When the expose event is received you can query QWindow::isExposed() to find out whether or not the window is currently exposed. The exposeEvent() is the notification to the window that its exposure, meaning visibility, on the screen has changed. We also call renderNow() when we get an expose event. The renderLater() function simply calls QWindow::requestUpdate() to schedule an update for when the system is ready to repaint. M_device - >setDevicePixelRatio(devicePixelRatio()) M_device - >setSize(size() * devicePixelRatio()) GlClear(GL_COLOR_BUFFER_BIT | GL_DEPTH_BUFFER_BIT | GL_STENCIL_BUFFER_BIT) Void OpenGLWindow ::render( QPainter *painter) 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. 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. Use OpenGLWindow::setAnimating(true) for render() to be called at the vertical refresh rate, assuming vertical sync is enabled in the underlying OpenGL drivers. The OpenGLWindow subclass can either reimplement render() for OpenGL based rendering, or render( QPainter *) for rendering with a QPainter. 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(). Our OpenGLWindow class acts as an API which is then subclassed to do the actual rendering.
In practice you should consider using the higher level QOpenGLWindow class. Note: This is a low level example of how to use QWindow with OpenGL.
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