We cannot set the x, y coordinate of the video frame at the dispmanx at
this point. We need to teach dispmanx backend to understand about
set_render_rectangle API to draw a video with other UI.
This patch keeps the current behavior which places video frame at the
center of the display if there is no set_render_rectangle call to the
dispmanx window.
https://bugzilla.gnome.org/show_bug.cgi?id=766018
Show the DispmanX window only if there's no shared external GL context
set up. When a window is required by the context a transparent
DispmanX element is created and later on made visible by the ::show
method.
https://bugzilla.gnome.org/show_bug.cgi?id=746632
Depending on the platform, it was only ever implemented to 1) set a
default surface size, 2) resize based on the video frame or 3) nothing.
Instead, provide a set_preferred_size () that elements/applications
can use to request a certain size which may be ignored for
videooverlay/other cases.
