gdk:display-shadow-width (object)

object -- a gdk:display object
setting -- true if surfaces can draw shadows or false if the display does not support this functionality

The accessor for the shadow-width slot returns whether it is possible for a surface to draw outside of the window area. If true is returned the application decides if it wants to draw shadows. If false is returned, the compositor decides if it wants to draw shadows.

Since 4.14