QOffscreenSurface Class
The QOffscreenSurface class represents an offscreen surface in the underlying platform. More...
This class was introduced in Qt 5.1.
Detailed Description
QOffscreenSurface is intended to be used with QOpenGLContext to allow rendering with OpenGL in an arbitrary thread without the need to create a QWindow.
Even though the surface is typically renderable, the surface's pixels are not accessible. QOffscreenSurface should only be used to create OpenGL resources such as textures or framebuffer objects.
An application will typically use QOffscreenSurface to perform some time-consuming tasks in a separate thread in order to avoid stalling the main rendering thread. Resources created in the QOffscreenSurface's context can be shared with the main OpenGL context. Some common use cases are asynchronous texture uploads or rendering into a QOpenGLFramebufferObject.
How the offscreen surface is implemented depends on the underlying platform, but it will typically use a pixel buffer (pbuffer). If the platform doesn't implement or support offscreen surfaces, QOffscreenSurface will use an invisible QWindow internally.
Note: Due to the fact that QOffscreenSurface is backed by a QWindow on some platforms, cross-platform applications must ensure that create() is only called on the main (GUI) thread. The QOffscreenSurface is then safe to be used with makeCurrent() on other threads, but the initialization and destruction must always happen on the main (GUI) thread.
Note: In order to create an offscreen surface that is guaranteed to be compatible with a given context and window, make sure to set the format to the context's or the window's actual format, that is, the QSurfaceFormat returned from QOpenGLContext::format() or QWindow::format() after the context or window has been created. Passing the format returned from QWindow::requestedFormat() to setFormat() may result in an incompatible offscreen surface since the underlying windowing system interface may offer a different set of configurations for window and pbuffer surfaces.
Note: Some platforms may utilize a surfaceless context extension (for example EGL_KHR_surfaceless_context) when available. In this case there will be no underlying native surface. For the use cases of QOffscreenSurface (rendering to FBOs, texture upload) this is not a problem.