Since gst_vaapi_window_vpp_convert_internal is created,
GstVaapiWindowX11/Wayland can use it for conversion.
Note that once it chooses to use vpp, it's going to use vpp
until the session is finished.
https://bugzilla.gnome.org/show_bug.cgi?id=759533
Currently, GstVaapiWindowX11/Wayland are not descendants of GstVaapiWindow.
This patch chains them up to GstVaapiWindow to handle common members in GstVaapiWindow.
https://bugzilla.gnome.org/show_bug.cgi?id=759533
Add GstVaapiWindowClass::get_colormap() hook to help determine the
currently active colormap bound to the supplied window, or actually
create it if it does not already exist yet.
Add GstVaapiWindowClass::get_visual_id() function hook to help find
the best suitable visual id for the supplied window. While doing so,
also simplify the process by which an X11 window is created with a
desired Visual, i.e. now use a visual id instead of a Visual object.
Use hardware accelerated XRenderComposite() function, from the RENDER
extension, to blit a pixmap to screen. Besides, this can also support
cropping and scaling.