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 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.