Function push_window_elements 

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

Push a window’s elements for an output at origin and scale: through the window policy’s effect where one runs on it (the surface tree scaled into the effect’s rectangle and blended at its alpha, the frame parts scaled and blended with it), else as the window stands with its frame parts beside it.