.org/opengles/2_X}{OpenGL ES version 2.x} is designed for
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| 14 | programmable hardware. It is worth noting that there is a significant
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| 15 | difference between the two, and that they are not compatible with each
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| 16 | other. OpenGL ES 1.x limits processing to a pre-defined set of fixed
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| 17 | options for drawing and lighting objects. OpenGL 2.x has a significantly
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| 18 | shorter graphics pipeline than 1.x. Instead of using function
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| 19 | transformation and a fragment pipeline, 2.x uses the \l
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| 20 | {http://www.khronos.org/registry/gles/specs/2.0/GLSL_ES_Specification_1.0.17.pdf}{OpenGL
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| 21 | ES Shading Language (GLSL ES)}. Instead of using the pre-defined functions,
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| 22 | the programmer writes small shader programs telling the hardware in detail
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| 23 | how to render each object.
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| 24 |
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| 25 | The \l {QtOpenGL module} offers classes that make it easy to draw 3D
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| 26 | graphics in GUI applications using OpenGL ES. Qt provides a plugin that
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| 27 | integrates both OpenGL ES versions \l
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| 28 | {http://www.khronos.org/opengles/1_X}{1.x} and \l
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| 29 | {http://www.khronos.org/opengles/2_X}{2.x} with Qt for Embedded. However,
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| 30 | Qt for Embedded can be adapted to a wide range of OpenGL versions.
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| 31 |
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| 32 | To translate QPainter operations into OpenGL ES calls (there are actually
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| 33 | two subclasses, one for OpenGL/ES 1.1 and another for OpenGL/ES 2.0), Qt
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| 34 | uses a subclass of QPaintEngine. This specialized paint engine can be used
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| 35 | to improve 2D rendering performance on appropriate hardware. It can also
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| 36 | overlay controls and decorations onto 3D scenes drawn using OpenGL.
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| 37 |
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| 38 | \tableofcontents
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| 39 |
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| 40 | \section1 Using OpenGL ES with Qt
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| 41 | To use OpenGL-enabled widgets in a Qt for Embedded application, all that is
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| 42 | required is to subclass QGLWidget and draw into instances of the subclass
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| 43 | with standard OpenGL functions. The current implementation only
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| 44 | supports OpenGL ES and 2D painting within a QGLWidget. Using OpenGL ES to
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| 45 | accelerate regular widgets as well as compositing top-level windows with
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| 46 | OpenGL ES are not currently supported. These issues will be addressed in
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| 47 | future versions of Qt.
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| 48 |
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| 49 | \note The OpenGL paint engine is not currently supported in regular
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| 50 | widgets. However, any application that uses QGraphicsView can set a
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| 51 | QGLWidget as the viewport and obtain access to the OpenGL paint engine that
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| 52 | way:
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| 53 |
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| 54 | \code
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| 55 | QGraphicsView view(&scene);
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| 56 | view.setViewport(new QGLWidget());
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| 57 | view.setHorizontalScrollBarPolicy(Qt::ScrollBarAlwaysOff);
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| 58 | view.setVerticalScrollBarPolicy(Qt::ScrollBarAlwaysOff);
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| 59 | view.setViewportUpdateMode(QGraphicsView::FullViewportUpdate);
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| 60 | view.setFrameStyle(0);
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| 61 | view.showFullScreen();
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| 62 | \endcode
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| 63 |
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| 64 | It is recommended that the QGraphicsView::FullViewportUpdate flag
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| 65 | be set because the default double-buffered behavior of QGLWidget
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| 66 | does not support partial updates. It is also recommended that the
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| 67 | window be shown full-screen because that usually has the best
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| 68 | performance on current OpenGL ES implementations.
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| 69 |
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| 70 | Once a QGraphicsView has been initialized as above, regular widgets
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| 71 | can be added to the canvas using QGraphicsProxyWidget if the
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| 72 | application requires them.
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| 73 |
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| 74 | \note OpenGL ES 2.X does not support PBuffers, so QGLPixelBuffer will not
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| 75 | work. In this case, QGLFramebufferObject should be used instead. However,
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| 76 | OpenGL ES 1.X does not support Framebuffer objects, with the exception of
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| 77 | some OpenGL ES 1.X extensions. In this case, please use QGLPixelBuffer.
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| 78 |
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| 79 | \note On most embedded hardware, the OpenGL implementation is
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| 80 | actually \l{http://www.khronos.org/opengles/1_X/}{OpenGL/ES 1.1} or
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| 81 | \l{http://www.khronos.org/opengles/2_X/}{OpenGL/ES 2.0}. When painting
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| 82 | within a QGLWidget::paintGL() override, it is necessary to limit the
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| 83 | application to only the features that are present in the OpenGL/ES
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| 84 | implementation.
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| 85 |
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