There is nothing guaranteeing there will be a paint request after
resizeViewportFramebuffer() is called. However we must not be left
with a framebuffer with uninitialized content. So trigger an update.
Include also a half-hearted autotest. QOpenGLWidget (or QGLWidget)
viewports have not been autotested at all. Try to verify that it
is functional at least, even if we cannot check the actual output.
Change-Id: I34d78fe32e94c39dad919216b5a4f4bb2aea3cc2
Task-number: QTBUG-52419
Reviewed-by: Friedemann Kleint <Friedemann.Kleint@qt.io>
Reviewed-by: Paul Olav Tvete <paul.tvete@theqtcompany.com>
61521b64a4