Function push_ghost_elements 

pub(crate) fn push_ghost_elements<R>(
    renderer: &mut R,
    elements: &mut Vec<CompositionElements<R, WaylandSurfaceRenderElement<R>>>,
    wm: Option<&WmState>,
    origin: Point<i32, Logical>,
    scale: f64,
)
where
    R: Renderer + ImportAll + ImportMem,
    R::TextureId: Clone + Send + 'static,

Push the ghosts of closing windows the policy animates, over the windows: each its last picture and frame scaled and blended through its effect.