gdk:display-composited (object)

object -- a gdk:display object
composited -- true if the display properly composites the alpha channel

The accessor for the composited slot of the gdk:display class returns whether surfaces can reasonably be expected to have their alpha channel drawn correctly on the screen. Check with the gdk:display-is-rgba function for whether the display supports an alpha channel.

On X11 this function returns whether a compositing manager is compositing on display. On modern displays, this value is always true.