Function ghost_elements 

pub fn ghost_elements<R>(
    wm: Option<&WmState>,
    renderer: &mut R,
    id: WindowId,
    origin: Point<i32, Logical>,
    scale: f64,
) -> GhostElements<R>
where
    R: Renderer + ImportMem,
    R::TextureId: Texture + Clone + Send + 'static,

The render elements of a ghost through its effect: the picture scaled from the client area it stood at into the effect’s rectangle and blended at its alpha, with the frame parts around it at the same scale. Nothing for a ghost without an effect.