Wayland 1.2 added support for display scaling, where wl_output has a "scale" event informing the the client that the compositor will scale the output surfaces by the given factor. The client then has the option of providing large surfaces to match the target pixel densety and bypass the compositor's scaling. This is done by calling wl_surface::set_buffer_scale. Re-use the current high-dpi support in Qt by implementing devicePixelRatio() for QWaylandScreen and QWaylandWindow. Provide high resolution buffers both for raster and OpenGL graphics. Introduce a new coordinate system: buffer coordinates, which is related to the window coordinate system via an "int scale" scale factor. This scale factor corresponds to Qts qreal devicePixelRatio, but we keep the name and the type in the QtWayland implementation. Change-Id: Ie10d7e5b4833480a9a25d96a26ad02150eb6e83f Reviewed-by: Giulio Camuffo <giulio.camuffo@jollamobile.com>