Scenario is using wayland with this pipeline: videotestsrc ! glupload ! qml6glsink.
First pipeline and qml construction works just fine. However if all GStreamer
and QML scenegraph resources are removed, GStreamer will call eglTerminate() and
sever the connection to the display server for Qt. When Qt attempts to do any
further GL operations like construct a new QML scene, it can crash in any number
of places as libEGL will start returning NULL or other unexpected values.
What we really need is to ensure that if an external API (e.g. Qt) will
eventually call eglTerminate(), there is no need for GStreamer to call
eglTerminate(). This is what the foreign display flags allows setting.
There is also another possible scenario where one may like to make GStreamer
assume ownership of an EGLDisplay and thus eventually call `eglTerminate()`. As
such, it is now also possible to mark an GstGLDisplayEGL as non-foreign.
Part-of: <https://gitlab.freedesktop.org/gstreamer/gstreamer/-/merge_requests/8504>
