The Qt example already does this. I hoped this was restricted to
QApplication only, but apparently Qt repeated this mistake with
QGuiApplication (QGuiApplication was specifically added for QtQuick at a
much later point, even though QApplication inherits from it).
We still keep the window pointer, because we want to call
QQuickWindow::resetOpenGLState() (which runs on the rendering thread
only). Interesting mess...
This one avoids use of a FBO. It's less flexible, because it uses works
around the whole QML rendering API. It seems to be the only way to get
OpenGL rendering without any indirections, though.
Parts of this example were insipired by Qt's "Squircle" example.
Also add a README file with a short description of each example, to
reduce the initial confusing.
