Qtopia Core and OpenGL

The Reference Integration

The Qtopia Core OpenGL for Embedded Systems Example is the reference implementation for integrating OpenGL ES and EGL with Qtopia Core's graphics acceleration architecture. ( EGL is a library that binds OpenGL ES to native windowing systems.)

The diagram below shows how OpenGL ES is used within the acceleration architecture:

The example implements a screen driver plugin that demonstrates all three uses of OpenGL in Qtopia Core: 2D graphics acceleration, 3D graphics operations using the QtOpenGL module, and top-level window compositing and special effects. The applications still do not talk directly to the accelerated plugin.

For 2D graphics, applications use the normal Qt painting API. The example accelerates 2D painting by using the QOpenGLPaintEngine, which is included in the QtOpenGL module.

For 3D graphics applications use the OpenGL API directly, together with the functionality in the Qt OpenGL support classes. The example supports this by creating a QWSGLWindowSurface whenever a QGLWidget is instantiated.

All access to the display is done through OpenGL. The example subclasses QWSGLWindowSurface implementation and uses the OpenGL Framebuffer Object extension to draw windows into an offscreen buffer. This lets the example use OpenGL to implement top level window compositing of opaque and semi-transparent windows, and to provide a 3D animated transition effect as each new window is shown.

The specific OpenGL library being used by the example restricts all OpenGL operations to occur in a single process. Hence the example creates instances of QWSGLWindowSurface only in the server process. Other processes then perform 2D graphics by creating instances of the standard QWindowSurface classes for client processes. The standard window surface performs software-based rendering into a shared memory segment. The server then transfers the contents of this shared memory into an OpenGL texture before they are drawn onto the screen during window compositing.