Function draw_app_mark 

pub fn draw_app_mark(
    scene: &mut Scene,
    transform: Affine,
    rect: Rect,
    icon: Option<&AppImage>,
    kind: AppKind,
    color: AlphaColor<Srgb>,
)

A window’s application mark at any size: the app’s own artwork when it has some, else the app-kind glyph its tab pill wears, scaled up from the pill’s 14 px design size. Every surface that names a window by its app (the tab pill, the window switcher, the overview) paints this one mark.